[sdiy] Lab antics and Synthacons (was KN-75 optocoupler)

[Gene Stopp]

Hey Magnus, long time no type!

The factory was like a frat house. Heat guns were for lighting cigarettes and isopropyl alcohol was for melting shipping styrofoam into giant puddles of white goo. High currents were for blowing things up (backward electrolytics and tantalums were popular), and card cages with front panel status LEDs were for programming scrolling obscene messages. Superglue was for fastening the handset to the telephone and then calling the person's extension. The running joke was to hide someone else's coffee cup (when it wasn't filled with solder) and they would have to hunt for it. The best hiding place is above a drop celing tile.

We actually did get stuff done and got product out the door back then, in our spare time. These days, fun at work is VNC'ing in to somebodys PC and messing with their mouse so they think they have a virus, or changing something in a lab router so they start pulling their hair out when they can't get some test to run. Not quite as hazardous as the old days...

Uh, synthesizers, oh yeah... how about a Synthacon review? Nobody ever talks about these.

It's a brilliant machine, absolutely brilliant. It's the most stuff packed into the least space with the cheapest circuits ever and yet still stays in tune. The VCO's go from fractions of a hertz to supersonic - we on this list know that it's easy to get a VCO to do this, but you just don't find it on many commercial machines. It's all transistors except for a few 741s for summing amps. We all know about the filter. Let me tell you, highpass is fun, especilly for heterodyning with the record bias on a space echo. The sample-and-hold is run by the "trigger generator" which has pulses so narrow that the S/H can easily capture the waveform of a VCO running supersonic. The trigger generator drifts a little so when you let the thing free run with some wild sample and hold patch, it morphs over time and does some really interesting wild things like it has a mind of its own. The panel layout is all messed up (traditionally speaking) with the VCOs on the right and the VCA in the middle and the EG's on the left. The modulation is all messed up (traditionally speaking) with the modulating signal attenuation happening at the SOURCE instead of the destination so if you are modulating two or more things they are tied together amplitude-wise. You can modulate VCO 1 with VCO 2 and VCO 2 with VCO 3 and VCO 3 with VCO 1 if you want which is totally dangerous. The whole design kind of forces even a seasoned synth-head to break with tradition and experiment. There's audio crosstalk especially when the VCO's are supersonic which adds even more unpredictable spacey background noises.

It's one big single-sided circuit board on standoffs behind the front panel, with all the panel wire connections along the bottom. It's not very complicated at all. If somebody cloned these (keyboard and wood sides included) and sold them for $2-3k I'm sure they'd had a neat little business going.

If you see one on eBay for cheap, beware, it's probably a hijacked account. I've seen four or five go by in the last few months that were fakes. If it says "don't bid, email me for buy-it-now" and the BIN price is half or a third of market value that's a dead giveaway. If the feedback is all about farm supplies or pet products that's another giveaway. If the seller's other items are digital cameras, mcintosh stereos, iPhones, and Hannah Montana tickets all for twenty bucks that's another giveaway. You guys probably already know this.

- Gene



-----Original Message-----
From: Magnus Danielson [mailto:magnus at rubidium.dyndns.org]
Sent: Friday, December 21, 2007 2:31 PM
To: Gene Stopp
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] KN-75 optocoupler


From: "Gene Stopp" <gene at ixiacom.com>
Subject: RE: [sdiy] KN-75 optocoupler
Date: Fri, 21 Dec 2007 14:11:37 -0800
Message-ID: <9C69FAED7CA00B44BAC4878C9081D1C50601933C at IXCA-EXCHANGE.ixiacom.com>
Gene,

> Back in my early tech days we used to blow up LEDs for the heck of it at work. We had a 5-volt gazillion-amp power supply that had voltmeter cables on it for destroying hard-to-find short circuits on newly assembled circuit boards (we called it the "f*ck-you" power supply). The LEDs would pop like a .22 going off and the pieces would go "tink" all over the lab - eye protection needed. We did other silly things too like pour solder from the solder pot into vaious molds like coffee cups and burn things up with heat guns but that's another story.

Now, fill in the gaps here. We do need the other story. Also, what modern
unorthodox practise do you perform in the current lab?

Had a quick look at the backplane OCXO while the hood was of the new 1600T.

A colleague of mine have been made more or less destructive testing of the
-48 VDC input blocks. The fun started when he finally did what I proposed and
started using one of our 70V 90A power supplies. More sparks, flying pieces
with associated accoustical effect from his side rather than the smell of
slowly burning resistors.

Cheers,
Magnus