Somehow, an Elka Synthex analog synthesizer made it onto [Mend it Mark]’s repair bench recently. It had a couple of dud buttons, and some keys produced the wrong tone. Remember, this is an analog synthesizer from the 1980s, so we’re talking basic 74LS chips and kin. Fortunately, Elka helped him with the complete repair manual, including schematics.
As usual, [Mark] starts by diagnosing the faults, using the schematics to mark the parts of the circuitry to focus on. Then, the synth’s bonnet is popped open to reveal its absolutely gobsmackingly delightful inner workings, with neatly modular PCBs attached to a central backplane. The entire unit is controlled by a 6502 MPU, with basic counter ICs handling tone generation, controlled by top panel settings.
The Elka Synthex is a polyphonic analog synthesizer produced from 1981 to 1985 and used by famous artists, including Jean-Michel Jarre. Due to its modular nature, [Mark] was quickly able to hunt down the few defective 74LS chips and replace them before testing the instrument by playing some synth tunes from Jean-Michel Jarre’s Oxygène album, as is proper with a 1980s synthesizer.
Looking for something simpler? Or, perhaps, you want something not quite that simple.
Ah. you saw that video on youtube too.
Now im curious how big the venn diagram overlap is between people reading hackaday and people getting this video as a suggestion in their feed.
Large overlap, me think.
All slaves to the youtube algorithm. Especially those people who are a bit bored or click around to fill some time.
“Remember, this is a completely analog synthesizer from the 1980s, so we’re talking basic 74LS chips and kin.” Actually, 74-anything is TTL digital. But yes, same era. Peerhaps 4-quadrant analog multipliers, VCAs, VCO, etc. in IC form.
In the synth world, the difference between analog and digital is whether or not there’s a CPU/microcontroller involved. The distinction makes sense from the musical perspective, but less so from an engineering perspective.
Just wrong. Nobody thinks e.g. Prophet is a digital synth just because it’s under computer control.
Even something like Korg DW-8000 is considered hybrid.
People make the distinction based on whether the signal path, not the control path, contains DACs.
“Analog” in the synth world usually only refers to the audio chain; a lot of “analog” synths, particularly the polyphonic ones like the Synthex, extensively use digital systems for controls, and that’s where the 6502 and TTL logic comes in.
From what I recall from the video the oscillator waveforms are actually digitally generated, using (somewhat disappointingly) a discrete 8-bit resistor dac, so not very accurate but I suppose that adds to the character ?
So basically a DCO + analog filter architecture
Great video, it was fun to watch the diagnostic steps!