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DIY top octave synth project
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Cfish



Joined: Feb 24, 2016
Posts: 477
Location: Indiana

PostPosted: Mon Mar 21, 2016 12:59 pm    Post subject: DIY top octave synth project
Subject description: My take on the PAIA OZ
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I always wanted a paia OZ, but could never find one at a price I could handle. I recently found the schematic on line. After about a month looking on eBay I found a set of boards from a Hammond transistor organ that had the top octave IC. 20 dollars for the set of boards and the top octave IC was in a socket. That made things a lot easier.

I used the PAIA schematic. But left out the capicitors and transistors for the gate and trigger signal.

Added a phase shift circuit and a PT2399 delay. It turned out great.

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

Here is a link to a link to a video with a little about it:
https://youtu.be/CInvZ5QZ7Cg
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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Mar 21, 2016 3:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm curious what it sounds like...
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PHOBoS



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PostPosted: Mon Mar 21, 2016 4:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

check the youtube video Wink

I watched it after watching the Easy DIY synth project and it sound pretty good, actually better than I expected.
Why doesn't my synth sound like that, it is a squarewave right ? could it be beacuse of the filter or did you add some
equalizing on the output.

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Cfish



Joined: Feb 24, 2016
Posts: 477
Location: Indiana

PostPosted: Mon Mar 21, 2016 4:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

It is a square wave. The pt2399 delay circuit has a lot of low pass filtering in it.

I am loving that IC. It really made that project shine.

I will try to find a link to the schematic I used
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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Mar 21, 2016 11:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

I ordered 5 pcs of PT2399 about two weeks ago, they will be here soon Very Happy
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Cfish



Joined: Feb 24, 2016
Posts: 477
Location: Indiana

PostPosted: Fri Mar 25, 2016 12:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here is a link to the pt2399 delay schematic I used. http://www.valvewizard.co.uk/smalltime.html

It's got a lot of low pass filtering. I tried it with less filtering and it gets really noisy fast. High frequencies seem to do strange things in the IC.

I left out the FET and used a switch instead.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Sat Mar 26, 2016 2:32 am    Post subject: Reply with quote  Mark this post and the followings unread

I think you have to figure out how fast this chip is sampling, then construct a pre-sampling filter (a low-pass filter at which the cutoff frequency is sample frequency / 3 >> nyquist theorem) and use multiple chips to obtain larger delay times. (these chips will cost you next to nothing)
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Cfish



Joined: Feb 24, 2016
Posts: 477
Location: Indiana

PostPosted: Sat Mar 26, 2016 5:30 am    Post subject: Reply with quote  Mark this post and the followings unread

The little bit of experience I have had with the pt2399 has Ben trial and error.

I found the filtering in the data sheet application schematic to be inadequate for my application of a delay.

I experimented a lot on the breadboard, and found I didn't like anything better than the filter capacitor values in the small time delay schematic.

If I did the calculation correct it can handle a lot more high frequency. It just does not have a sound that I liked when doing it.

Gets very digital sounding quick.

I'm looking forward to seeing what you think Grumble.
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Grumble



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PostPosted: Sat Mar 26, 2016 10:45 am    Post subject: Reply with quote  Mark this post and the followings unread

I have read somewhere that up to a delay time of 150 mSec, noise levels are acceptable, after that there will be more noise which is logical because the memory is only 44kbit. (and I don't even know if it's used in parallel (8, 10 12 bits?) or serial)
So if you need a longer delay, simply put another PT2399 in series! until you have the delay you need, with a triple bonus: better frequency response, less noise and you can use the taps for a more natural echo/reverb.
In my todo list there is a multiple PT2399 unit ( 3 or 4) where the delay is controlled with an arduino and digital controlled potentiometers so I will have a delay of about 50mSec up to 3 or 4 times 150 mSec (450-600mSec).
Imagine the phaser you can make with this setup Rolling Eyes
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