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 Forum index » DIY Hardware and Software
New DIY project - TOS polysynth :-)
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adamstan



Joined: May 23, 2008
Posts: 28
Location: poland

PostPosted: Tue Jul 16, 2013 11:39 pm    Post subject: New DIY project - TOS polysynth :-)
Subject description: A crossover between Polymoog and Polykorg
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Hello Smile

I've always wanted to have the Polymoog, however getting one isn't easy - and getting working one is even more difficult Wink, and that beast is HUGE. So I decided to build something similar myself. As with my first synth, this is mix of many designs. Currently I'm designing last boards, and going to order them today or tomorrow morning. They should arrive in two weeks, and then - soldering mayhem Twisted Evil Twisted Evil But, back to the design itself - what will it be?

- 61 keys
- Master oscillator section based on Polymoog - two VCOs driving two divide-down ranks using PLL
- Dividers built with CMOS counters - 4040 with diodes & 4024 for each note, like in TOG thread by AnalogCustom http://electro-music.com/forum/topic-45583-0.html&postdays=0&postorder=asc&highlight= - this is the biggest board Wink
- Waveshapers based on Polymoog too
- Digital envelopes and LFOs
- there will be 4 LFOs, like in Polymoog - one for each VCO, one for PWM and one for filter
- VCF & VCA from Korg PS-3100. Why? Because it has lowest parts count, that's why Smile
- Polymoog resonators and maybe some 4-pole master VCF at the output.

I will post current schematics when I get back home today. Here is waveshaper simulation done in falstad circuit simulator:
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Capacitors have to be selected for each note to provide consistent saw level & PWM range across entire keyboard.

The VCF/VCA modules will sit on small "articulator" cards, that will plug vertically into 5 motherboards (one for each octave). Each mobo will also have associated waveshaper and envelope card. So it will look like this:
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Green bars are the articulators, red one is waveshapers, and blue ADSR.

The nice thing about this design is that it will have no ASICs/proprietary parts - just off-the-shelf op-amps, CMOS and TTL cirucits. And a bucketload of transistors of course (almost 600) Mr. Green
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adamstan



Joined: May 23, 2008
Posts: 28
Location: poland

PostPosted: Thu Jul 18, 2013 12:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK - here are some schematics, for those who like looking at such awful things Wink
1. ADSR/LFO
Posted Image, might have been reduced in size. Click Image to view fullscreen.
2. Master oscillators/HFO
Posted Image, might have been reduced in size. Click Image to view fullscreen.
3. Frequency dividers
Posted Image, might have been reduced in size. Click Image to view fullscreen.
4. VCF&VCA-"voicecard"
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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xpmtl



Joined: Aug 10, 2007
Posts: 158
Location: Brussels, Belgium

PostPosted: Thu Jul 18, 2013 10:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Following this thread with much interest. Good job so far
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Taylor



Joined: Jul 13, 2006
Posts: 170
Location: us

PostPosted: Sat Aug 03, 2013 7:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Very interesting. Any chance you could post higher res schematics? The ones above are thumbnail size.
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Blue Hell
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PostPosted: Sat Aug 03, 2013 8:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Taylor wrote:
thumbnail size.


Click on them .. and then click on that again .. blows 'm up here beyond imagination Exclamation

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Taylor



Joined: Jul 13, 2006
Posts: 170
Location: us

PostPosted: Sat Aug 03, 2013 8:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Taylor wrote:
thumbnail size.


Click on them .. and then click on that again .. blows 'm up here beyond imagination Exclamation


For some reason for me this brings me only to

http://wstaw.org/m/2013/07/18/VCFVCA_png_300x300_q85.jpg

which is a 300p x 300p file. If I remove "_png_300x300_q85.jpg" and replace it with ".png I get the full file. Strange.

So is there a full voice card for each of the 61 notes? ....!!!!!

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adamstan



Joined: May 23, 2008
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Location: poland

PostPosted: Sat Aug 03, 2013 10:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Almost full Wink It looks like this:

- there are five motherboards, one for each octave
- on each of them there is one 12 channel waveshapers card, one 12 channel digital ADSR card and 12 VCFVCA cards, which I called "voice cards".

I've just received the boards from production house, and they are smaller than I thought - especially those voice cards are tiny - they looked bigger on the screen Wink


OTOH dividers board is huuuge compared to these Wink

Now I'm wating for parts to arrive.


04082013(001).jpg
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This image has been reduced to fit the page. Click on it to enlarge.

04082013(001).jpg


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adamstan



Joined: May 23, 2008
Posts: 28
Location: poland

PostPosted: Wed Aug 14, 2013 11:45 am    Post subject: Reply with quote  Mark this post and the followings unread

I started putting it together, and ran into big obstacle. The VCO doesn't oscillate at all Sad It just ramps up to +15V and stays there... And the weirdest thing about it is, that even shorting the timing capacitor (C102/C202) with wire doesn't bring integrator output down... The circuit behaves exactly the same when I remove capacitor and discharge transistor (T101/T201).

The HFO part works, producing 5V square wave @~2MHz.

I've made another test, and it seems that integrator output is stuck on +Vcc, but I don't know why... That rise or ramp I've mentioned before is just rise time of my PSU - I've connected oscilloscope directly to PSU positive rail and got exatcly same result as when it was connected to integrator output. Damaged chip? In both channels?
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adamstan



Joined: May 23, 2008
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Location: poland

PostPosted: Mon May 26, 2014 2:03 am    Post subject: Reply with quote  Mark this post and the followings unread

I've recently returned to this project after long break. I've managed to fix VCO/HFO, and now I have whole oscillator section working, with TOS outputs following master VCO frequency Smile

VCO wasn't working, because TL082 doesn't like to work on a single supply (U103/U203). Dave Luce used 3130 in this place in Polymoog. So I rewired this IC to split supply (+-15V) and put diode and pull-down resistor after comparator outputs, to block negative voltages. I've also replaced discharge transistors with ordinary NPN.

Next problem was, that even when I got VCO running, HFO wasn't following it. There was no signal on PLL return inputs (pin 3 of 4046). Why? Well, 4024 outputs are fully buffered, not OC, so pull-up resistors (R311/312/411/412) weren't enough to convert TTL levels to 15V, and 5V was too low to trigger 4011 gates powered from 15V. I had to add transistor there.
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adamstan



Joined: May 23, 2008
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Location: poland

PostPosted: Tue May 27, 2014 11:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've just tested the filter - it works Smile
http://www.youtube.com/watch?v=ZfIkoWUpIrE

Upper trace - square wave from divider, lower trace -"voicecard" output. I do some manual filter sweeps with and without resonance.
The high-pitched whine in background is crosstalk from VCO - it needs some proper decoupling Smile
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DES



Joined: Feb 28, 2003
Posts: 682
Location: New Jersey
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PostPosted: Sat May 31, 2014 8:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow -thats an ambitious project! I might have to dig out my Mostek TOGs . Knew I was saving them for a reason!

Good luck with the build!

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