Common values of FMV tone stack?

[sault]

So I'm sure that someone else has done it already, but I SPICE'd the FMV tone stack last night for fun and pleasure... it ain't Duncan's Tone Stack Calculator, don't get me wrong, but I'm planning on publishing it anyways, hopefully someone will find it useful.

Questions -

1. Is there a list somewhere of common values, or values from popular amps? I'd like to include that when I do publish all of this. I may not be able to include it within the schematic itself, but if I can provide a list in the blog post then that's better than nothing. If I have to dig them up manually I don't mind, but if someone's already done the work...

2. If I have to do it manually, what are some popular models that I should include? I'll definitely look at JCM800, JCM900, JMP1, those of course, and see what's under the hood of the Fender Bassman and Twin Reverb... but I don't really know what Fender or Vox models are or were considered popular.... are there certain years that are better than others?


I've been putting a lot of time into studying my theory and doing my research for this... its one more step towards creating an online calculator, akin to the TSC, but something that anyone can use (not just PC, but also Mac, smart phone, etc). Even if it's just for the FMV stack, I figure it would be pretty cool...


Thank you in advance for any help that you can give me!


Saul t

[teemuk]

. Is there a list somewhere of common values, or values from popular amps?

Yes and no.

Yes: Some amps - especially tube ones - use pretty generic values, often close to those of the Fender Twin or Bassman. If it's a Marshall type variation, they use similar values, Vox/Gibson type, similar and so on...

As is, the TSC already seems to use the somewhat "standard" values.

And no: Despite that, there still is quite a lot of variation. Besides, you really don't care so much about the component values per se but the resulting RC circuit responses. For example, for lower impedance circuits the stack could scale all the resistor values down by 0.1x and all the cap values up by 10x, still essentially resulting into same response than the higher impedance circuit. Naturally, with similar logic one can scale up or down the values by any arbitrary amount and as long as the cutoff points of the RC filters remain the same so will the response of the stack. So, just because component values may look different in some amps it doesn't neccessarily mean the responses will vary so much.

The tone stack doesn't even tell everything either. I've seen many amps with FMV stack where the mid-range control is "fixed" and in addition to the circuit's inherent notch the amp will also feature a variable notch-T filter for mid-range control. The FMV stack is just a tiny part explaining the overall amplifier tone. Drastic low or high cut filters are even more common design elements and can easily make two amps with totally identical FMV tone stacks to still have entirely different frequency response.

its one more step towards creating an online calculator, akin to the TSC, but something that anyone can use (not just PC, but also Mac, smart phone, etc). Even if it's just for the FMV stack, I figure it would be pretty cool...

I think it's a cool project but I'm not sure how beneficial it is for anyone else. As is, the TSC, despite including a bunch of generic stack designs, is still way too limited because you can't actually alter the stack architecture in any way, just component values. The next step is SPICE modeling, which at the point does about EVERYTHING because you can throw in virtually any circuit. So, I think about everyone who need an online calculator for tone stack will immediately try and use the TSC, and after getting dissapointed to its limits will pretty much upgrade to the SPICE modeling and never look back.  

[WGTP]

Cool idea.  I "zero out" different values on the James stack in the Duncan Stack to make notch filter variations. There is also this which I am still figuring out:  http://www.falstad.com/circuit/e-index.html