darkening the reverb in an ab763

[Chickenwings]

i have an ancient twin reverb (1967) and i love it to death, but i notice that the reverb can get a little bit overpowering when used with dirt.
Is there any particular component i can change to knock some of the tops off the reverb?
Its the regular AB763 circuit for the electronics gurus out there like glassman etc al....

[glassman]

Re: darkening the reverb in an ab763

Try this...

Add some small value capacitors to the recovery stage. Grid to ground, plate to grid, plate to ground and across the reverb level pot. Multiple small values are better than one larger value in this instance since it creates a shelf rather than a slope to the cut-off frequency. This will help keep a lot of the original voice of the reverb without dirt but still cut the upper level frequencies that result when you push some distortion into a spring reverb. Think 4th order Butterworth filter.

You can do the same with the driver tube but I would do that second if you can't get enough shelf on the recovery side but the results will be more muted overall.

This is a little non-traditional but I have also stuffed a little piece of wadded up paper in the end of one or more springs in the tank to cut some of the high frequency content but was never really happy with the results. It might work for you though.

[Chickenwings]

Re: darkening the reverb in an ab763

thats a cool idea, thanks...cutting off the frequencies of the upper harmonics rather than the fundamentals.
I have to admit i dont know what a butterworth filter is tho!
i was under the impression the reverb circuit had its own amplification system and therefore some kind of eq voicing circuit.
I was hoping you coukd say something simple like...change the the capacitor coming off v4 to a .1uf or something tho.
NOw ill have to do some real research! lol

[glassman]

Re: darkening the reverb in an ab763

i was under the impression the reverb circuit had its own amplification system and therefore some kind of eq voicing circuit.

Actually it does but the upper frequencies are tamed by the mechanics of the spring and the lower impedance tank feeding a high impedance recovery stage. But when you start adding a harmonic rich signal to the mix, the spring and the circuit loading can't quell the extra signal and the reverb swells like a cymbal.

[Chickenwings]

Re: darkening the reverb in an ab763

i think this one is too complex for me to try. I really appreciate your info tho glassman. Maybe i should look at darker speakers instead...
i have these : http://taweber.powweb.com/weber/cali12f.htm

In general, overdrive (from a pedal or from the amp) will sound somewhat nasally or harsh especially with the aluminum dome. Some players report good results using the California with paper dome and some distortion or overdrive. You will likely hear more higher-frequency distortion noise (especially with the aluminum dome) since this particular speaker does not aid in smoothing out the breakup, like most speakers do. In short, it gives you exactly what you give it.

If you are considering the California, and want clean AND overdrive tones, you may want to check out the Ceramic Chicago

So maybe i should look at a apir of these: http://taweber.powweb.com/weber/chicago12f.htm

[zzmoore]

Re: darkening the reverb in an ab763

Have you tried a different AT or AU in that slot.? It is a fairly easy and inexpensive experiment.