Brownface Tone Stack Mod

[jhawk]

So here we have the tone stack from a Brownface Vibroverb.
[IMG:279:292]http://i.imgur.com/CXCtrRG.gif[/img]
My question: will changing the value of R2 increase/decrease the mids? If so, will increasing the value increase or decrease the amound of mids?
And if I'm completely off base and R2 does something completely different, what does it do?

[Stevem]

r2 acts like a mid pot, increasing the value will up the mid content.
If you go to the Duncan amps site he has a tone stack cal you can down load and play around with.

[M Fowler]

About 10K to 15K should be about right.

[jhawk]

And the one I posted is different from the Blackface tone stack. Like this one from a Blackface Twin:
[IMG:206:258]http://i.imgur.com/qKq3TTy.gif[/img]

[Teleguy61]

jhawk, download the Duncan Tone Stack Calculator, it is very helpful for exactly your questions.

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

[M Fowler]

Depends on what you want but that first circuit has the tapped 350k pot which is available but you might like the black face circuit better which has the mid pot.

[matt h]

(deleted)

[jhawk]

Teleguy - the calculator doesn't have the Brownface stack on it.
M Fowler - I'm looking to maintain the signal strength and integrity of the Brownface sound, but I want to put in a three way switch that targets the mids. In pos 1 mids would be increased, pos 2 would be bypassed/stock resistor value, pos 3 mids would be decreased.
Would going with the Blackface stack and adding a "recovery" gain stage be a better solution?

[jhawk]

matt h - How about this other Brownface stack? Would R2 be the resistor to target again for "mids"?
[IMG:196:282]http://i.imgur.com/EdtKMU0.gif[/img]

[M Fowler]

Go ahead and use a mini SPDT switch with 10k on one end and 6k8 on opposite end of switch, middle position is off.

Simple enough mod that keeps the original brownface intact or use a push/pull bass pot to switch in 3k3 with the 6k8 already in circuit for slightly over 10k total resistance.

[matt h]

(deleted)

[Teleguy61]

Teleguy - the calculator doesn't have the Brownface stack on it.

No it doesn't, but you can adjust any value in each model and simulate a lot of different configurations.
It can help to give you a picture of what might happen before you start soldering.
Just my 2 cents.

[M Fowler]

You can also increase the slope resistor to shift the frequency for more mids.

[jhawk]

Thanks for all the input guys! And that tone calculator is pretty helpful. Almost makes me want to put the "James" stack in.

[rp]

just keep in mind that by increasing it's value, you won't just get more mids, you'll get more everything as well. so you may find that when you do adjust it, you may find you want to back the treble and bass off a hair to compensate.

First mod for me as a newbie was put in a mid pot - more better. I tried it in a few clones bit didn't like it, it threw me off, re-adjusting to the modded tone stack was more than just twirling the mid pot. I'll note I was too lazy to adapt and likely with a little patience it would have been a practical mod, but in my Lightning anything other than the stock position really bugged me, made the amp less Voxy more Fendery. The gain change/tone skew was definitely an issue. Reading above I now know why.