Sound Skulptor Forums

Hello!

I'm having trouble to get the MP12 working properly.
It's built with transformers CMMI-8-PCA and CMOQ-2S and the SK25 Opamp.
The input seems to be ok. All check from the Setup guide has been done but the Output Pad potentiometer doesn't act as I expected. Almost no difference between the min and the max setting of P2.
Here's some data:
0,5VAC on the input (1kHz sinus from my dac)
Gain selection set to mid and the gain knob adjusted just to get to my peak level (the led goes red at -3dB)
The output is measured to 4,5VAC when P2 is set to min, 4,54VAC when P2 is set to max.
When measuring the output resistance (no power connected) it shows 0,31 to 1,23 kOhm.
Jmp5 is set to 1-2 and 3-4. The DOA output voltage nulling is very close to zero (0,1-0,2 mV). I have double checked all components (resistors, capacitors polarity and value, all diods sort and polarity) and can't find any solder shorts or breaks. I have tried with and without U1 and J4 but with the same result.

Is it P2 that's not working or might there be other faults?
Grateful for answer!!
/ David

Do you mean 0,31 kOms ?
Can you measure the resistor across RL2 (2K7) ?
You should read around 36 ohms which is the DC resistor of the transformer secondary.
If it is so, then the pot is probably defective and I will send you a new one.
If not, you must check the transformer secondary connections (5 green, 6 blue, 7 violet, 8 grey) for correct wire colours and good solder joints.