The infamous PT2399 noise - What's acceptable?

[theundeadelvis]

I'm curious to know if I've always gotten bad batches of PT2399's or if they are inherently noisy? All of my builds using the PT have an annoying amount of hiss (I've built a couple Rebotes and a Little Angel chorus). My setup is pretty much dead silent, so when I kick on one of those pedals it's pretty noticeable (sounds like hiss from a high gain amp). I know others have mentioned noisy PT's before, but I'm wondering what's actually normal? Am I being too picky? Or am I doing something wrong? Thanks in advance!

[merlinb]

In this very recent thread:
http://www.diystompboxes.com/smfforum/index.php?topic=91535.20
It is noted that the Little Angel suffers some hiss because it uses the 5V rail as the reference voltage for the rest of the circuit. The PT dumps lots of noise onto that rail, which gets amplified a lot by the mixer stage.

Also, once the delay resistor goes above about 20k, the quantization noise gets extremely bad. You need heavy-handed filtering to try and get rid of it. Easiest mod is probably to increase the cap between pins 13+14 of the PT, or simply to avoid long delay times!

[theundeadelvis]

Thanks for the link merlinb. I think I'm talking about something different though. In that topic they seem to mainly be focusing on noise that exists at higher delay times. The noise/hiss I'm referring to is always there, even at minimum delay times. If you set the delay to the minimum, and switch the pedal on, you instant hear a constant hiss. I'm just not sure if this is normal or not.

[merlinb]

Thanks for the link merlinb. I think I'm talking about something different though. In that topic they seem to mainly be focusing on noise that exists at higher delay times. The noise/hiss I'm referring to is always there, even at minimum delay times. If you set the delay to the minimum, and switch the pedal on, you instant hear a constant hiss. I'm just not sure if this is normal or not.

Yes, the noisy 5V supply causes hiss all the time if it is used for Vref. Long delay times just layer more noise on top of that.

[theundeadelvis]

Thanks again merlinb! That's the answer I was looking for.

[slacker]

Pull out the PT2399 and see if the hiss goes away or decreases, if it does then at least some it is caused by the PT2399. Any hiss that is  still there it's coming from somewhere else in the circuit.