Footswitch internal reverb??

[niggez]

I have a Fender Hot Rod Deluxe with an onboard Reverb. I want to install a footswitch, so that i can switch between one fixed value and the value set by the Reverb control.
I could just use a cable with 2 wires to run it to a dpdt footswitch, but im thinking that will be a long distance, and might have bad effects on the sound?
Now, if thats no problem, thats how i'll do it. BUt - If it might be a problem, then I'm looking for a way to use my footswitch to switch another switch, one thats closer to the actual reverb section of the amp, and not meters away!
If it seems reasonable, what i'm trying to explain, some feedback would be very welcome!

[petemoore]

I have a Fender Hot Rod Deluxe with an onboard Reverb.
   
  I want to install a footswitch, so that i can switch between one fixed value and the value set by the Reverb control.
  So did I.
  I could just use a cable with 2 wires to run it to a dpdt footswitch, but im thinking that will be a long distance, and might have bad effects on the sound?
  Keeping the signal paths [and other wiring] short and inside the amp chassis to keep noise and problems down, well this wouldn't follow with that.
  Now, if thats no problem, thats how i'll do it. BUt - If it might be a problem,
   
   then I'm looking for a way to use my footswitch to switch another switch, one thats closer to the actual reverb section of the amp, and not meters away!
  Schematic...
  It may be possible to use the switch in the amp assigned to a control a different parameter, I believe it's a simple switch [SpDt or SpSt], either could give two different reverb settings.
  If it seems reasonable, what i'm trying to explain, some feedback would be very welcome!
  At this point..schematic, of the reverb switching, and the relevant portion of the circuit it controls.
  Interesting goal, often looking for better reverb control, never persueing it beyond that, perhaps that's about to change..

[Mark Hammer]

I don't know the HRD that intimately, but it is a very common practice for reverb defeat to consist simply of grounding the hot lead that either comes back from the reverb tank, or else the hot lead after the recovery stage.  Now, to the stage that follows that point in the circuit, the cable that goes to the footswitch can look like a zero ohm source with lots of shielding and no discernible signal (something it will essentially give priority to), OR it can look like, say, a 3 ohm source that picks up various noise sources around it.

So, shorter and shielded is better when it comes to such footswitches.

But what if you want it or need it to be longer?  Here, your optimal strategy is to use the remote footswitch to actuate something else inside the amp that actually does the switching.

There are lots of ways to follow up on that idea.  Here's a simple and dumb one.  Wire up a couple of low-resistance photocells from the reverb hot lead to ground in parallel.  On whatever little daughterboard you install them on, have them facing a superbright LED of some type with a series current-limiting resistor.  I imagine 10k might be about right for a superbright.  Run a wire from the resistor and the other unconnected LED lead out to your remote switch.  Doesn't have to be shielded since it carries no audio nor is it conected to the audio path in any way.  You could use a telephone cord if you felt like it.

In your remote foot unit, you have yet another LED and current-limiting resistor, a battery, and a SPST stompswitch.  When you close the switch and apply power both LEDs light up: the one you can see, and the one hidden inside the amp.  The one inside the amp forces an immediate drop of LDR resistance.  Because you have several LDRs in parallel, that ought to be a fairly low resistance to ground.  Maybe not zero ohms, but low enough that you shouldn't hear any reverb unless you have it cranked.  Open the switch and your foot-unit LED goes off and the LDR resistance goes back up, retaining most of the reverb signal you have it set to deliver.

[niggez]

Good idea with the ldr. I think it should work, because there isnt actually a switch, the reverb is simply off when you turn the pot to 0, and its maxed when its at 12. Although I'm a fan of cheap components, using an ldr is probably a smart idea. Using one will be enough, since I'm not looking for 0 ohm on the off setting. I need one high-reverb setting, which i set on the pot, and one low one, since i never have it all the way off. I guess the resistance using only one ldr to ground will be lower than my current "off" setting, but i think i can do with that.
Ah or if im not mistaken, i could just add a resistor with the desired value in line between ground and the ldr?   
Seems reasonable! That way i can swap between footswitchoff=value set by reverb-control-pot, footswitchon=ldractivates...
Ill open the thing up later and check if im not mistaken about how the reverb control works, but i think this should do it!

- If I'm not mistaken, it would be ideal to get a photocell which represents the exact value of my reverb-pot in the "off" position? And the "on" position being...as high as possible so no signal is lost to ground when "on"?  Im not so sure, havent been in contact with a lot of photo cell devices.

Right now im thinking this setup will give me the opposite of what i want, because the photocells are always low res when on and high res when off!

Edit: I noticed thats exactly how you explained it. Which brings me to another question...using a 9v battery to light up the 2 leds, would this be a permanent option, or will the 2 leds require too much power? If the current is so small, i guess it wouldn't be a problem, but if they run through a battery fairly fast, i would have to rethink so that the reverb is off when the switch is off...since thats my most frequent position! clear?

Edit2: I wont be using a status led. How does the power question look with only the led facing the ldr using energy?

Edit3: Would it be possible to have the reverb switch active only when the external switch is plugged in? Using a stereo jack to connect the switch. Ah...at the moment i can not think of how this would be done Need to do some more thinking!

Edit4: I think it could be done with the type of audio jack used to switch between headphones and external speakers on amplifiers? I think i have one of those lying around somewhere.

[niggez]

Soooo.... I installed the Photocell / LED setup today. When dark, the reverb set at the amp control is active. When the LED lights up, i bypass the reverb pot, and use a pot in my footswitch to control the brightness of the led. However, im still not sure about the power needed to run that LED. For my purpose, i have to use a 4,7kOhm current limiting resistor (most of the time) and as mentioned before, i usually have my reverb set at that value, meaning the LED will be ON most of the time.

Now im thinking about stealing Voltage to run my LED from somewhere inside my Amp, close to the reverb section. Heres the schematic, anyone got ideas where i could hook up? Currently Im running at 9V with a 4,7kOhm resistor, but i guess i could use 16V with a higher resistor current limitor? ANy ideas?

The reverb section is at the right hand side of the schematic, section "D1". My Photocell bypasses the top and left lead of the 25kOhm reverb pot.

http://www.blueguitar.org/new/schem/fender/hotrod_deluxe.pdf

[niggez]

bump