EMS Diode Filter - work but with very loud distorted output

[roman_f]

finally built the EMS filter - it works, all knobs and jacks are working too
but the output is very loud and distorted

adding the attenuator to the input doesn't really help - sound gets very quiet, but still a bit distorted

please help

[Mongo1]

Hello Roman -

Here's what I'd do.

1) Input a sine wave into the filter.

2) Examine the output of U1d (pin 14). See if that waveform is distorted. If so, we can see if the resistor values in that stage are wrong, or if there is some other problem.

3) If pin 14 looks ok, take a look at U1a (pin1). If that is distorted, I suspect that the resistor values R47 and R46 might need to change. I see that Yves has noted that they might, depending on the signal level.

4) If pin 1 looks ok, then the problem will have to be somewhere inside the actual filter network. That will require a more expert set of eyes than mine I think.

Yves may have some other suggestions, but I think this would be the place to begin

Gary

[roman_f]

dear gary
thank you a lot for your answer
pin 14 seems to be fine, pin 1 is distorted
does yves say which value should R47 be changed to?

[yusynth]

if you use a 2Vpp signal at the input there should not be distortion at the output (normally the values I gave are valid for a 10Vpp signal). I don't think it's a resistor trimming problem I would rather suspect that you had a mix up in the value of a resistor.

As usual I recommand posting a good photo of the circuit (component side) in order to verify the component values

[roman_f]

dear yves - i did not used the attenuators on the input (it's a 1u module)
so the signal is 10pp i guess
i will make a photo now

[yusynth]

Sorry Roman

I made a confusion with ARP filter. For the EMS Filter with a 10Vpp signal one must attenuate the signal at least 3 folds. Therefore you can change the value of R8 are indicated on the schematic , try 27k instead of 8.2K

[roman_f]

[yusynth]

Then there is a problem with your module...
Usual questions : did you etch the PCB yourself ? Can you post photos ?

[roman_f]

dear yves
please take a look on the pcb, maybe i did some mistake

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[roman_f]

dear yves
did you have a chance to look on the scan?
i still didn't manage it to work

i've scoped the output - it gives a sine output on any input
and increasing the frequency increases the amplitude, then it starts distorting (and becoming a very loud square, for sure)

thank you

[yusynth]

Sorry Roman

I have been rather busy these last days with the official announcement of the MiniBrute and I spent most of my spare time answering questions about it.

I'll your photo today...

[roman_f]

thank you yves and congrats with arturia collaboration
looking forward to see new synths from you