Switch "pop" sound

[GERPUD]

Hi,

I've done several mods on my amp. One of them is DPDT switching channel with two master volume (clean and overdrive)
The schematic:
https://fmic1.zendesk.com/attachments/t ... agrams.pdf

So, the amp now has two gain control and two master volume.
One side of the switch change the guitar channel, and the other side change the master volume.
The switch does what it should, but I get a loud "POP" sound when I use it. The pop is there even with all volumes to zero.
It is probably the master volume switching the problem, but I can solve that.
Attached is the simplified modified schematic

[John_P_WI]

Your output tube loses it's ground reference when switching. Add a pull down resistor to it's grid.

[GERPUD]

So i should add a resistor from pin 5 to ground?
What value?

[John_P_WI]

Yes, remember that the resistor to ground will be in parallel with the selected pot. Try a 1 Meg see if that makes any difference in the pop.

[GERPUD]

Ok thank you very much!
Other question: would it work having 200k equevalent resistance instead of 100k in R24?
From other schematic i ve seen, 100k seems low. Some design are showing 500k.

[John_P_WI]

Ok thank you very much!
Other question: would it work having 200k equevalent resistance instead of 100k in R24?
From other schematic i ve seen, 100k seems low. Some design are showing 500k.

Try it, little changes shouldn't make too big of a difference. It will set the loading on the previous stage and will change the frequency response of the stage and in the most elementary sense, it (the pot resistance value will be in parallel with the plate resistor) + the internal plate resistance of the tube and can be used for a local resistance equivalent. In this particular circuit there are two coupling caps that can be used with the calculated r equivalent to find the frequency break point value of the circuit.

Again, this is a very crude back of the envelope calculation. The higher gain guys will sometime use a smaller value pot here and load down the previous stage for a little more articulation. Higher resistance values are "more traditional".

[matt h]

(deleted)

[GERPUD]

Yes, remember that the resistor to ground will be in parallel with the selected pot. Try a 1 Meg see if that makes any difference in the pop.

Thanks it worked!

I ve tested r24 rom 0 to 167k. The best clean sound was at 100k. Over that value, treble was increasing. Not bad but not to my taste.