Another SQ80 Problem

Hello! I’m at a loss for this new problem on my SQ80… a majority of my sounds has this digital noise that sounds when playing the keyboard. It only happens in a specific sequence, which changes depending on the sound. Please see below video:

Since the strange noise happens in a perfect 8-note cycle, my guess is that two of the voices have some sort of issue. I would certainly try reinitializing the SQ-80 to see if that helps. There is also a procedure for tuning the eight filters that might help: press Record and Filter at the same time, press the button to start the tuning process, and see where each of the 8 values end up. That may cure the problem, or it may show two of the values that are way off (if this is a filter issue).

Try that and let us know what you find!

Hey Sam! Thanks for the response! I’ve recalibrated and retuned the filters multiple times now, but to no avail. Love the sounds I’m getting out of this keyboard, but again I’m at a loss for what this could be!

Hi again!

Could this sound be coming from a dying Filter Chip or more likely a dying Voice Chip?

There is no ‘voice chip’ for each voice - just the CEM3379 filter chip. I guess a good next procedure would be:

(1) Find one of the funky voices, by removing one filter chip at a time. This will simply cause that voice to no longer play, so pull one filter chip at a time until you eliminate one of the funky voices. These chips are socketed, and located on the right end of the main board; you can see them in this photo:

The lower right corner of this photo shows the identical circuitry for each of the eight voices.

(2) Once you’ve pulled a 3379 chip and silenced one of the funky voices, now swap that chip with the one next in line with it. Now play a note repeatedly, like in your video, and see if the pattern has changed. If so, then the 3379 chip is causing the weirdness - and if nothing changed, then it will take some serious signal tracing to locate the culprit.

usually its the 74LS377 which sends signals to the SSM2300s…which in turn send CV to the 3379 voice chips. There isn’t that much logic because ensoniq used a discrete chip to do all of that but the 74LS377 is prone to failure and latching on this circuit