Taming a Twin Reverb RI

[pickles_man]

I recently got a Twin Reverb RI. It is waaaay too much amp for me, but it still sounds beautiful even at bedroom volumes. And the reverb is deep and full. I play mostly melodic single-note lines with a strat.

Now, most of the time, the volume is between 2 and 3, and if I want to do some EQing, it quickly gets too loud even at those volumes. Also at such a low volume I get a lot of hiss and hum that would otherwise be less prominent relative to the guitar sound at higher volumes. (the old SNR...)

So I got the idea of attenuating the voltage right before phase splitter tube, ie a master volume. I was thinking either an actual pot, or maybe just a switchable voltage divider, so that my volume knob and EQ are more usable. Theoretically, it shouldn't affect the tone since all frequencies should still pass through in the same ratio (ie im not adding a cap or doing any sort of filtering). But of course theory and practice don't always coincide...

Has anyone done anything like this? Note, I'm *not* going for any sort of overdrive, I just want clean.
Why do people hate master volume on the old silverface amps so much? does it affect tone? why?

Also, please no responses of the sacrilege of this... I KNOW I would be better off with a smaller amp, but I got a very good deal on this. I even went to a store to play through a DRRI, and it sounded great, (but less "open"), but all told would cost me around $600 more than the Twin already sitting in my room, so the twin stays.

Thanks for any responses.

[pila]

The master volume does the job for getting the pre-amp tone without being so loud, but the tone is in the ears of the beholder.
Have you looked at schematics of older Twins for ideas on hook-ups?
Just a suggestion.....

[pickles_man]

No, but thats a good starting point I'd imagine. thanks.

I'm still curious as to why people dislike the master volume on old twins, never having tried one. is it cause people are trying to get distortion by only pushing the preamp tubes and the result being shitty? or does the clean sound thinner or something?

[Steve A.]

No, but thats a good starting point I'd imagine. thanks.

I'm still curious as to why people dislike the master volume on old twins, never having tried one. is it cause people are trying to get distortion by only pushing the preamp tubes and the result being shitty? or does the clean sound thinner or something?

Have you looked at the chassis of your Twin Reverb Reissue? With the printed circuit boards it is not like the old BF/SF amps so it can be vewy, vewy twicky (as my good friend Elmer Fudd used to say).

I have a DRRI myself and the Ken Fischer Type 2 master volume works great in it (which I have attached below). Of course if you try turning it down to 1 it's not going to sound very good... the idea is to get a good tone with the front panel controls and then back off the MV a little bit to attain the appropriate room volume.

A lot of people will pull two tubes out of their Twin Reverb *and* disconnect one of the speakers. By doing both items you cut down the volume coming out the amp considerably, and you don't cause an impedance mismatch of the OT.

FWIW when Fender added master volumes to their tube amps in the 70's most people thought that they sounded like crap because you lost the distortion in the phase inverter. (That would be a pre-PI master volume, which works in a Marshall MV design because you can have a lot of gain and distortion in the preamp section and can skip the distortion in the PI.)

HTH

Steve Ahola

P.S. You might want to download the entire Trainwreck Pages from Ken Fischer- very interesting stuff!

http://www.blueguitar.org/new/schem/...reck_pages.pdf

[pickles_man]

I haven't looked inside yet, only at the at the schematic. It seems that C20 is the link between the PI tube and the previous stage, so I could hopefully lift one of the leads and attach my pot/voltage divider there. But yeah, things would be much easier if it weren't a PCB.

As for the pulling two tubes and one speaker, already did that but it actually doesnt make a huge difference.

Thanks a lot for the PDF, I'm gonna have a read through. I've been also looking for a discussion of the twin reverb circuit itself, either online or in a book. Any ideas?

[my7of9]

I have a similar issue as well.

[Steve A.]

I haven't looked inside yet, only at the at the schematic. It seems that C20 is the link between the PI tube and the previous stage, so I could hopefully lift one of the leads and attach my pot/voltage divider there. But yeah, things would be much easier if it weren't a PCB.

As for the pulling two tubes and one speaker, already did that but it actually doesnt make a huge difference.

Thanks a lot for the PDF, I'm gonna have a read through. I've been also looking for a discussion of the twin reverb circuit itself, either online or in a book. Any ideas?

The master volume you describe is the pre-phase inverter type which does not work well in the older amps since you lose all of that nice distortion in the phase inverter. Your service information on the Twin Reverb Reissue should include a layout drawing that can be helpful in planning mods. But since it does not include the actual traces you do need to determine what each pad of a component is connected to once the boards have been removed (make no assumptions but follow the copper, using an ohmmeter when necessary).

Pulling two tubes cuts the power of your amp in half, but that is only a reduction of 3dB. It makes your amp more like a Pro Reverb that puts out 40-50 watts but that still is louder than a Deluxe Reverb (20-22 watts) or a Princeton Reverb (15 watts) or an old 5 watt Champ clone...

There have been a few good books on the history of Fender amps but I can't think of their names. You might check the user reviews over at Harmony Central to see how other people are using this amp.

Steve Ahola

[pickles_man]

The master volume you describe is the pre-phase inverter type which does not work well in the older amps since you lose all of that nice distortion in the phase inverter.

As mentioned, I don't want any distortion, nice or not

So just to update, I finally did this and I'm very happy with the result.
I took out the useless "ground lift" switch and put the 1M pot there. I had to take out the PCB (which was quite a pain...) and desolder cap C20. Ran a shielded cable to the pot, and soldered the ground to the Y ground at R40. If anyone wants more details or pics, let me know.

The best part is that in turning down the master volume, i can almost completely get rid of all the annoying hums/noise picked up by the preamp section and turn the regular volume way up so that I hear guitar, and only guitar. The tone sounds identical, though it's only been a day, so maybe I'll notice some subtle differences later.

Just for the hell of it, I listened to the pre-amp distortion, and yeah it sucks compared to preamp + power stage distortion, so I don't recommend doing this if that's what you're after. But if you want more manageable volume control (instead of 1-3..) and a much higher guitar signal to extraneous noise ratio, it's great.