51

MP573 Microphone preamplifier / Re: MP573 weird behavior (no volume after 20)

« Last post by camarada78 on August 26, 2025, 03:21:35 PM »

I measured the three transistors with a component tester and they are working fine (q1, q2 and q3)

52

MP573 Microphone preamplifier / Re: MP573 weird behavior (no volume after 20)

« Last post by camarada78 on August 26, 2025, 03:11:56 PM »

Thanks for the reply.

My version of the preamp is a little different than the one of the picture.

its the rev 1.3

But, if i measured correct, the voltages are

F = 12v9
A = -9v

53

MP573 Microphone preamplifier / Re: MP573 LED not behaving correctly

« Last post by davidfloegel on August 26, 2025, 10:29:15 AM »

Ok I've just tried testing it..

I've played the sine wave on a loop and put an Audix I5 in front of it. I can see the LED light up green and I'm getting:

~0.1 on the left side (towards the controls)
~0.4 on the right side (towards the back side)


Side note: 
My Q6 is getting pretty warm right away, I rested my finger on it while measuring. It's not so hot I can't touch it, just very warm.

54

MU524 Vari-Mu Tube Compressor / Re: Stuck on step 7

« Last post by soundguy937 on August 26, 2025, 04:19:53 AM »

Input transformer is in correct orientation.

TR1=202 2k
TR2=102 1k

B+ stable at 45.5VDC

R3= 3k3
R4= 3k3  
R5= 10k 
R6= 10k  
R7= 10k  
R8= 470R 
R9= 10k  
R10= 10k  

input transformer values (input on max)

2-4= 37.2 ohms
3-5= 37 ohms
7-9=100.1 ohms
8-10= 99.1 ohms

input resistance pins 2&3= 4.61 k ohms

everything mostly checks out excepts input transformer 8-10 being 99.1ohms. 

55

MP573 Microphone preamplifier / Re: Loud Pop When Changing dB Rotary Switch

« Last post by musicarr on August 26, 2025, 02:01:52 AM »

I checked all the electrolytic and tantalum caps. There was one tantalum cap that was backwards. I switched it to the correct polarity and the "bib pop" is gone. So that must have been the issue. There still is a slight "pop" going from 20 dB to 30 dB. It registers at about -30 db on the Pro Tools meter. The other positions don't seem to have that large a "pop", as they register about -45 dB on the Pro Tools meter. Is there something else I should look at, or is that "pop" going from 20 dB to 30 dB "normal"?

56

Discussions about the products / Audio Precision plots?

« Last post by det3 on August 25, 2025, 11:13:56 PM »

Hey All,

I'm curious - has anyone performed AP plots of Soundskulptor modules? I just purchased 4 kits and happen to own an older Series 2 AP. I would love to see what comes out after I complete my builds, and compare from any other measurements made if they exist. If not, I plan on sharing my test methods and results if I decide to do it.

Thanks!

57

MP573 Microphone preamplifier / Re: Loud Pop When Changing dB Rotary Switch

« Last post by musicarr on August 25, 2025, 10:31:11 PM »

With the electrolytic caps, it's easier to see where the negative and positive wires are. And on the tantalum caps, the "+" sign to the right of the labeling points to the positive lead. Is it possible, sometimes, that the "longer" lead of might not be the positive lead? I was going off of the longest lead on the tantalum caps. Is that reliable, or should you always look for the "+" marking to know which lead is the positive?

58

MP573 Microphone preamplifier / Re: Loud Pop When Changing dB Rotary Switch

« Last post by musicarr on August 25, 2025, 03:49:53 PM »

I was consciously, and verbally, careful to the direction of all caps set correctly. But it doesn't mean I missed one somewhere. I'll check every cap and let you know what I find. 

59

MU524 Vari-Mu Tube Compressor / Re: Stuck on step 7

« Last post by JPK on August 25, 2025, 03:32:52 PM »

Check that the input transformer is in the correct orientation.
Check that TR1 and TR2 have the correct value.
Check that R3 to R10 have the correct value.
Check that the voltage on B+ is stable.
Check the input transformer coils resistance (in circuit, input pot on max): 

• 2-4 : 37 ohms
• 3-5 : 37 ohms
• 7-9 : 100 ohms
• 8-10 : 100 ohms

Check the input resistance (between XLR pins 2&3, input pot on max): 4.6k

60

MP573 Microphone preamplifier / Re: Loud Pop When Changing dB Rotary Switch

« Last post by JPK on August 25, 2025, 03:16:16 PM »

Pops are often caused by a reversed electrolytic or tantalum capacitor.
So the first thing to check is the direction of these caps: The + sign on the layout must match the + side of the capacitor.