21

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

« Last post by JPK 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).

22

MP566 Tube microphone preamplifier / 5.66 Problems

« Last post by MRMNW on May 18, 2026, 08:37:45 AM »

Hi, 
built this a month ago and it has worked fine,
Now when switching the chassis on it clicks on and off before eventually working after switching it off and on again.
There is also a very low and thin sound. I think it may have overheated. 
Any help much appreciated.
Thanks

23

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

« Last post by Alex Harmer on May 18, 2026, 06:09:45 AM »

Hi,

I thought you would like a sound sample of what the SK49s can do on orchestra. I built these mics, but I had to buy extra long 7-pin XLR cable to hang them from the ceiling of the auditorium. 

Last week I recorded the Christchurch Symphony Orchestra live in the Town Hall, Christchurch, New Zealand.

There is no reverb, EQ, or processing. 

They are absolutely fantastic microphones! Thanks Sound Skulptor!

https://soundcloud.com/harmerny-productions/sk49-in-ortf-on-a-live

24

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

« Last post by spurton@gmail.com on May 17, 2026, 08:48:14 PM »

I found 2 bridges which I fixed. 1 was between 2 joints that connect the main PCB to the tube support PCB. The other was on the HPF pot connection. I hooked up a signal generator at 1k 0.020v and used my oscilloscope to trace the signal after I fixed the bridges. I was getting no signal from TP3,4,5,6. TP2 had a slight signal. I replaced the U2 and U3 op amps and no signal. Here are the DC test values. So something is messed up somewhere. 
VO to V+ 16volts
VO to V- 0.817 volts
V- to B+ 13.8v
H+ to H- 18.96v
V0 to TP2,3 14.58v
VO to TP1 -0.003 v
VO to TP4 0.04v
VO to TP5 2.25v
VO to TP6 1.38v

😞

25

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

« Last post by JPK 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?

26

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

« Last post by spurton@gmail.com on May 07, 2026, 09:10:04 PM »

I recently built the MP566-II Tube pre and when I first powered it on I could not get any sound out of it. So I removed it and discovered I had a solder bridge on the back of the header pins to the tube PCB. I fixed the bridge and ran it again. It puts out sound but very quiet, not enough to register signal but I can hear it faintly. It also distorts heavily when I turn up the gain knob or output knob. I know shorting leads can fry the ICs. Does this sound like what I did? If so I will order new ones. Thank you. 

27

Discussions about the products / Re: LA502T Tube Compressor Setup

« Last post by UrbanOsterman on May 01, 2026, 10:23:48 AM »

Thanks,
Later I looked closer and then I realised it was The SKTPS that was meant.

28

Discussions about the products / Re: LA502T Tube Compressor Setup

« Last post by JPK on April 30, 2026, 07:58:00 PM »

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

29

Discussions about the products / LA502T Tube Compressor Setup

« Last post by UrbanOsterman on April 30, 2026, 05:05:24 PM »

I have just finnished building the LA502T Compressor.
And I am trying to set it up.
But I dont understand 
point 3 Section 'High voltage check' and 'Heater voltage check'

High Voltage check:
  It says I should check the voltage Between V- an B+ pin on U5 
  (which is a TL431 chip).
  the Setup paper say it will start at 30V and rise up to about +225V.
  But I measure just 2,48V?

And in section
Heater voltage check 
it says  I shuld meassuer between H- and H+ on U5 (same TL431) ... it should go from 7 Volt up to 12 Volt.

I assume some thing is very strange here?

Urban Osterman

 

30

MU524 Vari-Mu Tube Compressor / pair of MU524 - crackling/noise/hiss

« Last post by herwig.scheck on April 30, 2026, 11:37:30 AM »

Hi,

I have a pair of MU524's. One has a cracklinkg/noise/hissing problem. When I turn down the gain (in as well as out) the noise goes down with it. After some swapping out of the tube and op-amps between the units the problem stayed. 

Until I swapped out the U6. They're different for both units and the problem moved with the U6. The "small" one behaves while the "tall" one is the noisy one.
When I touch/tap the small daughter board I can hear that in the circuit.


Is there something I can do on my end or should I contact support for this?


TIA,
Herwig