Thursday, 18 February 2016


16. May 2015
Alright then, I think it's time for a new analog synth project. I've done digital stuff for long enough. After having researched various options I decided to go for something big. I'm not that much into modular synths but I do like the idea of being able to manually patch a few connections for that special sound. I finally decided to go for the ASM-2.

The ASM-2 is an upgrade to a synthesizer called ASM-1 (somewhat expectedly...) and includes a few additional modules and some enhancements to some of the original ones. PCBs can be bought at Elby Designs and contain several practically self-contained modules allowing the builder to customize their systems as they see fit, e.g. as a modular, semi-patched or hard-wired system.

The ASM-2 consists of the following modules:
2 x VCO
2 x VCF (1 x state variable, 1 x low-pass transistor ladder)
2 x VCA
2 x ADSR
1 x Glide Generator
1 x Ring Modulator
1 x Noise Generator
1 x Sample & Hold

I just received the PCB in the mail, and after having admired it long enough I'm now in the process of ordering all the electronic components. I already sent an order for some of the rarer parts to I hope they arrive on time. In the meantime here's a picture of the PCB.

11. June 2015
It took me a while to shop around for all the electronic components but I finally managed to decide where to buy. The bulk of the components, in particular semiconductors and capacitors, arrived today. I ordered from Reichelt which I found to be the cheapest supplier. A few rarer items such as the LM394 matched transistor pair, the J108 JFET transistor and some germanium diodes I found on utsource. They arrived a couple of days before. Those few semiconductors that Reichelt does not stock, plus resistors in bulk amounts that are cheaper there, I ordered from Futurlec. Those items that in turn Futurlec does not stock, in particular the CA3080, I'll order from Musikding. Unfortunately, Musikding currently does not stock it either (apparently they ran out just when I was ready to buy), so that'll have to wait.

I've already got a heap of components, yet they are only the ones that go into the PCB. The panel mount components, i.e. all the switches, potentiometers and jacks will constitute another sizable order. But first things first.

24. June 2015
I just returned from Vienna. Not that anyone cares to know but because there's little else to report I figured I can just as well mention it anyway. I just saw that Musikding now has CA3080 OTAs in stock but instead they don't have any 2n2 polystyrene capacitors left. Life is hard at times.

23. July 2015
It appears that Futurlec ran out of some of the components that I had ordered. So I went back searching for them and eventually found them at Small Bear Electronics. They also stock a LM394 work-alike (AS394 by Erica Synth for US$ 4.95). They, too, slipped into my order.

I hope that the Futurlec order will arrive soon because the bulk of the resistors is in there. I'd like to begin stuffing the PCB with the lowest parts, and that'll be resistors and diodes.

28. July 2015
I'm still waiting for the Futurlec order to arrive. But I'm not waiting idly. Instead, I started stuffing the PCB with the components that I have. That would be all those resistors that I happened to have lying around, and all the IC sockets. It's coming along nicely.

The alert reader may be baffled by two blank areas on the left of the board where there's an IC socket outline but no socket. That's the spot where the matched transistors go. I bought a pair of LM394 fakes work-alikes in a TO-5 can that I'll solder there. Mystery solved.

12. August 2015
The Futurlec order has finally arrived, and I was also able to complete the order with Musikding (including the CA3080s that I ultimately need). In the meantime I also received the latest PCB overlays and bill of materials from Elby Designs. It appears that several resistor values have changed, including some that I already soldered in place. There are some new odd values that I don't have at hand and that require a follow-up order from Reichelt. But first I'll continue soldering those that I have, and that will take some time.

15. August 2015
I have finished soldering the resistors. Most of them anyway. There are some whose values had changed in the most recent schematics and that I must order first. Also, a kludge is required because of late improvements to one of the modules that were published but I hadn't noticed. It requires cutting two traces on the PCB and soldering two resistors in their place. I'm reluctant to violate the beautiful PCB by hacking at it with hacksaw, crossbar and hatchet. Or a precision knife. But there's no way around it, if the synthesizer is ever to be finished.

18. August 2015
The synthesizer is coming along nicely. I finished soldering diodes and most of the capacitors. There are some that a I bought too few of and others that I did buy enough of but somehow cannot find anymore. I'm adding those to the Reichelt order that I mentioned above. Also I need to have another email exchange with Elby Designs in order to clarify a few things regarding resistor and capacitor values that have changed in the BOM but not in the schematics. It is (and will be for some time) a lot of work but I'm confident that this thing is going to be my masterpiece!

PCB with most resistors and capacitors in place.
21. August 2015
Today I managed to complete ... nothing. I have plenty of other ideas that I want to explore, in addition to the couple of synths that are stalled in various stages of completeness. I also experiment with digital circuits, because you can only do so much analog stuff at any one time. The following picture shows an Auduino granular synthesizer, based on a "standalone" Arduino board. The alert, hawk eyed reader may notice that I wired the ISP connector the wrong way round. In any case, I'll open a separate thread to report on my experiments with (and potential enhancements of) the Auduino.
Midified Auduino synthesizer with front panel.
10. September 2015
The PCB is nearly completely stuffed. After quite an intense email exchange with Laurie Biddulph of Elby Designs, who has proven extremely patient and helpful, I'm quite certain now that I'm up to date with the most recent specs. I had to replace a few components but it was worth it. This is definitely going to be my masterpiece!

A handful of components is still missing, including several ones that I ordered the wrong number of, but mostly it's the trim pots that I'll do after I have given the board a decent cleaning using isopropanol to remove the solder resin residue. Also, I haven't soldered the germanium diodes yet. I'm a bit intimidated by them because I think they are quite delicate.

18. February 2016
The PCBis now completely stuffed, germanium diodes, trim potentiometers, missing components, voltage regulators and all. The only thing that's left are the three modifications that need to be done on the PCB:
  1. one leg of a capacitor in VCO1 is left unsoldered and needs to be connected to a leg of a nearby resistor
  2. one leg of the corresponding capacitor in VCO2 needs to be connected to a leg of a nearby IC
  3. two cuts need to be done on connections on the PCB and then bridged with resistors
That's next on my list. I've already started planning the layout of the front panel. I think I'll go for a prepatched ("normalized") design, yet with full patchability. The idea is that the most common connections can be done with switches on the control side of the panel, but for the extra flexibility, there's a patch panel to override the normalized routing (using switched jacks).

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