DIY Poly ARP

THeff · Last edited by THeff on Sat Sep 21, 2013 3:15 pm; edited 9 times in total

Well, after building my DIY ARP-2600 clone in 2010 I have had a great desire to build a polyphonic synth with ARP qualities. I mainly wanted something that would allow me to create chords and pads sounds and use my previous mono synths for lead sounds. I figured that four notes simultaneously would probably be the best I could hope for, without being impossibly complex. I have rolled the idea around in my head for quite a while and finally after finishing my analysis of the Simmons SDS-3, I decided to dive in.

Throughout the building I changed and adapted it for maximum efficiency. So here is the result which is not quite finished but enough to prove the concept.

The modules include the following:

(4ea) ARP 4027-1 cloned VCOs (my PCB design from the 2600)
(4ea) Sub Oscillator boards that divide by 1.5, 2, 3, and 4 (Roman Sowa’s design, my PCB)
(4ea) ARP 4035 Filters (AndR1960’s PCB design)
(1ea) Quad MIDI to CV board (ACX Synth’s design and PCB)
(8ea) ADSR Boards, one for each filter, and one for each VCA (Electric Druid’s design, ACX Synths’s PCB.
(2ea) Dual VCA boards (Thomas Henry’s 21st Century design, Fonic’s PCB)
(1ea) LFO Board (Electric Druid’s design, Frequency Central’s PCB)
(1ea) Quadrature LFO (Yusynth design and PCB)
(2ea) Dual Gated Slew boards (Yusynth design and PCB)
(2ea) Audio Mixer boards, wired for stereo, with L,R panning (Yusynth design and PCB)
(1ea) Bergfotron +/- 15 V Power Supply (Bergfotron design and PCB)
(4ea) ARP Explorer voice boards (my own design, tested, but not added yet)

Laying out PCBs is one of my least favorite things so where I could, I used designs from the web. I don’t mind actually making the PCBs themselves, so all of the boards were made at home.

I wanted the whole synth to be compact, not long and narrow. I also don’t like having the knobs to close together so as a result each module is a very strange format. They are double height MOTM size. Right now the panels are labeled with cheesy white labels, but at some point I hope to redo the panels with cool graphics.

I normalized the patching so that it can be played with just a MIDI keyboard cable, but the wiring bordered on insanity! There are 114 ¼” jacks that allow for patching if desired.

About halfway through the build process I decided to add Yusynth’s Quadrature LFO and this really expanded the sound. The four phases of the LFO can modulate the pitch, PWM, or filters individually.
Each VCO/VCF/VCA channel has it’s own input to the Stereo Mixer and can be panned anywhere from Left to Right. I usually set it so that VCO1 is Left, VCO2 is just Left of Center, VCO3 is just Right of Center and VCO4 is Right. This creates a really great stereo image effect, especially when the quadrature modulation is added.

I also added the Electric Druid LFO which provides eight different waveforms and can be synced to phase 0 of the Quadrature LFO if desired.

I decided on using eight of the Electric Druid ADSR boards because they have low parts count and allowed the VCA and VCF envelope parameters to be adjusted together simultaneously and yet they are gated individually.

I finished the Poly ARP synth about two weeks ago and after playing it the first day I realized that tuning the VCOs can be painful. I remedied this by adding a 4PDT switch that has a Normal and a Tune mode. In the Tune mode all of the VCOs are connected to channel one of the MIDI2CV output. This makes it easy to tune the oscillators to the same note and then switch back to Normal mode.

So there you have it, a four note Poly ARP Synthesizer with 92 knobs, 34 switches, and 114 jacks.

I would like to thank everyone below for sharing their designs on the web, which helps others expand their ideas and make cool music!

THANK YOU:
Roman Sowa
AndyR1960
Alain Coupel
Tom Wiltshire
Rick Holt
Thomas Henry
Matthias Herrmann
Yves Usson
Jorgen Bergfors

Regards,

-THeff

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Golliwogs Cakewalk - Poly ARP 2013.mp3

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Recorded in one pass with only reverb added.

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Ragtime - PolyArp 2013.mp3

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Recorded in two passes, 1st for the left hand, 2nd for the right hand.

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Ragtime - PolyArp 2013.mp3

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Broadwave · Posted: Wed Sep 18, 2013 4:26 am Post subject:

I was going to say something smart... but I'm too busy picking my jaw up off the ground!!!

Quite simply... amazing Very Happy

gdavis · Posted: Wed Sep 18, 2013 11:31 am Post subject:

That's great! Makes me more anxious to finish my own poly project.

The sound of Golliwogs Cakewalk totally reminds me of Yaz. The slightly out of tune nature of Maple Leaf Rag conjures images of the old out of tune saloon pianos Very Happy

THeff · Posted: Wed Sep 18, 2013 3:45 pm Post subject:

Thanks Andy! The front is not much to look at but I am very pleased with the sound and overall function.

Thanks GDAVIS, I first heard Golliwogs Cakewalk by Tomita and always liked it, he is such a master. I have to say the honky tonk piano sound really surprised me, and the bass notes sound cool in the car.

I added another MP3 recording that I played with the other night. It was recorded with multiple passes so that I could try out many different timbres. It has a lot of processing like delay and reverb as well.

All of the sounds are from the Poly ARP except the drums.

Regards,

-THeff

Elecmusi PolyArp 2013.mp3

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diablojoy · Posted: Wed Sep 18, 2013 5:42 pm Post subject:

ORSM !
I will think of something better to say eventually
too busy drooling for now.

elmegil · Posted: Wed Sep 18, 2013 9:00 pm Post subject:

Great choices of demo music too Very Happy

Impressive as always Smile

Paradigm X · Posted: Thu Sep 19, 2013 2:45 am Post subject:

wow, just wow.

Cool

richardc64 · Posted: Thu Sep 19, 2013 11:32 am Post subject:

MOST impressive. Agree about the demo music, too.

I'd like more info on what you used for 4-voice midi2cv.

THeff · Posted: Thu Sep 19, 2013 8:08 pm Post subject:

Thanks diablojoy & elmegil,

richardc64 here's the link for the MIDI2CV:

http://www.acxsynth.com/midi2cv/midi2cvfr.htm

I have built several of these MIDI2CV boards and they work really well. Alain Coupel (ACX) was very helpful and sent me new firmware when I had problems with notes sticking

I have added a few more pictures of each module before they were installed in the case.

I normalized the patching but still needed to be able to remove and work on each module. I used DB15 connectors to connect the various patching to the other modules inside the case.

I typically don't use the white molex connectors that many DIYers use for plugging in the PCBs. If I had it to do again I would have put connectors on every board. It would have made final assembly much easier.

-THeff

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diablojoy · Posted: Thu Sep 19, 2013 10:33 pm Post subject:

xpmtl · Joined: Aug 10, 2007 Posts: 162 Location: Brussels, Belgium

one word : WOW

That's quite an amount of work you achieved there.

Love the audio demos, that synth sounds really great.

Wish I had the courage to embark in such an odyssey Smile

isak · Posted: Tue Oct 01, 2013 8:20 am Post subject:

Hi THeff

Great piece of work youv got there.
Congrats, looks and sounds great!

BTW when you said that the acx midi2cv got stuck, you mean the notes got stuck like forever?
If yes, why do you think they got stuck?
Im asking cause in the prosses of building the same board and I wander what was your findings?

cheers,
Isak E.

THeff · Posted: Tue Oct 01, 2013 5:51 pm Post subject:

Thanks XPMTL, The DSP software guys look at this and say, why?

Thanks isak, I don't remember the exact scenario, I just remember that in polyphonic mode it would miss notes when I tried to play chords and hang on certain CV values. It was not permanent and would change on power cycle. I emailed Alain and he just sent me a new firmware load. I would assume he has updated the website with the latest version.

-THeff

isak · Posted: Tue Oct 01, 2013 11:40 pm Post subject:

Thanks for the input.

Yesterday I assembled your 2600 VCO design.
I needed to change solder head to very thin, you killed me with the small thin pads man Laughing

today I'll add pots, jacks and finally hear the sound of your vco Smile

Q...
The 2 x 100pF in the VCO, should they both need to be poly or ceramic will do the job?
I put 2 x mica's overthere cause I didn't knew if they impotent or not.

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.

thank you THeff.

sneakthief · Joined: Jul 24, 2006 Posts: 569 Location: Berlin

An upgraded version of the ACX midi to cv converter is available here:

http://www.modularsynth.ru/en/diy/acxsynth_midi2cv_firmware/

Among other improvements, it fixes the note-hanging issue.

isak · Posted: Wed Oct 02, 2013 3:44 am Post subject:

sneakthief · Joined: Jul 24, 2006 Posts: 569 Location: Berlin

Yes, the new firmware is 100% compatible.

More info (you may need to register for the forum to see this topic):
http://www.muffwiggler.com/forum/topic-93855.html&sid=b258d71c2d62d644e3269899fc967806

isak · Posted: Wed Oct 02, 2013 4:05 am Post subject:

thank you very much sir, thats help a lot!

THeff · Posted: Wed Oct 02, 2013 6:15 am Post subject:

Hi isak,

The VCO PCB looks good. Sorry about the small pads, those are the Eagle default sizes and I know some of them are small. Glad to see that you made the board. I have built seven of these VCOs so far with no issue. The only real critical capacitor is the 680 pF timing cap. I used poly styrene from Mouser.

BTW, I got some PCB drill bits off of Ebay and they came from Israel and they work great. They are used and re-sharpened but still work well. The guy sells a lot of them there.

Sneakthief, thanks for the info! I didn't know that anybody else created firmware for the Midi2CV, I will have to try it.

Also, if anybody is interested, Radio Shack is closing out their Vellemen kits and you can get the PIC programmer for $5.99. It is limited to what is in stock. It's a deal just for the parts if you don't need a programmer. I believe it came with a 16F627 PIC as well.

Regards,

-Tim

elmegil · Posted: Wed Oct 02, 2013 6:24 am Post subject:

There are a few of us who want to poke with that firmware. I have not tested the 5.4 version from the Muff's thread, but the stock version has an issue with Velocity in Mono mode as well. When I get to that I will likely post to that thread with any success I may have trying to resolve it.

The issue is that legato playing resets the velocity to zero. I did experiment last night with running the velocity to a S&H triggered by the MIDI2CV and it works a bit better, but still has issues.

None of this is meant to be critical of Alain or Hex, this is a great module. But like any software, bugs always arise... Smile

THeff · Posted: Wed Oct 02, 2013 9:56 am Post subject:

Just an update on the Radio Shack Vellemen PIC Programmer.

If you want to get this as your only programmer, look closely at it.

I just noticed these things in the user manual.

1.) The Vellemen programming software only supports Windows up to XP.

2.) Also, the stupid thing is that the manual says that it will NOT support a USB to serial cable. So, if your computer does not have built-in serial ports (like most recent computers) I guess it will not work. Maybe they have more recent software on their website that overcomes these problems, but I have not tried it.

I was attracted to it because the normal price was $59.99 and I bought it for parts at $5.99.

Regards,

-Tim

isak · Posted: Wed Oct 02, 2013 3:14 pm Post subject:

isak · Posted: Thu Oct 03, 2013 12:44 am Post subject:

THeff · Posted: Thu Oct 03, 2013 8:43 am Post subject:

Hi isak,

Thanks for the info on the Ebay PIC programmer. I actually have several PIC programmers. The one I use the most is the USB programmer from ME Labs. I just posted the Radio Shack stuff in case anyone was interested.

-Theff

THeff

I found this midi file on my computer from somewhere and thought it would be a challenge to perform it on the Poly ARP.

I put it together today and all of the sounds are from the Poly ARP except the drums and a little piano.

I used JH's Triple Chorus on some of the strings and pad voices. I also used JH's ARP Phase Shifter with the white noise. It's 8 minutes long so that's why the file is big Rolling Eyes

See if it rock's your windows... Shocked

-THeff

EXSTASIA - PolyARP 2013.mp3

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