Oscillation Problem with BYOC Mega Chorus, please help!

Started by Zwachi, October 29, 2018, 07:10:11 AM

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Zwachi

Hi guys,


Some time ago i build a BYOC Mega Chorus but I never came around the high pitched oscillation noise that I got from the delay control turned up.
I tried to replace the LFO IC with a TL062 for less current draw but that didn't help.

Can someone give me an advice what else I could try? Maybe replace the clock or the MN3207 delay IC?
Wires are already quite short but not shielded yet.

Probably changing some component values?
On other chorus projects I saw switching a 100p cap parallel to C21 (47p) for lusher effect. Maybe I should rewire the delay pot to a serial resistance with a parallel 100p cap?

Here's the schematic: http://byocelectronics.com/megachorusschematic.pdf

Looking forward for suggestions!
Thanks
Thanks for help!

ElectricDruid

It sounds like clock feedthrough. You said that it's worst with the delay turned to the longest setting, right? That's the point at which the clock frequency starts to come down into the audible range, and the only way to remove it is filtering.

The things I would want to check are:

The LFO - is it dragging the clock frequency down lower than it is supposed to go?
The clock itself - what frequency range does it cover? How low does it go?
The post-BBD filtering - are all the components there correct and soldered correctly? A fault in that filter would allow a lot of clock noise through. When the clock is ultrasonic, you probably wouldn't notice, so you might not realise there was a problem, but then when you turn the delay time control to the "longer delay" end, suddenly a horrible whining noise is audible.

Zwachi

Thanks for your answer!

Component values should be okay. I measured the post BBD filtering and values around the clock. I had another MN3207 laying round which I replaced and I think it's slightly better now but still not acceptable. 3102 clock chip isn't replaced yet.
Thanks for help!

ElectricDruid

How's the soldering? A dry joint on the filter could stop it working effectively, and that would give you more clock noise than you should expect.