# Need help reverse-engineering the RMI Electrapiano (model 386/386x)

**URL:** <https://lookmumnocomputer.discourse.group/t/need-help-reverse-engineering-the-rmi-electrapiano-model-386-386x/3762>\
**Category:** DIY STUFF\
**Created:** [July 12, 2021, 6:43pm UTC](https://lookmumnocomputer.discourse.group/t/need-help-reverse-engineering-the-rmi-electrapiano-model-386-386x/3762 "2021-07-12T18:43:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Timmy73](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/timmy73/32/7552_2.png) [@Timmy73](https://lookmumnocomputer.discourse.group/u/Timmy73)\
**Post date:** [July 12, 2021, 6:43pm UTC](https://lookmumnocomputer.discourse.group/t/need-help-reverse-engineering-the-rmi-electrapiano-model-386-386x/3762/1 "2021-07-12T18:43:36Z")

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So I recently discovered the RMI Electrapiano. Its a analog polyphonic “synthesizer” designed to replicate the sounds of a piano, harpsichord (although it sounds a lot like a clavichord), and others. However, I was blown away by how accurate and true it sounded:

[https://youtu.be/cMI9brWq\_kw](https://youtu.be/cMI9brWq_kw?fbclid=IwAR1NeuS-wmV5WADQSP5z8MS4QZwskK9aQpPeNmL1ja2-uawweuoONwUQhOo)

I found a service manual containing schematics for various parts:

[http://juggernautmusic.com/…/2014/08/RMI\_368X\_SM.pdf](http://juggernautmusic.com/wp-content/uploads/2014/08/RMI_368X_SM.pdf?fbclid=IwAR1YjvEUO7A1zmk0jKtWbPXxw-arc-9EGz2K7Dqpvq6uN_y9x7NH3pD79bI)

Each note has its own oscillator circuit comprised of 2 transistors: one for a inductor-based oscillator and one for a surprisingly simple VCA and AREG-type circuit, along with a bypass for a long sustaining “organ mode”.

I don’t know what waveform this circuit outputs on its own (if someone better at electronics than me knows, please tell me!), but it seems that the waveform output goes into some tone-shaping stages. They are all really simple, mostly comprised of passive components. Yet somehow, they can turn the waveform created by the oscillator into one with just the right harmonics. I have looked at the schematics for a while (and tried to replicate the various stages on VCV Rack), but I cannot figure out how it worked. I would like to build a “replica” out of modern parts, so any help would be appreciated. Thanks!

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**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\
**Post date:** [July 12, 2021, 7:25pm UTC](https://lookmumnocomputer.discourse.group/t/need-help-reverse-engineering-the-rmi-electrapiano-model-386-386x/3762/2 "2021-07-12T19:25:21Z")

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> [@Timmy73](#):
>
> I don’t know what waveform this circuit outputs on its own

You could try to simulate the circuit in [falstad](http://www.falstad.com/circuit/).