Author Topic: Fender Twin Reverb Footswitch?  (Read 4084 times)

mr.adambeck

Fender Twin Reverb Footswitch?
« on: April 14, 2008, 04:30:51 PM »
Hey I have a reissue Fender Twin Reverb (Black face).  The chnnel switch is supposed to switch the tremelo on/off and the reverb on/off (it's a two button through a stereo jack), however, it's never worked.  Anybody have a schematic or know anything about how to fix these?  Thanks!

SolariEGO

Re: Fender Twin Reverb Footswitch?
« Reply #1 on: April 14, 2008, 06:32:23 PM »
Hi,

My silverfaces do not use the stereo jack but two RCA jacks connecting at the amp, but the principle should be the same; a shielded cable with two leads, one lead to a spst switch for vibrato, that shorts hot to ground, the other lead and the shield go to another spst switch for reverb. The shield would be connected to the sleeve connection on the stereo jack going to the amp. I don't know which of the leads (vibrato or reverb) that should connect to ring and which to tip, but you could probably trace it or just solder them in and see what switch switches what. Good luck!

Steinar
Rockin' in the Axis of Evil

petemoore

Re: Fender Twin Reverb Footswitch?
« Reply #2 on: April 14, 2008, 06:39:16 PM »
  Tip to ground
  Ring to Ground
  Ground being the sleeve
--------------------------------
  Other position of switches:
  Tip floating
  Ring floating
  ---------------
  You can test the footswitch alone: Connect continuity tester to tip and sleeve of footswitch plug, hit both switches look for continuity / open / continuity / open.  Do the same for the other switch's ring and sleeve.
  IOW you can't mess up if you're using a TRS cable, other than it might still not work.
  'Open' condition means 'on' so that the tremolo and reverb should work without the footswitch.  
Convention creates following, following creates convention.

Radical CJ

Re: Fender Twin Reverb Footswitch?
« Reply #3 on: February 02, 2021, 10:48:54 PM »
I realise that this thread is 13 years old, but I am wondering if anyone knows about the voltages/amps involved here in grounding the tip and ring?

I just bought a secondhand Twin with foot switch gone AWOL, and I'm wondering whether soft switching with a relay is possible for a DIY replacement. 

danfrank

Re: Fender Twin Reverb Footswitch?
« Reply #4 on: February 02, 2021, 10:57:42 PM »
Yes, the footswitch handles 1-2 volts at most... On the tremolo, it grounds the grid of the oscillator tube (IIRC) so the tube oscillates. On the reverb, it grounds the the output of the tank.
Using relay switching should make it quieter since the audio doesn't go to the footswitch

Radical CJ

Re: Fender Twin Reverb Footswitch?
« Reply #5 on: February 02, 2021, 11:41:48 PM »
Yes, the footswitch handles 1-2 volts at most... On the tremolo, it grounds the grid of the oscillator tube (IIRC) so the tube oscillates. On the reverb, it grounds the the output of the tank.
Using relay switching should make it quieter since the audio doesn't go to the footswitch

Thanks. That's good to know. I did get the multi-meter out, but as I'm not an expert on tube amps I thought best to ask in case I was missing something.

PRR

Re: Fender Twin Reverb Footswitch?
« Reply #6 on: February 03, 2021, 12:09:12 AM »
The footswitch is nothing special and there's no reason to do relays (how you gonna switch the relays?). The footswitch is still available, one supplier here. Another. Fender made a lot of these with two RCA; cut it and install a stereo 1/4".

Schematic: https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-65-Twin-Reverb-Reissue-Schematic.pdf

That's a mess; here's the key parts. The Reverb just switches low-level (sub-Volt) audio, at a fraction of a mA. The Trem on this amp uses a heavy negative voltage to force the LFO off, and kick-start it when needed. While it starts from 65V, it gets divided-down before it gets to the jack so it is less than 9V.

« Last Edit: February 03, 2021, 12:13:09 AM by PRR »
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Radical CJ

Re: Fender Twin Reverb Footswitch?
« Reply #7 on: February 03, 2021, 12:34:00 AM »
The footswitch is nothing special and there's no reason to do relays (how you gonna switch the relays?).

I was actually thinking of using a NE555,  la this: http://effectslayouts.blogspot.com/2016/06/555-relay-bypass.html

Obviously this is a pretty dumb idea because the switch will require its own power source when it doesn't need to be anything more than a mechanical switch. However, it would be a simple project for playing around with methods of using momentary switches for bypasses.

Anyway, thanks for collating that schematic info below.