Obsolete parts… did I just waste $12?

[Blue Jinn]

Pretty sure I tried to do the 2181 deal and my notes related to that. My build was functional but not behaving--popping/frapping on pick attack.

If you eliminated R31, you'll need a 2180 that is pre-trimmed and there is no connection to pin 4. The 2181 are expecting bias there. Look at the design notes https://www.thatcorp.com/datashts/dn137.pdf which will show what pin 4 is for. That may or may not be your problem, but you are using the 2181 wrong. I want to put this compressor in an amp I'm building, and intend to go with 2180s and just omit those resistors. The trimmable VCAs have the lowest noise/THD specs, but this circuit doesn't allow for any trimming, so it doesn't make sense not to use the pre-trimmed. THe 2180A has superior specs to the 2159.

 

[comradehoser]

If you eliminated R31, you'll need a 2180 that is pre-trimmed and there is no connection to pin 4. The 2181 are expecting bias there. Look at the design notes https://www.thatcorp.com/datashts/dn137.pdf which will show what pin 4 is for. That may or may not be your problem, but you are using the 2181 wrong. I want to put this compressor in an amp I'm building, and intend to go with 2180s and just omit those resistors. The trimmable VCAs have the lowest noise/THD specs, but this circuit doesn't allow for any trimming, so it doesn't make sense not to use the pre-trimmed. THe 2180A has superior specs to the 2159.

I installed 2181C into the stock build and had popping/ frapping. I have a troubleshooting thread with a recording of it [edit: Here. My issue is dependent on the high expression/expansion knob]. Jumpered R31, aggravated the problem. The pedal behaves pretty much as it did before regardless of the presence or absence of R31.

2180, then?

 

[comradehoser]

This thread claims the 2159 is the lowest spec 215x series. https://groupdiy.com/threads/that-2159.2258/

If you look at the design notes for THAT 218x DN137, the Creamery is using a trimmable VCA like the 2181, but omits the trimming resistors in favor of a fixed resistance. It makes more sense to use the pre-trimmed 2180 and omit R23 & R31. There are three grades of both chips. Otherwise you could probably drop in a 2181C and leave it alone, See DN121.

The Coolaudio part is dirt cheap, and correlates to a 2181B. If it was me, I'd omit those two resistors and first try a 2180C. If that's not satisfactory, install those two resistors and and a 2181C. Or, you could plop a trimmer in there and use the Coolaudio part.

If the 2180C works, you could upgrade to the 2180A.

Like I said, I'd start with the 2180.

Am I right that cool audio only has the 2181 sub at $2.50?

Only 2180 vCA I can find is starting at $10 per chip. I want to fix this; I'm not sure I want to get into $20 worth of fixing based on speculation.