Switching noise

[Studio Mollan]

Hi, I've got a problem i hope someone can help me with.

I recently built a pair of spring reverbs and just added a mod for variable HP filter feeding the springs. It's a switch with 12 different capacitors in series before the spring giving 12 steps of HP between 70Hz and 1kHz.

Heres the issue:
A prety loud pop whenever i turn the filter switch. Anybody got a clue on how to minimize this?

 

[ruffrecords]

This is most likely due to a dc voltage charging each capacitor as it is connected. You need a way to let the dc trickle into all the caps so they are already charged up when you switch them but without affecting the way the cap works. The 'standard'  way to do this is to add 4M7 resistors between all adjacent pairs of the 12 contacts. When you turn the unit on, the dc charges up the capacitor that is selected and trickles into the others via the 4M7 resistors. This was standard practice at Neve back in the 70s so I guess it works OK.

Cheers

Ian

 

[Studio Mollan]

Thank you Ian!
Worked like a charm.
/
Emil

This is most likely due to a dc voltage charging each capacitor as it is connected. You need a way to let the dc trickle into all the caps so they are already charged up when you switch them but without affecting the way the cap works. The 'standard'  way to do this is to add 4M7 resistors between all adjacent pairs of the 12 contacts. When you turn the unit on, the dc charges up the capacitor that is selected and trickles into the others via the 4M7 resistors. This was standard practice at Neve back in the 70s so I guess it works OK.

Cheers

Ian