building my own synth

[sporsmaal2]

hello there

i am currently embarking on building my own synth.

i have moderate experience of basic electronic circuit design, ive also done a bit of circuit bending here and there.
i have tons of experience in building software synths, using reaktor, synth edit and stuff like that.
ive even made my own fm synths purely in code using visual basic.
check out http://sporsmaal2.free.fr for free downloads of them.

i intend to build some kind of FM or even AM synth
ive got 2 'velleman' signal generators to start off with.
these are besicaly 555 timers in astable mode.

Has anyone done this kind of thing before? any tips or links?

im really looking for simple circuits, in particular Envelopes and Filters

i managed to make a decay envelope using a couple of capacitors, but i have no idea how you would make an attack envelope.

any help would be much appreciated
thanks

[Bogus Noise]

hello there

i am currently embarking on building my own synth.

i have moderate experience of basic electronic circuit design, ive also done a bit of circuit bending here and there.
i have tons of experience in building software synths, using reaktor, synth edit and stuff like that.
ive even made my own fm synths purely in code using visual basic.
check out http://sporsmaal2.free.fr for free downloads of them.

i intend to build some kind of FM or even AM synth
ive got 2 'velleman' signal generators to start off with.
these are besicaly 555 timers in astable mode.

Has anyone done this kind of thing before? any tips or links?

im really looking for simple circuits, in particular Envelopes and Filters

i managed to make a decay envelope using a couple of capacitors, but i have no idea how you would make an attack envelope.

any help would be much appreciated
thanks

I've not personally built these, but there's a good range of schematics, including envelopoes, on this site:

http://www.musicfromouterspace.com/analogsynth.php?page=ANALOG

Hope that helps!

[Gordonjcp]

I was going to post a link to MFOS, but the site appeared down and then I got distracted by a shiny object ;-)

Anyway, the key to it is this - you have two resistors, and two diodes.  The diodes and resistors are wired in series, with one diode the opposite way round from the other, and then the diode/resistor pairs are wired in parallel.  One end of this then goes to the gate signal, and the other goes to a capacitor and is buffered by an opamp.  The other end of the cap is connected to ground.  Have a look for this arrangement in any ADSR circuit, including the AD envelopes on the MFOS page.

How it works is this:  When the gate is low, the capacitor discharges through the diode with the cathode nearest the gate pin, through the resistor.  If that's a variable resistor, you can vary the discharge time.  No resistance = instant discharge, big resistance = slow discharge.  Simple, eh?

When you then pull the gate input to the supply rail, the cap charges through the other diode and resistor.  Again, if there's only a little resistance it will charge instantly, but if there's a big resistance it will charge slowly.

When the envelope level reaches maximum, one comparator goes "Aha! We've hit the top of the envelope" and its output switches on, pulling the gate pin to ground and starting the decay phase.  Some synths just have an AD envelope, which usually has a switch to control this - you can have it do the attack phase then the decay phase, or you can have it do the attack phase and wait until the gate goes low again to do the decay phase (which acts like a release phase).

So how do sustain knobs work?  Well, the sustain knob forms a voltage divider.  This feeds a comparator, which is connected to the envelope output.   The output voltage begins to fall in the decay phase, but at some point the comparator connected to the sustain level control will switch - "Oh now the level has fallen below my setting" - and disconnect the gate input entirely.  With the A and D resistors no longer connected to anything, the capacitor has no way to discharge (well, it will gradually leak away but we can mostly ignore that).  As long as we hold the gate on, the comparator and its associated flipflop will keep the A and D resistors disconnected, and the output from the envelope is whatever the capacitor charged to.

When we let go of the key, the gate input goes low, and the circuit switches the release resistor in across the cap, allowing it to discharge.  This works pretty much like the A and D resistors.

Although an ADSR envelope circuit looks complicated when you see it drawn out ("What are those AND gates doing?  Why so many analogue switches?") it's really pretty straightforward.  If you start by looking at an AD envelope circuit, it should become clear.

[computer at sea]

And that's why I check this site several times a day! 

[Signal:Noise]

Definitely deserves some karma for that.

[sporsmaal2]

hey thanks guys
i love this site!

[sporsmaal2]

so what about a filter?
a band pass one would be ace
i found a lowpass, it looks well complicated

[Gordonjcp]

There are lots of filter designs out there.  Some are good, some are bad, and all are difficult to some degree. 

Personally I quite like the look of the Synthacon filter design.  I built a Korg early MS-series filter, but found that it wasn't terribly reliable or repeatable - very sensitive to minute changes in the components.  One of the big advantages of the Moog ladder filter design was that it was highly repeatable and just needed some well-matched transistors for good results.

Basically all these work by varying the current through a semiconductor junction to vary the R part of an RC circuit.  You can cascade stages and apply feedback to get the classic synthesizer filter sound, otherwise it's just a groovy tone control ;-)

[sporsmaal2]

here are some links to sites with lots of audio circuits that some of you may find usefull 

http://www.epanorama.net/schematicsforfree/Audio/Circuits/index.php

http://www.mitedu.freeserve.co.uk/Circuits/Audio/audio.html

http://www.synthdiy.com/  > a very good site with tons of info and stuff about synths

http://www.electronics-tutorials.com/oscillators/oscillators.htm

http://www.armory.com/~rstevew/Public/SoundSynth/00_PenfoldSynth/pench2.html

http://www.electricdruid.net/index.php?page=projects

http://www.aaroncake.net/circuits/

http://www.uoguelph.ca/~antoon/tutorial/xtor/xtor7/xtor7.html

http://members.lycos.co.uk/rsquare/viewthread.php?tid=11  > info about 555 timers

http://www.uoguelph.ca/~antoon/gadgets/555/555.html  > more about 555

http://www.musicsynthesizer.com/

http://www.uni-bonn.de/~uzs159/

http://www.kpsec.freeuk.com/index.htm

http://www.queencircuit.com/Audio/

there

have fun!

[sporsmaal2]

a lot of the more interesting circuits (for synth building anywayz)  come from here:

http://www.paia.com/manuals/docs/2720-buildamodular-article.pdf

it also contains lots of useful info about the different parts
its some instructions to build a modular synth from 1979

there is also a couple of other good ones from here:

http://www.paia.com/manuals/

the 3 at the bottom of the page