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Original mono EHX Polychorus investigation

 
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NickS
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Joined: 14 Jan 2008
Posts: 9309
Location: Nr. Basinggrad, UK

PostPosted: Wed Jan 23, 2019 2:08 pm    Post subject: Original mono EHX Polychorus investigation Reply with quote

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Someone found it and asked me if I had any suggestions about why his wasn't working.
Mk 1 Polychorus, from the web (a site in Greek if I remember)

Enquirer's Polychorus

Windows and the browser are arguing about jpg metadata so I might replace those pics with PNGs to get them consistently the right way round. First step is to ID the components. Hang on, someone already did an EchoFlanger overlay that's been archived here.
Schematics for the near-identical Echoflanger:.
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Note, these are copyright EHX but contain devices that can no longer be obtained so I don't see any commercial value to them. They are posted here in the interests of education.


What I get from the schematic is:
1. When the unit is powered on, I would expect the LED to be lit and the buffered guitar signal should be available at the Direct out. The LED goes straight to the supply pins of the SAD1024A bucket-brigade-delay (BBD) chips. If this is not lit either the 15v supply has shut down or something drastic has happened with the SAD1024As. The Bypass switch should cause the buffered guitar signal to appear at the Effect Out.
2. When in Filter Matrix mode with Blend engaged, only one BBD is used, IC4 - which is the one nearer the rotary switch; for the signal path to Effect Out to work practically everything has to be working except the SAD1024 nearest the edge of the board, IC3, half of IC1 and the low-frequency oscillator (two of four op-amps in IC3). If no output on Effect Out I would switch off and allow power to decay, carefully remove IC4 (observe antistatic precautions) and jumper pin 15 to pin 11; if the signal now appears there's something up with the BBD or clock.
3. When in Flange mode again only IC4 is used and the LFO is engaged.
4. In the other modes both BBDS are used.
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NickS
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Joined: 14 Jan 2008
Posts: 9309
Location: Nr. Basinggrad, UK

PostPosted: Wed Jan 23, 2019 9:27 pm    Post subject: Reply with quote

The EchoFlanger PCB is different, though..
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