A synth for the 21st century keyboard project

[bod]

evening all!

I've come to the conclusion that after purchasing several of TH's books from Magic Smoke(via lulu) that i really should put them to good use!

having built a vartiety of things, soundlabs, XR VCO, a take on the SN Voice and a load of other modules from every one possible and designs of my own, i want to build something i'm really proud of next year and (try ) to work on one super project!! i'm also experienced on designing PCB's so there no issue with that side of things.
to be honest i'm more of a building addict, so its likely to go the same way as most of my kit, on long term load of one of my friends....

i should say that i've been thinking about this for a long time, and considering using lots of different options for the different modules from different folk and clones of vintage synths, but i kept coming back to the 21st century synth schematics. it looks brilliant on paper, and the 4 modules i've built from it have been hassel free and just brilliant to use.

i cant play the piano (or keyboards ), but in order to push myself further into doing this, i've taken piano lessons just to learn the basics... i've noticed its very different to using the piano roll on a squencer like ableton.

the intent is to take the modules from the 21st century synth and a cv keyboard controller (probably TH's) and build myself a patchable keyboard synth.

so, in the planning stages i've come up with a few questions, and i was wondering if you lot would mind chipping in with your take on things?

I plan on using the:

ADSR (possibly x2)
XR VCO (x2, maybe three if i can fit it in, one for hard sync duties, one for a normal vco and one for fun/sub octave duties/stuff)
VC Noise Source
LFO Deluxe
State Variable Filter
Sample and Hold
VCA
VC Phase Shifter (which i dont know if it would be over kill on a keyboard, but if it fits....)

i really like the XR VCO, and have one i built on strip board, and its never needed tuning since i built it. maybe i shouldnt over look the LM VCO and try it out first.
incidently, i do plan to build them all on strip board first before sending anything off to be made up for PCB's.

first issue is pcb design. i cant decide on individual modules with pots mounted one the pcb, which would allow me to use them to build a modular if it all proves a little too much... or if i make a final decission on what i want in there, and build it all in to one long single pcb?
if i do that, or even if i dont, do i use slider pots as per your usual keyboard synth, or pots?
now i know that this one is ultimately down to personal preference, and to be honest, i like my knobs.... as much as i love the look of vintage synths with sliders, i always felt they are kind of fiddly to use, i like the clean steady sweep up and down you can get with pots.

i think i may have answered my own question, but opinions would be nice!

then theres the keyboard. 3 or 5 octaves? now i'm a little short on spare space for this, so i'm edging to 3 octaves for size, that would be 50cm wide for the keyboard, which would give me more than enough room for everything i think, plusan octave shifter will give me all i need.

front panel and enclosure design.... well that can just wait a few months yet!!!

so what do you think, am i mental?

answers on a postcard please, or below... and huge thanks to Thomas Henry and everyone else who designs and shares wonderful synths for us all to build!!


cheers,

bod.

[modius13]

Everything I've heard everywhere says that two ADSRs are the way to go in a monosynth like this... one for the filter and one for the VCA. and I think separate boards with the pots on one edge so you have a bunch of "cards" that just slot into the control panel.

[richardc64]

[State Machine]

I have lots of this item in stock and ready to ship. This keyboard controller I designed is indeed, as Richard pointed out, an integrated version of Thomas Henry's digital keyboard with a bunch of functions added. It started out as an example of how to do a small scale logic conversion to programmable logic but grew into a nice little project to make your own personal, high quality, Monophonic CV/MIDI keyboard.

Here is a picture of the a stuffed PC board and connection to a 5 octave Fatar Keybed assembly.

Bill

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[bod]

@ modius13: yeah, it was suggested by a few other folk that a dual adsr would be a better idea, so i think i'll go down that route. the module is one of the simplest (imo) in the book so wouldnt be an issue (unlike the LFO which i'm not looking forward to bread boarding!!!), but a very good suggestion, cheers!

@ richardc64 & State Machine: i'd completely forgotten about that project! midi implementation was always on the cards, but i was just thinking about the doepfer midi/cv which i have a couple of anyway, or creating something on an avr for keyboard and midi control, but IKC would be a sweet all in one solution and far less work involved! veeeery tempting!

and no, moog destruction isnt on the cards so its a 3 or 5 oct keyboard from fatatr.... do they do a 4 oct key bed? might have to check that out.

i'm just reproducing the schems in eagle at the moment, but i'm a bit concerned the lite/free version isnt going to give me a big enough pcb size for the lfo, so it my have to be spread over 2. the things freakin huge!!! or i might have to try out kicad instead.

cheers for the suggestions, i'll update whenever i get anything of worth done.


bod.

[magman]

bod,

You can buy the Fatar keyboards from Deopfer, here:

http://www.doepfer.de/home_e.htm (navigate to the prices page).

And yes, they do do a 4 octave version.

For the 21C LFO, why not have a look at the Magic Smoke TH-301 LFO, which is an improved version of the TH 21C design. You wouldn't have to worry about designing a complex PCB then. I'm in the process of building one at the moment and the PCB is excellent quality.

Regards

Magman

[bod]

yeah, doepfer appear to be the only eu suppliers for fatar, and i bought a keyboard from them for a previous project myself and a friend were working on, but thats bolted into a case now. thanks for the tip on th 4oct keybeds though! never bothered to check that out.

are there many major changes to the lfo in the TH301? my works access wont allow me to look at the magic smoke site.... maybe the thinks its something dodgy!

are the pots mounted on the pcb?

cheers,

bod.

[magman]

The Magic Smoke design is very close to the TH 21C circuit, I believe there are a few changes that have been discovered from practical implementation of the circuit.

All controls (apart from presets) are mounted off board (as there are 5 of these, that's not unreasonable) along with a good collection of switches. The board itself is 101mm by 127mm.

Regards

Magman

[bod]

nice one, cheers magman! i had a look when i got home last night as well. i think this lfo is going to take up a lot of panel real estate!

now i need to find a comedy sized bread board to test this out first!

[modius13]

Is there a place to get Fatar keyboards in the US? Or possibly something comparable? I found the things on Doepfer's site but I don't know how bad shipping one of those keyboards to the US from Germany would be...

[magman]

I believe Analogue Haven stock them as a part of their Doepfer stock, here:

http://www.analoguehaven.com/doepfer/oemdiy

But the link wasn't working last time I tried.

Regards

Magman

[State Machine]

This will get you directly to the keyboards I use the 5 octave unit and it works perfectly with my IKC controller.

http://www.analoguehaven.com/doepfer/mke/

Bill

[modius13]

Thanks for the link Bill... I swear I poked through that section before but couldn't find the keyboards.

How many octaves would you recomend for a bass synthesizer?

[State Machine]