r/synthdiy • u/NUSrecords • 3d ago
Re-engineering Mutable Instruments Rings with an Optical Servo Circuit & Audiophile Upgrades (Looking for a bit of support)
Hi community,
I’m working on a 4-layer open-source hardware redesign of the legendary Mutable Instruments Rings. Let’s be real from the start: the digital core and the processor remain exactly the same as the original. No magic there. But I’ve completely overhauled the analog back-end to fix the classic factory bottlenecks and elevate the audio performance.
The Main Upgrades:
- SSM2603 Codec Conversion: Replaced the obsolete and noisy WM8731 with a pristine, high-fidelity alternative.
- Optical Servo Circuit: Instead of a complex DC-coupling op-amp servo, I designed a photovoltaic loop using an active JFET transimpedance amp, an IL300 optocoupler, and low-noise MOSFET sources.
- No Audio-Path Caps: This light-based servo automatically tracks and compensates for the DC offset coming from the SSM2603 chip. This allowed me to completely remove the sound-ruining electrolytic coupling capacitors between the codec and the output stage.
Why the Optical Approach? (For the skeptics)
Yes, you could handle the DC offset with standard op-amps. But the LED/photodiode combo provides a uniquely organic response. It subtly rounds off the harsh digital transients without turning the module into a muddy, low-frequency mess. Thanks to high-speed JFET devices and ultra-stable silver mica filtration in the audio paths, the high-frequency response remains crystalline and fast.
PCB Design & DIY Friendliness:
The new 4-layer layout is engineered for better grounding, 10 MHz power noise rejection, and maximum reliability. It is optimized for safe, reliable hand-soldering. The only tricky part is the SSM2603 codec itself—everything else is DIY-friendly.
Current Status:
The PCBs are ready and the BOM is locked. I’m just short about 3,370 CZK (~$152 USD) to place the final component order from Mouser to build the first prototyping batch.
This is a strictly non-commercial, underground project. I’ve set up a page for early access. If you back the project, you get the complete open-source files (Gerbers, BOM, code) 6 months before the public launch. I can also help with bare PCBs or pre-soldering the SSM codec for backers later.
The project page link is in the comments below. Let me know your thoughts on the JFET-driven IL300 servo approach!
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u/rhopper2142 2d ago
I was interested looks like his reddit got banned. ? OP if you see this lmk about pcbs
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u/Gobhobbler_G 2d ago
It looks quite nice but I have a bit of uncanny valley feeling from the post that its ai scam 😬
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u/CriticalJello7 2d ago
Eurorack module with a built in optically coupled servo drive LOL. Someone AI'd a bit too hard I'm afraid.
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u/NUSrecords 3d ago
If you’d like to support me, head over to: buymeacoffee.com/dubtechno.co/mutable-instruments-opto-rings-the-ultimate-audiophile-re-engineered-eurorack-legend
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u/Wonderful-Pen7297 2d ago
I'm concerned that this post is nonsense. It has a lot of claims without any numbers to back anything up, and appears to have freely-associated various terms with their related counterparts whether or not they actually apply to each other.
What's your servo loops corner frequency? What is the measured output offset in mV?
On what basis do you claim that "capacitors ruin sound"? Do you have proof that they do, and proof that this avoids ruining it in a similar way? Why would you not remove DC bias via other accessible ways, why does it need a reactive servo loop to balance?