Drebbel thump

[PJS]

Hi, I have built 2 Drebbels and they both thump when engaged. Is this just the nature or this schematic or is there a way to reduce the thump?

 

[Mentaltossflycoon]

Just hooked mine up and I get no pops with the bypass switch.

 

[PJS]

Thanks. I will investigate more

 

[Robert]

You can try lowering the value of R12.

Rather than risk damaging the board you could just temporarily tack a 100K resistor across the existing resistor to see if it helps.

 

[PJS]

Seems like it is time related. For the first few switches after power is applied, or during the first few seconds/maybe minutes after power on there will be a pop - after that it is silent. I am starting to think that it might have something to do with the power supply I use to test maybe taking some time to settle down and regulate properly or similar. Certainly after I switch off the power the supply will be putting out voltage for about 60 seconds afterwards. Anyway, at worst it is a minor issue, and at best it won't be a problem at all with a different power supply. Thanks.

 

[PJS]

If all else fails I'll try lowering R12, but so far it doesn't look like it will be an issue in a real world use.

 

[PJS]

OK. Another question but still on the Drebbel thumping. I have 4 of these that don't thump when switched, but 2 that do. The difference is that the 2 that thump have a DI out in the box as well. I am assuming that this is the problem - just looking for ideas on solutions. The DI has a pulldown resistor on the input, and also is always on. I have tried an extra 100k and 1M resistor on the output of the switch breakout PCB. Still thumps. Any ideas?

 

[PJS]

FWIW I did try soldering a 100k resistor in parallel with R12 and if anything that made it worse