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 Forum index » DIY Hardware and Software » PAIA Equipment
PAiA 3790 Stereo Chord EGG Remake
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stefanv



Joined: May 09, 2009
Posts: 17
Location: Moorefield, Ontario, Canada

PostPosted: Wed Dec 23, 2015 7:43 pm    Post subject: PAiA 3790 Stereo Chord EGG Remake Reply with quote  Mark this post and the followings unread

I recently became interested in the PAiA Chord EGG, a random flowing chord generator based on a 1970s top-octave generator chip. My application was a source of music in an alarm clock, but of course neither the kit nor the TOG chip are available any more.

I decided to undertake a redesign of the Chord EGG, using only off-the-shelf commodity ICs (such as quad op-amps). I stuck to the original architecture wherever possible, but started from scratch in other areas. The end-result is a Chord EGG sound-alike. It uses the same number of chips as the original (5), but they're all the same (TL074 quad op-amps).

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

I built it on a 7.7" x 3.2" piece of stripboard. If anyone's interested in building their own, there should be enough detail in this article I wrote:

Chord EGG 2015: Remaking a PAiA Classic

There's an audio sample at the end of the article too.

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Stefan Vorkoetter
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varice



Joined: Dec 29, 2004
Posts: 918
Location: Northeastern shore of Toledo Bend
Audio files: 29
G2 patch files: 53

PostPosted: Wed Dec 23, 2015 9:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool

I built a PAiA Chord EGG kit (and many other PAiA kits) back in the 70’s. I still have it Exclamation Oh, such fond memories... It is good to see that you are reviving this classic in analog hardware Very Happy

For those with a Clavia Nord Modular G2 or the free G2 Demo software, check this out:

http://electro-music.com/forum/topic-22930

And this topic:

http://electro-music.com/forum/topic-22782.html

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varice
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DES



Joined: Feb 28, 2003
Posts: 783
Location: New Jersey
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PostPosted: Thu Dec 24, 2015 11:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

I believe the original used the Mostek Top Octive chips, right? I still have 4 or 5 of those lying around....might be fun to cobble a chord egg together...

Can you select the key or is it totally random?

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Dave
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stefanv



Joined: May 09, 2009
Posts: 17
Location: Moorefield, Ontario, Canada

PostPosted: Fri Dec 25, 2015 10:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, the original used Mostek (or equivalent chips). I'd hang on to those as a retirement fund. Smile

In the original EGG, the chip is driven by an RC oscillator. I would be easy to make it tunable to let you select the key. But the circuit itself just cycles between the I, IV, and V chords (two inversions of the first) of whatever key it's tuned to.

Of course, you could have a bank of jumpers connecting the TOG to the rest of the circuit, letting you, for example, rewire it for a minor key.

In my remake, the oscillators are individually tuned, so of course it would be possible to retune to a minor key.

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