Calling MN3207 gurus.

[skiraly017]

I made the MN3007 to MN3207 conversion in a Small Clone with one small issue. I get a faint thumping at the extreme setting of the Rate pot. I used to have the same issue using a MN3007 and remedied it by putting a stopper resisitor in place so the Depth pot never went wide open. Unfortunately the thumping seems to be brought on by the Rate pot. I can get rid of the thumping by turning the Rate down but in doing so I lose the faster speeds. While the noise is certainly liveable, I know it's there. Anyone have any experience with this or any ideas/suggestions? Thanks.

[snap]

Which conversion did you do?
http://www.diystompboxes.com/smfforum/index.php?topic=36077.0
http://www.diystompboxes.com/smfforum/index.php?topic=39693.0

[Jonaz]

Sounds like you're describing clock feedthrough. The pulses of the LFO leaking through to the output causing the "thump" sound.

I've seen some amplifier schematics that have on-board tremolo that kill that thump with heavy high-pass filtering. Try setting a filter
between 10Hz-100Hz and see if that takes care of it. As I understand the Small Clone already has a filter before the 10K Depth pot so you could
mess with that and see if it gets better.

From my limited undertanding, this has little to do with the voltage rating of the BBD i.e. 3207 vs. 3007 but a lot more with the LFO.

Good luck!

[nelson]

Put a small resistor in series and a capacitor to ground with the V+ to the LFO opamp. Or, change the LM358 for a low current type like a TL022.

[R.G.]

It's been my experience that with the 3207, the PCB layout must be immaculate in terms of power supply decoupling, grounding, and short, direct traces to eliminate clock noise and other feedthroughs.

Your mileage may differ, of course.

[skiraly017]

Which conversion did you do?
http://www.diystompboxes.com/smfforum/index.php?topic=36077.0
http://www.diystompboxes.com/smfforum/index.php?topic=39693.0

Neither one really.

As I understand the Small Clone already has a filter before the 10K Depth pot so you could mess with that and see if it gets better.

Even though the thumping is not affected by the Depth pot at all like it was with the MN3007? With the 3207, the thumping is brought on by the Speed pot in the last 10% of the travel. The position of the Depth pot has no effect on it at all.

Put a small resistor in series and a capacitor to ground with the V+ to the LFO opamp. Or, change the LM358 for a low current type like a TL022.

Will do.

It's been my experience that with the 3207, the PCB layout must be immaculate in terms of power supply decoupling, grounding, and short, direct traces to eliminate clock noise and other feedthroughs.

Your mileage may differ, of course.

Understood and I'll check to be sure. Thanks everyone.