Tone Stack Switch... Loading Problem??

[diddymix]

Hello everyone.

I was hoping someone with technical knowledge of tube electronics could help give me any pointers with regard to something I'm trying with an amplifier, in regard to modifications.. Its in particular with regard to impedance and loading of the signal.
Ive basically tried two quite different tonestacks with an amp and cabinet thats been made for me.. the thing is I really would like to have both tonestacks as an option on a switch as they both give a nice different voice.... Sio I thought of this and have drawn it up here... This would be quite easy for me to do but I am concerned about whether it would present any loading problems on the signal.. Can anyone tell me, that even if one of the tonestacks on the switch is NOT connected.... (open circuit) would the other unused tonestack + gain pot still be a problem with its paths to ground?? Would this path to ground actually load the signal in any way even if its not connected to a triodes input upstream?

Also just as a side question.. if in a normal setting V1 clean channel of an amp operating as normal... if V1B is feeding V2 (OD) as well as the PI (CLean)... how does this affect the output impedance and volume.? SO basically V1 feeding two different tube stages off one plate.... Does this cause any serious side affects with regard to frequency response and signal strength??

Thanks so much everyone, and any pointers one at all most appreciated!

[xtian]

Your schematic does present a problem. But you can solve it by using a DPST switch instead of SPST. Switch both ends of your tone stack, not just one.

[diddymix]

Your schematic does present a problem. But you can solve it by using a DPST switch instead of SPST. Switch both ends of your tone stack, not just one.

Oh Ok thaks... could you describe in what way?? The thing is I have a 4P4T switch this is actually what Im using as there is 3 other circuit changes with the switches action... I also dont want to add another large coupling cap before the switch really... (the switch is a cheap toggler, I dont want to try running high voltage through that..)

Cheers!

[diddymix]

Your schematic does present a problem. But you can solve it by using a DPST switch instead of SPST. Switch both ends of your tone stack, not just one.

Oh Ok thanks... could you describe in what way, how would i implement a switch at the other end?? The thing is I have a 4P4T switch this is actually what Im using as there is 3 other circuit changes with the switches action... I also dont want to add another large coupling cap before the switch really... (the switch is a cheap toggler, I dont want to try running high voltage through that..)

Cheers!

[xtian]

This:

IMG_3520.jpg

[diddymix]

This:
IMG_3520.jpg

Ah Ok man, thanks.. i'd rather not do it like this as I would have to add a coupling cap before the tonestacks, is there really a problem with what i first posted??.. Would it work ok or signal loss or ?

[xtian]

This:
IMG_3520.jpg

Ah Ok man, thanks.. i'd rather not do it like this as I would have to add a coupling cap before the tonestacks, is there really a problem with what i first posted??.. Would it work ok or signal loss or ?

Why is adding a DC blocking cap a problem?

There's no reason there will be signal loss with this switched system....unless you add miles of hookup wire getting it done...

[diddymix]

This:
IMG_3520.jpg

Ah Ok man, thanks.. i'd rather not do it like this as I would have to add a coupling cap before the tonestacks, is there really a problem with what i first posted??.. Would it work ok or signal loss or ?

Why is adding a DC blocking cap a problem?

There's no reason there will be signal loss with this switched system....unless you add miles of hookup wire getting it done...

Thanks man i suppose i could.. .. the main reason really is that my switch is actually a 4PDT switch and I am already using three of the poles for other duties... which leaves me one pole and 2 throws... I guess i could just add another switch to the chassis.. but I really wanted just one switch to complete all the tasks and routing on my amp (with the tonestack switch included here)... is there any other way you can think of?

[Colossal]

Be sure to add a high value pulldown resistor on the front and back end of that switch to soak up the pop. 4M7 or 10M usually work fine and won't load the circuit.

[diddymix]

Be sure to add a high value pulldown resistor on the front and back end of that switch to soak up the pop. 4M7 or 10M usually work fine and won't load the circuit.

thanks colossal!

Do you mean that I need a resistor between the plate of V1A and the 1st pole (on the left)... then a resistor between the 2nd pole and V1B grid.... (on the right)?? In each case do I just connect that resistor to ground??

[Colossal]

Be sure to add a high value pulldown resistor on the front and back end of that switch to soak up the pop. 4M7 or 10M usually work fine and won't load the circuit.

thanks colossal!

Do you mean that I need a resistor between the plate of V1A and the 1st pole (on the left)... then a resistor between the 2nd pole and V1B grid.... (on the right)?? In each case do I just connect that resistor to ground??

Like this:

Note the 100nF cap coming off the plate. That is to keep DC off the switch and the user safe(r). Note the location of the pulldown resistors. That will sink the pop with the switch is thrown. Use a DPDT.

Tone Stack Switch.jpg

[pompeiisneaks]

umm the image is flipped and inverted when I view it? Wha?
(when I click the image itself)
~Phil

[Colossal]

umm the image is flipped and inverted when I view it? Wha?
(when I click the image itself)
~Phil

I figured it out. AmpGarage doesn't like .png files. If you post a .jpeg...it posts normally. I converted the .png to .jpeg and reposted.

[pompeiisneaks]

Weird, I am trying now:

testpng.png

~Phil

Edit: Weird, that worked fine when I did 'place inline' maybe if you click the attachment as an 'image link' is what does it?

[diddymix]

Be sure to add a high value pulldown resistor on the front and back end of that switch to soak up the pop. 4M7 or 10M usually work fine and won't load the circuit.

thanks colossal!

Do you mean that I need a resistor between the plate of V1A and the 1st pole (on the left)... then a resistor between the 2nd pole and V1B grid.... (on the right)?? In each case do I just connect that resistor to ground??

Like this:

Note the 100nF cap coming off the plate. That is to keep DC off the switch and the user safe(r). Note the location of the pulldown resistors. That will sink the pop with the switch is thrown. Use a DPDT.



Tone Stack Switch.jpg

Thanks so much!! I've never really understood these resistors.. my switch currently (without TS function discussed) does have pop and its very annoying... can I ask with regard to them... is it a case of just adding them as you describe whenever there is a switch and a tube input/output.. on either end ?? You see as I mentioned the switch is actually a 4 way 4PDT... so there is also a couple of other functions on it.. on of which feeds the phase inverter directly from V1B... Just wondering whether I need to add more pull down resistors like this accordingly?

By the way I think that the DC cap you suggested should be higher value.. otherwise the series capacitance affects the tone stack bass range ... 100nf would pull my 100nf bass cap down to 50 nf.. I think 1uf should do it