Build Your Own Clone Message Board

Hi,
I don’t get any wet signal on my mimosa compressor. I have reflowed the solder joints numerous times. The pedal works on bypass, the diod lights up when the pedal is engaged, the volume knob works as it should, but as I turn the blend knob clockwise the sound gets lower until it disappears altogether at the end. I have biased the transistor to 1.6V. When I touch pin 7 on the IC with my voltmeter I get noice that works the same way as the guitar signal, but if I touch pin 10 the noice can be controlled with the blend control. Is it just C2 and C3 that are blocking the noice, or is one of them faulty? Any other idea what it could be?

Could you post a better photo of the top of the PCB? Currently too small and too dark to be of much help.

A set of DC voltage measurements for the IC pins may be helpful, as well.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Voltages on the IC:
4.39
4.42
4.40
8.80
4.42
4.37
4.40
4.80
4.81
4.71
0
4.40
4.40
4.41

Thanks for your help!
Pontus

Voltages look good--power source voltage at pin 4, ground at pin 11 and everything else at 1/2 of PS voltage.

It's apparent from your description that the "wet" (compressed) signal isn't getting through to the blend pot, so as you turn it CW and the "dry" signal is being reduced, the wet signal isn't increasing at the same time.

You mentioned getting sound at pins 7 and 10 of the IC when touching them w/ your meter probe. How do pins 8 and 13 react?

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Pin 1 scratch noice that decreases with blend
Pin 6 hum that decreases with blend
Pin 7 scratch noice that decreases with blend
Pin 8 scratch noice that increases with blend
Pin 10 hum that increases with blend
Pin 13 scratch noice that is independent of blend
Pin 14 scratch noice that is independent of blend

If I touch R3 in the end connected to C3 I get a scratch noice that increases with blend
If I touch R3 in the end connected to C2 I get a scratch noice that decreases with blend

R3 measures the specified 82kOhm and I have reflowed its solder joints one more time..

Pontus

A signal probe would be very useful here. Based on your description, it sounds like signal can pass through the compressor portion of the circuit. So the problem is that signal just isn't getting into the compressor portion of the circuit, suggesting that the problem is at C2.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

I made a simple probe using one of the extra .33 capacitors and some leads. If I connect the pedal to the guitar and the probe to the amp, I get sound on pin 7 and also after C2, but not after R3, and not on pin 8
If I connect the guitar through the probe to pin 10 and the amp to the output,I get sound that increases with blend, if I connect to pin 6 I get sound that decreases with blend. Connecting the guitar to pin 7 or 3 doesn’t give any sound, which I find confusing.. pin 2 results in sound..


Pontus

Drain and Source on Q2 has the exact same voltage and it varies the same way as I move the trim pot. That can’t be right, can it? It doesn’t look as I have created a solder bridge between them, but I’ll have another look. Could Q2 be faulty? Measuring continuity with the pedal turned off, D and S are connected.. to me it sounds wrong.

EDIT: I had forgotten how jfets works. With no voltage on the gate that would be right, and suppose this is the part of the circuit that actually do the compressing?

Thanks for your help

Pontus

Hi again,
If attach my probe from my guitar to the point between R3 and C3 I get no sound. I think I should.. I’ll have a look at C3

Pontus

Changed C3, but no difference…

Pontus

This type of compressor is sort of a reverse noise gate. Q2 is either bleeding signal to ground or blocking signal from bleeding to ground. When there is no output at pin 8, Q2 is "closed" and not bleeding any signal to ground. The louder the signal from pin 8, the more "open" Q2 becomes and the more signal is bled to ground.

So it sounds like your Q2 is stuck in the "open" position. If you are certain that there are no shorts that are connecting Q1 or 2 to something they shouldn't be connected to, then I would probably assume that Q2 is faulty. You should contact sales@buildyourownclone.com for a replacement.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Changed the j-fet and now the pedal is working. Thanks so much for all help! Learned a lot about the workings of a compressor in the process.

Pontus

Excellent news! Enjoy the pedal!

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2