Vox Vibrato Channel with Fender TMB tonetack?

[roseblood11]

Would this work?
I`m building a 3-channel Vox AC30,  close to1963TB specs, but the Weber 6V30 layout and schematic. But instead of the fixed filters at the end of Vibrato channel, I`d like to have a Fender Blackface TMB or TB tonestack.
My idea is:
Remove everything from Volume pot to C28, remove C46, replace R44 and R52 with one 62k resistor
Take the signal from where R47 and R48 meet. Add AB763 tonestack, 1M volume pot, go into C9 coupling cap.

[sluckey]

Remove everything from Volume pot to C28

I think you'll find the fixed filters are necessary to remove the vibrato signal from the instrument signal.

remove C46, replace R44 and R52 with one 62k resistor. Take the signal from where R47 and R48 meet.

This will greatly increase the instrument signal, maybe even enough to offset the loss of the tonestack. I have suggested this mod to the AC-15 as a way to increase the vibrato channel volume but have not actually tested it.

Add AB763 tonestack, 1M volume pot

If you removed C28 you will still need a coupling cap just prior to the tonestack.

[roseblood11]

So, you`re suggesting to leave the filters in place and add the tonestack after them? To be honest, I don`t really understand, why there are multiple identical filter stages in series?

[sluckey]

So, you`re suggesting to leave the filters in place and add the tonestack after them?

yes

To be honest, I don`t really understand, why there are multiple identical filter stages in series?

Vox borrowed that vibrato circuit from Wurlitzer. The high pass filter is to remove the low frequency vibrato oscillator signal from the instrument signal. It may help to just consider the filter as a single filter with 4 or 5 poles. Vox used a 5 pole filter and Weber used a 4 pole filter. I've attached a pdf that explains the theory of the Wurlitzer (Vox) circuit. On page 3 I circled the paragraph about the filter.

[Dave]

That filter is very important. If you try to build it without the filter you'll get nasty sounds. Also, the filter works great after the fender version of harmonic vibrato.


Dave

[PRR]

why there are multiple identical filter stages in series?

The audio, 80Hz on up, is a part-volt.

The tremolo control, maybe 8Hz, may be a hundred volts.

If not blocked or cancelled it will overload later stages.

One-pole filtering would only knock it down 10:1 (between 8Hz and 80Hz). Two-pole better but still marginal. Another pole is less than a buck; why be cheap?

The good Fenders inject trem in high-level push-pull stages. The OT alone seems to be enough filtering. The several which do low-level trem have various sorts of cleverness.

[HotBluePlates]

I`m building a 3-channel Vox AC30,  close to1963TB specs ... I`d like to have a Fender Blackface TMB or TB tonestack. ...

Maybe I'm curmudgeonly, but I'd recommend building the AC30 as-is and instead buying a parametric or graphic EQ pedal.  You can add the tone-shaping you think you might want without messing up what the Vox circuit has going.

Saying this as someone who owns a 1963 AC30 Bass model (plus a few other mid-60s Vox amps).