madbeanpedals::forum

Projects => Tech Help - Projects Page => Topic started by: midwayfair on November 21, 2012, 06:43:44 PM

Title: "Ocean" hissing in a klone [solved]
Post by: midwayfair on November 21, 2012, 06:43:44 PM
One of my klones (an Apis) started making some "ocean" hissing that I don't remember it having when I first built it. Thermal noise I guess? (Enclosure's grounded and the leads are all short, so I don't think it's RF.) It's definitely in the circuit as turning down the treble or volume makes it quieter.

Any ideas what could cause it and what I can do about it?
Title: Re: "Ocean" hissing in a klone [solved]
Post by: midwayfair on November 26, 2012, 01:09:13 PM
Just putting the "solution" here in case anyone else runs into this issue:

Audio probe told me IC1 was fine and that the noise was appearing in IC2 at Pin 1. Cut the chip out and soldered in a socket. Tried a bunch of different chips, all of them made noise except the OPA2134 and TL072/62.

The solution is "don't substitute a BJT op amp for a JFET op amp without using a socket." I had used a 5532 for IC2 thinking I was being clever because it's usually a little "cleaner" sounding -- that's a no go here. And apparently I just didn't notice the noise before. This is the second circuit I've run into this problem with recently. Sometimes you'll get a circuit that used a TL072 just because and a 4558 or 5532 will work just fine. This is not one of those cases. The OPA2134 sounds excellent here, though, a much more noticeable difference than elsewhere (probably just its better performance at higher voltages).
Title: Re: "Ocean" hissing in a klone [solved]
Post by: jimmybjj on November 26, 2012, 01:19:21 PM
Thanks for posting the solution! The will save a lot of learning for me in the future :)