1

AB528 Microphone preamplifier / Re: Problème de gain sur AB528

« on: August 23, 2024, 01:19:50 AM »

Est-ce que cette erreur explique les symptômes décrits
A 100%

et, surtout, cela a-t-il pu provoquer un endommagement quelconque ?
Non.

2

AB528 Microphone preamplifier / Re: Problème de gain sur AB528

« on: August 22, 2024, 08:18:30 PM »

You must start by checking the solder joints on SW3, R9...R14, J1a, J1b.
Next, you can check the DC voltages as shoxn here: https://www.soundskulptor.com/forum/index.php?topic=498.msg2966#msg2966

3

CP554 Diode bridge compressor / Re: What is the correct way to stereo link two CP554 units?

« on: August 21, 2024, 02:46:43 AM »

I have selected the 'stereo' button on both units.
Correct.
My inputs/outputs are 7 XLR in & out, and 9 XLR in & out.
Correct.

You also need to set the COMP BUS 8-9 switch to ON. This will link the 2 side chains together.

4

MU524 Vari-Mu Tube Compressor / Re: Different output levels

« on: August 21, 2024, 02:31:13 AM »

It will work with the 25k pots, with a smaller range in the max attenuation area. The 18k resistor won't change the result much so I wouldn't care.

5

MU524 Vari-Mu Tube Compressor / Re: Different output levels

« on: August 19, 2024, 06:52:45 PM »

The input pot difference could be caused by the tolerance on the pot resistance value (20%). You can check the resistance value of the pots between the 2 side pins, pot at max.

Regarding the 20VAC output it might be OK. Simply check that the input transformer is mounted in the correct orientation, label facing towards the back of the module.

6

MU524 Vari-Mu Tube Compressor / Re: MU524- output potentiometer voltage, meter adjustment, and ringing in audio

« on: August 18, 2024, 06:10:35 PM »

Actually this is fine. The 12VAC value mentionned in a previous post was for one single phase of the output. When measuring accross the two phases, you can reach 20V. Sorry for the confusion.

7

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 14, 2024, 06:21:37 PM »

Yes it happens. Electrolytic capacitors are the most fragile components, especially if their temperature is high.

8

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 12, 2024, 11:27:40 AM »

These voltages must be measured against TP2.
So they don't look so bad.
Can you redo these measurements relatively to TP2 from A to L ?

9

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 10, 2024, 06:00:30 PM »

Could be caused by a bad input?
No.

I would start by just replacing the cap which is the most likely to fail.
The other parts replacements are only if this doesn't work.

10

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 07, 2024, 12:17:17 PM »

TP2: 13.1
The minus voltage doesn't go through.
Check the diode D4 (DMM in diode mode), resistor R27 (ohmmeter), U1 and U2 (by replacing).

11

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 06, 2024, 03:52:53 PM »

The dead cap could be the symptom of something else.
Check the DC voltage on TP2 against the 0V pin. It should be -9VDC.
If OK, replace the cap and make a check of the other DC voltages: 

12

MP573 Microphone preamplifier / Re: MP573, Ripped up pad at R39, location of GND(V) ?

« on: August 06, 2024, 03:46:19 PM »

Should I still proceed with connecting the top of R39 to the right side of R37?
Not necessary as you've already restored the ground connection via R38.

will that affect the entire ground connection for other components connected to GND(V)
No. You are OK now. The ground connections are made via the ground plane on the top side of the PCB.

13

MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 06, 2024, 03:37:50 PM »

14

MP573 Microphone preamplifier / Re: MP573, Ripped up pad at R39, location of GND(V) ?

« on: August 05, 2024, 05:54:17 PM »

I just wanted to confirm if connecting a wire between these two is indeed correct
Yes correct.
Be carefull this circuit uses 2 different grounds, separated by 9VDC.
The ground you want on R39 is the one connected to TP2, different from the 0V ground of the lunchbox.
The closest ground point from R39 top is R37 right.

15

MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 05, 2024, 05:44:03 PM »

The issue is very probably somewhere in :
R24, R27, R40 ... R47, Q4 ... Q6, U1, U2. Check value and solder joints.
Also check all the electrolytic caps direction.

16

MP573 Microphone preamplifier / Re: Input impedance of older, non-switchable MP573?

« on: August 04, 2024, 06:32:00 PM »

The input impedance can be set with the jumper JMP1 (in front of the input transformer):
o   o - o   o     1200 ohms
o - o   o - o     300 ohms

17

MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 02, 2024, 06:00:11 PM »

TP2 to V0 is 1.5V
It should be -9V. Too much current flowing. There is a short somewhere.

is it possible that the IPA caused a short and klilled a component?
No, not possible.

Check the DC voltage on TP2, relative to 0 V with the output transformer disconnected.
Check the output transformer DC resistances as shown here. Measure with the transformer unplugged then plugged.

18

MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 01, 2024, 05:59:13 PM »

You have a short circuit somewhere.
On the output transformer connector assembly, check that there in no short between adjacent wires.
Check that no component lead can touch the chassis plate.
Check the position and direction of U1, U2 and Q6.
With the output transformer connected, apply a very brief power on and measure the DC voltage on V+ and on TP2, relative to 0 V.

19

First Aid / Re: MP512 Outputs random static

« on: July 19, 2024, 08:34:29 AM »

I don't believe the tranformer can become faulty. Try reflowing the solders.
Reinsert the DOA to make sure the connections are good.
Try tapping on the large caps to check if it increases the noise.
Also do the same on the pad potentiometer.

20

MP566 Tube microphone preamplifier / Re: C4 and R51 specs

« on: July 17, 2024, 11:20:40 AM »

No problem, you can move forward.
The 315V is still well above our B+  which is at 225V.
If the colour code on the resistor is correct (violet, green, black, silver) then the resisor is correct within 1%. The typical ohmmeters are generally not very acurate for the extreme values (very small or very large). Also, it adds the resistance of the leads, and connections to the resistor value.

21

CP4500 Stereo Bus Compressor / Re: Meter Light not working

« on: July 09, 2024, 08:39:49 AM »

Be carefull to ground your body when handling the 2N7000 (removing your shoes does the trick). It is very sensitive to static electricity.

22

CP4500 Stereo Bus Compressor / Re: Meter Light not working

« on: July 08, 2024, 10:58:50 AM »

You should replace these components.
The diode protects the meter against too larger voltages: BZX55C2V4-TAP
The transistor prevents the meter moving when it is bypassed: 2N7000
Two very common and cheap components.

23

CP4500 Stereo Bus Compressor / Re: Meter Light not working

« on: July 07, 2024, 09:27:37 AM »

Try removing Q1 and D18.

24

MU524 Vari-Mu Tube Compressor / Re: AudioPath Test Question

« on: July 03, 2024, 04:38:29 PM »

25

MU524 Vari-Mu Tube Compressor / Re: AudioPath Test Question

« on: July 02, 2024, 03:39:20 PM »

The upper side of R8 should be at 46 Volts.
It is only connected to R6, R7 and C7.
Check these components. There must be something wrong here, like a solder bridge of a bad solder joint.