Tone stack question, new amp circuit

[bluefoxicy]

Does anyone know how this tone stack is wired in?



There's a picture but "out" isn't even on a pin and I can't tell if "In" should be shifted right or if "Out" is on the wrong side...




I want to know because I want to add it to this work-in-progress Valve Junior clone amp:

http://www.musictechforum.com/wiki/i...lones/Valve_34

(Which I will eventually have to redraw but...)

[Paul P]

There's a picture but "out" isn't even on a pin and I can't tell if "In" should be shifted right or if "Out" is on the wrong side...

Just shift both "out" and "in" right one wire.

Paul P

[bluefoxicy]

Okay. Also can I drop these after the first gain stage of a 12AX7 or should it ONLY be in the input?

[Paul P]

You could do it like Fender :

http://www.schematicheaven.com/fende...a764_schem.pdf

Paul P

[bluefoxicy]

You could do it like Fender

K that schematic shows it after gain stage 1, which is where I want to put it. Thanks.

[bluefoxicy]

Oh for...

http://www.aikenamps.com/ToneControlScaling.html

Okay, I'm using that output stage of the 12AX7 running on a 220K plate resistor, so 1/48.67k ~= 20.5 ohm.

I suppose the impedance doesn't matter since my tube has minimal impedance anyway.

The default values for these pots should land at T=250k, B=250k, M=10k; I want to avoid the reduction of gain associated with a tone stack like this. How do different pot values affect gain and tone? What about the slope resistor R1? Will scaling all the pots up allow me to avoid so much loss, or should I scale Mid and Bass and keep Treble lower?

I THINK I want 500k Bass, 50K Mid with the same frequency impacts. My math falls as follows:

250k+250k+10k = 510k
250k+500k+50k = 800k
800k/510k = 1.5686...

C1 = 250pF / 1.5686 = 159.375pF ~= 160pF +/-10%
C2 = 0.1uF / 1.5686 = 0.06375uF ~= 0.064uF ~= 64nF +/-10%
C3 = 0.047uF / 1.5686 = 0.0299625uF ~= 0.030uF ~= 30nF +/-10%

I don't know how the slope resistor affects this. My best guess is that increasing it directs more power to Treble, giving less control over Bass and Mid; but that blocking cap bugs me, it probably filters Bass and Mid anyway, so raising R1 probably tightens the bass and gives a brighter overall tone.

I'm thinking keeping treble small will prevent bass/mid attenuation when treble is higher, keeping more gain. Raising bass should prevent bass attenuation, at the cost of mids. Raising mid should smooth out the bass/treble response by preventing so much attenuation to ground. Right? I think raising Mid 5 times and raising Bass 2 times should get better gain and a smoother tone stack.

Just a guess. I don't know how this works at all... comments?

[black_labb]

http://www.duncanamps.com/tsc/index.html

try that. its a tone stack calculator that has some standard tone stacks in it. it allows you to input some different values and view the frequency response graph, including the signal loss in db. great tool.

[Shea]

Oh for...
Okay, I'm using that output stage of the 12AX7 running on a 220K plate resistor, so 1/48.67k ~= 20.5 ohm.

I suppose the impedance doesn't matter since my tube has minimal impedance anyway.

I think 48.67k is the output impedance -- that's the 62.5k plate resistance of a 12AX7 in parallel with a 220k plate load resistor. I don't know how you got to 20.5 ohms.

Anyway, I would double the values of all the pots and the slope resistor, and halve the values of the capacitors, to scale the impedance of the tone stack upwards. Or even try a scaling factor of four. Either way would reduce the insertion loss of the tonestack - that is, it would preserve more gain.

For all your other questions, check out that Duncan Tone Stack Calculator like black_labb said.

[bluefoxicy]

I think 48.67k is the output impedance -- that's the 62.5k plate resistance of a 12AX7 in parallel with a 220k plate load resistor. I don't know how you got to 20.5 ohms.

1/220k + 1/62.5k == 1/48.67k

you're right. Heh.