VCO-1 Project Resources
Finding Parts - The Eternal Quest
There are really only two parts in the VCO-1 design that may be moderately, but not overly difficult, to get: The 2K Tempco resistor (R8) and the CA3080 (IC1) which was sadly and misguidedly discontinued by Intersil (apparently, it's not used in any current cellular phone or video game designs these days). Fortunately the CA3080 is still quite available, and thanks to the remarkable and irreplaceable Ray Wilson, the 2K tempco is a Paypal purchase away. All of the other parts are very common - you can get them at all at the usual suspects: For us in the States, Mouser Digikey, Jameco, Allied. For those of you in Europe, the RS's and Reichelts, etc. For you lucky, lucky Japanese, the Akhibara, etc. For the people down under, it looks like you have some nice places left to find parts.
Monolithic PNP Transistor Pairs (Q5, Q6)
As the age of electronics is supplanted by the digital age, some things are winding up left in the dust. Things that are left in the dust seem to be items that are not vital to the manufacture of cell phones, MP3 players and game consoles. Unfortunately, one item that is not required by any of these devices is the matched transistor pair. This fact has not escaped the MBE's running the electronics joints, and, as a result, you may find that actually getting your mitts on a matched transistor pair is getting to be quite difficult. Not to worry: you still have a few options. This section touches on the subject of what to do when you can no longer find the matched transistor pair so crucial to analog synthesis itself.
Matched XSTRs: Cruise Surplus Outlets
One alternative is to search through the on-line surplus electronics houses. This will require extensive use of your Google powers. Remember, for this particular project, you need a matched PNP pair. At this writing (May 2010), Electronic Surplus still has the matched 2SA798 PNP pair. This was the mached part when I made this sample; it definitely works and I recommend you glomming onto a few of them. The will be useful not only for this project, but will, in all likelihood, be useful for other projects as well.
Matched XSTRS: Existing Manufacturers
There are a few manufacturers that do produce matched transistor pairs. It seems the only one that makes their product available to anyone who does not have the word "Inc." following his name is THAT Corp. Despite the "Who's on First" nature of the THAT Corp's name, they are a seriously solid company if you are interested in all things analog. I've used a number of their products (matched transistors, VCAs, RMS detectors) and have never been anything less than impressed. THAT Corp produces a number of different matched transistors, but (at least for DIP parts) their transistor pairs are usually in quad packages. In other words, they produce DIP parts that have two pairs of matched transistors on them. That simply means that if you want to use one of these packages, you will have to adjust for a 16 pin package instead of an eight pin package in your design. Now, having said that, THAT CORP produces an IC that has a both a matched PNP pair and a matched NPN pair on the same device. This could be used to your advantage, particularly with this design. For example, you could use the matched PNP pair for the exponential converter, and the matched NPN pair for the sine converter. This would eliminate two transistors from your layout. Now, THAT is cool....heh......
THAT Corps parts are sold through Mouser, Small Bear and KA Electronics.
Matching Your Own XStrs
The third option, and this may be the one that benefits you the most, is to match your own transistors. Back in the day when Dr. Moog was designing things that would change our lives forever, a bag of transistors would have characteristics that were all over the map - it was difficult to find two transistors that agreed with each other about exactly how they would pass current or how much gain each should have. It was quite a deal to match two of these scurrilous louts together. In modern times, manufacturing processes have become so refined that a bag of transistors will contain devices that are already matched very closely together. This does not mean that you should randomly solder a couple of transistors from the same Mouser bag together for your exponential converter, but it does make the job of matching transistors much easier.
So how does one actually match transistors together? There is an old Moog procedure floating around the web that is quite handy to use, but be aware that certain versions are missing a resistor in the PNP portion of it, if I remember correctly. To make things easier, enter Ray Wilson, of Music From Outer Space fame. Ray has a wonderful page, and a circuit to boot, detailing the methods used to properly match transistors.
The 2K Tempco (R8)
Music From Outer Space. To any Synth DIYer, that's usually 'nuff said. But, I'll expound anyway. I can't even begin to count how many of Ray's designs have found their way into my synthesizer, or how his writings have enhanced my own otherwise feeble attempts at design. If it weren't for Ray, Thomas, Ken Stone and Rene Schmitz, I doubt if I'd be much past installing batteries in a flashlight. Ray Wilson's Music From Outer Space site is one of my greatest inspirations - I firmly believe his Sound Lab music synthesizer design is arguably the single most successful DIY project of all time, and that's not all Ray offers - he's got all sorts of filters, oscillators, yin-yang contemplating dinosaurs, VCAs, wacky sound generators, phase shifters, spacemen and documentation, all magnetically and gravitationally encased in that juggernaut of a site of his "Music From Outer Space". Not only does Ray have all that, but he also makes available the coveted 2K Tempco resistor, without which I'd just fold up shop and call it a day. I'm sure you've been there already, but go again - and enjoy. The link is to the page where he dangles the words "PT146 2K @25C 1% +3500ppm Tempco" hypnotically on your computer screen.
The CA3080 (IC1)
Intersil certainly didn't earn any brownie points with Synth DIYers when they discontinued both the CA3080 and CA3280. Fortunately, both are still around (apparently there were scads of them made before the bean counters realized they weren't on the BOM of the Playstation 2). Here are a few places they can be found. I'm sure there are other places you can get them before resorting to the 'bay'. In fact, other than playing favorites with Small Bear, and referencing Banzai over in Europe, I'd say you probably won't have a terribly hard time finding the CA3080 (BTW, I'm pretty sure the LM3080 will just as well). If you *do* have problems finding one, I highly suggest joining the Electro-Music forum and start frequenting the DIY forums there - particularly the Thomas Henry Designs forum. As the song goes, there are plenty of "gentle people there", though I doubt there are flowers in their hair, or, for that matter, many probably even don't have that much hair left either. But, they can still probably get you hooked up.
First on my list of personal recommendations would be Small Bear Electronics. Steve Daniels, the proprieter, is one stand up guy. Small Bear not only stocks the CA3080 for a price considerably less than the first born other dealers seem to think it's worth, but he has one slobberknocker of a DIY inventory. It's guys like Steve Daniels that make looking for that certain part sooooooo much easier.
Jameco Electronics is one of my favorite suppliers. You can find CA3080s there with ease.
Banzai Effects. I've never done business with Banzai, but I recognize them from Aron's Stompbox Forum, and from that know they're on the up and up. They're in Berlin, so I include them for those of you in Europe.
On-Line Resources
The ultimate source of information for building analog synthesizers would certainly have to be Bernie Hutchins' legendary Electronotes. Bernie still offers these documents for sale, and they could not be more highly recommended. Electronotes is literally the bible of Synth DIY.
Howard Moscowitz's vision of a community of Electronic Music without borders has become reality with his award winning electro-music site. Howard has created a phenomenon that simultaneously nurtures, inspires, and promotes the blossoming electro music movement. If you are an electro musician or afficianado, I cannot recommend this forum enough. The Electro-Music forum not only provides resources for composing and enjoying electro music of all types, but also encompasses information on the instruments and use of the instruments used to create this artform. Within Electro-Music is a subforum entitled "Thomas Henry Designs" and it is populated by a number of people who are both enthusiastic and knowledgable about Thomas' designs. Even Thomas himself is known to show up there. This link is for the Thomas Henry forum, but don't hestitate to explore the whole experience that is Electro-Music.
Magic Smoke Electronics offers an extensive line of Thomas Henry publications and projects. Check'em out!
