Posted by admin on 2009 Dec 2

How to test an Oberheim Matrix 1000’s voice chips

Oberheim Matrix 1000

I recently purchased an Oberheim Matrix 1000 analog synth in “excellent” condition from someone on Ebay who had good feedback.
Upon receipt of the unit and to my dismay, the unit could play only three voices out of six. The seller denied shipping me a damaged unit, so after pouring through the manual (in PDF format) and reading a few online forum posts of people having problems with the unit, i discovered that i could play all six voices in the unit by putting the unit in mode 2 cascade mode (the Matrix 1000 has a cool feature that allows you to link several units to multiply their polyphonic voice count.) However after playing the unit for a while i noticed there was also something wrong with the voices as well.

It is very simple to find out if the Matrix 1000 synth has a dead voice: Just play an arpeggio with 6 notes, holding each note, and listen to how many notes play. However it is very hard to find out if any voice chips have other problems, because most patches are setup to cycle through all six voice chips to handle polyphony.
So when you play a note in the Matrix 1000, the synth will usually start playing on any of the six chips, so playing the unit through a keyboard is not a proper way to test the keyboard, because you don’t always get the same results.

I found out a way to test the voice chips without having to open up the unit and physically swap the chips one by one. To do this, the following must be done:

1-Isolate the voice chips by using a synth patch that only uses only one oscillator.
2-Play all MIDI keys (i used 88 keys, C1 to A7) by using a MIDI file at velocity 120 to cycle through all six CEM3396 narrow-body voice chips and check their frequency and amplitude consistency.

To accomplish step 1, i used the (now defunct) free Editor Librarian JsynthLib to edit any one of the free library patches into what you see here:

JsynthLib setup
JsynthLib setup

To accomplish step 2, i used Ableton Live 8, connected the MIDI out of my DAW into the Matrix MIDI in and the synth audio output into my computer’s audio interface.
You don’t need to use Ableton, i am sure you can use any DAW.
I created a MIDI file with all 88 notes. Unfortunately I noticed for some strange reason that when i was playing back the MIDI data, the synth would play one note and skip the next, so i added an extra short dummy note between each long note, and the data played fine.
Ableton setup

Here you can download the MIDI file i used and bring it into your Audio workstation:

  Test MIDI file with 176 notes. (1.6 KiB, 100 hits)
You need to be a registered user to download this file.

I recorded the outcome of the MIDI data playback back into Ableton and analyzed the Wave file in Sound Forge:

Oberheim Matrix 1k Wave DCO Bad Chip

By looking at the wav file, the cycle through the six voices is very obvious. The chips do not have a consistent amplitude output, and one of the chips actually drops out completely but then it picks up the output at higher frequencies.
This means this unit not only needs at least two of its voice chips replaced, it probably has some more serious issues since the voice is not consistent across the keyboard.

To find out exactly what chip needs replacing do the following
1-Put the synth in Extended Function mode by pressing the Select key until the Ext Func. LED is lit.
Press 7 and press Enter.
Press the + key until you see 1 in the display and press Enter.
Now you have the synth in Voice Display mode, where the number of highest gated CEM3396 chip is displayed – counting from right to left on the circuit board.

2-Run the MIDI test again and listen for any audio dropouts and frequency shifts while watching the display. There you will be able to spot the location of the chip or chips that are having a problem.

Leave me any comments if you have any questions, and if you are an Oberhein Matrix 1000 owner, don’t forget to check my review of the different editors / librarians available for the synth HERE

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13 Responses to “How to test an Oberheim Matrix 1000’s voice chips”

  1. 0=0 says:


    i think mine are really well calibrated..but if they go out..i’ll leave it like that…the soul of the machine..aslong as my patches sound GOOD!

  2. admin says:

    Thanks for your reply.
    The problem with the Oberheim Matrix 1000 is not that the oscillators go out of tune (they are digitally controlled so they don’t drift that much). The problem is that the oscillator voice chips just die, and you lose voices, so the synth patches sounds “thin” when played.
    The voice chips are not that hard to replace, but it is a hassle for someone who’s never done any electronics work before.

  3. Will Puckett says:

    A secondary issue is with the filters – Cutoff and tuning. This problem is not IC related but is due to the support capacitors leaking or no longer operating at spec. Of the two Matrix1000’s in my studio, one of them had a defective filter circuit that caused A)voice level to be louder at lower frequencies, quieter at hiher frequencies, and B) color, cutoff and resonance differences at all settings. These caps are common poly .0068/50v type available from Mouser or Digikey.

  4. admin says:

    Hi Will
    I’ve been having intermittent problems with my M-1000, i know it is not the voice chips, because they work when i swap them around. I will probably do a cap job on the unit.

    Thanks for the tip!

  5. acemonvw says:

    What I really want to know is how to get in touch with this Will Puckett guy who mentions the secondary issue, because that’s what I have and I’d love to figure out how to fix it!!!

  6. acemonvw says:

    Does anyone know, based on looking at this diagram (link below), where the capacitors are, relative to each voice-chip would need to be replaced?


  7. John says:

    I have problem with my Matrix-1000 – when I play notes in octaves sometimes one random note has sound without 2-nd oscillator, I run Test mode and it show voice chip 2 in current problematic note… I tried to change IC voice chips between 2 and 3 or 1 but problem still there… (as well tried re-initializationa and calibrate mode) I hope that issue not in a voice chips? Please anyone help if possible, thanks!

  8. admin says:

    My advice would be to reseat the SEM (Voice) Chip in question.
    Open the unit, the voice chips will be visible.
    The voice chips are numbered in the board.
    You can use a small screwdriver to carefully lift the chip from its socket and then carefully push it back in. Be careful not to bend any pins.
    You may want to use a ground strap to avoid any static damage to the chip.
    If your chip is fried, you may be able to purchase a replacement from:

  9. fritz says:

    Yes! Reseating the cem chips solved my issue. My M1K was troubled with an open filter on one voice, so every sixth note you hit had the filter wide open. Tried the easiest suggestion above first, reseating the chips, and it seems to have solved not only the filter issue but my subsequent sorrows. Now I can rock this great synth again. Thanks!

  10. Lorne says:

    Hi the downbload matrix midi file link is dead. Could you fix or email file please

  11. davros303 says:

    Hi there,

    I purchased an M1000 and the seller let me know upfront that 2 of the CEMs were dead. So I purchased it anyway thinking I could just replace them, however going through your test – it appears all 6 are working. The problem it has, is every couple of notes in a 2 voice patch, it only plays one DCO. What would cause this? Is it an issue for reseating?


  12. davros303 says:

    OK worked it out. Matrix has 2 x DCOs per voice, so one of the DCOs was dead in 2 of the CEMs. Have replaced them both and works perfectly now. Thanks for this guide – was very helpful.

  13. admin says:

    Lorne: I just tested the MIDI file download and it works just fine.
    Davros303: Thank you, i am glad this guide helped you!

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