ZPSX Technical Queries

[ChrisM]

Having just finished  a ZPDX I have two questions...

1. The build docs mention how R31 (2K2) can set the delay time/range. This is on page 8 of the build doc. I can't possibly see how this resistor would set the delay time. It is setting the gain of that particular filter op-amp stage. This R31 must surely be a type no?

2. My feedback pot increases the feedback well too quick  I start getting run away oscillation too early for my liking. Would increasing the 5K1 resistor (R41) cure my issue?

Thanks
Chris

[jkokura]

1. It should be R48, which is 470K.

2. Yes, R41 can be adjusted to a higher value. Also, you could try an A50K pot instead as well.

Jacob

[ChrisM]

Cool beans, just as I expected.

Thanks


Edit: Went with 12K. Probably could have gone with 15K or 18K. Self oscillation starts at 2 o'clock now.

[jkokura]

I like my oscillation to start pretty much when you have the knob dimed. So, I would go with 22-47K depending on where that would start. Thanks for the heads up.

Jacob

[ChrisM]

Ya I'll play with it more before finalizing a value. I just know that 5K1 was way to small for me. It would be interesting to hear what other ZPDX owners have to say abou the feedback control range.

The build doc makes note of how the tape mode may be louder compared to the other modes but I'm not finding that at all. The deep mode is the one that stands out the most and is the loudest. It's by far the simplistest filter mode with just a low pass filter so it has the least signal loss making it louder compared to the others.

I am thinking of putting a resistor in parallel with C46 so I get a voltage divider in conjunction with R39. I was thinking 10K for about 20% attenuation in deep mode.

[ChrisM]

Why does tape mod have diodes in one op amps feedback loop?

Looks like they would be clipping. Though they are limited by that resistor in series with them I could still see them clipping. Is this to add a bit of grit and dirt that is associated with tape delays?

[ChrisM]

Changed the feedback resistor to 24K.