My Mini Moog Voyager. Click to go to my web site...

Sunday, June 13, 2010

No Pain, No Gain, seriously, no gain...

So, the envelope generator works flawlessly. I was instantly in love with the damp and quathin switches. I have to find out where the term quathin came from.

But, the VCO is a different matter. I didn't want to risk destruction of one of my original 2N5163s, so I used a NOS which I bought on Ebay. Turned it on and no oscillating. I removed the NOS 5163 and installed an original one. The saw core started to work fine. The frequency adjust takes it from below hearing to above and all seems good. I then decided to try all my old stock and found two JFETs which had died. None of the NOS worked, very disappointed. I then tried the 2N5246 JFET Nyle spec'd in his later VCO core and they worked like a charm. I tried the NTE312s, and NTE132s, and they worked great. I then tried the 2N5246s which did not work. So, I think I'll probably just go with the 2N5246s.  They are in production, and inexpensive. To that end, I changed the schematics to reflect the 5246 footprint as it is different than the 5163.

The bad news is that the saw core output doesn't make it through any of the shapers. I really don't understand why. I have checked the original schematic against mine several times now and I don't see any errors. I've eyeballed it logically and the connections appear to make sense as far as I can understand them. I double checked the pinouts on the Eagle models against the data sheets for the SSM2210s, THAT340, and the transistors. I even put my transistor analyzer on the transistors to verify which pins are which and checked that against the PCB footprints, and how I installed everything. So, I get a nice sawtooth out of the core, but no gain, no shaping, no output.

I'm out of town for a couple of days, but when I get back I'll have another look. I'm not too worried because I've changed a lot for the next revision, so I will probably wait til I get the next prototype ordered and stuffed.

I've also made some decisions regarding the schematic capture and PCB design. I am doing the schematics exactly as Nyle had them electrically. For example, 2 meg pots are hard to find, but I'm entering them anyway with the associated capacitor values. I didn't do that to start, but I think it is important to get them entered the way Nyle had them for the sake of history and preservation. Later, when I build one or two for my other modular,  I might make some "improvements". Use OpAmp buffered outputs/inputs, etc. But for now, I want this thing to be as close to what I would have had in 1975 as possible.

For little things, I will make value adjustments accordingly as I build and order parts. Like, there are several places where 2 Meg audio pots are used. 2 Meg pots are not easy to find. I'll use 1 Meg and then up the capacitor to get the same time constant, but the board and schematic will reflect the 2 Meg pot. It will also reflect the 2N5172s and the in production PN5138s (different case from the 2N5138 and slightly different footprint, straight line instead of a semi circle). The pins will be marked so anyone can use the NPN/PNPs they want with relative ease.

 That said, I am using footprints which will allow newer parts, like NPN matched pair ICs to be used i f wanted. I confirmed the THAT340 NPN/PNP IC works fine in the exponential convertor and for my personal production, I'm going to use them. I'm trying to include copious notes on the PCBs to help in construction and am labeling the PCBs with component values instead of component number. I am also including any notes, etc. Nyle made on his schematics to preserve the archive.

Last, I got hold of Nyle by phone last week. I was as  nervous as I was that first time I met him in 1975. Weird how the psychology of that works. Anyway, we chatted for a few minutes and decided we should meet and talk about what I'm doing. As Nyle put it, he likes to be involved with people doing fun things. I was flattered he thought what I was doing with his designs was fun. Anyway, I'm hopeful now after talking to Nyle these unique designs will be shared in some form. I don't know what, how, when, or where, but I have my fingers crossed.

Stay tuned...

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