THAT 2181 without distortion trim

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saint gillis said:
How should we set up our circuit if we don't want to trim the THD TRIM on a THAT 2181, should we just leave pin 4 not connected?
Why would you want to do that? Cost?

And what about the same thing with a cool audio 2181?
You must add the 51 ohms resistor at least, but you're left with a VCA that has significant distortion (compared to a trimmed one or a 2180)

 
abbey road d enfer said:
Why would you want to do that? Cost?
The cool audio is much cheaper yes.. And also availability, for instance you need to build something in the week, and your parts supplier only has 2181s for instance..

For some synth stuff distortion is not a problem.. I recall trimming thd on 2181s for a gssl and I think the thd was not bad even untrimmed, but I might be wrong, it was a long time ago.
 
saint gillis said:
The cool audio is much cheaper yes.. And also availability, for instance you need to build something in the week, and your parts supplier only has 2181s for instance..

For some synth stuff distortion is not a problem.. I recall trimming thd on 2181s for a gssl and I think the thd was not bad even untrimmed, but I might be wrong, it was a long time ago.
THD with untrimmed 2181 is a kind of lottery. In most not too demanding applications, it's acceptable.
But why not implement the symmetry control? It's just a trimmer and a resistor...
 
Back to the original post.
You need the 51R because the V2181 (number not withstanding) documentation would imply it's a THAT 2151 clone, so read those data sheets and documentation.
The THAT 2181 has this resistor built in and has better matched transistors and is just better!
Don't want to trim........use the 2180x then.
 

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