Push-pull pot for tone circuit

[A.M.]

Hi everyone, as a mod for the tweed deluxe I'm currently building I thought it would be nice to add a mini switch in order to choose between two cap values for the tone circuit (the stock value - bright/fendery - and a smaller one to get a warmer, middier sound).
I know I can use a mini toggle switch (on-on) for this mod, but for the sake of keeping the look of the amp stock, I figured I could use a push-pull tone pot. I got one of these SPST CTS 1-meg pots: can I wire this to switch between cap 1 and 2? Or do I actually need a DPDT push-pull pot?

Thanks,
Arrigo

[bepone]

you can use it, just wire this switch in series with one cap, and 2 caps in parallel. one cap will have switch on-off , so you can select cap in-or out.
other cap will be in circuit all the time. to avoid pop, when engaged , add 4.7Mohm (or so) over this switch.

[A.M.]

you can use it, just wire this switch in series with one cap, and 2 caps in parallel. one cap will have switch on-off , so you can select cap in-or out.
other cap will be in circuit all the time. to avoid pop, when engaged , add 4.7Mohm (or so) over this switch.

Thanks bepone! Will this wiring work?

[bepone]

which cap in the circuit you want to have on selector?
this one to the ground= 5nF? if you want to increase the value, add then this blue connection, paralel.

af.png

if you want to reduce, then connection must be in series with 5nF

[A.M.]

which cap in the circuit you want to have on selector?
this one to the ground= 5nF? if you want to increase the value, add then this blue connection, paralel.
af.png
if you want to reduce, then connection must be in series with 5nF

Thanks bepone! I'd like to have the .005 as the stock value, and switch to a 680pf. Based on what you wrote, on the wiring I originally drew I should add the blue connection in series with 5nF, correct?

[martin manning]

I'm assuming you want to have 680p to ground when you pull the knob out, correct? That's not going to be possible using a SPST switch that closes on pull.

Let's work in pF: 0.005u is 5000p, but you will probably find that 0.0047u or 4700p is what you can get.

680p in series with 4700p is 594p, so use 820p if you want a net result closer to 680p (698p). However, you want the switch closed (to short the smaller cap) in normal (knob not pulled out) position, which is opposite to what you have, I believe.

In parallel the values add, so 4700 + 680 would give you 5080p, but you want to disconnect the larger cap (open the switch) when the knob is pulled out.

[sluckey]

I really don't think this switch mod is gonna be useful. I suggest to temporarily disconnect the .005 cap and temporarily connect a 680pF in place of the .005. See what you think of the sound. If you don't like what you hear then ditch this mod.

That pot switch could be used to switch cathode caps which will give you a big change in sound.

[A.M.]

So much to learn, thanks guys!

I'm assuming you want to have 680p to ground when you pull the knob out, correct? That's not going to be possible using a SPST switch that closes on pull.
Let's work in pF: 0.005u is 5000p, but you will probably find that 0.0047u or 4700p is what you can get.
680p in series with 4700p is 594p, so use 820p if you want a net result closer to 680p (698p). However, you want the switch closed (to short the smaller cap) in normal (knob not pulled out) position, which is opposite to what you have, I believe.
In parallel the values add, so 4700 + 680 would give you 5080p, but you want to disconnect the larger cap (open the switch) when the knob is pulled out.

Thanks Martin, looks like I need a DPDT push-pull pot then.

I really don't think this switch mod is gonna be useful. I suggest to temporarily disconnect the .005 cap and temporarily connect a 680pF in place of the .005. See what you think of the sound. If you don't like what you hear then ditch this mod.

Maybe you're right. I did try having a 680pF in place of the .005 and the difference in sound was not subtle, on the contrary it sounded quite different than stock: the smaller cap leaves more mid freqs in place and this gives the impression of a darker voice, quite useful with some bright guitars. I thought it made the overdriven tones sound smoother too. The stock .005 value on the other hand is very Fendery, it sounds almost scooped compared to the "680pF voice". For country, clean tones the stock value would be my preference; for a blues/rock gig the darker voice it's good in its own way. That's why I thought that having the option to switch between the two would be kind of cool.

[sluckey]

Since you kinda like the sound you can do it with your switch circuit. However, replace the .005 cap with the 680pf cap. Now put the .005 between the switch and ground and the 100K across the switch. This will give you 680pF with the switch pushed in and .005uF + 680pF = .00568uF when switch is pulled out.

[bepone]

this is using the same switch and components, adding only 820pF ceramic cap,
5nF/700pF (approx 680pF),

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