Monday, July 19, 2010
There is no high frequency trim and Nyle and I discussed this, and in the end, I don't think we will add one. those with perfect pitch might be annoyed, but then, no analog oscillator can be perfect. I have two or three VCOs with high frequency trimming and I found that if you trim the high end for good tracking, it can tweak the tracking in other parts. On a really quick tune job today, I got it tracking almost perfectly at about 440 to 880 Hz. At two or three octaves higher, I was off by about 1%. I was pretty pleased with that as from note to note, I really couldn't tell.
Nyle also wanted to add an additional possible trimmer to the triangle shaper. The 2N5163s they used were varying wildly and there were some which would not allow you to properly shape the triangle wave with the default trimmer. He found if you take the trimmer on the collector and put it on the emitter, you could trim the triangle wave. He wanted to make sure the end user could do that if the FET was problematic. So, I have trimmers on the collector and emitter. In normal building, the trimmer on the emitter will be jumpered to ground. See the partial schematic above. So if the FET doesn't let you properly shape the triangle, take out R63, jumper it to +12, take out the jumper to ground at R72, and install the trimmer. Or, you can just install both trimmers and start with R72 full CCW (shorted to ground). That said, the 2N5246s Nyle used in the later VCO cores haven't given me any grief and I've tried several random ones.
I tested the sync, and it works perfectly. I didn't try trimming the Sync Bias though. The only thing left really is the mismatch in output gains. I'm honestly tempted to just leave them. I've got enough trimmers already!
I've got the sequencer about half stuffed. Nyle found a couple of errors in my schematic capture, and thankfully I can easily take care of them when building the prototype. It may also explain why my simulation didn't work right, too...
Next up, I'll give the VCO a final check and blessing from Nyle and order some more boards. I want to build the VCA next and then get it's next revision and the classic Steiner filter boards off for prototype. I also need to get the type III EG and the next revision of the type I/II off.
I've checked the VCO panel and the VCO PCB will fit fine parallel to the panel, so shallow euro rack guys be happy if you want a Steiner VCO. Sorry, but it will be 28 HP wide. I could make it more narrow, but then you will need about 6 inches clear behind it. The panel would also seriously depart from the original layout and I want it to be a close as possible.
Enough for now.
Expensive, but exciting.