Sjöström Audio DIY forum

Projects => Headphone amplifiers => Topic started by: BMF on May 24, 2016, 12:24:34 AM

Title: QRV08 Setup Instructions
Post by: BMF on May 24, 2016, 12:24:34 AM
I'm looking for a setup guide for each section of the board. No luck despite web searches.

I have the power supply populated and I'm ready to test it.

Any help much appreciated,

BMF
Title: Re: QRV08 Setup Instructions
Post by: peranders on May 24, 2016, 07:06:47 AM
What kind of setup do you mean?
Title: Re: QRV08 Setup Instructions
Post by: BMF on May 24, 2016, 11:50:01 AM
P-A,

Is there a systematic series of DMM tests that should be followed to insure each section is functioning as you designed?

For example, I followed Ti's guide "Initial Setup" instructions for CK2III:
http://www.amb.org/audio/ck2/

And Alex's "Setup" instructions for EHHA Rev A:
http://www.cavalliaudio.com/pages/ehha-rev-a

and Bijou:
http://www.cavalliaudio.com/pages/bijou

Thanks
Title: Re: QRV08 Setup Instructions
Post by: peranders on May 24, 2016, 10:05:11 PM
Basically you can use two methods and that is the big bang method, just solder all parts in their right positions or start with the power supply in order to have a correct supply voltage. After that you solder the amplifier. Since its dual mono you could take one channel first. I do really recommend that you work slowly and with precision.
Title: Re: QRV08 Setup Instructions
Post by: BMF on May 28, 2016, 11:02:44 PM
I'm going forward with the Big Bang method!

All I have left are the ICs, NPNs, LEDs, and larger caps.
Title: Re: QRV08 Setup Instructions
Post by: BMF on May 31, 2016, 02:17:33 AM
I Big Banged populating the PCB and it took 4 days! My QRV08 is ready for testing, biasing, etc. I'm hesitant to just power it up and see what happens. I've read everything I can find on your site and on the web via Google searches but cannot find information on how to systematically test and bias.

I see there are jumpers (J3 and J6) but I don't know what to do next. After all the time to get to this point, I really don't want to leave it to chance and risk it going up in smoke.

I read RudeWolf's comments on Changstar.com:

"Initially Fishski was ahead of me and had made a handy BOM with corresponding part numbers for Mouser. I was very surprised that the board had to be populated by more than 300 smd parts which meant filling about 800 pads. I took the BOM from Per-Anders (PA) himself as it had also ELFA Distrelec part codes. The board itself, despite containing a large number of parts can be populated for about 250 - 400 dollars, depending on what provider you use. As far as I know almost all of the parts are readily available, with the non-230V on-board EI transformers being the exception. None of the parts used are anything close to audiophile grade.

If you are systematic, populating the board is a breeze. I'd recommend starting ground up with PSU first so you can test it. After all the PSU circuit takes about 2/3 of the pcb. Due to the QRV-08 using a current feedback topology, its PSRR is very low so clean power is a must. I made three mistake while populating the PSU part which comprised of untouched pads and a solder bridge. The design uses self-resetting fuses, so overcurrent can be easily detected by looking at the dimmer PSU LED (the fuse lets through some current when tripped). Populating the amp part was a breeze as I had already mastered the technique by working on the PSU. Dialing the amp in initially seems counterintuitive as you need to jumper either of two pads per each channel. Then set the bias and you're ready to get your jaw dropped on the floor."

Any assistance/guidance on what to do next will be greatly appreciated.

Many Thanks,

~BMF



Title: Re: QRV08 Setup Instructions
Post by: BMF on May 31, 2016, 02:18:35 AM
Second picture.
Title: Re: QRV08 Setup Instructions
Post by: BMF on May 31, 2016, 02:20:12 AM
Third picture.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 01, 2016, 02:08:05 AM
J3 and J6 are clearly labeled. Should they be jumpered?

Where are J1, J2, J4, and J5?  And, what are their functions?

What is a "Tin Bulb Jumper?"
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 01, 2016, 06:06:12 AM
J1, 2, 4, 5 they are located on the solder side and you put a tin drop on tow of them depending of the sign of the input bias. This can be determined by measure the voltage across the R1. This bias network is ment to inject bias and eliminate most of the output offset and the DC servo will take the rest.

J3 and J6 are for changing the output impedance.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 01, 2016, 01:57:27 PM
Thank you for this information, P-A.

Would you identify the location of J1, 2, 4, and 5 on the underside of the PCB?

For J3 and J6, what are the output impedances jumpered vs not jumpered?

The attached picture shows the location of a problem LED circled in red. It does not light up, at all. The other 3 light up for 2 seconds then turn off simultaneously. I removed the one that did not light up and installed a new one but it did not light up, either. I will go through each connection.

Can you suggest likely problem components / connections to focus on?

And, what do you suppose is causing the other 3 LEDs to briefly light up and then turn off?

Many thanks for your support.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 01, 2016, 06:36:08 PM
J1, 2, 4, 5 can be seen in the solder mask if you look carefully.

The output impedance is milliohms or 110 ohms (jumper off).

Do you get ±15 V out from the regulators?

Have you checked the placement of the parts after the soldering? Print out the BOM and take part by part. My guess is that you have a couple of parts in the wrong place.

Next step could be to disable the bias by lifting the R3. This resistor sets all currents in the design.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 05, 2016, 08:58:15 PM
P-A,

I verified each component, placement, and orientation. Everything checks out correctly. I used all the stock components listed in the QRV-08 BOM. I found no errors, no cold joints, and no solder bridges using magnification.

Thank you for any ideas you care to share,

Keith

Measurements, so far:

Transformers are torroidal 15v x 15v, 7VA:
Primaries = 122 VAC
Secondaries on Bridge A/C side = 19.5 to 20.5 VAC

There are significant differences in some of these "side-to-side" measurements:

Bridge 1 = 17.8 VDC   H1 On
Bridge 2 = 20.2 VDC   H2 Off
Bridge 3 = 17.8 VDC   H3 On
Bridge 4 = 20.3 VDC   H4 Off

LED Voltage Drop
H1 = 1.7 V
H2 = 0.7 V
H3 = 1.7 V
H4 = 0.7 V

BCP53          BCP53              BCP56         BCP56
T27 = 8.35 V       V27 = 8.74 V      T28 = 13.89V      V28 = 13.78 V
T33 = 3.28 V        V33 = 3.53 V      T34 = 16.44 V      V34 = 16.32 V

OPA134
IC1 Pin 6 to PCB ground plane = 12.9 V
IC3 Pin 6 to PCB ground plane = 12.9 V

AD825
IC2   Pin 6 to PCB ground plane = 7.15 V
IC6   Pin 6 to PCB ground plane = 266 mV
IC11 Pin 6 to PCB ground plane = 7.2 V
IC15 Pin 6 to PCB ground plane = 308 mV

LM317                 LM337
IC7    = 16.4 V         IC10 = 703 mV
IC14 = 16.3 V         IC18 = 937 mV

R1 = 6.3 V                 E1 = 6.7 V              R32 = 25.7 V      E32 = 25.4 V
R2 = 39 mV         E2 = 41.8 mV      R33 = 20.4 V      E33 = 20.4 V
R3 = 7.41 V         E3 = 2.19 V      C32 = 25.8 V      G32 = 25.8 V
R4 = 526 mV         E4 = 5.46 V      C31 = 20.3 V      G31 = 20.4 V
R5 = 501 mV         E5 = 460 mV
R8 = 4.2 V                 E8 = 3.72 V
R9 = 609 mV         E9 = 761 mV      R44 = 6.9 V      E44 = 3.1 V
R12 = 4.2 V         E12 = 3.69 V      R45 = 2.2 V      E45 = 6.9 V
R13 = 608 mV              E13 = 761 mV
R16 = 4.2 V         E16 = 3.71 V
R17 = 630 mV              E17 = 786 mV
R20 = 12.7 mV              E20 = 19.7 mV           R21 = 0.0 V      E21 = 0.0 V

Odd Behavior:

1. During testing on two consecutive days, H3 and H2 were lit. After about 45 minutes, H2 went out and H1 lit. Of course, the values of all measurements changed that correspond to H1 and H2. Very puzzling!

2. On the first day, the resettable fuses associated with the “dead” sections were very hot. On the second day, none of the fuses got hot. The only change I made was blowing out the liquid flux. I suppose it’s possible that there were some solder balls shorting some connections under some of the components.

3. I read on the QRV-08 forum that voltage across R1/E1 should be no more than 5 to 10 mV. I’m getting almost 7 volts so something is way off! Turning P1 and P2 to the CW and CWW sides has no effect except changing the polarity readings…the values remain the same.

I installed C/G 41 and 42 = no effect so I removed them.

I have not yet removed R/E 3. Not sure what to check to see if doing so offers any benefits or clues.

Title: Re: QRV08 Setup Instructions
Post by: peranders on June 06, 2016, 03:37:32 PM
I'll suspect that you still have parts in the wrong place since both channels are similar.

In order to reduce the current consumption: Lift R3/E3 the amp amp will be shut off.

I'm interested in the power supply.

Voltages of the AD825: Pin, 2, 3, 4, 6 and 7
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 06, 2016, 10:03:35 PM
P-A,

I will check those values after work. I will also reconfirm parts and placement.

I'm still trying to understand why / how H1 and H2 alternately worked without making any changes.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 07, 2016, 12:08:52 AM
AD825     IC2           IC6          IC11          IC15

Pin 2       6.9V        635mV         6.9V         611mV

Pin 3       6.9V        240mV         6.9V         231mV

Pin 4       0.0V        920mV         0.0V         902mV

Pin 5       5.5V        601mV         7.0V         415mV

Pin 6       7.6V        265mV         7.1V         321mV

Pin 7      14.3V        0.0V           13.5V         0.0V

All 4 LEDs light up for 1 second at Power On, then go dark. Within 10 seconds H1 and H3 light up but H2 and H4 remain dark. Powering down, H2 and H4 Flash On.

While I was preparing to make these measurements, I saw H1 and H2 once again alternately switch On and Off. In other words, H1 was On and H2 was Off; a few seconds later H1 was Off and H2 was On; then they reverted back to H1 On and H2 Off. H4 remains Off and H3 remains On...???

The pads for the C/G 10, 11, 33-36, 39, 40, and 47-50 are the same size as the tabs on the caps. This makes it very difficult to solder the caps in place. I pre-tinned the pads and the cap tabs, off-set the tabs on the pads so a little bit of each pad was exposed, and re-flowed them in place. I checked continuity of each cap tab with its connection to other components using the schematic and all are continuous. Considering that the solder mask should prevent shorting from one PCB pad to the other (under each cap) from the reflow, it's not likely but I suppose it's possible there are some shorts I cannot see. Would circuit connections to other components confound results from testing for shorts across each cap's pair of tabs using my DMM set to ohms?

I re-flowed all joints. Upon Powering On, all 4 LEDs light up for about 1.5 seconds, blink off, then H1 and H3 light up within 7 seconds. I noticed the resettable fuses associated with H2 and H4 were hot for a few seconds when Powering On...this happened before and after reflowing al the joints. I removed them and installed new ones....same result.  A short somewhere? I don't see any solder bridges. Where / what are the most likely shorted components given my description of odd behaviors and measurements?

Title: Re: QRV08 Setup Instructions
Post by: BMF on June 08, 2016, 12:05:15 AM
After Power On, all 4 LEDs go dark. About 7 seconds later, 2 LEDs light up.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 08, 2016, 05:36:48 PM
You have high power consumption on the negative side and the same problem in both channels. when the opamps has exactly the same voltage on pin 2 and 3 then regulator works. Pin 6 should also be within the linear range of the opamp. You have 7.6 volts which is as expected.

A brutal way to confirm the power supply is to cut the copper to the amp but you may find the fault avoiding cutting.

I recommend you to lift R3/E3 then the consumption would be the DC-servo opamps only. Have you put any tin on the jumpers on the solderside? Only one, not both if so you have a short circuit (see the schematics).
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 08, 2016, 08:30:11 PM
I tried a blob of solder on the negative bias jumpers (solder side), only. This had no effect so I removed the blobs.

All measurements posted, above, are without any Jumper connections.

The resettable fuses for the Negative Rails get HOT.

What should I expect to find / measure after removing R3/E3?

How do I get any readings on Pin 5 since the data sheet shows it's NC (Not Connected)?

What could explain random On/Off of LEDs at H1 and H2?
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 08, 2016, 09:57:48 PM
When the LED is on then the regulator _might_ work. Do you get -14 V at some point?

The R3 is shutting of the whole amp as I write in earlier posts.

Pin 5 of the opamp is not interesting...
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 09, 2016, 10:20:54 PM
All PNP and NPN transistors at the output and power supply measure 0.6 to .7 V.

E3 and R3 have been removed. Not sure what/where to measure for the next step.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 09, 2016, 10:45:13 PM
The whole amp (as I write) shall be completely shut off. You are sure you don't have mixed up PNP/NPN? If the current consumption will drop you will end up in a stable supply voltage.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 11, 2016, 11:57:10 PM
P-A,

I reconfirmed that all PNP and NPN transistors are properly placed across the entire board.
I reconfirmed that all ICs are correctly positioned.
I have no Jumpered connections.
I checked continuity between all connections...all are good....including transistors, ICs, resistors, and caps.
I replaced all ICs and transistors on the bad sides of the regulators.
I can find no solder bridges or other shorts.
All measurements previously posted were almost identical when retested.
All LEDs blink on at Power Up, go out, and the positive LEDs light up; negative LEDs stay dark.
The negative resettable fuses get Very hot for a few seconds and then cool down. Positive fuses do not get hot.
I removed R3 and E3. The amp transistors heat up to 100 F and 135 F at the PNP And NPN sides of both channels. Shouldn't removing R3 and E3 cut off power to the amps; if so, why are they heating up?

I'm stumped!    :?
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 12, 2016, 05:31:25 PM
I assume that R3 is removed.

Measure the voltage across all resistors starting from R4.

Which is your output voltage?

Voltage across C12?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 12, 2016, 09:01:36 PM
R3/E3 Removed for these measurements:

R4 0v       R5 0v        R6 358mv        R7 10mv        R8 4.6v        R9 0.85v        R10 148mv        R11 16mv        R12 4.5v

R13 0.85v        R14 6.7v        R15 2.2v        R16 4.6v        R17 0.87v        R18 0v        R19 40mv        R20 16mv

R21 0v        R22 16mv        R23 0v       R24 0v        R25 0v        R26 3.3v        R27 3.3v        R28 0v        R29 3.8v       R30 3.6v

R31 3.6v        R32 25.3v        R33 19.7v        R34 1.3v        R35 1.3v        R36 1.3v        R37 1.3v        R38 6.5v

R39 15.7v        R40 0v        R41 1.1v        R42 2.7v        R43 290mv        R44 3.1v        R45 7.9v        R46 305mv

R47 4.5v        R48 170mv        R49 2.5v        R50 230mv        R51 0v        R52 2.9v        R53 7v        R54 629mv

R55 7v        R56 Jumpered        R57 Jumpered        C12 9.3v        G12 9.1v

Thank you!
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 12, 2016, 09:43:55 PM
You have a problem already at R6.

Could you tell me the marking of the transistor and what type and brand you have?

R4 has no current but still you have current through R6.

Could you also measure the base-emitter voltages on all transistors?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 13, 2016, 01:29:38 PM
I have looked at this board and components for many hours over many days. I just found a problem. T/V 13 and T/V 14  are the exceptions to the Odd - Even numbering of these components. I misread and installed BC850 on T/V 13 and BC860 on T/V 14. I assumed these were correct so each time I looked at them under magnification, I could see the symmetry and assumed "all transistors are correct and properly placed."

Could this be my problem and solution? If so, why do the Positive rails work?? 

I will change them out after work and see what happens.

Anyway, here are the measurements you requested?

Parts from mouser.com

771-BC860C235
771-BC850C235
771-BCP53-16115

T1 3.1v     T3 5mv     T5 3v    T7 2.8v     T9 2.5v     T11 565mv     T14 ???     T15 0.64v     T17 0.64v     

T19 0.62v     T21 0.62v     T23 0.61v     T25 0.61v       T29 2v     T31 0.93v

T27 27mv     T33 555mv
 
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 13, 2016, 07:28:40 PM
is this measurements with corrected transistors? My basic theory was (if you remember) that you have some parts in the wrong positions. when you lift the R3 ALL transistors should be shut off. You can easily check that with measuring the voltage across all emitter resistors.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 13, 2016, 09:34:00 PM
P-A,

I apologize for my last confusing post.

The measurements listed were made Before changing out T/V 13 and T/V 14.

All 4 LEDs are now ON! Voltages appear to be within spec.

Next up, biasing and then trying it out.

Thank you for all your support!

I would like to emphasize the importance of making sure T/V 13 and T/V 14 are reversed from the rest of the "odd" and "even" numbered transistors... for newbies like me!

Keith
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 13, 2016, 09:52:55 PM
Good news. Now calibrate the amp!
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 14, 2016, 01:36:54 PM
All 4 LEDs light up at power on and stay lit.

R1 = 0.7v
E1 = jumps around from 20 mv to 0.0v
Trim pots have no effect.

Pin 6 of IC2 = 9v
Pin 6 of IC6, 11, and 15 = 7v to 7.3v

Should my next step be jumpers?
If so, which ones?
If not, what do you recommend?
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 14, 2016, 08:18:08 PM
Next step is to adjust the input bias current.

Put tin on J5 (to start with) and measure across R1. Adjust down to 0 mV. If you don't succeed, put tin on the J4 instead.

Observe also the voltage on the DC servo opamps IC1 and IC3 and their outputs, pin 6. The voltage should be within the linear range of the opamp.

The DC offset on the amp output should be a few millivolts.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 15, 2016, 12:09:58 AM
I jumpered J5 and LED H2 went dark
I remove J5 Jumper and LED H2 lit.
Next, I jumpered J4. LED H1 went dark.
Neither jumper helped to reduce the bias so I removed them...each tested separately.
All 4 LEDs are lit.

I replaced R1 and E1 with new 100K resistors.

I replaced P1 and P2 with new trim pots.

The lowest I can get is 120 mv to 220 mv.
Turning the trim pots CW and CCW had no effect.

OPA134 Pin 6 on both opamps = 13.7 v


BTW, I just hooked up the amp and I'm listening, now. Awesome! I wonder how it will sound once I properly bias it?

Very clean sound quality...wonderful detail...no hyperbole, I'm hearing details I've not heard before.

Odd behaviour, though...H2 went dark after I hooked it up but the sound is great....??

Many thanks for this audio marvel,

Keith
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 15, 2016, 06:44:24 AM
How much voltage did you get over R1?

How much can you tune this voltage, over R1?

The DC servo is saturated and doesn't work so you must do some fault tracing. The output should be around 0 mV. If you have the same problem in both channels, then you have some part in the wrong place or the wrong value.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 15, 2016, 03:00:42 PM
Well, it seems I started to celebrate too early. Last night the amp sounded great despite H2 being off. This morning there's nothing but loud hum from both channels but H1, H3, and H4 are lit. H2 shows 1.0v and the other 3 that are lit show 1.75v.

Voltage across R1 and E1 are approximately 120 mV with trim pot all the way CCW, 150 mV at center, and 185 mV with trim pot all the way CW.

What should OPA134UA show at Pin 6? I get 18.5 v on the left channel and 13.5 v on the right channel with black DMM probe touching one of the ground terminals on the input terminal block.

I will re-check all components, placement, and values.

Is there anything else you recommend?

Thank you
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 15, 2016, 09:35:43 PM
The voltage across R1, was it + 120 mV or -120 mV?

Which pad did you have a tin drop ion, J5 or J4? I'll none.

18.5 V? How much is your supply voltage really?

Your supply voltage should be 13.9 V ± 5% The opamp output should be between 2 and 11 volts, if not it's not in it's linear range.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 16, 2016, 12:24:11 AM
P-A: The voltage across R1, was it + 120 mV or -120 mV?
BMF: Black probe on ground side, Red probe on other side of R1 and E1:
P1 Full CW,   R1 = -60mv
P1 Full CCW, R1 = -60mv
P2 Full CW,   E1 = -62mv
P2 Full CCW, E1 = -61mv

P-A: Which pad did you have a tin drop ion, J5 or J4? I'll none.
BMF: None for previous and for these measurements.

P-A: 18.5 V? How much is your supply voltage really?
BMF: Black probe connected to Ground terminal of Input Terminal Block, Red probe on Pin 6 of all of the following VDC:
IC1 = -12V
IC3 = -12V

IC6 = -18.9V
IC2 =    8.9V
IC15 = -7.1V
IC11 =  7.1V

Black probe connected to Ground terminal of Input Terminal Block, Red probe to Pins 4, 3, and 2 for all the following VDC:
IC6 = -21V, -21V, -10.6V
IC2  = 0.00V, 6.95V, 6.95V
IC15 = -13.6V, -6.92V, -6.92V
IC11 = 0.00V, 6.91V, 6.91V

Black probe connected to Ground side, Red probe connected to other side of all the following VDC:
C32 = -23.6V
C31 =  23.5V
G32 = -23.4V
G31 = 23.5V

R32 = -23.7V
R31 =  23.5V
E32 = -23.4V
E31 =  23.5V

Black probe connected to Ground side of LEDs, Red connected to Positive side of LEDs for all the following VDC:
H2 = 1.05V Not On
H1 = 1.73V On
H4 = 1.73V On
H3 = 1.73V On

Black and Red probes connected to ~ and ~ terminals of Bridges for all the following VAC:
Br2 = 19.7VAC
Br1 = 19.7VAC
Br4 = 19.7VAC
Br3 = 19.7VAC

Primary Transformers = 122VAC

P-A: Your supply voltage should be 13.9 V ± 5% The opamp output should be between 2 and 11 volts, if not it's not in it's linear range.
BMF: Do I need to measure anywhere else?
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 16, 2016, 06:33:26 AM
The Input bias is positive, flowing into the amp, then you'll need and positive current for compensation, use J4 and adjust down to zero mV. It's not critical since the DC servo will take care of the rest.

The raw voltage of 23 V DC is OK

IC6, something is wrong.

Correct values if you have a working regulator is

Pin 2 6.9 V
Pin 2 6.9 V
Pin 4 13.9 V
Pin 6 Around 6-7 V

Do you really have a LM337 in the IC10 position?

If you check the schematics where you have 15V_L, 15_R you should have around 14 V and extremely stable and the same goes for -15V_L and -15V_R.

What is your output voltage from the amp? Should be some mV only if the DC servo works.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 16, 2016, 01:48:55 PM
P-A: The Input bias is positive, flowing into the amp, then you'll need and positive current for compensation, use J4 and adjust down to zero mV. It's not critical since the DC servo will take care of the rest.
BMF: I jumpered J4.
P1 @ Full CCW = 0.67 mv
P1 @ Full CW = -1.5 v

Jumper J2 (J1 Not Jumpered) had no effect on the Right Channel at P2 set to Full CW and Full CCW so I removed it and Jumpered J1

I jumpered J1 (Jumper 2 removed).
P2 @ Full CCW = 0.55 mv
P2 @ Full CW = -1.24 v

.

The raw voltage of 23 V DC is OK

IC6, something is wrong.

Correct values if you have a working regulator is

Pin 2 6.9 V
Pin 2 6.9 V
Pin 4 13.9 V
Pin 6 Around 6-7 V

P-A: Do you really have a LM337 in the IC10 position?
BMF: I used 926-LM337IMP/NOPB from mouser. The Code on top is: 5915 N02A.
All continuity checks from all 4 pins to surrounding components of the Left Channel LM337 match those of the Right Channel LM337 at IC18. BTW, I used 926-LM317AEMP/N0PB for IC7 and IC14 with Code: 5AE6 N07A.

P-A: If you check the schematics where you have 15V_L, 15_R you should have around 14 V and extremely stable and the same goes for -15V_L and -15V_R.
BMF: Voltage across R44 = -15.5v. Voltage across R45 = 9.0v.

P-A: What is your output voltage from the amp? Should be some mV only if the DC servo works.
BMF: Voltage at the Output Terminal Block for the Right Channel = 119mv; for the Left Channel = 0.0v. Note that Black probe to Ground and Red to Left and Right Out terminals gave Negative measurements. Reversing the probes gave Positive measurements. The Left Channel flashed 14 mv and then went to 0.0v.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 16, 2016, 02:05:07 PM
Close up of IC10

I suppose if all else fails I can remove all components on the bad side and install new parts unless you have another suggestion.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 16, 2016, 02:06:28 PM
Please pick the right spot for measuring the supply voltage. Use the opamp supply pin (in the power supply) or at either side of R43/R42 down to ground. +14 V and -14 V is what you should have. Notice also that you should have 2.5 V across emitter-collector of T34 and T33. The LM317/337 fix a constant voltage across the pass transistors.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 16, 2016, 10:03:50 PM
P-A: Please pick the right spot for measuring the supply voltage. Use the opamp supply pin (in the power supply) or at either side of R43/R42 down to ground. +14 V and -14 V is what you should have.
BMF: I'm sorry to have to ask...Which opamp, which pin, and to which ground?

For R43 to ground terminal of Output Terminal Block = 14.8vdc on AD825 side and 15.1vdc on R53 side.
For R42 = 21.4v on AD825 side and 21.6v on R52 side

P-A: Notice also that you should have 2.5v across emitter-collector of T34 and T33. The LM317/337 fix a constant voltage across the pass transistors.
BMF: T33 (BCP53) = 0.91vdc, T34 (BCP56) = 2.54vdc
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 16, 2016, 10:31:57 PM
I'm talking about the power supply. The thing is to confirm that everything works OK and supply voltage is the thing. You must have a stable voltage at expected level which is 14 V.

You have only 0.91 V across the T33, should be 2.5 V. How about the other channel? It's important that you compare the channels because they should be very much alike.

What is your negative voltage? It seems not to be -14 V? It seems to be 21 V? Same for both channels?

Voltage across IC8 (LM431) should be 6.9V. IC6, pin 3 also 6.9 V and likewise the pin 2. T29 is a BC850?

Once again, if both channels are the same, some part is in the wrong place.

IC2, pin 2 and 3, which voltage?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 16, 2016, 11:40:16 PM
During the time between my last query and your most recent reply, I found that IC6 Pin 3 was not continuous with the "ground hole" next to C43. I removed IC6. I had to make a jumper with a small segment of lead from a resistor and grind it down very thinly so the new IC6 could make contact with all the PCB pads. I soldered this jumper in the copper "hole" beneath IC6 and then soldered the new IC6 in place. All contacts are continuous with their nearby component connections. I now have proper measurements including T33 emitter to collector = 2.56v. And, all LEDs are now lit.

With no jumpers at J4, J5, J2, or J1 and with P1 and P2 set to Full CCW, R1 = 35mv and E1 = 56mv...measurements made with Black probe on the Ground side of the resistors and Red probe on the Positive side.

...BUT, I have loud hum in both channels. I can hear music but it's very low SPL with pre-amp and QRV-08 volume pot turned up all the way.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 17, 2016, 12:24:38 AM
I'm talking about the power supply. The thing is to confirm that everything works OK and supply voltage is the thing. You must have a stable voltage at expected level which is 14 V.

P-A: You have only 0.91 V across the T33, should be 2.5 V. How about the other channel? It's important that you compare the channels because they should be very much alike.
BMF: T33 now = 2.56v

P-A: What is your negative voltage? It seems not to be -14 V? It seems to be 21 V? Same for both channels?
BMF: R42 and E42 = 13.6VDC; R43 = 15VDC and E43 = 13.5 VDC

P-A: Voltage across IC8 (LM431) should be 6.9V. IC6, pin 3 also 6.9 V and likewise the pin 2. T29 is a BC850?
BMF: IC8 = 6.9VDC; IC12 = 6.9VDC
IC6, 2, 15, and 11 = 6.9VDC
T29 is BC850
Once again, if both channels are the same, some part is in the wrong place.

P-A: IC2, pin 2 and 3, which voltage?
BMF: All 4 AD825 at Pins 2 and 3 = 6.9VDC

Still the loud hum and low SPL playing music.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 17, 2016, 06:19:45 AM
Do you have a hum when playing at low volume?

Duo you have a stable supply voltage at high output level?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 17, 2016, 01:12:51 PM
Hum at low volume. Hum becomes progressively louder as the volume pot is increased. No music at all.

Repeated Measurements:

R42 to ground terminal = -13.9 vdc on R52 side at Low and High volume pot settings
R43 to ground terminal = 15.01 vdc to 15.7 vdc on R53 side at Low and High volume pot settings
E42 to ground terminal = -13.8 vdc on E52 side at Low and High volume pot settings
E43 to ground terminal = 13.8 vdc on E53 side at Low and High volume pot settings

IC6 Pins 2, 3, 4, and 6 = -6.9, -6.9, -13.6, -7.1 vdc
IC2 Pins 2, 3, 4, and 6 = 6.95, 6.95, 0, 8.9 vdc
IC15 Pins 2, 3, 4, and 6 = -6.9, -6.9, -13.7, -7.1 vdc
IC11 Pins 2, 3, 4, and 6 = 6.9, 6.9, 0, 7.0 vdc

IC3 Pin 6 = -6.1 vdc
IC1 Pin 6 = -13.6 vdc

T33, T34, V33, V34 = 2.5 vdc

R1 =-31 mv
E1 = -39 mv

R3 = 24 vdc
E3= 25.6 vdc

Amp Output:
Left to Ground = a few mv then goes down to 0
Right to Ground = a few mv then goes down to 0

Amp Input:
Left to Ground = 0
Right to Ground = 0

Volume Pot:
RCAs to In = 0 for both channels
Out to Amp In = 0 for both channels

RCAs Positive to Negative:
A few mv then goes to 0
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 17, 2016, 01:41:44 PM
It seems that you are getting things together. You have a slightly higher positive supply voltage in the other channel but this doesn't matter.

I'm interested how your DC servo outputs are in stable state. They should be +-11 V or so max, well within their linear range. I see that you have IC3, 6 at 13.6 V which is a bit much. Try to adjust the input bias a bit so the opamp will work a bit less hard.

About the hum. If you have shorted inputs and no hum, then everything is OK. If you get hum using your volume control, then you have the problem there.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 18, 2016, 12:32:57 AM
P-A: I'm interested how your DC servo outputs are in stable state. They should be +-11 V or so max, well within their linear range. I see that you have IC3, 6 at 13.6 V which is a bit much. Try to adjust the input bias a bit so the opamp will work a bit less hard.
BMF: Actually, it's IC1 that shows 13.6v. IC3 shows 6.94v
I jumpered J1 and retested: no change, still 13.6v but the polarity changes from full CW to full CCW.
I removed J1 jumper and jumpered J2 with the same results.
I removed J2.

P-A: About the hum. If you have shorted inputs and no hum, then everything is OK. If you get hum using your volume control, then you have the problem there.
BMF: You are correct. I have a bad Blue Velvet volume pot. None of the contacts are shorted but it HUMS like a banshee! I borrowed a Blue Velvet from another one of my DIY amps and installed it in QRV-08 and it works like a charm. The sound quality is stellar! Nicely micro-detailed, balanced FR, balanced channel SPL, punchy bass, crystal clear mids, very nice treble extension.

I remain puzzled about the Right Channel Servo. Maybe I should install a new IC1?

P-A, thank you so much for your patience helping this newbie troubleshoot all these problems. As you know, I ordered another QRV-08 board from you. I just received all the bits from mouser needed to build another one. Maybe it will perform better than this one!

Best Regards,

Keith
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 18, 2016, 09:56:55 AM
You should take a look at the IC1 DC servo. If you adjust the input bias the DC servo should move. If the opamp is OK (should be) then you should have 0.0 mV at both pin 2 and 3 plus some offset, a mV or two.

If the DC servo is saturated it can have a bad influence of the sound.

IC3 has 6.94 V and is well within the linear range.

So with this small DC servo check up the amp is up and running. Nice!

Lessons learnt: Extremely important to solder the right part in the right place.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 18, 2016, 04:08:32 PM
Amp is still running and sounds great out of both channels.   :-D

There are obvious asymmetries in these readings:

Left Output = 0v (P1 at Full CCW; no jumpers)
Right Output = -196mv (lowest value I can get with P2 at Full CCW; no jumpers)

R28=0v,        R29=-34mv       R30=-2.9v     R31=-2.8v
E28=13.4v     E29=-220mv     E30=6.9v      E31=280mv

R1=-30mv     E1=-37mv (these are the lowest values I can get with P1 and P2 at Full CCW settings. Which jumpers should I try?)

R3=25.6v      E3=23.95v

C18=-2.9v    G18=540mv
C17=-2.1v    G17=12.7v
C16= 0.0v    G16=13.6v
C15=-15.4v  G15=13.8v
C14=-13.9v  G14=13.8v

           IC1          IC3     
Pin 
1         13.5v       15.2v
2         -0.8v         0.0v   
3         -13.6v       0.0v
4         -13.8v      -13.9v
6         -13.6v      -5.85v
7          13.8v       15.4v
8          13.5v       15.2v

Maybe I should start with replacing IC1?
If that doesn't work, I suppose I could remove all its associated resistors and caps and install new ones.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 18, 2016, 05:08:03 PM
I think you should check all parts around the soldering first.

E28, on both sides? If you have Almost zero to the left and 13.6 to the right, then the opamp might be a bit fishy.

Is it OPA134 you use? If yes you have nA current at the pin 2 and 3 and getting 0.8V across E29 is totally wrong.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 18, 2016, 08:30:38 PM
Quote P-A: I think you should check all parts around the soldering first.
BMF: I will reflow these parts. If no good, I'll install new ones.

Quote P-A: E28, on both sides? If you have Almost zero to the left and 13.6 to the right, then the opamp might be a bit fishy.
BMF: -12.87v, 12.87v with probes reversed. If you mean check the solder joints, yes I will.

Quote P-A: Is it OPA134 you use? If yes you have nA current at the pin 2 and 3 and getting 0.8V across E29 is totally wrong.
BMF: Yes, OPA134.

Sorry, I don't understand...
nA current is at pin 2 and 3 of IC3 (the good one) and R29=-34mv
Current at pin 2 and 3 of IC1 (the faulty one) = -0.8v and -13.6v and E29 now = -158mv

BTW, I'm using a new Klein MM6000 DMM

I will check the solder joints, now.

Thank you
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 18, 2016, 11:10:11 PM
Notice that you can't reflow the pcb many times. It's a huge stress. I'll recommend that you use a soldering iron with a small tip when you rework the soldering.

34 mV over 470 k (plus 10 Mohms from your DMM in parallel) = 72 nA That is much more than the data sheet tells me. According to the data sheet it should be around 10 pA.

I think it looks like a good idea to the change the IC1 but I wonder how you have succeeded doing that?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 19, 2016, 02:19:28 AM
Quote P-A: Notice that you can't reflow the pcb many times. It's a huge stress. I'll recommend that you use a soldering iron with a small tip when you rework the soldering.
BMF: Yes, I know and learned the hard way on IC6, IC15, T33, and V33 where I had to make DIY jumpers! I use a tiny tip and a lot of Kester no-solids liquid flux.

Quote P-A: 34 mV over 470 k (plus 10 Mohms from your DMM in parallel) = 72 nA That is much more than the data sheet tells me. According to the data sheet it should be around 10 pA.
BMF: You're using terms and math I don't yet understand...I'm a newbie.  :-(

Quote P-A: I think it looks like a good idea to the change the IC1 but I wonder how you have succeeded doing that?
BMF: I used liquid flux and a solder sucker with my Weller WES51 set to 625 F. Then, I used flux and MG Chemicals Super Wick .075" until almost all the solder was removed. More flux and quickly dragging the soldering iron tip back and forth across all 4 pins on one side released the pins from the pads and then, the other side. Double-checked continuity between each pad and its connection...all good; dabbed a bit of solder onto the pads, then reflowed holding OPA134 in place with micro tweezers.

The measurements were not significantly different from those before I switched out OPA134...output from Pin 6 = 12.5 v.

The amp sounds great! I do not hear any channel imbalance or reduced sound quality from the Right Channel. Unless you have other suggestions, I'll leave well enough alone...and build another one!   8-)
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 19, 2016, 02:23:16 AM
New OPA134UA installed.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 19, 2016, 08:55:22 AM
Quote P-A: 34 mV over 470 k (plus 10 Mohms from your DMM in parallel) = 72 nA That is much more than the data sheet tells me. According to the data sheet it should be around 10 pA.
BMF: You're using terms and math I don't yet understand...I'm a newbie.  :-(

If you don't know Ohm's Law I think you should learn it. In Sweden they teach this in the 7th grade I think (13-14 years old).

https://en.wikipedia.org/wiki/Ohm%27s_law

I my example above you know the resistance and the voltage across it, then you can calculate the current through it. When the resistors is getting higher in value the 10 Mohm from the volt meter will introduce an error. Sometimes it is necessary to take this into account.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 19, 2016, 05:59:49 PM
Quote P-A: Notice that you can't reflow the pcb many times. It's a huge stress. I'll recommend that you use a soldering iron with a small tip when you rework the soldering.

34 mV over 470 k (plus 10 Mohms from your DMM in parallel) = 72 nA That is much more than the data sheet tells me. According to the data sheet it should be around 10 pA.

I think it looks like a good idea to the change the IC1 but I wonder how you have succeeded doing that? ...End Quote
_____________________________________________________________________________________________

Quote P-A: 34 mV over 470 k (plus 10 Mohms from your DMM in parallel) = 72 nA That is much more than the data sheet tells me. According to the data sheet it should be around 10 pA.
BMF: You're using terms and math I don't yet understand...I'm a newbie.  :-(

If you don't know Ohm's Law I think you should learn it. In Sweden they teach this in the 7th grade I think (13-14 years old).....End Quote

BMF: LOL...  Despite our inferior educational system, I know Ohm's Law.  You were talking about stressing the PCB and changing out IC1. I didn't realize you were talking about something else (current across a resistor) in between, and I was unable to relate it to IC1.

I did not know it was necessary to compensate for the DMM. I thought the DMM automatically calculated and applied the compensation.

Anyway, thanks for all your patient assistance. I've learned a ton and expect the next one to be easy. The additional board you sent should arrive this week and all the parts are sorted and ready to go.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 19, 2016, 07:59:49 PM
Notice that some DMM's has a very high input impedance (Ohms) and some has only 10 Mohms. You have to look in the technical data for the DMM in mind to determine that. When you measuring over 1 Mohms and above your DMM will have an influence of the measurement.

When you have changed the faulty IC1 I'll hope that you amp is in perfect condition. I don't mind a small review when you have used he amp for a while. Some pictures would be nice.

This design is my favorite because it took a lot of time to design and the result became very well although one person though it was too good since it revealed all flaws in the recordings.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 20, 2016, 02:15:59 AM
P-A,

I'll "live with" QRV-08 for a while and compare to my other amps. I remain impressed with QRV-08's clarity, bass and treble extension, micro-details, and Wide soundstage. Truly remarkable sound reproduction...and, yes, I am familiar with and guard against expectation bias.

BTW, as it turned out, the hum was not from the ALPS Blue Velvet pot. It was due to a faulty set of RCA cables. I switched them out with another set of RCAs (a cheaper set!) and both ALPS pots I tried work without hum. In addition, the sound quality improved noticeably.

Keith
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 20, 2016, 02:45:31 PM
What can cause a LED to randomly turn off and come back on while music still plays and sounds the same whether the LED is On or Off?

Is 18 volts at the LED and associated resistor too high? Would there be any benefit in changing the value of the resistors and/or caps?

Changing out IC1 had no effect. I still get 12 to 13 volts at Pin 6.

Turning P1 and P2 has no appreciable effect on the measurements.

Still sounds great.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 20, 2016, 03:33:36 PM
The LED's must always be lit, if not the regulators won't regulate properly. You may too low raw voltage. It must be 5 V more than the output voltage. 14 V out gives 19 V in as the very lowest.

Can you measure the voltages at the replaced opamp?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 20, 2016, 11:17:13 PM
Quote P-A: The LED's must always be lit, if not the regulators won't regulate properly. You may too low raw voltage. It must be 5 V more than the output voltage. 14 V out gives 19 V in as the very lowest.

Can you measure the voltages at the replaced opamp? ...End Quote

BMF: H1 had a cold joint. I reflowed it and it works fine, for now.

Raw A/C voltages are 23 to 24 vac.

           IC1 (replaced opamp)     IC3
Pin
1         13.41vdc                       15.0vdc
2        -1.14 vdc                        0
3        -355 mv                         0
4        -13.8vdc                       -13.9vdc       
5           5.9vdc                       -106mv
6         12.7vdc                        -5.7vdc
7         13.8vdc                        15.6vdc
8         13.5vdc                        15.5vdc


LEDs Red probe to positive terminal, Black probe to ground plane:

H3=16.3
H4=-14.7
H1=18.2
H2=-14.7

Sound Quality remains excellent.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 21, 2016, 06:31:59 AM
IC1 is not doing the job properly. It's saturated, Do you have -355 mV offset on the output? Since you have a quite different voltage at pin 2 and 3 , I see that it doesn't work. What is you voltage at the P2 and the wiper (left side of the E27)? Voltage across E1?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 21, 2016, 01:26:32 PM
Quote P-A: IC1 is not doing the job properly. It's saturated, Do you have -355 mV offset on the output? Since you have a quite different voltage at pin 2 and 3 , I see that it doesn't work. What is you voltage at the P2 and the wiper (left side of the E27)? Voltage across E1?

BMF:
IC1 Pin 3 now = -380mv, it jumps around from -370 to -380mv

At the output terminal:
Right Channel offset -380 to -400mv
Left Channel offset 0.0

E1 = -41mv
R1 = -31mv

P2 centered between Pin 1 and Pin 3. Sorry, I'm uncertain where to probe to get a proper wiper measurement:
Black probe to ground plane at input terminal, Red probe to Pin 1 = -4.3mv for 1 second then = 0.0; about the same to Pin 3.

Black probe to ground plane, Red probe to P2 metal case = 8mv that climbs to  21.5mv; P1 = -8mv that descends to 0.0. Are P1 and P2 shorted to metal case?
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 21, 2016, 07:16:07 PM
You see that the output offset is way to much. Try to make the voltage across E1 more positive. Put the jumper on J1 to get positive bias. The pin 6 och IC1 should be under 10 V and the voltage at pin 2 and 3 should be 0 mV.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 22, 2016, 01:37:23 AM
How do you spell C-A-T-A-S-T-R-O-P-H-E?!

My wife rescued a small pit bull a few weeks ago. I called the mutt a "Demon Dog" even before this catastrophe. She escaped from her kennel this afternoon before my wife could grab her and ran upstairs to my "lab." I heard a CRASH...she pulled my QRV-08 from its shelf onto the floor. Several parts were broken off the PCB and others I cannot see may be damaged.

Bottom line, I think this amp is destroyed. I re-soldered the broken bits and searched for other faults but still no joy.

My plan to build another QRV-08 is based on the stellar sound quality I enjoyed but for a brief moment.

My wife OWES me BIG TIME!!!
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 23, 2016, 01:34:29 AM
Against all odds I was able to patch the amp back together. I jumpered J1, then J2. Neither one had any effect on the measurements. Still 13 v on Pin 6 of IC1. Pins 2 and 3 are screwy with mv on Pin 2 and 5 v on Pin 3.

IC3 Pins 2 and 3 = 0.0v. Pin 6 = 5.95v.

R1 and R3 measure -30mv.

Despite all the abuse, removing/re-installing components, and faulty offset the amp still sounds great!
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 23, 2016, 06:16:01 AM
You must fix the IC1 DC servo. Do you still have -400 mV at the output?
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 23, 2016, 07:56:37 AM
Output Left Channel  = 0.0
Output Right Channel = 214 mV

P1:
Pin 1 = 0.0 V
Pin 3 = -13.9 VDC

P2:
Pin 1 = 0.0 V
Pin 3 = 13.7 VDC

P1 CW at R1 = -7.35 VDC; CCW = -14mV
P2 CW at E1 = 1.27 VDC VDC; -32 mV

R3 = -12.1 VDC
E3 = -12.1 VDC

IC1 pin 6 = -13.6 VDC
IC3 pin 6 =- 5.1 VDC
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 23, 2016, 02:41:57 PM
A couple of posts above you had -400 mV output offset, now you have +204 mV?

You should concentrate your efforts to the right channel since the left one seems to work.

You should try to adjust the input bias to see if you can force the offset to change and put the IC1 into their linear working range.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 23, 2016, 04:31:06 PM
I know, it's odd but remember the amp was nearly destroyed and I patched it back together. I double checked the most recent measurements and will repeat them, today, after work.  Troubleshooting continues until the new QRV-08 board arrives.

IC1: Pins 2, 3, 4, 6, and 7 are all continuous with their associated components. I don't know how to check the offset trim at Pins 1 and 8, if it's necessary to do so.

I'll try J2 again to see if adding some negative bias helps pull it down from 214 mV.

Three AD825's show 7.0 to 7.3 VDC at pin 6 and their corresponding LEDs to ground show 14 to 16 VDC.
The fourth one (IC2) shows 8.8 VDC at pin 6 and its LED (H1) to ground shows 18.5 VDC. Is this too much? 

All 4 LEDs show voltage drop across their pos/neg terminals of 1.75 VDC.

Title: Re: QRV08 Setup Instructions
Post by: peranders on June 23, 2016, 08:54:10 PM
You can leave pin 1, 5 and 8, not used.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 23, 2016, 11:46:16 PM
OK on pins 1, 5, and 8 of the servo.

I jumpered J2 with no effect except lowering the voltage from ~5 v at P2 CW to 1.25 vdc. P2 at full CCW remains -35mV  with and without J2 jumper.

I re-verified all resistors across the entire board and they're all correct Left Channel and Right Channel.

In your BOM, you indicate jumpering R/E 56 and 57. Is there any potential benefit of installing 470R at E 56 and 57?
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 24, 2016, 07:19:53 AM
If you go from -14 V till + 14 V at the pot P2 you have a constant -35 mV at the input?

E27 (left side in the schematics), do you get there -14 to +14 V when you jumper J1 and then J2?

Between E27 and E26 you should have half the voltage. and across E1 you should have varying mV's.

R57/E57 is good to have just in case but you should have zero ohms there to start with because the impedance seen from pin 3 and pin 2 should be the same. For my super regulators I use 499 ohms in the R51 place but this is nothing you have do to here.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 24, 2016, 02:00:19 PM
I'm sorry but I don't fully understand your first comment.

Here are the measurements you requested:

                      P2 CCW           P2 CW
No Jumper:
Across E1       -33.8 mV         -241 mV
E27 to Grd        0.0               105 mV
E27 to E26    33.7|16.6 mV    12|6.1 VDC
Output           203 mV            5.5 VDC

J1:
Across E1       -33.4 mV         1.3 VDC
E27 to Grd        0.0              13.8 VDC
E27 to E26    32.2|16.8 mV  12.4|6.1 VDC
Output            205 mV           5.9 VDC

J2:
Across E1     -34.3 mV         -1.34 VDC
E27 to Grd      0.0               -13.8 VDC
E27 to E26   33.7|16 mV     -12.4|-6.1 VDC
Output          203 mV             5.5 VDC

J5:
Across R1   -27.8 mV          -1.3 VDC
R27 to Grd    0.0               -13.9 VDC
R27 to R26  28|13 mV         -12.4|-6.1 VDC
Output          0.0                -5.5 VDC
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 24, 2016, 08:10:29 PM
Could you tell me the voltage at IC1, pin 2, 3, 6 for the same measurements as you did?

Output voltage at the amplifier output also?

1.3 V in lead to 5.9 V out

-1.34 V lead to 5.5 V out. Is it really plus or is it -5.5V?

It's really important that IC1 pin 2 and 3 will land on 0 mV and the pin 6 within ±10V or so.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 25, 2016, 12:47:22 AM
Quote P-A:Could you tell me the voltage at IC1, pin 2, 3, 6 for the same measurements as you did?

Output voltage at the amplifier output also?

1.3 V in lead to 5.9 V out

-1.34 V lead to 5.5 V out. Is it really plus or is it -5.5V?

It's really important that IC1 pin 2 and 3 will land on 0 mV and the pin 6 within ±10V or so....END Quote

BMF: My mistake...it's -5.5V

Measurements You Requested:

No Jumper at J1 or J2:
IC1
Pin         P2 CW         P2 CCW
2           12.97V         12.98V
3           12.88V         12.85V
6          -13.70V       -13.70V
Output      5.5V         201mV

J1 Jumper:
IC1
Pin        P2 CW         P2 CCW
2          12.99V         12.86V
3          12.94V         12.80V
6         -13.65V        -13.65V
Output    5.9V           192mV

J2 Jumper:
IC1
Pin       P2 CW        P2 CCW
2         12.70V        12.99V
3         12.90V        12.91V
6        -13.66V      -13.65V
Output   5.5V         204mV

J5 Jumper:
IC3
Pin      P1 CW         P1 CCW
2        -3.2mV         0.0V           
3        -5.2V            0.0V           
6       -13.69V        -5.9V 
Output  -5.5V          0.0V         

How can the Right Channel be so out of spec but the amp sounds fantastic?!  There is no channel imbalance or diminished sound quality from the Right Channel.
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 25, 2016, 09:27:46 AM
The IC1 seems to be broken. Pin 3 shall always follow the output of the amp. Notice that the OPA134 has pA on the inputs which means you can use Ohm's law very easily for faultracing.

Having DC on the output doesn't have any influense on the sound itself but your headphones doesn't like.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 25, 2016, 09:46:14 PM
I carefully removed IC1, E28/29/30, and C14/15. Next, I verified all PCB pads were in good shape and continuous with their components, using the schematic. I checked resistance and capacitance of the parts before installing them. I verified each part, placement, and orientation of IC1. I very carefully installed all new parts and did not overheat anything. Last, I verified continuity of all connections. Everything looks good.

The results were the same as before. J1 vs J2 vs neither jumpered:

Across E1 = -38mV
Pins 2 and 3 of IC1 measure in the range of 500 to 750 mV.
Pin 6 of IC1 reads -13.7 VDC
Right output only slightly better with J2 = 164 mV vs no jumper = 204 mV and P2 full CCW.

So, this one goes on the shelf and I'll start another QRV-08....the PCB arrived today...Thank you!
Title: Re: QRV08 Setup Instructions
Post by: peranders on June 25, 2016, 09:52:19 PM
The output offset is? Do the same as in your previous post. The goal is to get 0 mV out.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 26, 2016, 07:48:53 PM
The PSU for my second QRV-08 is complete, tested, and working. I used Phoenix terminals to make transformer connections and disconnections easier. For the Primaries, I drilled 2 mm holes with 5 mm pin spacing to accommodate the unused terminal pin for stability.

Mains Input              Varistor               Transformer Primaries          Transformer Secondaries
122 VAC                  122 VAC               120 VAC                              20.9 VAC

Bridge 3 ~~             Bridge 4 ~~          Bridge 1~~         Bridge 2~~
20.96 VAC               20.96 VAC             21.02 VAC          21.04 VAC

Bridge 3 + -            Bridge 4 + -          Bridge 1 + -       Bridge 2 + -
27.54 VDC              27.53 VDC            27.61 VDC          27.62 VDC

G31                        G32                     C31                    C32
27.52 VDC             -27.53 VDC           27.62 VDC         -27.52 VCD

I'll work on the Regulators this afternoon.
Title: Re: QRV08 Setup Instructions
Post by: BMF on June 30, 2016, 02:23:53 AM
Making progress on Build 2. Regulators are up and running.
-24.9 and 24.9 VDC from the PS
Pins 2 and 3 of AD825 show 6.9 or  -6.9 VDC depending on the rail.
Pin 6 from all 4 AD825's measures 7.09 and -7.1 VDC.
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 05, 2016, 01:34:05 AM
A week's worth of spare time and my second build is finished. This one went much faster than my first.

I built and tested the power supply, first, and it checked out...all good.

I built the regulators and tested them and they meet specifications, too, so I finished with the amp sections. All transistors measured 0.6 to 0.7 volts; 15 volts regulated. Proper voltage across LEDs. All connections are continuous and the Left and Right Channels are mirrored. PLUS, I remembered to swap NPN/PNP at T/V 13 and 14! 

One of the servos is a little "wonky" but I installed a previously used OPA 134 at IC3...not a wise choice in retrospect, but I know how to desolder it and will replace it with new a one when it arrives from mouser, this week. I can get its output offset down to 0.00 volts but then IC3 is saturated = -13.6 volts. I can get it down to ~ -6 volts by turning P1 but then the offset goes up to around 20 mV.  All this is with J1 and J5 jumpered. I tried J1 with J4, J2 with J5, and No jumpers. J1 and J5 jumpered offered the best measurements, so far, but this will hopefully change with a new OPA 134 at IC3.

Correct me if I'm wrong, but...I put the black probe to the ground plane at the input terminal and the red probe on Pins 2, 3, 4, 6, and 7 of the servos and Pin 6 of the regulator ICs (all 4 = 7.01V or -7.01V). IC1 Servo Pins 2 and 3 = 0.0 Volts but I get 55 mV and -35 mV on IC3 Pins 2 and 3.

Anyway P-A, thanks for the fun and Great sound ---> Dynamic, Detailed, Killer SQ from Bass to Treble, Silky Mids, Micro Details, Transients...QRV-08 delivers it all!

P1 and P2 are super sensitive but maybe this if because of the servos?  I ordered some multi-turn (9 turns) 10k SMD pots. If they fit, I may give them a try, if all else fails.

Despite these little problems, the amp performs and sounds wonderful.
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 08, 2016, 03:27:52 AM
I received new OPA134's, today, from mouser. I removed both the originals and installed the new ones. I "ohmed-out" all connections and get 0.0 to 0.1 resistance at all the IC1 and IC3 connections. All measurements check out...Done.

Sounds great.
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 09, 2016, 03:21:38 AM
9-turn Trim Pot makes it easier to adjust offset.

The pot I ordered doesn't  align with all 3 pads. I used a segment from a resistor lead to reach the wiper pad.
Title: Re: QRV08 Setup Instructions
Post by: peranders on July 09, 2016, 11:54:18 AM
Normally it's not necessary to have a offset trim of the DC servo opamp since the value you will get is around a 0.5-2 mV untrimmed (according to the datasheet).
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 09, 2016, 09:56:37 PM
I must be doing something wrong, then.

I can adjust the value at R/E 1 to 0.0 but the offset is around 150mv. Conversely, I can adjust the offset to 0.0 but R/E1 measure around 80mv.   The servos range between 6 and 13 v -/+ depending on bias jumpers.

The amp sounds excellent irrespective of the measurements.

Title: Re: QRV08 Setup Instructions
Post by: peranders on July 10, 2016, 07:09:28 PM
Notice that the offset at the amplifier output should be zero and if you have some 80 mV at the inout doesn't matter as long as the DC servo can remove the output offset.

Do you mean that the output offset is 150 mV no matter what?
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 13, 2016, 12:32:26 AM
I can adjust P1 and P2 so that the output offset = 0.00 ... and R1/E1 = -85 mV.

Here's what I do:
1. black probe inserted in either input or output terminal ground
2. red probe inserted in the Left output and then the Right output
3. Then, trim P1 and P2 so that the Left channel and Right channel output offset = 0.00; R1/E1 then = -85 mV

I've done this with various combinations of J1, J2, J4, and J5 (but never both on the same side) and with the Left/Right inputs shorted vs not shorted...and I get similar measurements.

Adjusting R1/E1 to 0.00 results in offsets around 150 mV at both channels.

The power supply and regulator measurements are spot on.

I have confirmed that all components on each negative and positive amp sections are correctly placed, mirrored, continuous, and close to 0.0 resistance between components. I cleaned up the flux with 99.99% isopropyl alcohol.

As I've said before, the sound quality is balanced and excellent.

The photo text is a bit blurry and says, "This Jumper improved the offset bias after a couple of IC3 changes."
Title: Re: QRV08 Setup Instructions
Post by: peranders on July 13, 2016, 06:22:14 AM
The goal is to get 0 mV on the output, do you get that? You should also have a voltage on pin 6 of the DC servo opamp which is somewhere within ±11 V. The opamp must not be saturated.
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 13, 2016, 01:00:42 PM
The power supplies and regulators function perfectly. No issues. I cannot find any component errors at the amp sections and no cold joints or resistance issues. As you've said before, when the same problematic measurements are found on both sides, there's probably incorrect component values somewhere.

I get 12 vdc on both sides of R3/E3.

R1/E1 measure 0.5 to 0.8 vdc.

IC 1 and IC 3 are saturated at Pin 6=-13.6 vdc and Pins 2 and 3 are not equal and range between 200 to 300 mV.

With no jumpers, P1 and P2 have little to no effect on offsets, CW as well as CCW; same for R1/E1. And, shorting the inputs makes no difference.

Jumpering or no jumpering does not change -13.6 vdc at Pin 6 of IC1 or IC3.

Since the sound quality remains good (I'm using AKG 7 XX and Sennheiser 650) and my measurements are unreliable from one "testing session" to the next, I wonder if I'm going about measurements all wrong?

As always, thank you for your help.
Title: Re: QRV08 Setup Instructions
Post by: peranders on July 13, 2016, 05:46:42 PM
I think you don't understand what I want to know.

Adjust the input bias and observe the voltage on pin 6 of the DC servo opamp and the amplifier output. Notice the pin 6 voltage when you still have 0 mV at the amplifier output. What I want to know is if the DC servo is in its linear range.
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 23, 2016, 03:32:29 PM
The positive rail on the Right Channel of my second build suddenly failed after several hours of normal functioning.

I discovered that G49 on the positive side is shorted to ground at all grounding "holes" across the Right and Left channels of the regulators, and at the negative sides of regulator caps and resistors.

E55 to E53 are shorted on the sides closest to the negative side of G49/G39. I have not been able to determine the cause or specific component responsible for the short.

I changed out the following components on the failed rail with no benefit:

Regulator chip
Red LED
G49, G39
G37
E45, E55, E53, E57

The board is clean. I found no solder bridges or cold joints; no solder balls or other conductive debris.
Title: Re: QRV08 Setup Instructions
Post by: peranders on July 23, 2016, 06:20:25 PM
The board is working now?
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 23, 2016, 07:22:05 PM
Sorry, no. I meant the board is clean of flux, etc. The positive rail on the Right is faulty.

I'll keep searching but I can't imagine why it worked for several hours and then simply stopped working; I had done nothing to it so the positive short to ground is puzzling.
Title: Re: QRV08 Setup Instructions
Post by: peranders on July 24, 2016, 10:56:21 AM
Have you found where the short circuit is?
Title: Re: QRV08 Setup Instructions
Post by: BMF on July 25, 2016, 05:28:38 AM
No luck, yet. I'll keep searching.