TTSH, VCO sync mod

Heyyy I’m once again catching up my TTSH build documentation with yet another modification. Yayyyy!

This mod is based on Altitude909’s add-on board, which adds a Arp Odyssey style hard sync between oscillators. The build has been well-documented in this thread @ Muffwiggler, so please check there if you’re planning to add one to your TTSH (Hi Vlado!). I did a slightly alternate version for myself and on this post we’ll look at that instead! But first, here’s a video by Stephen Drake on what hard synced oscillators sound..:

The add-on board offers a number of source-to-target options to select how the oscillators sync, and so to boot with I spent some time trying to figure out which I’d like the best. You could have either one or two sources, with one syncing two targets or vice versa.

Schematic for TTSH Osc Sync board by Altitude909.

Schematic for TTSH Osc Sync board by Altitude909.

I ended choosing Osc1 as the main source, but then assembled the board so that sync is constantly enabled (switches S1 & S2 bridged to ‘on’ position), and the panel switches instead route the sync signal rather than toggle the field-effect transistors (FET) Q2 and Q4 on / off. This made it possible to run the sync in following configurations:

  • Osc 1 to Osc 2 or Osc 3
  • Osc 1 to Osc 2 and Osc 3
  • Osc 2 to Osc 3

As to installing the board, I decided to once again go about it with a modded MTA100 (similar to the Gate Booster mod) to attach the osc sync PCB to the main board, component side down.

Osc sync board connected to mainboard power header

Osc sync board connected to main board power header (MTA100).

..and cabling on the front panel

..and cabling (v1) on the front panel. Kapton tape to secure the cable.

Board cabling on the mainboard..

Cable connections on mainboard.

One issue with the above front panel cabling was (call it v1), that the oscillators would also soft sync at random. Apparently the vertical portion of the panel cabling (with wires running next to another) was enough to cause interference between individual wires. I have no clue why the randomness but I assume it may have something to do with my alternate wiring scheme (sync FET running at all times). Occasionally I could run through a patching session without any soft sync, and sometimes it would be there immediately from the get-go and not disappear. So I eventually ended up replacing the flat cable with a shielded one, ground connected to only one end on the board. Soft sync issues solved.

Panel cabling (v2)

The much improved panel cabling (v2). Not a very good photo really, but since I took one.. :P

As for the switches, well, I probably have confessed this a number of times before, but I don’t like the visual look of regular toggle switches much, meaning like the ones in photo below. But they’re wayyyy easier to install than slide switches. For a while there I was seriously considering to use slide switches (more consistent with the visual look), but then snapped out of my daydreams. I currently have no good method of cutting clean rectangular holes, so toggle switches it is then.

Switches lined up with existing panel items

Switches lined up with existing panel items

Oh well, at least I did one thing right by lining up the switches to the ‘grid’ of the jacks / slides. So it’s marginally more visually pleasing than just installing them wherever. Using a sub-miniature size switch, it just barely fit between the front panel and main board. Close call!

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