quick question: when switching input caps

[pinkjimiphoton]

better to switch the "input"
or the "output" of the cap?

i'm trying to parallel a second bigger cap with a small value input cap on a treble boost.. sounds great, but when the second cap is switched in getting quite a bit of rfi crap... assuming that's from longish leads from the board, so thinking i'll mount the cap  on the board, and run wires to the switch rather than mount the cap on the switch.

should i shield these wires? twisting them tightly didn't seem to help at all.

tia
pjp

[Mark Hammer]

Neither is really better, since there is current sitting in the cap just waiting for ANY way to get out.  It doesn't particularly care if the front door or the back door is suddenly opened.

Probably the sensible way to switch between input caps is to either:

a) stick a high-enough value resistor in series with each of the "additional" caps that will be placed in parallel with the default one, and then use a toggle or whatever to bridge that cap's resistor and bring it into effect,

b) do all your cap switching when in bypass mdoe so you don't hear the pop.

[pinkjimiphoton]

thanks Mark,
not getting a "pop" problem, more like background hash which i'm assuming is from the wires to the switch.
trying to justify an extra hole i wanna fill in a case i hated to trash..

shielding the cables maybe? telescope the shields?

thanks bro

[Mark Hammer]

Or just keep those leads away from any point where the signal has acquired some gain.

[Johan]

Switch Wich ever end is less likely to charge up and if possible put a bleed resistor across the switch so that it is shorted out of the circuit when the cap is in circuit
J

[pinkjimiphoton]

thinking the cap itself may block some dc if i leave the "output" junction of the two caps connected and just switch the input of the second in and out. so add maybe a 1m resistor from the node being switched to ground just to be safe?

gonna try telescoping some shielded wire to the switch, and will rout it down underneath as close to the chassis as possible and try to keep it away from high gain signal wires. man.. that'll be a challenge!! spaghetti city in there with all the footswitches and stuff!!

[thelonious]

There was an interesting thread about pull down resistors on a rotary switch a while back - http://www.diystompboxes.com/smfforum/index.php?topic=88943.0

If you can keep the cap pulled down, it will probably fix the hash, too - shunting to ground. Last time I did this, I used shielded wire, and it helped for sure.

[pinkjimiphoton]

thanks tristan, i will read it and try the shielded wire. 

[davent]

How 'bout going with a pot rather then a switch, à la the Easy Face tone control, that gives you the freedom to dial in to suit various guitar/amp combos.



dave

[pinkjimiphoton]

great idea, dave, but right now it's all about salvaging the board i messed up months ago before is do any re-designing.
pretty sure i've got it sussed out, the easiest way is probably to mount both caps on the footswitch, but i think i'm gonna add the second to the last fraction of  the vero and squeeze it in and just run the wires to the switch... that way, i can just switch the input of the second cap in and out, and for all intensts may not have as much radio antennae.

you guys rock... all vaild suggestions... thanks!!

[pinkjimiphoton]

when all was said and done, i mounted the cap on the vero itself in a small spot that had a little room. i connected the "output" of the second cap to the first ones where it connects to the base,  and then ran a a wire from the "input" of each cap and connected it to a simple spst footswitch. the cap (i think) absorbs the pop.

thanks for all the insights!!