Fender footswitch: problems replacing old RCA plugs with one stereo 1/4" plug

[bram9206]

Hi,
I have here my old 1972 Fender Deluxe Reverb and I got a bit tired of resoldering the RCA plugs every 10 gigs, so I decided to replace the RCA plugs with one stereo 1/4" jack (just like the reissue fenders).

Took out the (reverb-side) RCA female and replaced it with a stereo 1/4" female. Then soldered the reverb to tip and vibrato to sleeve. There is also a capacitor that goes to the ground of the former vibrato RCA plug. Here is a pic, not mine though:

But since it simply goes to ground I left it there at the ground of the "former" vibrato RCA.

Seemed like a perfect fix, but I have two problems:
- there is a loud click sound when I push the vibrato knob. It's not always there, sometimes I push it five times and I have no click at all, then I click it another five times and it's there... unpredictable, but it wasn't there before.
- when I turn up the reverb there is quiet some hum that was not there before the "fix"...

Anyone any idea? Can I actually just replace the RCA jacks with a 1/4" jack? Or did I overlook something? Why is there a cap at the ground of the vibrato RCA? Because I can't find it in the blackface models...

Thanks a lot!

 

[dmp]

Then soldered the reverb to tip and vibrato to sleeve.

The reverb should go to tip. The vibrato should go to sleeve. The ring should be grounded.
Both are turned off by grounding the wire, i.e. when the vibrato wire is connected to ground, the vibrato is off. When the reverb wire is connected to ground, the reverb is off.
If you have it wired correctly, it should work exactly as before.
Sorry if this is no help, just confirming that I think you planned it correctly and just need to doublecheck it.

The cap looks unrelated to me, and leaving it grounded on the vibrato rca should be correct.

 

[bram9206]

Well, the switch does work, but not for a 100%... I sometimes have the loud "click" noise when pushing the vibrato knob and too much noise/hum when I turn up the reverb. And it's those two problems that are a mistery to me... I don't understand what I did wrong or where I changed something that could cause these problems.

 

[dmp]

Are you using the same footswitch?

 

[Walrus]

Have you used insulated jack sockets? Because I think the original RCA connectors will be isolated from the chassis and have wires tacking the earth to a specific point.

 

[fazer]

Original RCA jacks are not isolated from the chassis.  No need to isolate.  However the ground point on the reverb is prone to hum if you made the wire length longer.  It grounds out the grid I believe so if the wire is longer than the original, you will get hum on the reverb from the wire outside the amp.    I noticed this and put a small relay in. It grounds  both verb and tremolo at the RCA connection so no signal is out of the chassis through the switching.    You may not want to go this way due to being original , never mind the change to TRS jack.    I'm not sure what is causing the pop on Tremolo but if the cable is longer that could be causing it as well.    Also the Cable fender uses is braided and if you changed to modern cable , its spiral wrap mostly with foil shield maybe.  Could also be a source of the problem.

 

[bram9206]

Still using the original footswitch with original cable (so length too did stay the same).

 

[mjrippe]

The cap is probably there to dump switching transients (clicks) to ground.  Make sure it is well soldered to your 1/4" jack and maybe move the other side to the 1/4" ground connection as well.  Also, be sure that this ground point on the 1/4" jack is really well grounded either mechanically or electrically (star washer to chassis or wire to ground lug on chassis).

 

[bram9206]

Well, actually I don't think this cap has anything to do with the footswitch. In the picture I've shown in the beginning of this thread you can clearly see the positive side of the cap (the new black Sprague Atom with green letters) goes to a tube and the negative goes (of course) to ground, which in this (and my) case is a ground lug screwed to the chassis by the RCA plug. So I doubt the cap has anything to do with it. Or would it...? Maybe I need to ground that cap directly to the 1/4" ground for better grounding?

 

[mjrippe]

My mistake, I thought we were discussing the ceramic disc cap on the 2nd RCA jack from the right.

 

[bram9206]

Ok, this is where I'm at: I changed the 1/4" plug with a decent plug (not the ones used by Fender for their RI footswitch) and the noise/hum in the reverb went away. So that problem is solved!

But I still have this loud "click" sound when I push the vibrato switch. Here's the problem in detail: when the reverb is switched OFF and I push the vibrato their is never a click sound. So in this case the vibrato can be switched on and off without any noise...
But when I switch the vibrato on and off with the reverb switched ON I always have the loud "click" noise!

Does anyone have any idea what could be the problem here? I'm a bit surprised that it's so hard to change the RCA plugs to one stereo 1/4" plug... Then how is it done in the reissue Fenders?

Thanks!

 

[bram9206]

Here are some pictures I took this afternoon of my Deluxe Reverb with the 1/4" mod and footswitch. Hope this helps locating the problem. Vibrato is tip, reverb is sleeve, the 1/4" chassis is grounded to the amp's chassis via locking washer.

 

[bram9206]

Today I did notice something I didn't mention before: the "click" does get louder with the reverb volume pot higher. With reverb at 10 the "click" is very loud, with reverb knob at 1 the "click" is very silent, not gone, just silent. And like I said before, with the reverb switched off, the "click" sound is just gone. The strange thing is that the "click" occures when pushing the vibrato knob, but somehow the "click" is related to the reverb setting...

Some new theories? Does the pictures above say something?

 

[PRR]

Is there a schematic posted here and I don't see it?

 

[bram9206]

There you go: http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/fenderamps/fender_deluxereverb_a1172.pdf

 

[PRR]

It's a kick-start trem oscillator.

When "off", there's -60V applied to the AX7 grid. This holds it OFF.

When you switch "on", this -60V goes to zero. The 60V transient "kicks" the oscillator into life.

Most other ways of killing the trem, there is a long start-up because of the long time-constants in a low-frequency oscillator. This kickstart technique actually starts the first quarter-cycle of oscillation, so it starts-up at nearly full output and with consistent phase.

So we have a 60V switch-on transient. Meanwhile over in the reverb we are switching the tank output. Which is typically 10mV. 6,000 times weaker than the trem-start kick.

So even 1/6000 of sneak current or stray resistance or capacitance between trem and reverb WILL make a loud sound.

I think you have found why this amp used two connectors.

I don't see a no-drawback way to cure this.

Perhaps a JFET on the reverb point, turned off/on by a -10V feed from the reverb pedal switch. This also gets the reverb signal out of the pedal cable, reducing hum pickup.

 

[bram9206]

Interesting, thanks PRR!

Well, I now changed the plug again to its former state of being: the old RCA plugs, everything soldered back to how it used to be before the mod.
So now I'm back at the very beginning, but I still have a "click" sound, BUT it is a bit different and if I remember well it was there too before I started working on the Deluxe. Here's detailed description of the current "click" sound:
with reverb switched on: still a "click", but it is much more silent now (I could live with it in a live setting, but couldn't live with it for studio work). Again the loudness of the "click" depends on the volume of the reverb.

Also what is different now, I ONLY have the "click" when I switch the vibrato ON. Whereas with the 1/4" plug I had it both when switching on AND off. Now I don't have a "click" when I switch the vibrato off.

Anyone? I must say the footswitch is a reissue footswitch and I've been told the switched in there are pretty cheap. Maybe that is it?

 

[sambatyon]

So I am late to the party, but I was researching to do this mod and this is the one forum I found. I was checking how the schematic changed between the original and the reissue and I found these differences.

The components circled by purple were added from the original. You get and RC circuit which based on my old electronics knowledge will slow the transient.

The point where the reverb connects was moved from the base to the anode so we dump the amplified signal instead. This definitely will reduce mixing bag noise. I would expect it will also reduce the click sound if it were to come through the reverb signal, as the click would not be amplified by V4A.