THAT 2181 Variants

[JMan]

I'm wondering if anyone can speak to the differences between the various THAT 2181 chips (2181a, b, c).  Given that the "A" version is often what is called for in builds that use this chip, and is twice the price of the others, I imagine there must be something, I just can't seem to find it.

Looking at the specs provided by Mouser for the A and B versions, everything is identical except for a 2nA difference in input bias current.  The datasheet is no more illuminating, as it gives a detailed explanation of the 2181 chip itself but does not seem to outline, as far as I can see, the differences between versions.

My guess is that it ultimately comes down to distortion.  That's the only comparison I can see on the datasheet -- the 2181A lists ~0.0025% while the 2181C lists ~0.005%, with no mention of the B version (maybe somewhere in between?).  Is that the distinguishing feature?  And if so, how meaningful is that difference in a typical application (say, an SSL-style VCA compressor)?  Honestly, I know it's terrible, but distortion figures are expressed in such low actual numbers sometimes that my brain has difficulty translating them into practical terms.    ;D

Anyway, thanks to anyone who wants to take the time to sate my curiosity!

 

[JohnRoberts]

Distortion is how they keep score and measure/quantify improvement in modern VCAs.

In dynamics processors the side chain gain manipulations are far more audible. Used for console automation the distortion floor may be considered significant by some.

JR 

 

[living sounds]

They're all the same chip, but selected for different specifications. The 2180 has guaranteed distortion values according to the A (best) to C (worst) designator without external trimming, while the 2181 is guaranteed to achieve the respectively given specs with external trimming.

Anyone not believing this can try and trim a 2180, they behave exactly the same as the 2181.