Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

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Re: transient test - Part II

Posted by 13th Duke of Wymbourne on July 31, 2003 at 14:46:20:
For another follower twist how about measuring the difference between follower output and input voltage and subtracting it from the input. This could be done quite easily by multiplying the measured difference voltage with a transconductance and simply add that gm to the gm of the preceeding voltage gain stage. I tried this in simulation and it worked nicely, for example at a given output power the third harmonic distortion at the follower output is -60dBc (0.1%). At the follower input the third harmonic is -80dBc (0.01%). Add the differencer/subtractor and the situation reverses - the 3HD at the follower output is now -80dBc and at the input it's -60dBc.
This was discussed somewhat over at diyaudio.com (see link) sparked by patents held by Bruce Candy of Halcro. This technique probably predates Halcro but it's likely they use it. One intriguing possibility is that it should be possible to implement such a scheme so that it can be easily disabled and you could compare the sonic qualities of with vs. without.
John & Charles - you must have seen this, if you haven't tried it yourself. What do you think?
Regards
13DoW