QRV08 Setup Instructions

[BMF]

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

[peranders]

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.

[BMF]

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.

[peranders]

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.

[BMF]

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!

[peranders]

The output offset is? Do the same as in your previous post. The goal is to get 0 mV out.

[BMF]

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.

[BMF]

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.

[BMF]

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.

[BMF]

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.

[BMF]

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.

[peranders]

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).

[BMF]

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.

[peranders]

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?

[BMF]

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."