2
\$\begingroup\$

A friend of mine who is a layman in terms of electronics asked me to teach him how to synthesise audio with some analog circuit and how to build it. For some reason it has to be analog. Probably because that's so cool these days. I don't really get this.

The problem is that I'm not into discrete electronics either.

I concluded that there are many circuits that can produce oscillating signals and thus sound. The astable multivibrator came to my mind. However, for audio the signal cannot be just periodic. It is necessary to produce the desired shape like sine, triangle, rectangle, etc. without overtones (or at least as few as possible)

In theory for example, a simple \$RLC\$ circuit can produce a nice decaying waveform of a single frequency. But in the real world, a component is part of an electrical network that influences its behaviour.

The answer I gave was "Just use a microcontroller." However, I received the the answer that programming is "very complicated". I have a feeling that behind this lies the fallacy that designing analog oscillators is an "easy task".

Am I on the right track that it doesn't make too much sense to create audio with analog circuits these days? I found this upvoted answer from Olin, which supports my reasoning. I don't want to be the downer and due to my own lack of experience I might be on the wrong track entirely. Maybe there are simple ways to create oscillators for audio synthesis with analog components?

\$\endgroup\$
  • 2
    \$\begingroup\$ Someone that says "digital is hard" when they can't do the same in analog is a [colorful pejorative] as far as I'm concerned. \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 6 '15 at 23:07
  • 1
    \$\begingroup\$ youtu.be/n3K_fZDvINs you can buy a brand new one for $35K \$\endgroup\$ – Scott Seidman Jul 6 '15 at 23:58
  • \$\begingroup\$ @IgnacioVazquez-Abrams that's why I recommended starting with a microcontroller. I have the feeling that building this with analog components from scratch is an order of magnitude more complicated than just writing some sine values to a pin. \$\endgroup\$ – Magic Smoke Jul 7 '15 at 15:09
  • 1
    \$\begingroup\$ @ScottSeidman plus a few bucks for drywall and paint to build that secret room to hide it from the wife. "Oh honey, you're home early, didn't you want to go shopping for some new shoes?" "I couldn't, there was an issue with the credit card...wait, isn't this room smaller than it was this morning?" "I have no idea what you are talking about." \$\endgroup\$ – Magic Smoke Jul 7 '15 at 15:14
  • \$\begingroup\$ Analog modular synth may be what he's looking for: lots of modules you can plug together to make noises. More cheaply there are lots of moog-like kits at various levels. \$\endgroup\$ – pjc50 Jul 7 '15 at 15:56
3
\$\begingroup\$

Yes, you can create complex waveforms without needing a microcontroller, by making use of the audio blocks such as oscillators and filters that are part of an audio synthesizer.

The document titled "How to Design and Build an Analog Synthesizer from Scratch" includes lots of schematics and theory for building these various audio blocks.

One of the comments has already mentioned a Moog synthesizer costing $35,000. However Moog also sells many other synthesizer models in various price ranges, at the bottom end is a kit for $329 called the Werkstatt-01 which is shown below. But you don't have to buy one; you can download the schematic from their website, and use bits and pieces of their design. Combined with the document referenced earlier, you should have plenty of ideas.

enter image description here

\$\endgroup\$
  • 1
    \$\begingroup\$ I'm pretty sure that one only goes up to 10, and the modular goes up to 11. \$\endgroup\$ – Scott Seidman Jul 7 '15 at 15:26
  • \$\begingroup\$ @ScottSeidman I don't know what you are referring to (10 and 11). \$\endgroup\$ – tcrosley Jul 7 '15 at 15:46
  • 2
    \$\begingroup\$ it's a reference to a scene from spinal tap, a movie about a fictional rock band. The guitar player has an amp that "goes to 11" It is rather hilarious, take a look at this video It is commonly used on the internet. \$\endgroup\$ – Magic Smoke Jul 7 '15 at 15:49
4
\$\begingroup\$

Of course it's feasible. Everything (well, just about everything) that was feasible in the 1970s and 1980s is not only feasible today but actually MUCH easier.

You can make LC oscillators. The capacitors and pot cores are easily available. Capacitors with a negative temperature coefficient (to compensate for the potcore tempcos) might not be so easily available. VCOs that cover the audio range are easy to make with op-amps

Generally the simplest method of synthesizing sounds consists of generating some sine waves, and some noise (a zener diode can generate noise) and filtering the noise and gating the sounds through some envelope generators that have specific attack, decay and sustain characteristics. Something like a cymbal would have a bunch of noise, a piano much less so.

But just because it's feasible doesn't mean that just anyone can do it. They could always find an old construction article in dead-tree format and attempt to adapt it even if they were not capable of doing the design. Probably most of the stuff is still available.

Unlike back then anyone can get boards made cheaply and reasonably quickly, so assembling some hundreds of parts is not such a big deal.

This is not going to be something that sounds like a modern electronic instrument that uses DSP and sampling techniques, but something that sounds like something from a foregone era, and with annoyances (or perhaps charms) such as frequency drift and so on.

Anyway, I'm sure if you troll through the archives of the Brit publication Practical Electronics and similar publications you should find some inspiration.

You could start with the Russian invention Theremin? Not much circuitry there.

\$\endgroup\$
  • 1
    \$\begingroup\$ +1 for the Practical Electronics reference! I built my own synth based on the designs published there in 1973 and while the tuning wasn't entirely stable, in every other way it worked well and was tons of fun. \$\endgroup\$ – peterG Jul 7 '15 at 1:01
  • \$\begingroup\$ @peterG Great! Thanks for confirming the hazy memory banks. \$\endgroup\$ – Spehro Pefhany Jul 7 '15 at 1:19
  • \$\begingroup\$ I know the theremin and played one before, this is probably not the direction he wants to go. It's more about modular synths systems. The thing is that doing this with a microcontroller appears to be even easier. I'm also not sure if the "charms" are actually desired, as a stable frequencies have been named as a requirement. I have to ask back what the eventual goal is. \$\endgroup\$ – Magic Smoke Jul 7 '15 at 15:42
  • \$\begingroup\$ I don't think it is at all easy with a microcontroller unless it's quite a high end one. If he wants to go digital I'd be looking at something like a decent DSP (digital signal processor). You can do stuff like echo cancellation that's totally impractical to do with analog electronics. \$\endgroup\$ – Spehro Pefhany Jul 7 '15 at 15:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.