1

EQ573 Equaliser / Re: EQ573-II ran in my lab

« on: Today at 06:34:38 PM »

It is a shelf but it is followed by a high frequency attenuation after 20kHz caused by the compensation caps in the circuit.
Can you make another diagram with a +/-6dB correction?

2

LA502 Optical Compressor / Re: 502 Compressor not working - test results.

« on: Today at 06:26:40 PM »

Remove U1 and check again R5 right pin.
You can keep U1 removed until this is fixed.
Check the value of R5. It will be lower than 100k because of the other components around.
Checl the optocoupler is in the right direction.
Look for solder bridges or bad joints around R2, R3, R4 and the ratio switch.

3

LA502 Optical Compressor / Re: R5 100K reads 26.6K after soldering it in... correct? DOC24

« on: July 05, 2026, 06:12:28 PM »

This is perfectly normal, as this resistor is connected in parallel with several other components, which affect the resistance reading.

4

First Aid / MOVED: True Grit (Kit) not working

« on: July 05, 2026, 06:08:00 PM »

This topic has been moved to True-Grit Tube saturator.

https://www.soundskulptor.com/forum/index.php?topic=7421.0

5

True-Grit Tube saturator / Re: True Grit (Kit) not working

« on: July 05, 2026, 06:06:53 PM »

6

SK49 Multi-patern Tube Microphone / Re: Shockmount elastic

« on: July 05, 2026, 06:04:23 PM »

We are going to purchase some spare elastic bands for shockmounts so we can supply our mic customers.
I will tell you as soon as available.

7

LA502T Tube Optical Compressor / LA502T REV1.4 modifications

« on: June 18, 2026, 06:53:57 PM »

D1, D2, D3, D4 diodes connections
These diodes add soft clipping, thus preventing abrupt clipping of the output stage.
The connections for these diodes are missing on the REV1.4 PCB. They can be restored by soldering short wires at the red line positions in the picture.

R16 replacement
It is recommended to replace the resistor R16 by a film capacitor of 100nF.
The leak current of C5 creates a voltage offset of about 20mV in the output stage when the gain pot is at 0. The cap eliminates it.

8

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

« on: June 07, 2026, 04:52:32 PM »

9

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

« on: June 04, 2026, 05:30:55 PM »

10

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?

11

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.

12

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?

13

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.

14

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.

15

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.

16

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

17

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?

18

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?

19

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,

20

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).

21

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?

22

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.

23

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

« on: April 29, 2026, 09:13:34 AM »

24

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.

25

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?