Building a DIY footswich to trigger the amp's overdrive

[eh la bas ma]

Hello,

I am trying to build a simple footswitch, without Led, for an old avenger amplifier (AX-50RC).

It's my first attempt, and i can't find any official documents from Avenger online.

Obviously,  i did something wrong because the prototype I already built isn't working.
I tried it on the amp with the overdrive switched on, it didn't switched off when i used my prototype.

There is an overdrive, a reverb and a chorus on this amp, and only one footswitch input. So i am not sure what kind of footswitch I should build. I just want to trigger the overdrive, the chorus would be a nice addition, but I don't want to get ahead of myself here.
I hope this is very easy for more experienced people than me. Your help would be greatly welcome.






Edit : the 3PDT footswitch's notch is turned toward the mono jack

[Mark Hammer]

Cute play on "Alabama", there (la bas). 

Many, though not all, amplifier footswitches will involve a simple grounding out of a contact.  That's why they can use a standard 1/4" phone jack whose own ground is connected to the amplifier chassis.

Some amplifiers will use a stereo phone jack to allow for switching of two functions by grounding the tip or ring contacts, or both, if you want to turn two different function on or off.  And some amplifiers only permit remote switching of one feature.  For example, my Fender Champion 110 has an overdrive channel and also reverb, but the footswitch only enables/disables overdrive.  If you want to engage or disable the reverb, you have to turn the control knob manually.

So, perhaps the first thing to do is to determine if the footswitch jack is stereo or mono.  You can do this my inserting a bare stereo plug into the jack, and testing with your meter to determine if there is a separate ring and shaft contact.  Set your meter for continuity testing (beeper?), and touch the probes to the ring and shaft solder lugs on the bare plug.  If your meter beeps, then it is a mono jack, and if it doesn't beep, then you have a stereo footswitch jack.  To test what the footswitch actually does, you can use an alligator clip cable to connect between the ground lug of the plug and the tip and ring contacts.

[eh la bas ma]

So, perhaps the first thing to do is to determine if the footswitch jack is stereo or mono.  You can do this my inserting a bare stereo plug into the jack, and testing with your meter to determine if there is a separate ring and shaft contact.  Set your meter for continuity testing (beeper?), and touch the probes to the ring and shaft solder lugs on the bare plug.  If your meter beeps, then it is a mono jack, and if it doesn't beep, then you have a stereo footswitch jack.  To test what the footswitch actually does, you can use an alligator clip cable to connect between the ground lug of the plug and the tip and ring contacts.

Ok, thank you.
So i just did the test and the multimeter isn't bipping. I assume i am going to need two 3PDT and a stereo input jack for the next attempt ?

I turned the amp on (OD and chorus on), connected the black probe to the ground lug, and touched the other lugs with the red probe,  nothing happened.

[Mark Hammer]

I guess the question to be answered is whether their switching scheme assumed a latching footswitch (i.e., maintain the contact to ground) or a momentary contact, like what we find in Boss pedals.

[eh la bas ma]

The reverb goes off when there is contact between the ground lug and one other lug (tip i guess). nothing noticeable with the last lug. Does it mean i only can trigger the reverb with this footswitch input ?

[eh la bas ma]

I guess the question to be answered is whether their switching scheme assumed a latching footswitch (i.e., maintain the contact to ground) or a momentary contact, like what we find in Boss pedals.

I did a new prototype : two 3PDT connected together and to the jack's GND lug, by one of their middle lugs. One 3PDT is also connected to Tip and the other to Sleeve. I can turn the reverb on and off with one switch. So I guess it needs a latching footswitch. The other switch does nothing. I hope I did the wrong wiring or I guess I am desappointed with this amp.


Is it totally out of reach and incredible to add a new footswitch input on the amp to trigger the overdrive ?

[Marcos - Munky]

I don't think it makes any sense to have a 2 channel preamp + reverb, a footswitch and a stereo jack, to switch the reverb only. I mean, if they were switching one thing only, it would be the preamp channels.

Can you open it to take a few pictures and maybe do some simple measurements?

[GGBB]

I agree with Marcos - if it's a stereo jack, two things are being switched. My guess would be distortion and chorus - based on the fact that they both have front panel switches.

Whichever gets switched, the most common two-button stereo jack footswitch scheme toggles tip to sleeve for one and ring to sleeve for the other via latching switches. Sleeve is usually ground but it doesn't have to be. Each switch only needs to be SPST latching for this to work.

Be aware that it's possible that the front panel switches need to be either on or off in order for the footswitch to work.

[eh la bas ma]

Thank you, this is giving me new hopes.

Can you open it to take a few pictures and maybe do some simple measurements?

Sure, I never opened an amp before and it seems quite difficult. I know there is some components that can be dangerous if I touch them, so I was a bit nervous while taking off all knobs and screws. I tried to pull the faceplate but all pots and inputs are installed on a big metallic frame. Nevertheless, I pulled it as far as possible (the HP is in the way of something looking like a transfomer if I had to guess). here is some pics


















I hope these pics are good enough to help. If not, just tell me. I will look closer to find a better way to open this thing.

[eh la bas ma]

Is this big component, installed under the preamp, safe to touch (I don't mean the HP : I mean the other thing) ?

[eh la bas ma]

tip to sleeve for one and ring to sleeve for the other via latching switches.

Ok, so what kind of change could I do on my prototype's wiring to achieve that ? (picture posted in reply #5)

[GGBB]

tip to sleeve for one and ring to sleeve for the other via latching switches.

Ok, so what kind of change could I do on my prototype's wiring to achieve that ? (picture posted in reply #5)

I can't tell from the photo which wires are tip, ring and sleeve. But it looks correct assuming white wire is sleeve, and green and red are tip and ring.

Remember to try toggling the front panel switches.

If that isn't successful, try measuring voltage and polarity between tip, ring and sleeve of the jack (footswitch disconnected) - with the amp on of course. That might indicate that the footswitch is powered either for an LED (or two) or some kind of active circuit. Also check if the sleeve is actually ground by checking resistance/continuity between it and the input jack's ground/sleeve.

Another possible reason for the stereo jack if it's not for two switches is to make a connection between ring and sleeve when a mono plug is inserted. That might mean there is only one thing that can be switched, or the footswitch type is not the typical on/off manual switch kind.

Could also be like Fender or Peavey footswitches that use diodes to control polarity of two opposite voltage signals - Fender with a mono cable. Example:

Peavey:


Fender:


There are quite a lot of possibilities here. You really need an amp schematic, or else be able to do some tracing of the back side of the circuit board.

[Rob Strand]

There are quite a lot of possibilities here. You really need an amp schematic, or else be able to do some tracing of the back side of the circuit board.

With things like this as possibilities you're really up against it!      It could even turn out not all effects are switchable!

Two switch - two wire


Three switch - two wire!


Three switch - two wire!

[Rob Strand]

From what I can work out the amplifier is made in South Korea by Muse Inc. (Muse Incorporated); same name as the speaker.   They appear to make stuff that other companies re-badge.

One name that came-up was "Prime" another was Hiwatt (!).

The trick would be to find a 30W to 50W amp made by that company.


You can see some similarity to this Stone amplifier,
https://reverb.com/item/4158861-used-stone-sga-40rc-40w-guitar-amplifier