Supreme Compressor (Engineer's Thumb) Distortion

Forum dedicated to helping people debug and troubleshoot non-functional pedals or builds. Please use an clear and informative title, indicating circuit and basic problem. Don't forget to mark the issue as fixed if this is the case.
Post Reply
User avatar
Wake22
Information
Posts: 2
Joined: 22 May 2022, 10:22
Has thanked: 1 time
Been thanked: 1 time

Post by Wake22 »

Hello all.

I'd really appreciate some help with my build please, if possible. I have followed the troubleshooting steps in the FAQs but nothing seems to have had any effect. This is my first build with a PCB rather than a veroboard which I though would be more straightforward. That was certainly the kiss of death!

The kit is the Supreme Compressor from Effect Pedal Kits. It is based on the Valvewizard Engineer's Thumb, with 4 control knobs.

A lot of fuzz-like distortion is being produced when the input signal is higher, i.e. when a string is played hard. Sounds ok when played gently. Exhibits the behaviour with both humbuckers and single coils. Can be reduced by playing with the vol and ratio pots but not removed entirely. Sounds as though when trying to compress it is distorting instead. Bypass works fine.

Schematic:

Image

No modifications to circuit or parts subs.

Battery voltage 9.02V

Voltage at the circuit board end of the red battery lead = 8.88V
Voltage at the circuit board end of the black battery lead = 0V

For the following, vol, attack and threshold turned fully clockwise, ratio turned fully anticlockwise. From looking at these, my instinct is that the problem is to do with U2:B function, but I quickly reach the limits of my understanding at this point!

Q1
C = 1.08V
B = 4.80V
E = 4.41V

U1
5.23V
4.45V
3.98V
0V
4.17V
4.43V
4.43V
8.83V

U2
1.08V
30mV
4.42V
4.42V
4.44V
0
0
0
100mV falling
0
8.82V
0
0
0
0
0

U3
4.46V
4.45V
3.98V
0
4.21V
4.45V
4.86V
8.83V

D1
A = 4.21V
K = 4.45V

D2
A = 4.46V
K = 4.46V

D3
A = 4.84V
K = 4.45V

Any pointers very much appreciated!

User avatar
Manfred
Tube Twister
Information
Posts: 1937
Joined: 04 Apr 2009, 23:42
Has thanked: 1671 times
Been thanked: 1344 times

Post by Manfred »

There is no schematic and image visible.
Open the Full Editor mode by clicking the "Full Editor & Preview" field at the bottom.
Click on the "Attachment field" and then on the "Add files" field to attach the files.

User avatar
Wake22
Information
Posts: 2
Joined: 22 May 2022, 10:22
Has thanked: 1 time
Been thanked: 1 time

Post by Wake22 »

Hi Manfred,

Thanks for the heads up. Is this working now?
Supreme Compressor Schematic.jpg

Post Reply