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Building a new synth - Suggestions welcome
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defog



Joined: Aug 24, 2011
Posts: 113
Location: Philadelphia

PostPosted: Fri Feb 03, 2012 9:15 am    Post subject: Building a new synth - Suggestions welcome Reply with quote  Mark this post and the followings unread

I'm currently building a minimoog style cabinet (slightly wider) for an old 44 key j-wire keyboard I got for free. It's not going to be a minimoog, but something similar as far as knob size, layout and general vibe. So I'm brainstorming on what I want to stuff into it.

Shout out for your favorite VCOs, VCFs, VCAs, ADSR Generators, LFOs, Noise, S&H, etc. I would love to hear what some of your favorites are so I can consider them. I'm quite partial to most of the MFOS designs, Roland filters and ADSR, Minimoog VCOs and Filter.

My only requirements are that it is built with 100% inexpensively, easily obtainable parts.

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tokyomatik



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PostPosted: Fri Feb 03, 2012 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

wait till april to buy a minibrute..... Wink
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frequencycentral



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PostPosted: Fri Feb 03, 2012 11:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Not to blow my own trumpet too hard, but:

Roland ADSR: http://www.muffwiggler.com/forum/topic-49355.html

Most excellent VCLFO: http://www.muffwiggler.com/forum/topic-49661.html

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defog



Joined: Aug 24, 2011
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PostPosted: Fri Feb 03, 2012 12:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Freq, the links didn't work. But I found your ADSR 140 board, only the images are all missing. I'd really like to take a look at that one.

And a VCLFO sounds like a lot of fun. I'm looking for more unique features like that for this build. I don't want it to sound anything like my SH-101, Soundlab Ultimate, OB-Xa, or Prophet 08.

I'd like the VCF to have a 24dB LPF. Band and hi-pass would be fantastic addition to that too, if anyone has any suggestions for something that fits that bill.

A VCO with a variable waveform/waveshaper would be fun too, like the MicroMoog.

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frequencycentral



Joined: May 25, 2008
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PostPosted: Fri Feb 03, 2012 12:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, they work for me, maybe you need to be logged into muffwiggler to see them?

The Roland ADSR is also here:

http://electro-music.com/forum/topic-24627-25.html

The VCLFO is also here, I'm just finishing up the build docs before I post them:

http://electro-music.com/forum/topic-51579.html

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Blue Hell
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PostPosted: Fri Feb 03, 2012 1:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

frequencycentral wrote:
Ah, they work for me, maybe you need to be logged into muffwiggler to see them?


There seems to be no need for that, I can see them alright.

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defog



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PostPosted: Fri Feb 03, 2012 2:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmm, working fine for me now too. Not sure what was going on earlier. Nice information on the ADSRs.
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fluxmonkey



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PostPosted: Fri Feb 03, 2012 7:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

ASM...
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defog



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PostPosted: Fri Feb 03, 2012 11:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

fluxmonkey wrote:
ASM...


That looks amazing, only it looks like I'll have to wait for ASM-3.

I think I want the full experience of building something from individual components and coming up with my own switching/routing scheme. This is definitely going to be more like a modular synth, pieced together from my favorite components, minus the patching part.

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defog



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PostPosted: Fri Feb 03, 2012 11:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Does anyone have any schematics or designs for adding on a sub-oscillator to a VCO? I was originally thinking of building 3 of Ray Wilson's VCOs, but I think I could definitely do with just 2 if I had the option of a sub oscillator on one of them. On two of them would be even more disgustingly amazing, with octave switching, like two SH-101s.
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LektroiD



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PostPosted: Sat Feb 04, 2012 1:40 am    Post subject: Reply with quote  Mark this post and the followings unread

tokyomatik wrote:
wait till april to buy a minibrute..... Wink


Are you serious? That thing is a heap of crap. Single oscillator and a filter that sounds like it's being dragged through a rubbish dump backwards... Were you really taken by their crappy marketing video?
http://www.youtube.com/watch?v=T7O946lG7Ik

If you want a proper 3 oscillator synth, check out the Macbeth Micromac. Serious piece of kit.
http://www.youtube.com/watch?v=V8B3e038tCc

...Anyway, back on topic. I was thinking of building some kind of minimoog style synth, once my modular is finished. I planned to use all my left over and duplicate PCBs that never made it to the modular.
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defog



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PostPosted: Sat Feb 04, 2012 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Agreed about the minibrute. I didn't hear a single nice sound out of that thing in the entire video. Sounds like it has a permanent distortion on it.
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jordroid



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PostPosted: Sat Feb 04, 2012 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Sounds like a really fun project, i'm in the planning stages of something similar myself.

For interesting filter modes, i have been having a lot of fun with a setup similar to what Jurgen Haible describes here http://www.jhaible.de/jh5/jh5.html with two LPFs you can get a bunch of cool bandpass and phaserish sounds by mixing them together in or out of phase and by mixing in some unfiltered signal.

Jurgen also has schematics for a "filter scanner" here http://www.jhaible.de/additional_schemos.html using one 24dB/oct filter and one state variable filter, lots of nifty sounds in there.

Another fun VCF setup that gets you way more than just your standard LPF sounds is a low pass and high pass filter in series, that way you can get a variable band pass as well.

For a really wild LFO i have been messing around with the LFO part of Jurgens variable slope filter project. It's a big circuit for an LFO, but you get delayed vibrato and dynamic depth FM if you normal one of your VCOs to the "aux" input, pretty useful options that go beyond the common monosynth options. Schematic is here http://www.jhaible.de/varislope_filter_phaser/varislope_filter_phaser.html

The electric druid LFO that frequency central has been messing with is also lots of fun, and it's a pretty tiny circuit for what it does. His ADSR on a PIC works well also and is a small circuit.

Keep us posted!

jordan

:edit: almost forgot, my favorite VCO is the Ian Fritz one from this thread http://www.electro-music.com/forum/topic-28713.html it is the most stable and easiest to get in tune over a wide range out of the ones i have tried, and does not require anything that you can't get at mouser.

:edit some more: for sub octaves i like the Scott Stites "wave thing" from this thread http://electro-music.com/forum/topic-33149.html way more fun to have more waveshapes than just a 50% square like you get with a standard 4013 divider, and not too big to build. Since the design only uses half of the logic chips you can make two of them in pretty much the same space as one.

Cheers!
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Dave Kendall



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PostPosted: Sun Feb 05, 2012 3:39 am    Post subject: Reply with quote  Mark this post and the followings unread

If you can find room, maybe cram two different filters in there. A Moog ladder style LPF and a 12dB SVF with LP, BP and HP outputs (like the MFOS one) would be a useful combo.

Also - don't stint on the LFOs. A lot of monosynths suffer from having only one - SH101, SCI pro-one and others. A couple of extra SQR/TRI LFOs can really help - clocking a sequencer or the Sample and Hold, or sweeping PWM or hard sync, or adding vibrato for example.
A CGS58 utility LFO http://www.cgs.synth.net/modules/cgs58_lfo.html is ideal for adding a couple of simple LFOs to the main VC LFO, and is a simple build with no unobtanium parts. It can be easily modded to go down to very slow rates if needed - notes how to do this are on the page.

I've been planning a sort-of-similar MIDI rack synth for far too long now.... (*cough*).......... Embarassed'

Good luck with it!

cheers,
Dave

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defog



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PostPosted: Sun Feb 05, 2012 9:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Dave I'm in total agreement with the LFOs. I'm thinking at least 3.
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defog



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PostPosted: Sun Feb 05, 2012 2:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

What about an even simpler LFO design?

Posted Image, might have been reduced in size. Click Image to view fullscreen.[/img]

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Dave Kendall



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PostPosted: Mon Feb 06, 2012 7:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi defog.

That diagram is pretty much the same as the circuit in the National semiconductor LM358 datasheet, and is designed for a single rail supply.
It's certainly a simple and neat design, but I don't know how well it would work on a dual rail supply with +VCC/2 being GND and GND being -V.
I suppose it would be fine as it is, if you only needed positive voltages from the LFO, but that would make some uses like vibrato tricky.
Might be worth trying it on a split rail supply..... Maybe someone smarter than me can comment on whether this would work?

cheers,
Dave

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jumunius



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PostPosted: Mon Feb 06, 2012 8:59 am    Post subject: Reply with quote  Mark this post and the followings unread

defog wrote:
What about an even simpler LFO design?


You could try the Magic Smoke 8kLFO -- it's really simple to build with a very wide range. I added a switch to choose timing caps (C1 = 330pf for going further into audio range) and use it as either an LFO and as a triangle wave to feed a ring modulator -- maybe that routing option would be useful to you too. Not voltage controlled but might work for a utility LFO or two.

And then Tim Servo expanded this into the LFX with some interesting waveshapers.


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Dave Kendall



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PostPosted: Tue Feb 07, 2012 4:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi all.

I got a reply from Jim Patchell on the [sdiy] list to a question about the LM358 datasheet VCO, and he's cool with it being posted here for info for us all.
Cheers to Jim for that... Cool

Quote:
Yes, you can run it on split rails, BUT, and it is a big BUT...

Because of the nature of the LM358/LM324, you may find that this causes more problems that it may solve. The common mode input range of the LM358 includes ground, and the designer of this VCO took advantage of this fact. Also, you will note, that the control voltage range is from 0 to 2 * VCC - <some>. If you were to run it from +/- 15 V, well, you can see the problem.

I used this VCO in the first synth I built, which was the circuits for the Paia 2700. I did not like the VCO circuit that was in the magazine (Paia later made some major improvements on it), and when I built it discovered it worked a lot better. The supply rails in the 2700 were +18, +9 and -9 volts. I ran the VCO on 0 to +9, and with the 18 volt rail, I was able to provide the VCO with all the voltage it needed to go through its tuning range.

My recommendation is to use it in the single supply mode. If need be, use level shifters to get the signal swings (using op-amps running on split supply rails) to get what you need.

Oh, yes, and this VCO is a true VCO. That, of course, has its own problems. This VCO will never be anything more than a linear control VCO.

-Jim


cheers,
Dave

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defog



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PostPosted: Tue Feb 07, 2012 11:35 am    Post subject: Reply with quote  Mark this post and the followings unread

That magicsmoke LFO looks great Jumunius. Thanks for sharing it. I'll breadboard it up tonight and test it out on my SoundLab to see how it sounds.

Would there be any potential issues with using two different VCO designs? I'm worried about tracking and how they'd play off of each other, but I think it would be more fun to have McCartney and Lennon singing together than a doubled-up track of McCartney.

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nicolas3141



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PostPosted: Tue Feb 07, 2012 1:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

That LM358 datasheet circuit has been designed around an assymetrical supply with the CV referenced to the negative supply. If you have a symmetrical supply available you would be better to go with a more conventional approach which really just means rearranging those four resistors and the transistor on the CV input side. For symmetrical supply and CV referenced to 0V that resistor network would be:
- 50k between the CV-in and the transistor collector.
- 50k between the transistor collector and the -ve in of the integrator op-amp.
- 100k between the CV-in and the +ve in of the integrator op-amp.
- 50k between the +ve in of the integrator op-amp and 0V.
- transistor emitter connected to 0V.

That would then be pretty similar to my VCLFO circuit - http://electro-music.com/forum/phpbb-files/vclfo_139.jpg discussed half way down http://electro-music.com/forum/topic-32372.html

Nicolas
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defog



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PostPosted: Tue Feb 07, 2012 8:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Great information everyone. Thanks a bunch.

I think I've got a few of my design choices narrowed down. Just a few more to choose.

Here are my current thoughts:

2 MFOS VCOs with Complimentary Scott Stites Sub Oscillators
1 Minimoog VCF
2 Roland 100m ADSRs
1 MFOS 1v/Oct Keyboard Bus controller

I'm still considering which dual VCA design to use, VCLFO, a possible secondary VCF (probably the MFOS 12db/oct) and utility LFOs. The electric druid LFO & ADSR looks nice due to the sheer simplicity of it. I also considered messing with the arduino, but then I'd have to deal with the voltage and stepping issues associated with using a micro controller, as well as the interaction with a normal VCA. But a single micro-controller could replace a lot of complex analog circuitry. I may just hack together some crude code and test out some envelopes and LFOs to see if it is even an option. At the least I should be able to muster up some usable as well as interesting utility LFO shapes and some quasi-S&H stuff out of it. For the non-traditional stuff, I've played around with the code on Beavis Audio's site feeding into the CV input on Tim Escobedo's Q&D VCF design. But that's simple stuff when you're not dealing with a bipolar power design. I'm still a bit of a hack when it comes to this stuff, so bear with me if I'm saying anything that sounds like nonsense. Smile
http://www.beavisaudio.com/projects/DSWF/

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defog



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PostPosted: Mon Feb 27, 2012 9:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

So I've started making some progress on my synth project. I've got most of the minimoog style case built, minus the sheet metal hinged panel with wooden ends/trim and some oil stain I still have to do on it. I've narrowed down the following modules so far:

2 MFOS VCOs
2 Sub Oscillators - 4024 Logic Based
1 YuSynth Minimoog VCF
2 Roland 100m 140 Envelope Generators - Frequency Central
1 Roland 100m 130 VCA - Frequency Central
1 MFOS 1v/Oct CV keyboard Bus
2 Magic smoke LFOs
MFOS Power Regulator/Filtering section

I've transfered, etched, drilled, and started populating most of the boards. I've started on the sub oscillators, 2 LFOs (see board layouts below), MFOS 1v/Oct CV Bus, VCA, EGs, VCF and the power filtering section. I just have to do a big parts order from mouser to get some of the remaining parts, as well as ordering the 2 VCO boards from MFOS (didn't want to deal with the two-sided etching).

Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.

I'm still going to add in another VCFLO most likely, another simple 13700 based VCA, and possibly a second 12db VCF with bandpass ability. I got pretty much all the pots, switches, transistors, and IC sockets from Tayda. I'm very satisfied with them, having got the order in about a week, all for around $35. Can't beat $0.02 ic sockets (even if they're not the best). Got some of the more difficult to source transistors and ICs off eBay already. Now I just need the free time to get more finished!

EDIT - STAY AWAY FROM eBAY for VINTAGE IC PURCHASES - See the 2nd page for an explaination to that one. I also updated that Magicsmoke layout and it is confirmed in a separate thread

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aladan



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PostPosted: Mon Feb 27, 2012 10:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

For something a little unusual and flexible you could also have a look at Ken's (recently re-released) Serge Dual Universal Slope Generator: http://www.cgs.synth.net/modules/cgs114_dusg.html I also found this page helpful in understanding what it can do: http://www.carbon111.com/alphabet1.html

Unless you're building a modular system you'll want to think carefully about exactly how you incorporate it into your design though - a lot of the power (and fun) of the DUSG is in how you interface the generators (both to each other and to other modules.)
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defog



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PostPosted: Tue Feb 28, 2012 6:49 am    Post subject: Reply with quote  Mark this post and the followings unread

aladan wrote:
For something a little unusual and flexible you could also have a look at Ken's (recently re-released) Serge Dual Universal Slope Generator: http://www.cgs.synth.net/modules/cgs114_dusg.html I also found this page helpful in understanding what it can do: http://www.carbon111.com/alphabet1.html

Unless you're building a modular system you'll want to think carefully about exactly how you incorporate it into your design though - a lot of the power (and fun) of the DUSG is in how you interface the generators (both to each other and to other modules.)


Thanks for the link! I forgot to mention that I'm also building a ribbon controller into it that runs across the wooden bar above the keyboard. Using a Spectral Symbol membrane pot. I'll be running it into the Keyboard bus CV converter, using the keys to trigger notes like how the old moog ribbons worked.

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