QRV08 Setup Instructions

[BMF]

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?

[peranders]

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.

[BMF]

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

[peranders]

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.

[BMF]

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

[peranders]

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.

[BMF]

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?

[peranders]

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.

[BMF]

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.

[attachment deleted by admin]

[BMF]

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.

[attachment deleted by admin]

[peranders]

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.

[BMF]

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

[peranders]

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?

[BMF]

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.

[attachment deleted by admin]

[BMF]

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.