Tone control calculator anybody??

[italianguy63]

I've been playing with this Valvecaster 2.0 design for a few days.. And, I am having problems with the tone stack.  It seems to be totally ineffective.

I built a 2nd prototype with sockets so I can change values, and I have swapped the values of C8 and C9 up and down, and nothing seems to work.  I checked the traces and they are correct.  It is wired as it should be.

I am not an EE, and would appreciate if someone would look at C8/C9/VR3 and tell me what this should be doing.  Is it supposed to be a treble cut, a bass cut? etc.  Can anyone suggest other values for these components?

Thanks!
MC

[alexradium]

not a tonestack,its a treble cut,C8 is just a coupling cap that passes all the frequencies,almost,the reason it is not working is probably the low impedance of the preceding stage,you need a resistor in line after the C8.
You could rewire this putting in line a 1k resistor after C8,then the 100k pot in series,then C9 to ground,hear what you get.

[italianguy63]

That will be easy to try.  Thanks-- I'll give it a go.

MC

[italianguy63]

not a tonestack,its a treble cut,C8 is just a coupling cap that passes all the frequencies,almost,the reason it is not working is probably the low impedance of the preceding stage,you need a resistor in line after the C8.
You could rewire this putting in line a 1k resistor after C8,then the 100k pot in series,then C9 to ground,hear what you get.

To make sure I understand.. will a 1K added between C8 and C9 suffice?  MC

[alexradium]

its 1k and 100k pot in series,then c9 to ground,similar to the Proco Rat

[antonis]

1k in series with 100k pot will only lift up a bit the low end pot setting..
(thought adding 1k as it is now)

At its best (C9 grounded), 1μF/10nF voltage divider exhibits a ratio of slightly less than 1%...
Adding series resistance with C9 (via pot setting) lowers more that ratio..

IMHO, for an audible tone alter, C8 & C9 should be at least of equal value (max -6dB attenuation) or C9 even bigger than C8..

[j_flanders]

You can try some values in this online app:

https://tinyurl.com/utyw3ym
(I've drawn the tone stack already, but with your values it does nothing)

Double click components or mouse scroll when hovering above one to change the values.
Reduce response db scale to get a better view.

[italianguy63]

You can try some values in this online app:

https://tinyurl.com/utyw3ym
(I've drawn the tone stack already, but with your values it does nothing)

Double click components or mouse scroll when hovering above one to change the values.
Reduce response db scale to get a better view.

I don't really know what I am looking for!  I am not familiar with the tool.

But, I put in 22n for C8 and 47n for C9 and it looks like I get a good amount of change.

Would you look at that and see if that is what I am seeking.

Now, the funny thing to me is that the "published" 1uF and 10nF are in pretty much every Valvecaster schematic out there.. so, they are all incorrect I assume.

Also funny, in reading peoples posts, it appears many people say "Omit the tone control" -- now, I think I know why!!

MC

[antonis]

But, I put in 22n for C8 and 47n for C9 and it looks like I get a good amount of change.

Apart from C8/C9 ratio, actual caps values should be considered together with Tone pot value for setting frequency range margins..
(i.e. lower cut-off frequecy is set by C9/(C8+C9) where upper is set by (C9+Pot)/(C8+C9+Pot)..)

[italianguy63]

But, I put in 22n for C8 and 47n for C9 and it looks like I get a good amount of change.

Apart from C8/C9 ratio, actual caps values should be considered together with Tone pot value for setting frequency range margins..
(i.e. lower cut-off frequecy is set by C9/(C8+C9) where upper is set by (C9+Pot)/(C8+C9+Pot)..)

OK-- so we know the pot is 100K.
What would be an appropriate value for the caps, lets just assume we keep them at a 1:1 ratio (equal value)?

[antonis]

Plz define filter's upper/lower cut-off frequency..

[italianguy63]

Plz define filter's upper/lower cut-off frequency..

Ha!  See, that is what I don't know.  What would be the range for a "typical" treble bleed application?

I assume the intention of this is to bleed off the highs...

[antonis]

It depends on beholder's point of view.. 

As it is, it could be considered as a HPF (negleting tube output impedance) or a LPF (considering tube high output impedance)
To shake hands, let's say it's a band-pass filter..

Band margins could be set by C9/(C8+C9+Zout) and (C9+Pot)/(C8+Zout+C9+Pot), where Zout = Tube output impedance..

If you've experienced good results with 22nF & 47nF caps, tweek them around this order of magnitude..

[italianguy63]

Still not having any luck..

Although it seems to have effect in the tool, chart..

I'm still not audibly hearing any effect...

[Mark Hammer]

Use an SWTC.  Jack Orman has a couple of nice pieces about it on his labnotes page, and it has been discussed at length here too.  It's stupid simple, and wonderfully effective.

http://www.muzique.com/lab/swtc.htm
http://www.muzique.com/lab/swtc3.htm
https://www.diystompboxes.com/smfforum/index.php?topic=112382.0

[italianguy63]

I may have to revert to that Mark... But, was trying to salvage the current design so I don't have to revise the PCB. 

MC

[iainpunk]

I may have to revert to that Mark... But, was trying to salvage the current design so I don't have to revise the PCB. 

MC

you could also use a daughter board to change the tone stack without revising the PCB

[PRR]

> I've drawn the tone stack already, but with your values it does nothing

You must model the tube output impedance. Else C9 has nothing to work against. The simulated power source would pull Hoover Dam out of the river, and laughs at a mere 10nFd.

Link

I also think C9 could be much bigger to give a strong effect (100nF may be too much).

Because of scaling (which I can't figure out) it looks like a small slump, but is >20dB above 2kHz.

Almost all the action of Tone happens at the right end of slider.

[hippo]

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.claredot.net/it/sez_Audio/cross_over_passabasso_12dB.php&ved=2ahUKEwiq583XorbmAhUF3qQKHfl0DKcQFjAAegQIARAB&usg=AOvVaw2Ljp-Q_O5UEBHYtUV75svn&cshid=1576365467568

[j_flanders]

You must model the tube output impedance.

Correct. I should have added that or at least mention it.

Because of scaling (which I can't figure out) it looks like a small slump, but is >20dB above 2kHz.

I did mention that however.
There's a slider at the top right labeled "Response dB scale". Slide it to the left.

Almost all the action of Tone happens at the right end of slider.

As such, it could be a nice example of why you ned a log pot sometimes. Too bad the tool doesn't include it as an option.