QRV08 Setup Instructions

[peranders]

Do you have a hum when playing at low volume?

Duo you have a stable supply voltage at high output level?

[BMF]

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

[peranders]

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.

[BMF]

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

[peranders]

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.

[BMF]

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.

[peranders]

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.

[BMF]

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

[peranders]

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?

[BMF]

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-)

[attachment deleted by admin]

[BMF]

New OPA134UA installed.

[attachment deleted by admin]

[peranders]

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.

[BMF]

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.

[peranders]

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.

[BMF]

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