DOD - 490 Phasor [gut shots]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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jamjuice
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Post by jamjuice »

DOD 460 circuit board
DOD 460 circuit board
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DOD 460 traces side
DOD 460 traces side
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OdgeDOD460underpot1.jpg
OdgeDOD460underpot1.jpg (125.97 KiB) Viewed 881 times
OdgeDOD460Underpot2.jpg
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blindtoe
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Post by blindtoe »

DOD 490.pdf
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I found the 490 schematic. Here it is.
If you cannot open it let me know. :shock:

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culturejam
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Post by culturejam »

Got Digitech to send me the schematic. The one in the previous post is incomplete. Use this one instead. :thumbsup

dod490.pdf
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Yonatan
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Post by Yonatan »

Looking at the schematic, I'm having some trouble understanding a few things. Can someone please help me? I've perfed and breadboarded several effects by now, and looked at many schematics, but sometimes the "factory" schematics give me trouble. I guess that I've gotten spoiled by the "modern" schematics around here that have everything spelled out explicitly, use "standard" 3pdt switching, use separated sections with connection points (e.g. for power, lfo, etc.)

1. It's not shown explicitly here, but does 9v and GND get connected directly to each TL022?

2. Similarly, does 9v and GND get connected to directly to each CA3094?

3. What is the convention of showing IN->9VDC->OUT all connected to each other, with the 9VDC in between them?

4. How does the bypass work here? I read somewhere that the 490 "sucks tone" in bypass mode, but from the schematic, it looks like it is true bypass. O.k., it's not the standard modern 3pdt switching, but isn't the IN here connected directly to the OUT when the effect is switched off?

5. And this is really more of a circuit analysis question, but normally I've gotten used to seeing that in schematics where opamps are used with a single power supply, then the power section creates a vref that gets used for biasing the opamps. But I don't see that here. So how are the input/output opamps in the aduio signal (not lfo) being used in this case without a vref?

Yonatan
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Post by Yonatan »

Can anyone explain my question about the lack of vref in the opamp buffers, even though it's a single supply setup? This is really the main point that's giving me the most trouble understanding, compared to many other circuits I've seen.

For homework, I went ahead and breadboarded the buffer sections, just to prove to myself that it's passing audio :)

(Now if only I had those CA3094s . . .)

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