abbey road d enfer

Re: summing large amounts of channels.
« Reply #60 on: June 29, 2020, 12:06:39 PM »
I'm sure I have shared this before but back last century I used the improved howland current pump,
Litt seems to be a tad inconsistent as to what an "improved" Howland pump is; is it just the one with the current sense resistor, that reaquires compensating the PFB resistor for the current sense resistor, or is it the version with the voltage follower, that uses equal values for teh PFB and NFB paths? My inpression was the latter...

that I first saw in a national applications manual back in the 70s 
I discovered it in RTS intercoms, where it constituted the basis of their party-line system, allowing many beltpacks to be connected on a single line.

but with impractical values for audio use (they used 1M resistors trying to get highest possible output impedance).
Actually, the absolute value of the resistors is not as important as their matching. In fact, with 1k resistors it is still possible to achieve a dynamic impedance of about 200k. There may be other consequences, though.

For today's TMI, early this century I discussed with a senior engineer at THAT corp
Would that be Gary Hebert? I spoke to both him and Les Tyler about this.

** ICs are fabricated with subcomponents that get connected together by the final metallization layer, kind of like how traces on a PCB connect discrete components together...  ICs are like an upside down PCB but without the board.
It's the culmination of the PCB concept. "Printed" circuit boards are actually etched; metallization is a real positive print.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: summing large amounts of channels.
« Reply #61 on: June 29, 2020, 03:17:36 PM »
more significantly buffer the inputs to the improved Howland. The varying source impedance from the pan pot position imbalanced and degraded the current sources output impedance. The fully loaded bus noise floor was lowest with all pan pots hard panned left or hard right

The active pan also has the benefit of better left-right isolation or "offness" (90dB) and a closer to desired pan law.   
Note to self:  Don't let c**ts wind you up


Re: summing large amounts of channels.
« Reply #62 on: June 29, 2020, 04:58:21 PM »
Seeing op amp schematics with the output connected somehow to the + input always gives me the jitters. I know it is common practice (JLM VU buffer for instance) but I just cannot get used to it. Seems to me to be contrary to nature.



'The only people not making mistakes are the people doing nothing'


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