QRV08 Setup Instructions

[BMF]

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.

[peranders]

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?

[BMF]

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.

[peranders]

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]

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?

[peranders]

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.

[BMF]

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!!!

[BMF]

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!

[peranders]

You must fix the IC1 DC servo. Do you still have -400 mV at the output?

[BMF]

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

[peranders]

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.

[BMF]

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.

[peranders]

You can leave pin 1, 5 and 8, not used.

[BMF]

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?

[peranders]

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.