Sound Skulptor forums

Build help and troubleshooting => MU524 Vari-Mu Tube Compressor => Topic started by: UrbanOsterman on February 21, 2023, 03:48:02 PM

Title: My testresult initial conditions
Post by: UrbanOsterman on February 21, 2023, 03:48:02 PM

DC  Volt
      TP1 to ground = 40,46  VDC
      TP2 to ground = 40,41  VDC
AC Volt
      TP1 to ground = 0,003  VAC      ?!?
      TP2 to ground = 0,0023 VAC    ?!?

      TP3 to ground = 1,761  VAC
      TP4 to ground = 1,762  VAC

Output (Pin 2-3)    = 3,534  VAC

B+ = 42,5   (Voltage From power supply = 49VDC)


After Changed conditions

TP3 = 0,2460 VAC
TP4 = 2,753 VAC
TP5 = 2,735 VAC
TP6 = -3,280 VDC
Output = 5,53 VAC
Meter = -6dB

Title: Re: My testresult initial conditions
Post by: JPK on February 21, 2023, 06:19:56 PM

The DC voltage on TP1 & TP2 is too high.
Is the tube correctly heated? Is it glowing orange? Do you have the correct 6V between the 2 extreme pins of the tube holder PCB?
Are you sure you had the jumper removed when doing this measurement?

The null AC voltage on TP1 & TP2 could be caused by you meter not liking the DC component?
The other voltages look quite right.

Title: Re: My testresult initial conditions
Post by: UrbanOsterman on February 24, 2023, 11:04:24 AM

Hi J-P
I did a total resetup, and now I get 28,52 VDC on TP1 to ground
and 28,47VDC from TP2 to ground..... To low?

I must have forgotten to remove the JM1 before??
because I now get about 42VDC from TP1 to ground when JMP inserted (as before), and about 28,5 VDC when jmp1 reoved.

I do my setup using a SoundSkulptor 501.

Regards

Title: Re: My testresult initial conditions
Post by: JPK on February 27, 2023, 09:26:46 AM

These values look good

Title: Re: My testresult initial conditions
Post by: UrbanOsterman on February 27, 2023, 02:55:21 PM

Question for Modification??

If I drive the compressor hard I cannot reduce the output volume to Unit gain.
Its pot P2 (2,2K) and R16 (220 Ohms) and the two capacitors C10 and C11, that works together.

Is it possible to lower R16 to lets say 100 Ohms or something?
To be able to turn the output volume lower.

Something you would recomend?

Regards
Urban

Title: Re: My testresult initial conditions
Post by: JPK on February 28, 2023, 11:44:57 AM

How much attenuation in dB do you get when you drive the compressor hard?
A 1.5VAC signal (+6dBu) should give more than 15dB attenuation.

Lowering R16 will increase the maximum gain.