Inside the Korg Polysix. Analog synths with Storage

Bob Weigel of http://sounddoctorin.com goes over the layout of some of the more significant components in the Korg Polysix, a synthesizer which sold around 22,000 units produced from 1981 to 1983 or thereabouts. Korg simplified and cut cost in many ways on these units but they stand as one of the few fully analog (with a discrete VCO for each voice if not two) polyphonic synthesizers ever mass produced along with the Prophet 5/10, the Oberheim OBX, OBXa, and OB8, which had BOTH memory and full editing from the panel without toggling through menus etc. Later a MIDI retrofit was also introduced bringing this unit and a rather nice one I hear. Hopefully I can get mine working that I just purchased broken :-). That unit is not shown in this demo though. The MIDI board lays over the top of the CPU's and a connector actually goes into the cpu sockets and the cpu's set on the new MIDI retro board.

Category:

Music

Tags:

• Korg
• Polysix
• analog
• storage
• synthesizer
• technical
• overview

[synthpro]

The polysix is built almost like the Akai AX-80. It is also a 80's poly synth. I am taking electronics at college and hope to learn a little more about this kind of stuff. Great video and thanks for posting!

[sounddoctorin]

Welllll not quite 'almost' :-). It was assumed on some websites that the AX80 had VCO's. However it's very similar I believe (though I still haven't seen a diagram) to the JUNO's and other DCO synths of the day which use an op amp integrator that is digitally controlled to generate the saw waves. Otherwise the signal path thereafter is analog though all controls for envelopes are digital also. Whereas the polysix is completely analog on all those things. I have been inside the AX80..

[synthpro]

That is neat to know! So just to make sure I am correct, a DCO still uses a viberating chip to produce the sound, but it is digitally controlled insted of voltage controlled. Is that right?

[sounddoctorin]

There are various things labelled "DCO". The first things were apparently the Crumar DS-1 and the JEN Sx-1000 I believe someone told me also around the same time. At least the DS-1 used multivibrator chips that actually had a preset R/C with analog CV mixed in from the bender etc. So I guess it was really a VCDO. :-) Then the polysynths were at first using DCAO's like ax80. Curiously Akai went the other way and most of the rest of their synths used the CEM3394 VCO/VCF/VCA chip!

[sounddoctorin]

Continuing, then synths like the Korg DW's, DSS-1, Ensoniq Mirage and ESQ-1/SQ80, SCI Prophet VS / 2000, and Kawai K3 came along that had still analog filters but used entirely digital processing to generate the waveforms right out of a DAC. This of course allowed the flexibility to do some more interesting timbres since the data could be read right from a ROM chip or in the case of the samplers, sampling RAM. So these were DCDO's I suppose. The siel DK600 Is unique. VCDGAO's :-)

[sounddoctorin]

PS and on my sounddoctorin website in the global synth section under production synths you'll find akai and the ax80. I archived the document akai used to have up about the ax80. That's the only 'official' info I've been able to locate on it to date.

[kr61ab67]

Congratulations to the designer(s) of this beautiful and great sounding machine, and thanks Doc for posting this video !

[synthpro]

@geox19801 well, I have never been under the hood of a Korg polysix yet but based on other synths I have worked on, you may have some bad filtering capacitors in some of the audio circuits. I have had rare cases where dust created noise as well.

Hope this helps somewhat.

[geox19801]

i noticed on mine that it makes a lot of background noise without playng any keys.

anyone have the same problem??

cheers

[TheReasonWhyGuy]

I love to just look at hardware...

[synthpro]

Very Interesting! I enjoy learning about things like this. Thanks for the information!