Simulate schematic tone stack in tone stack calculator

[Rod]

Hi!

Need some help here in how to simulate the tone stack in the attached schematic in tone stack calculator app, http://www.duncanamps.com/tsc/.

I think that i have to select the Marshall kind of tone stack tab, but what values should i have to put in the following parameters, Zrsc and R5 based on the schematic?

[pdf64]

I think that it would be 'near enough' to make Zrsc 10k and R5 1M.

[Rod]

I think that it would be 'near enough' to make Zrsc 10k and R5 1M.

Hi pdf64!


How do you get those values?

[pdf64]

R51 and R31.
The actual Zrsc will be a little lower than R51's 10k, and the actual TSC R5 will be a bit higher than R31's 1M.
In both cases what's required is the impedance (at the relevant node) to ac 0V. For the bandwidth of interest, I think the impedance is mostly going to be resistive.

[eschertron]

+1 ^^^
Changing the default values of Zsrc and R5 to the suggested values has minimal effect on the displayed graph. For any reasonable values used, the results aught to be 'close enough'. Only when using a (for example) Marshall TS after a (for example) Fender plate-driven stage - where the Zsrc may be off by a factor of 40 - will the result be visually and audibly different.

[J M Fahey]

Agree and add: Rod is showing us only *half* the schematic

That tone stack serves 2 channels, selected by Relay S12.

When down, tone stack is fed from R51, but when up, sound comes through C8 from ... ????????????

So please show us what´s at the left of C8.

[Rod]

Heres the full schematic.

ValveKing2_20MH.pdf

[eschertron]

Heres the full schematic.

[ATTACH]50009[/ATTACH]

I didn't do the arithmetic, but use the 150k plate resistor in parallel with the 68k nominal impedance of the triode to get the Zsrc when that channel is selected. It will be rolled off (loaded down by the TS) a bit more than the (10k Zsrc) channel we saw previously, but the basic shape of the tone controls will remain unaffected. Split the difference between 'about' 10k and 'about' 40k to get a representation of how the tone stack looks in this design. Changing the Zsrc from 10k to 40k will have minimal effect.