Korg Lambda ES-50

I have blogged extensively about the Korg Lambda (model ES-50), an analogue synthesizer from the late 1970s. Below is a list of links to posts detailing how it works, and what I have done to repair and/or modify one or more examples of it. I shall be updating this list as required over time.


How it works:

Repair and modifications:

12 responses to “Korg Lambda ES-50”

  1. John says :

    Hey, Synthnerd,

    I picked up a Korg Lambda at the flea for $50. Got it home and the B and C keys weren’t working on the Percussive side. Thanks to the info I gleaned from your write ups, I had an idea of where to start with the multimeter.

    One swapped out S10430 later and I’m in business! Thanks for doing this blog. It’s super helpful!

    Now I need to fix up the finish.

  2. Magnus says :

    Hi synthnerd,

    I just want to thank you for your excellent walk through of the Korg Lambda functionality on your blog! It really helped me to fix mine. I had two keys sounding strange and sometimes no sound at all. It turned out to be two faulty TOG IC:s (S50241) and (I think you call it) dry joints on one of the connectors on the board connecting the keyboard.
    Your info was invaluable!

  3. Basher says :

    How similar is the Korg Delta in terms of TOC, dividers etc?
    I picked one up for peanuts the other week, and it’s A# keys don’t work. I’m advised it’s likely one of the S10430 chips rather than the AY3-0214?
    There are other issues which I’ll be working through as I get to them..

    • synthnerd says :

      The circuit is not quite the same, but the principle is: the TOG generates one octave from an incoming clock, the 12 frequencies are sent to the S10430 dividers, and each keypress generates its own envelope that also goes to the S10430 dividers to govern the amplitude of that note. If you are missing *all* the A#, I would first check that the A# output of the TOG is working. If it is, I would suspect the divider that handles the A# notes. It should be easy enough to do with a scope or frequency counter.

  4. Dimitri says :

    hello, thanks for this explaination about how the Lambda works.
    I have some doubts about divider/keyer parts.
    If I play C3 on the keyboard, on the output of the S10430 dividers I get 4 sound, right?
    but what if I play the C4 and C3? I get 5 sounds (4 of C3 + C4) or 2*4 sounds? If the latter, don’t 4 of the 8 sounds overlap (since they are the same frequencies?

    • synthnerd says :

      Hi, sorry for the delayed reply. This is a very good question, thanks for asking! OK, so if you play C3, you get a square wave on all four outputs from that keyer: 2′, 4′, 8′, and 16′. On the 2′ output, you get a 2′ C3 frequency, and so on. If you play C4 instead, you get the same outputs but at half the frequency on each. Now, the level of each note is governed by the envelope present on that note’s K input, its frequency is determined by the signal at the N input (taken from the Top Octave). I never put a scope on the output of these keyers directly to measure what happens when two frequencies overlap, but you’re right, if you play both a C3 and a C4, you will get a combination of two layered octave-separated square waves on each of the four outputs. I’d need to scope these to see how this looks.

      • Dimitri says :

        thank you!
        It’s a little bit more clear now!
        I draw this small diagram to figure it out better, can you tell me if I understood correctly?

        now, if this is correct, that means that there are (inside the keyer/divider chips of course) 6 steps of division for each top note (even if the octaves are 4 and not 6),
        furthermore, if I’m not wrong, it doesn’t use the top note directly for F to B, since the highest note must be E

      • synthnerd says :

        That’s more or less correct 🙂

        I’m interested in finding out how the keyers prevent multiple simultaneous square waves from vanishing into each other…

      • Dimitri says :

        actually I think I made a mistake, the division stages should be 7, not 6, because keys lower than the lowest E on the keyboard need to be divided by 128 on the 16′ outputs.

        about mutilple simultaneous square waves (of the same frequencies), why should they vanish into each other? they should be phased locked (because they all come from the same master osc), so I guess they can’t really cancel each other..right?

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