Korg Poly 800 - My most extreme repair yet

[@rot_studios]

I'm going to upgrade the Poly800 with an Raspberry Pi Pico, which is a very cheap but stupidly powerful (32-bit dual core at 133MHz, overclock to something like 400 haha) little board in a DIP 40 format, which makes it a perfect upgrade for the DCO emulation. I plan to greatly increase the oscillator audio quality (62KHz audio interrupt, 32-bit counters, with two dual channel PWM outputs) and polyphony. Also thinking of maybe adding a supersaw esque ability with a twist which you can see in action on the Pico in my Shorts :)

[@rot_studios]

Here it is: kzbin.info/www/bejne/eYO2qK1sf711r5I

[@jschnabel2113]

Amazing job keeping this synthesizer alive. It definitely sounds spot on like the original it might be a little different but I cant tell if maybe i have bias in knowing its modified.

[@rot_studios]

Thanks. It's probably ever so slightly different, you can definitely hear it's not as bright on the high registers (due to oscillators now being digital). But yeah it does seem pretty close :D

[@artlythere6014]

Nice work. :)

[@rot_studios]

Thanks

[@DrUmSensitive]

You're a genius. My Poly 800 has aliasing, but only on certain velocities! I thought this synth has no velocity? I distinctly hear this high pitch sound following the actual synth sound (albeit with some latency). Strange. :)

[@rot_studios]

That's because the DAC circuitry used is only 8-bit and also constantly needs to be cycled to keep the sample-and-hold on the right value. This introduces quite a bit of zipper and high-freq noise unfortunately. To be honest, now that I've upgraded the DCO with an Raspberry Pi Pico I could delegate DAC duty to the Pico as well and greatly improve things, but on the other hand there's some charm to the cruddyness?... Maybe? :D

[@rot_studios]

PART 2 is up, with the new RPI PIco DCO upgrade: kzbin.info/www/bejne/eYO2qK1sf711r5I

[@federicovincent8996]

Hi! I bought a while ago a yamaha pss-570 that did not turn on, according to its former owner. I could see that it not only turned on but also emitted sound ... although this sound was nothing more than a constant buzz coming from the speakers. Probing the audio signal verify that the hum was starting at the DAC ym3012 portion of the drum section. Well, I changed the DAC and the corresponding opamp ... and nothing changed, the drone continues. I am afraid that the fault is higher up in the CPU part and the repair will be too cumbersome. Could I pass you a photo of the circuit plan where I mark in which sectors the buzzing appears, so that you can give me a hand if possible? regards!

[@rot_studios]

Sure, email is on contact page on my website evilturtle.nl I won't guarantee to be of help, hard to judge things from a photo but who knows.

[@federicovincent8996]

@@rot_studios capo! I'll send you an email shortly ... who knows. Thank you

[@richardsmith4992]

Very nice project. Is there a market for producing these at a small scale? The Poly 800 wasn't the greatest build quality from the outset, and over time and poor storage over the last 40 years many will be pretty much junk. I've had 2 over the last few years, both of which developed several faults due to board corrosion and chip failure etc - these would have been ideal candidates for a Poly 800III (!) board replacement, which would just plug straight in.

[@rot_studios]

I don't know, to be honest. What would be extra neat for something like this is if the filter chip was replicated too. Then you can have them last another 40 years :) I guess I should make schematics someday, so someone else can make PCBs :P

[@richardsmith4992]

@@rot_studios Definitely look into publishing a schematic, maybe something PCBway (etc) could handle. If the hard to find ICs were socketed on a new board, maybe some of the old parts could be salvaged? You've probably heard of the KIWI 106 (and others) range of boards, would they be interested? Sorry for giving you a job list, feel free to let me know NO, GO AWAY!😄

[@rot_studios]

@@richardsmith4992 I'll make no promises, but I'll put it on my list :D

[@rot_studios]

I'm making a webpage with all the details, code and schematics: evilturtle.nl/projects/poly800.html Keep in mind it's a WIP!

[@TheNaboen]

wow!