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adaptive output impedance?
adaptive output impedance?
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Old 9th October 2011, 12:58 PM   #1
SashaV is offline SashaV  Canada
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Default adaptive output impedance?

Does anyone know of any amplifier that employs adaptive output impedance such as the one in PSI Audio amplifiers?
PSI AUDIO: Technology AOI:Adaptative Output Impedance System composed of a movement detection of the moving coil
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Old 9th October 2011, 03:11 PM   #2
KSTR is offline KSTR  Germany
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It's not clear whether they used a true independent sensor in the transducers and string that up in a classic control loop, or wether they just used the voice-coil itself as its own velocity sensor, whose linearizing effect can be increased beyond the damping available with shorting the coil, by applying more effective damping at LF (via a synthesized negative Zout that cancels part of the Re of the drivers) while increasing it at HF, or in general by shaping the impedance to whatever makes the driver behave best. For the LF part, think of it like more local degeneration used, in the transducer. Target response is simply dialed in by EQing.

As they don't emphasize the first which they surely would if they really did it that way, we may assume they did the latter (or something close to it)... which is not a new concept... but its is exactly what I try to do, too, and I'm completely sold to it. We should build approbriate amps for each specific raw driver, then active speakers can make a real difference.

Last edited by KSTR; 9th October 2011 at 03:14 PM.
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Old 9th October 2011, 03:21 PM   #3
Michael Bean is offline Michael Bean  United States
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Maybe something like this?
Variable Amplifier Impedance

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Old 9th October 2011, 04:15 PM   #4
SashaV is offline SashaV  Canada
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They definitely used voice-coil itself as velocity sensor, and I would like to try this concept in actively amplified speakers.
Since I am not good at designing electronics, do you know of any such kits or even commercial products (PSI Audio does not sell suck amps but use them in their own active speakers)?
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Old 9th October 2011, 05:45 PM   #5
jcx is offline jcx  United States
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the simplest method is to use "mixed feedback" to sythensize negative resistance at your amp output

effectiveness depends on matching/cancelling a portion of speaker DCR with the negative resistance

but the amp + load has to be stable, the amp's negative output R always shunted by a smaller real R load
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