1

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 17, 2026, 09:43:04 AM »

So the issue is in the final gain stage around U1.2.
Check the value, direction and solder joints of U1, R14 to R16, R18, C9, C10, C11.
Do you get a signal on TP4 when the front PCB is completely removed, with power on?
Also try with U2 removed.
All voltages should be measured against 0V.

2

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 16, 2026, 10:59:14 AM »

TP4 = .054vac
TP1 to TP3 all good except TP4?

Do you say that TP4 is back to 1.22VAC when U4 is removed? 

3

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: April 16, 2026, 10:14:20 AM »

(+probe) on collector (-probe) on base gives (+27.93V)
It shows that Q7 is dead.

So measuring from cathode of d20 to tp3 should give the same measurement as tp2 to tp3.  Is this correct?
No. Measuring from cathode of d20 to tp2 should give the same measurement as tp3 to tp2.

When I measure from the anode of d20 to tp2 I do see voltage but not from the cathode of d20 to tp2.
It just shows that there is no current flowing through Q7. The voltage you see is the voltage drop in the Zener, normally a little above 4V.

4

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: April 15, 2026, 05:00:54 PM »

TP3 is at the cathode of D20, not the anode.

Collector -base 27.93V
What do you mean?
- Collector and base @ 27.93V or
- Collector to base is minus 27.93V

I know Q7 was cold where normally it’s pretty warm. 
 It confirms that is is dead or disconnected (check the solder joints).

Is this the correct replacement for Q7?
Yes, correct.

5

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 15, 2026, 04:51:24 PM »

I get 67mvAC across T1 pins 7-10
It should be 650mV!

Check the value and solder joints of R1 and R2.
What resistor do your measure between the 2 left pins of R1 & R2? It should be 200 ohms, the transformer input DC resistance.

6

EQP501 Passive Equalizer / Re: Signal gain increase when engaged

« on: April 15, 2026, 04:36:20 PM »

Is this less < 1 dBu increase in level I’m measuring at 1 kHz when engaging the unit considered normal behavior?  Or should I investigate anything?
The increase is caused by the tolerance on the potentiometers value. All your measures are within specs.
If you need an absolute no gain change, you need to temporarily replace R13 (15k) by a potentiometer, adjust the pot for 0 gain change, measure the pot resistance and replace it by a fixed resistor of equal value.

I do hear a small tick when it passes through the “off" positions of the KCS switch.
Normal. It is caused by the relay switching with an audio signal not null.

if I put pressure on the switch towards the right, the unit disengaged intermittently.
Did you solder the rotary switch absolutely flat on the PCB? Normally, this should not happen because the potentiometer shaft inside the hollow switch prevents it from bending.
If it happens with very little pressure, it will be necessary to replace the switch.

7

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: April 14, 2026, 05:14:09 PM »

E: 28.1V
F:0.001V

This can only happen if Q7 is dead or disconnected.
Can you measure the DC voltages directly on the pins of Q7?

8

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: April 13, 2026, 03:40:21 PM »

Is it time to send it to our workshop for a check?

9

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 13, 2026, 11:33:34 AM »

With a 1VAC signal at the input, IN pot on 10, power off, how many millivolts AC do you get on the input transformer between pins 2 and 5?

10

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 11, 2026, 06:49:12 PM »

TP2=  0.057 VDC
Here is the issue. You should get around 30VDC.
You must check the solder joints on R7, on the tube socket, on the connector that links the tube PCB to the main PCB.
Check that the 48V gets to both sides of R7 (you can check without the tube inserted).

11

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: April 07, 2026, 09:04:14 AM »

Can you please also report the values on TP2 and TP3?

12

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: April 01, 2026, 05:46:35 PM »

Check the solder joint on D20.
If solder joints are OK try to replace D20 (Zener 4V7-1.3W).

13

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: March 30, 2026, 11:19:39 AM »

The diodes D10, D11 on the front PCB have no effect on the the output stage bias setting.
Is the voltage on TP3, against 0V stable, around -11.5V ?
Is the bias voltage bouncing when you tap the PCB or specific components with a pen ?

14

MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« on: March 27, 2026, 04:08:55 PM »

Remove U4.
What values (DC and AC) do you get on TP1 to TP4 in the initial conditions here.

15

CP5176 FET compressor / Re: My CP 5176 is very quiet on the input stage

« on: March 27, 2026, 04:01:52 PM »

D -1.35VDC
Something wrong here.
Check Q4 (BC550C), R11 to R15.

16

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: March 24, 2026, 05:03:39 PM »

No problem, these diodes are very close.

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: March 21, 2026, 09:48:02 AM »

You could look for a continuity between ground and C8, C9, C10. But the best thing to do will be to shorten the pins.

18

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: March 18, 2026, 12:14:19 PM »

I only get resistance from 0.3ohms to about 1.6Kohms
Normal because the trimmer is in parallel with R31+R32.

I have added some DC voltage checks to do here. Please compare with your values.

19

CP5176 FET compressor / Re: My CP 5176 is very quiet on the input stage

« on: March 17, 2026, 05:33:08 PM »

I changed Q1 but that was not the issue
Did the sound return when Q1 was disconnected?

I see that R56 and R57 changed color a little.
This means you have a short circuit somewhere. Are they getting hot? 

A little burned the resistance is correct and they are just for power right? But that cannot be an issue?
You can check their value with your ohmmeter (in circuit).

Do you think it might be transistor or capacitor?
Not a capacitor. Neither a transistor if you got the DC voltages right in the picture here.

20

CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« on: March 17, 2026, 05:23:21 PM »

I moved on and could not get past step 6
What happened at step 6?

Check the solder joints on R26, Tr2, R31.
Check the wire connections to the transformer, look for a thread that might be causing a short circuit.

I was checking for shorts anywhere and did find continuity between two pins on U3
Pins 1 and 2 are connected by a 7R5 resistor, whick way look like a short.

21

MP573 Microphone preamplifier / Re: Inline-attenuator after MP573 and before interface

« on: March 15, 2026, 09:56:49 AM »

It should work. Just check in the specs that they can handle the high line level.

22

TS500 Tape Simulator / Re: “bump” problem

« on: March 05, 2026, 04:57:16 PM »

I noticed a bump when I switch to 30ips from 15ips, and from 7.5 to 15ips.
Do you also get these pops when there is no input signal?
You can compare to the other unit when it is finished.

I have one 100pF to insert in c65.
Sorry for the mistake. Yes, a 100pF will be OK.

23

CP554 Diode bridge compressor / Re: V+ and V- voltage

« on: March 05, 2026, 04:40:02 PM »

Not an issue. The Wes is just a little above the standard voltage.

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CP5176 FET compressor / Re: My CP 5176 is very quiet on the input stage

« on: March 05, 2026, 03:55:57 PM »

Try removing Q1 on the broken unit. If the sound is back then Q1 is the culprit.

25

EQ573 Equaliser / Re: EQ573-II doesn't play sound

« on: February 22, 2026, 10:09:45 AM »

Check if you get the signal on U1 pin 5.
- If not, the issue is around the high pass filter. Check the solder joints on rotary switch SW1, connectors J5a-b and J6a-b.
- If true, the issue is in the relay RLY1 or in U2. Check the solder joints. Try replacing.