Preamp Ck/Rk switch values...

[chocopower]

Hi, again...

I,m going mad with Ohms Law!!

I want to add a Rk/Ck selector to my ampŽs tweed channel, 2nd stage (Pin8)

Using a 3 position, center off switch, i,m looking for this values:

2.7k - .68uf

1.5k

1.5k - 25uf


No problem with the caps. Problem are the resistors...
I calculated a lot of paralell combinations and always fail.. The problen is the center position.... If ground a 2.7k resistor in pin8 and paralell it with a 3.4k in the 25uf position = 1.5k... no problem.
In the the .68uf position no paralell resistor is needed..
My headake is the center position.... the 1.5k position without cap....no way!!

Here are a layout of the switch. (3 position, 3 circuit)

(1) (2) (3)

(4) (5) (6)

(7) (8) (9)


thanks!

[Enzo]

Resistors are a few cents each. Why go nuts with switches to save one or two?

WHy not have a simple three way switch. On on on, like a rotary. Common switch contact to cathode, now you can make any RC you want at each of the three positions, with their other ends all grounded. Instead of trying to figure out how to switch one parallel thing but not the other and vice versa, just use three resistors and two caps. Very simple.

Or for that matter, use your on off on for the caps alone, then a second toggle for the resistor value. Even more versatile than the first idea, it yields six combinations instead of three.

[chocopower]

Hi!

I was trying the paralelled method beacause this way it never break the cathode ground.
I supoused break the ground conection could damage the amp...

I,m gonna check the 2 switch option...

Thanks

[Enzo]

It will not hurt the amp to have a momentary break in the cathode path to ground. Might pop some, but won't hurt it. And if it did pop, you might get some relief by adding a parallel larger value part like maybe 50k. That would also have the effect of lowering the resistance of the various resistors since they would be in parallel with it, so 1.5k becomes 1.6k or whatever. Frankly I'd accept a little pop when channel switching myself.

[chocopower]

Ok! I think iŽll try a rotary switch....thanks!


ah!!! paralleling 50k and 1.5k youŽll droop the final value to 1.46k, so....gain will increase (a bit)...

[Enzo]

I picked 50k at random. Try 100k if you like. And while there might be a difference between 1.5k and 1.46k, in reality that is a difference of less than 3%, and likely as not, if the amp is buiilt with typical 5% resistors, your 1.5k could easily measure 1.46k and be perfectly within spec. I am sure your "increase" in gain will be less than a decibel. You won't hear the difference.

In the same space as a three position switch, you could even mount as 10 position switch. Lots more combinations then, it woud be like the big selector on those modelling amps. You could make up names like VIntage, and British, and so on for each setting. Or maybe not...

[chocopower]

Hey Just jokeing.....

thanks a lot....