Circuit Board Update 4/23

gstopp at fibermux.com gstopp at fibermux.com
Tue Apr 23 19:10:50 CEST 1996


     Hi DIY list,
     
     Well I got the prototype of my new circuit board up and running, at 
     least on the test bench. All the little prototype tweaks have been 
     made and I'll be ready to go out for the new film as soon as I can 
     gerber up the artwork file.
     
     The thing is called the "ASM-1", for "Analog Synthesizer Module One".
     
     The frequency range of the VCO's are from below 1 Hz to above 125 Khz 
     (wow!). I had not-so-good luck with this VCO design last year on the 
     breadboard, but seems like I had some construction problems at the 
     time (solder flux contamination), because these suckers work great. I 
     *had* to give it another chance because in Electronotes it says that 
     of all the designs that have ever graced those pages, this VCO is the 
     most stable and accurate. The parts count is low and the hardest part 
     to find is the 2N4856 FET, which is over-the-counter at the local 
     electronics store (NTE part number = NTE466). The exponential 
     converter uses a pair of NPN's, so that means that a couple of 
     hand-matched 2N3904's should work fine. That's what I'm using right 
     now, and they're not even matched.
     
     I've listened to the filter and it's your typical high-quality 
     multi-mode sound. It's another "best of Electronotes" design so it 
     should be a real work-horse. The ADSR's, the VCA's, the noise source, 
     and the LFO all appear to be working fine.
     
     I've drawn up the schematics and the suggested panel connections. next 
     I'll write up a text doc about building, trimming, and 
     troubleshooting. I also need to make an assembly drawing and parts 
     list.
     
     Oh yeah, I'll be building a simple little modular soon for actual 
     music-playing tests. I'll want to check out the sound since I'm 
     predicting that the ADSR's will be real snappy (see my previous DIY 
     posts).
     
     Here's a list of the critical parts:
     
     (5)  CA3140
     (4)  CA3080
     (19) Dual op-amp, TL082, LM358, etc.
     (2)  CD4002
     (2)  CD4053
     (2)  2N4856 N-channel JFET
     (6)  2N3904 NPN
     (2)  2N3906 PNP
     (13) 100K 10-turn trimpot
     (2)  10K 10-turn trimpot
     (1)  100 ohm 10-turn trimpot
     
     A bunch of resistors and capacitors (yet to be tallied up)
     
     Optionally:
     
     (2) 1K or 2K +3300ppm/C' tempco resistors
     (2) MAT-02 matched NPN pair (or equivalent)
     
     Looks like there's about 2 dozen good requests so far, and I was 
     pretty good at my first guess of $60 per board.  I know that some of 
     you out there will think that's a little pricey if you call around to 
     the local PCB shops, but keep in mind that I'm trying to recoup my 
     fabrication costs which will be over a grand when all is said and 
     done.
     
     Okay, let me think out loud here, uh, I'll make the first price break 
     at quantity (4) in the same order to $50 per PCB. This'll get you 
     started on a cool Oberheim 4-voice clone for 200 bucks for example.
     
     Don't order yet, I'll have to make the purchase first. I'll post when 
     I do. Also I'll have to figure out how to do this - how about I get a 
     couple "beta-testers" who are willing to part with the money and trust 
     me to ship out the PCB's? Then they can relate their experience to the 
     list and tell everyone I'm a good guy. Suggestions????
     
     - Gene
     gstopp at fibermux.com




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