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Thread: Amp build enquiry

  1. #1

    Amp build enquiry

    Hi all, this is my first time posting and I was advised to post here by Arduino support, so please forgive me if I'm asking something dumb.

    A friend and I are in the process of building a guitar amp, and I am currently trying to get my head around a means of swapping between 2 amp channels (low-gain and high-gain/distortion) using a footswitch.

    I think that what I need is some component which will be incorporated into the amp. I'm hoping to use a Line 6 HX Effects as the footswitch/controller, which has the ability to change amp channels on compatible amps with via MIDI jack or a 1/4" jack which can be used for controlling amp channel changes - from the manual, "... the jack can be connected to your traditional guitar amp to switch its channels or turn its reverb on and off. Use a TRS cable for dual operation (A=tip, B=ring)."

    We've dealt with standard electronics before but this is the first time delving into the world of MIDI/microcontrollers etc, so I might find that I'm out of my depth, but I thought I may as well ask the question.

    Any suggestions or tips would be greatly appreciated.

  2. #2
    Senior Member oddson's Avatar
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    If the effects box's pedal outputs work with conventional amps as a channel selector then why bother with a microcontroller?


    If you want to add MIDI functionality to the amp, Teensy can do that for you... but I don't see the need for what you want to do.
    Last edited by oddson; 04-26-2019 at 03:02 PM.

  3. #3
    Senior Member oddson's Avatar
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    Click image for larger version. 

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    Here's an external switch box schematic that shows one way to switch audio with a contact latch switch.

    Teensy could pull the the BJT base low instead of the footswitch doing it directly; meaning either a midi command or a switch on a digital pin could control the channel.

    A Teensy sketch to control this would be very simple, but if you just want that pedal to switch channels you shouldn't need a Teensy.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by sideshowlinc View Post
    I was advised to post here by Arduino support
    Was this advice given on their forum? If so, please at least give us a link to that prior conversation....

    A friend and I are in the process of building a guitar amp, and I am currently trying to get my head around a means of swapping between 2 amp channels (low-gain and high-gain/distortion) using a footswitch.

    I think that what I need is some component which will be incorporated into the amp. I'm hoping to use a Line 6 HX Effects as the footswitch/controller, which has the ability to change amp channels on compatible amps with via MIDI jack or a 1/4" jack which can be used for controlling amp channel changes - from the manual, "... the jack can be connected to your traditional guitar amp to switch its channels or turn its reverb on and off. Use a TRS cable for dual operation (A=tip, B=ring)."
    That HX product looks like it has 2 places to plug in pedals. Most pedals are just switches which short 2 wires together when the press (simple on/off action), or a pot that chances resistance as you as the move (gradually altering something).

    Assuming the HX can do what you want with pedals, maybe start with buying or borrowing a supported pedal. Use the ohms measurement of a mutltimeter to check what the pedal actually does to the wires when you press it.


    We've dealt with standard electronics before but this is the first time delving into the world of MIDI/microcontrollers etc, so I might find that I'm out of my depth, but I thought I may as well ask the question.
    I see both serial MIDI (5 pin DIN) and USB device MIDI. If you're going to use MIDI, probably the very first step is to plug it into your PC or Mac and use MIDI test software to send it MIDI messages. I see the HX manual has several pages about the MIDI messages it supports. I didn't study it carefully, and even if I had the time for that, I don't fully understand what you want it to do. But my general advice is to run a MIDI message utility on your computer and practice sending it MIDI messages until you have figured out exactly what messages (if any) cause it to do the things you want.

    When you know this, then you'll want to make Teensy send those messages. Serial MIDI is probably simpler. For transmitting only, you can normally just connect Teensy to the MIDI IN using a couple resistors.

    https://www.pjrc.com/teensy/td_libs_MIDI.html

    Scroll down to the recommended schematics. If you're not trying to have Teensy receive MIDI, you won't need the optocoupler circuit.

    If you want to have Teensy connect to the USB, as your PC or Mac does, then you'll need Teensy 3.6. That's currently the only Teensy with USB host, which is needed to connect to a USB device port. The main USB port on every Teensy is a USB device port. USB only works when devices connect to hosts, so even if you manage to wire up two USB devices to each other (the USB standard forbids selling such cables) no communication is possible in a device-to-device connection. For USB, that HX can only work if connected to the USB host port, which is only on Teensy 3.6.

    You'll also need this cable.

    https://www.pjrc.com/store/cable_usb_host_t36.html

    All Teensy models can have hardware serial ports needed for serial MIDI, so if you go with the serial MIDI way, any Teensy can work.

    But they key to success is first experimenting with sending MIDI messages from your computer. Learn exactly which messages make the HX do the stuff you want before you jump into using Teensy.

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