Retro Stereo SID Synth Looks And Sounds Sensational

Two circuit boards with bright seven segment displays

Over the years, plenty of work has gone into emulating the Commodore 64 6581 SID chip, but as [SlipperySeal] puts it, nothing beats the real thing. His take on the MIDI SID-based synth not only sounds fantastic, but looks the business.

The 6581 SID arguably blessed the Commodore 64 with some of the best sound capabilities of any home computer in the 8-bit era (make sure to ‘sound off’ in the comments if you disagree). The 6581 was a three-voice analog synth with a dizzying array of settings. This was at a time when most home computers could just about manage a ‘beep’ of varying lengths and frequencies.

When you mix MIDI with the capabilities of the SID, you get something like [SlipperySeal]’s awesome looking synth, known as ‘Monty’. While the road to this point unfortunately resulted in several blown-up SID chips, the sacrifice seems to have paid off.

Realizing the limitations of having ‘just’ three voices, Monty is designed to use two SID chips in parallel, for a total of six voices in pleasing stereo sound. MIDI commands are transferred to the dual SIDs by way of an ATmega1284p microcontroller. The SID is well understood by this point, and [SlipperySeal] goes into great detail explaining the fundamentals of SID programming over on GitHub.

This isn’t the first MIDI synth that is based around the C64 SID chip, but [SlipperySeal] made sure that his stood out from the crowd. The seven-segment display centered on the board makes for a delightfully simple visualizer, an effect that looks even better when running two Monty boards at once, each responding to alternate MIDI channels (check out the video below). Naturally, we’re also fans of projects that include ominous, cryptic keyswitches.

36 thoughts on “Retro Stereo SID Synth Looks And Sounds Sensational

    1. I kinda agree but I wonder why.

      Is it because they came later than other LEDs and we therefore see red, yellow and green LEDS as the ‘classic’ LEDs?
      Is it because they seem to be used a lot in cheap gear and therefore must be ‘cheap’ themselves?
      Is it because blue LEDs seem to be much brighter and distracting at night in your room?

          1. White LEDs are made by putting a mix of phosphors over an UV LED. By changing composition one can achieve different light temperatures and spectral composition. That’s why unpowered white LED is yellow or orange…

      1. Blue LEDs are almost always too bright. Especially at night. But the worst part is, how much they get overused in just about everything. My monitor has tiny blue LED that is on, when monitor is off. It’s dim, but still I had to cover it with something – it was too much at night. Blue naturally draws your sight towards itself at night. More than any other LED color…

        Hobbyists are partially to blame – most projects end up with at least one blue LED. And it’s almost always the high-brightness one set to full power. And if it’s a 7-segment display, there will be no filter over it to dim the light. I have a special hatred for people who place blue LEDs under Nixie tubes or other thermionic valves. These don’t need any backlight at all, and especially not blue. It ruins the appeal of the old tech and makes it look like chineese toy from dollar store…

        Best color for any indicator light that will be on at night is either red or amber. Next is green, then yellow, and at last white. No blue. Blue is okay for RGB effects or for special effects lights, like police flashers…

      2. The _original_ LEDs were in RED only, and were too dim to be seen in direct sunlight.

        Yellow and Green came a lot later (maybe 70s).
        Blue came in in the mid 90s.

        I guess the marketing people thought they looked “futuristic”, hence they got plastered on everything long before we understood what blue light did to sleep patterns.

        1. LEDs existed in this sixties, but not much hobby use till the tail end or early seventies. I’d say they were still “new” in 1971.

          It was about 1973 before I had any, and yes quite dim. But almost as soon as that, I had dim green, orange and yellow LEDs.

          They really did improve a lot in brightness.

          It was a big gap before blue and white, and I can’t remember which came first. They didn’t come concurrently.

          1. Yeah, I recall my father mentioning the first time he struck LEDs… and at that time (working for Telecom Australia at the time), it was any colour you liked, so long as it was red. Hence why I guessed that the other colours must’ve been some time in the 70s.

            Perhaps it’s a regional thing: took a bit longer for the alternate colours to make their way across to this side of the Pacific ocean.

    1. Really nice.
      And good to hear a retro synth which actually sounds nice, and the creator has sequenced something nicely for, rather than the cacophonous noise a lot of synth projects here seem to stop at.

      1. In the video you can see I have some heat sinks sitting on one of the boards. The SIDs get quite hot and I should probably make sure they all have heat sinks at all times.

        And I think I blew up a few SIDs on the breadboard because of lack of capacitors to draw away spikes. Monty has this well covered though.

        (oops I thought my first comment about sockets got lost so there are two responses to chose from :)

  1. “make sure to ‘sound off’ in the comments if you disagree”
    Ha, nice. Okay, well SID is great, (I have 2 breadbin C64s) but I have recently been reacquainted with my first tech love: the Atari 8 bit line via my 65xe, and reminded how good Pokey is. I think Pokey would be a close second to the Sid. Specifically, it has 4 voices and only pulse or square wave but the polynomial distortions it can do make for some really nice effects. Bass lines, percussion, and sfx are particularly nice, crunchy and unique. SIDs filters are better and having multiple waveforms of course… and ring modulation, but Pokey is no slouch either, and a bit different than most of the other (mostly TI related) sound chips in the 8bit era.

    1. I loved seeing projects such as MIDIbox. They were my inspiration 15 years ago when this project was only on a breadboard. Monty has been on my todo list this whole time and with the help of a friend learned how to EDA and I’ve finally got the board together. I thought about a more advanced display but decided to keep it fairly simple. If anything my “software engine” isn’t particularly advanced at the moment. I’ve started on the effects but it’s mostly just letting the notes ring out without any intervention.

      1. You’ve got the whole ‘minimum energy solution’ thing going, which I think is great, (and beats the amount of manual poring and head scratching I had to do learning how to use the MB6582 I built).
        It’s a great looking, tidy module. Adding some modulation stuff might be nice, but other effects are better added externally I think. It’s good piece of work; and it’s your own!

        1. Thanks MikPep! I’d made one board before this and it was certainly minimal viable product. But then when I’d decided on the 1284p that left the doors open to key switches and the gloriously offensive blue seven seg. Iv get the basic waveforms going but I’ve added a sine table so I can modulate frequency etc over time. So I need to learn how all the vintage effects were done.

  2. That’s a great project! Nicely executed – too bad that there is more discussion about Blue LEDs than about the actual project. Love the SID.

    And here is my “me too!” project – the Amstrad CPC had the infamous AY-3-8912 sound chip. Chip tunes have their own charm of course, but the AY cannot compete with the sonic capabilities of the SID. So I needed to build a SID soundcard for the CPC – boy did I get hatred from the CPC community for doing that!!

    So here is my “Speak&SID” CPC SID soundcard. And this is where it relates to this project – I have also programmed the CPC to act as a MIDI IN synthesizer. So, like this project here, it receives Note On / Note Off message, but currently only monophonic (need to extend the CPC program). I am also playing the AY sound chip at the same time with this program. Here is the MIDI IN -> CPC -> SID + AY sound demo. Sorry, I am a bad keyboard player:

    However, the SID sound card shines much more when we are using a SID song player for the CPC:


  3. Been thinking about playing around with such synth chips as they seem like fun, but they also seem so out of reach. The SID itself apparantly sets you back 50 bucks with ease at time of writing and i don’t think i could forgive myself damaging one.

    Did learn that there are these projects like SwinSID that do a good job mimicking the chip both in input and output being meant to give drop-in replacements. Ought to get me one of those. I know it ain’t the genuine article, but i just want to mess around and i think its better for everyone if i just play with a hardy ATmega88 faking it than the real deal ^^;

  4. So I did something a little crazy. But it worked. I wanted to play the Monty On The Run SID chip tune on the Monty Synth. These chip tunes are 6502 processor code and binary data which actaully ran on the Commodore 64. But rather than try to sqeaze a 6502 emulator on the AVR, I cross assembled the play routine and data. I mapped 65 of the 6502s 151 instructions to AVR assembler, intercepted write the SID chip at $d4xx and handled one peice of self modifiying code. I got stuck for a while getting it to run properly, but then finally discovered for at least one instruction, the 6502s carry flag is set inversely to how it’s done on the AVR. Fun times.

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