1

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« on: June 07, 2026, 04:52:32 PM »

2

AB528 Microphone preamplifier / Re: AB528 build has an abnormally high noise floor

« on: June 04, 2026, 05:30:55 PM »

3

AB528 Microphone preamplifier / Re: AB528 build has an abnormally high noise floor

« on: June 04, 2026, 03:46:34 PM »

on the heatsink of Q5 (test point I) I get around -0.07V instead of -0.5V.
How much do you get on point F? and on the low side of R22?

4

AB528 Microphone preamplifier / Re: AB528 build has an abnormally high noise floor

« on: June 02, 2026, 03:38:24 PM »

You may have an HF oscillation in the output stage.
Check the value and solder joints on C14 and C16.

When adjusting the Out Level there's some crackling like there's DC on the pot.
Measure the DC level on TP2 and TP3. It should be 0 mVDC.
Check the direction of the lytic caps C12, C13, C18.

5

AB528 Microphone preamplifier / Re: AB528 build has an abnormally high noise floor

« on: June 01, 2026, 03:29:29 PM »

Does the noise disappear when the OUT potentiometer is at 0?

6

TS500 Tape Simulator / Re: Tape head coil signal audible

« on: May 23, 2026, 03:29:43 PM »

the varnishing of the coil is probably insufficient.
Contact me for a replacement.

7

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« on: May 23, 2026, 03:24:35 PM »

You mean R53, right? Replace it.
Before applying power again, check that you don't have a short circuit between V- and 0V.

8

TS500 Tape Simulator / Re: TS-500 VU meter setup

« on: May 21, 2026, 04:36:25 PM »

TAPE SAT to the left (-).
The other switches have no effect on this setting.

9

MP566 Tube microphone preamplifier / Re: 5.66 Problems

« on: May 21, 2026, 04:29:03 PM »

what do you mean by sequenced?
When you turn on power, the high voltage comes up after 2-3 seconds and the heater voltage after 5-6 seconds.

Check that you don't have any DC voltage on TP4.
Try to follow the signal: https://www.soundskulptor.com/forum/index.php?topic=209.msg981#msg981

10

MP566 Tube microphone preamplifier / Re: 5.66 Problems

« on: May 20, 2026, 05:47:34 PM »

The voltages are OK.
Check that the 2 voltages are sequenced and come up after a few seconds.
Check that it is not the chassis that is loaded too much. What brand is it? Did you add more modules recently?

11

MP566 Tube microphone preamplifier / Re: 5.66 Problems

« on: May 19, 2026, 04:14:54 PM »

Can you do the high and low votages check in the test guide, steps 3 and 4?

12

SK49 Multi-patern Tube Microphone / Re: SK49 pair on a live orchestra

« on: May 19, 2026, 04:09:22 PM »

The recording sounds fantastic, thank you so much for sharing!
We love seeing our kits built so well and put to such great use. Thanks for the support, and happy recording!
Kind regards,

13

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« on: May 19, 2026, 03:58:57 PM »

VO to V- 0.817 volts
Problem here: you have no negative -16V rail.
Check again after unpluging the U5 module.
Check if R53 is OK (1 ohm).

14

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« on: May 08, 2026, 08:46:01 AM »

Can you tell me which pins were shorted?
What results do you get from the voltages checks in the test guide steps 2 to 5?

15

Discussions about the products / Re: LA502T Tube Compressor Setup

« on: April 30, 2026, 07:58:00 PM »

Sorry for the mistake, it is not U5 but U9, the large préassembled module.

16

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

« on: April 29, 2026, 09:13:34 AM »

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

« on: April 28, 2026, 09:07:39 AM »

7  0.05vdc
This should be 0.00VDC.
Maybe something prevents the output from changing.
Check that there is not a short circuit between TP4 (output of U1.2) and 0V or an other point around J1-pin17-18, C12, C9, R15.

18

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

« on: April 26, 2026, 08:57:29 AM »

What are the DC voltages on each pin of U1, against 0V?

19

SK49 Multi-patern Tube Microphone / Re: How long is the 7-pin XLR cable that comes with the SK49 kit?

« on: April 23, 2026, 11:55:51 AM »

I just made the test with five 6m cables connected together for a total of 30m.
The voltage accross R13 was still adequate at 3.61V and this include 4 additionnal male/female XLR junction.
So I think you are OK with the standard PSU and a 25m cable as long as it is a 7 wires good quality cable.

20

MU524 Vari-Mu Tube Compressor / Re: MU524 is noisy

« on: April 23, 2026, 11:28:44 AM »

It should be cold to the touch.

21

MP573 Microphone preamplifier / Re: Second hand MP573 with -6dB level drop

« on: April 21, 2026, 11:29:51 AM »

Perform the checks described here, starting by Try to follow the signal:
https://www.soundskulptor.com/forum/index.php?topic=5.msg5#msg5

Report any difference.

22

MP573 Microphone preamplifier / Re: Second hand MP573 with -6dB level drop

« on: April 21, 2026, 09:59:19 AM »

Is the 6dB drop the same for a gain set to 20dB and a gain set to 30dB ?

23

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

« on: April 20, 2026, 11:19:16 AM »

Now I lost ac voltage at TP1 and I still get 1.64vac at TP3 and 0.055vac at TP4
You can debug without the front panel PCB connected. This will help to narrow down the search area.

Just to confirm
Normal. 2 pins are connected together. 10kohms max between the 2 other pins.

24

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

« on: April 20, 2026, 11:09:08 AM »

Contact me here for a repair.

25

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.