8 FM poly voices in one

Not sure where to put this but as it’s a link to a video I’ll start here.
Always been more of a synth module fan rather than keyboards. My first FM synth was the wonderful FB01 sound module which as it had 8 note poliphony gave me 8 single, Midi addressable voices. (shit ones but it was the 80’s)
I also had a DX7 which broke down every time it left the house.
I’ve been loosely following the Minidexed development on git hub and this latest config and build, all superb so far, uses a single Pi3 to give you the equivalent of 8 independent DX7s, each with controllable volume and panning. (See the unaffordable then and now TX816 for an idea)
I’m building one for my main rig. An hour’s work for 8 FM modules. Who’s game?


I’ve a MicroDexed, which is a similar concept built around a Teensy. It runs two DX7 clones in parallel and I was messing around with it this very afternoon, good fun!

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I looked at the MicroDexed but at the time I only had the one 3.2 teensy between several projects and I’m too cheap to buy them :smile:
Have you compared the audio direct from the teensy to that after adding the audio hat? (Another saving; yes there’s a theme)

Have you any audio or video we could see?
Did you build yours?

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Yes I was watching this too. I’ve use the bare metal circle environment for the Pi myself a little, after encountering it after an MT32-Pi build (a bare metal Pi version of the Roland MT-32 module, if you’ve not come across it before).

I was idly wondering what it would take to build a simulated TX816 front panel interface for it… or even individual FT1 modules out of Pi Zeros for “racking” together :slight_smile:



The TX1 panel was awful and though I’m no fan of menu diving I think either this is better. You could go headless and put a snazzy interface on a phone or web.

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There’s this post I put together when I built the thing:

An audio hat is part of the build, so I haven’t tried/heard without that.

I’ve used it in a few of my tracks - in this one it’s the high pitched chord stabs with some phaser fx from the DAW here.

The one I’m working on at the moment I’m using an chimey kind of patch (Sonus1 “ECHO ECHO”), but I fiddled around with the delay effect and the portamento time and it sounds kooky and rad. I’ll try and get a raw recording of it when I get the chance.


what is the latency like?

I haven’t noticed any big latency problems with the Microdexed. There’s the standard DAW->MIDI Interface->Sound Module->Audio Interface->DAW latency, but it seems fairly balanced across all the synths I have, no single instrument seems to stick out too much.


I’ve built one of these over the last few days. I really like it - there’s rough edges but it’s being worked on actively (seriously, look at the commit logs on GitHub) and will end up an absolute gem.

The problems I’ve found are within the UI. The reliance on a rotary encoder and its single clicky switch isn’t great - double clicking to select and a single click to go back up the menu isn’t intuitive on a rotary encoder (especially when you’re used to the one on your MPC One) - and the actual scanning of the movement of the encoder is a bit hit-and-miss. (I managed to turn the knob on mine 180° without it registering a single update, and other times it’ll update on a single click of it.)

It also doesn’t like my MPK Mini Play keyboard when I plug it in unless I’ve already powered it on with batteries and leave it like that. I think that’s a peculiarity of the keyboard that operating systems handle with ease but the bare metal USB stack takes issue with.

But! The sound quality is great (even with the normally crappy Pi analog audio) and there’s no latency I could feel. Somewhere in my big pile of things I’ve started and not finished I’ve got all the bits to make a proper Pi ‘HAT’, with the I2S audio circuitry and everything. When I find it I’ll be wiring the whole thing up permanently.


I’ve built one for my studio, Pi 4 model B, rack mount case, OLED instead of the LCD. I like fact it’s being developed and the encoder action is being changed to make editing easier and also sysex midi editing is being included. I mean it’s cost around £150 including the case etc but well worth it as I was about to buy a TX802, but now, why bother


I “love” the non-insulated 220V power pins :scream:

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Yeah I would get those death traps insulated ASAP.

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They are insulated now, this was during the initial build. Too many people got nervous.


That’s groovy. Where do you get your blank rack mount cases from ?

Thanks, I get them from my local electronics store, they are about £15, so not expensive and made of 3mm plastic hence I wasn’t too concerned about the exposed mains connections.

G17081UBK (Gainta, case, black ABS UL94-VO, 431x203x43mm)


For what it’s worth, here is my “I’ve built it too” post with my “notes to self” filling in some of the gaps from the video for how to get it up and running. I’ve tried with both an original Pi V1 Model B (Rev 2) and a Pi 4, with and without PCM5102 DAC, serial MIDI and USB. I think it’s great!

I now have thrown together versions of Zynthian, MT32-Pi, and now MiniDexed.

What I’d really like now is a RPi/embedded CZ synth, but so far haven’t been able to find one (there are Phase Distortion engines, but no actual CZ emulators that I can find, although it looks like MAME might be able to do something with a CZ101…)



What a superb build! That case is amazing.
I was about to sacrifice a spare 3u metal blank.
Thanks for posting!
Edit: Still pretty pricey here in the UK. Does anyone have a large 3d printer?


Just thinking…
I helped a pal with a POE set up (power over Ethernet). It’s got me thinking, would it be possible to add some utility to use an ethernet connection to provide midi and multiple channels of audio over IP.
I’m just picturing a brick pi with one cable to my studio’s Lan.
Am I dreaming?



I wrote some words about my build and the results will shock you: Yamaha DX7 For The Masses #clickbait