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Have you ever been in that situation when you want to make a patch change on your multi-effects guitar processor mid song?


You stomp down on the pedal and a tiny moment of silence occurs, because your Multi FX is a few years old. Or do you just want some more control over those fiddly little buttons while you’re playing live? Obviously some of the higher end guitar effects pedals have almost complete control over every parameter and these can be assignable to foot controls, but not all do exactly what you want - when you want.


Some years ago I was using a Vox Tonelab ST. I had basically forgone the use of an amplifier due to a back injury. I knew I was going to be out of action for a good 12 months in terms of carrying amplifiers so I purchased a multi-effects processor. At the time I was playing in a dirty blues band so didn’t require many effects, maybe a bit of delay and reverb and some cabinet and amplifier modelling at most. I auditioned almost every effects processor on the market and finally ended up getting the Vox Tonelab ST. It was actually the lower model in the range but I preferred the modelling algorithm the larger one had more control but the algorithms didn't cut it for me. To me it seemed more realistic or appropriate for the band I was playing in at the time. Of course impulse response modelling has really progressed and taken off and multi-fx have moved on a lot since.


Fast forward a number of years and I’m back on to valve amps. But the Tonelab ST has taken a role in effects send loop of my rig, it also gets occasional use as an interface for writing on the go (as it has a USB audio interface) and also gets use with my electric violin if I have gig involving that.


What Was The Solution?


So how do I overcome the microsecond of silence when changing patches and the annoying lack of foot control? Well I decided to add some implementation for external control. I messed around with doing this via MIDI using an arduino to send messages via USB but all patch changes gave me a tiny fraction of a second silence. Annoyingly the MIDI implementation lacks real-tine parameter control as far as I could tell. I could have just used a different unit for my delays, but having the flexibly of processing for my violin and guitar plus lots of pedal/modulation/amp modelling options in such a small unit seems too good to give up yet. In recording sessions, I often use the amp models for background guitars and get my crunch from there rather than the amp Pre. It's just another option to add a different variety of tones around the real amp sounds.


There are three sections of interest that can be turned on and off with small push button microswitches on the face of the unit. The PEDAL section which models a variety of pedals, the MODULATION section that supplies delays and modulation effects (there is also a tap tempo button in this section) and finally a Reverb section.


So what did I do? Well as you can see from the video, I added two additional 1/4” TRS jack sockets, drilling the unit where I could find enough space to host the jack sockets. Since there are four controls the main aim of doing this modification was to allow conventional guitar pedal control with each of the four buttons (that are too tiny to be accessible whilst playing live). As it is at the moment I have only implemented Control in three of these controls, but the scope is there for two controls per plug.


You may not be familiar with how guitar amp pedal controls work but generally they just make a connection between the Sleeve and the Tip of a jack plug. Fancier models will have a switch for the Ring as well so you may be able to control two parameters per plug. For example Channel change and Reverb bypass. In some pedals a fancy lighting system is seen, this is generally an LED in series with the switch, when the switch is closed the LED lights. Obviously the pedals are supplied with a small voltage usually somewhere around the five faults mark I think.


Watch the accompanying YouTube video and you will see how I’ve modified the inside of the Vox. There were a number of issues however, the common line that I could use between the two buttons on each socket was 5V not earth. This was just an artefact of the circuit. This shouldn’t make any difference in terms of actual practical use unless I am automating these controls from some kind of guitar switcher pedal that simply sends voltages rather than making connections with a relay. However it did mean that I had to use plastic sockets as the Sleeve connection is connected to the chassis of a metal socket. Since I had this at 5V I could not connect it to the earthed casing of the unit. Since this is a digitally controlled unit the external switches would have to be momentary not latching.


Was it worth it?

All in all the system works rather well and the most effective part of this is the ability to tap tempo with an adjacent pedal. I can simply tap along with the song and adding dotted 8th notes etc. is a breeze. Delay swells can be implemented with the expression pedal and the delay can be cut in and out as required with the modulation switch.


So is it worth modding your pedal? Well there are a few things to bear in mind.


  1. BE SAFE! DO NOT MEDDLE WITH MAIN VOLTAGE (if you are qualified you can ignore this)

  2. Please don’t hurt yourself.

  3. Make sure your unit is out of warranty as opening it up will void that.

  4. Look for switches and controls that you can solder onto the pads to add parallel control

  5. Test thoroughly before getting that iron out.

  6. Solder at a low temp on your iron to begin with.

  7. If you are removing components – use as low a heat as possible to avoid lifting tracks, use desolder braid or a solder pump and a flux pen.


  8. TAKE A LOAD OF PHOTOS so you can check component values and positions – should you damage anything.


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