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Old 20th November 2002, 10:42 AM   #1
diyAudio Member
Join Date: Oct 2002
Location: Bulgaria
Default TDA 7294 -negative outlet resistance ?!!

Hi !
I wrote somewhere that negative outlet resistance of Amp. It will decrease the interinflexion distortshans on the loudspeqaker.Is It truly ..?!!
I tried make TDA-7294 to works as a source electricity ,he sound become cleaner but ther is wheeze .
What is wrong,how improve it ?
Let me know if you alredy did it or where cane I get a help .
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Old 20th November 2002, 11:03 AM   #2
halojoy is offline halojoy  Sweden
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Join Date: Nov 2002
I am usually not understanding "negative resistans".
To me that say a material conducts current
Must be some better way to describe the thing.

TDA7293 is almost the same IC.
He is working now with some TDA7293
This Thread:
Qs about a two-channel quad paralleled TDA7293 amp...
Discuss with him.
Wheeze could come from Input or from Feedback.
Or from Power-Supplies or from Grounding.
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Old 20th November 2002, 12:12 PM   #3
diyAudio Member
Join Date: Oct 2002
Location: Bulgaria
Default I'm sorry!

Sorry for my bad English I 'll try to describe what I mean to sey:
I am trying to join the loudspeaker in feedback (negative feedback by voltage ) so loudspeaker drives the Amp.If loudspeaker's magneto resist rise Amp. also rise.
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Old 20th November 2002, 12:30 PM   #4
halojoy is offline halojoy  Sweden
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Thumbs up Interesting Amplifier Technique

So the Current going into Speaker is Proportional to the input Voltage
The speaker is instead of feedback-resistor.

TDA7294 is not made for this. Not many amplifiers in the world are!

It could work, but it would be better
to make a special Amplifier
that is made for it.

Your thinking is right! (we think same)

I have only read ONE design in 20 years, with this technique.
It is a low power amplifier.
The Current Sensing Resistor has to be low in value
and not inductive
and you can use a buffer to change the impedance.
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Old 21st November 2002, 03:00 PM   #5
diyAudio Member
Join Date: Feb 2002
Location: Belgium
You guys seem to mix two different things. There are amplifiers with a negative output resistance and there are transconductance amplifiers.

Amps with a negative output resistance have a specially arranged feedback so that if you measured the impedance conventionally you end up with a negative number. The idea is to cancel the DC resistance of the voice coil and wires. Take a look here

Transconductance amps deliver a current that is proportional to the input voltage, they have a (almost) infinite output impedance. There is a thread about them on the analog forum. THE reference work on this was done by M. Hawksford. It can be found in the JAES. There has been a smaller amp described in EW&WW. The first is 75W, the second 10W.

Both types are intended to drive the speaker direcly, no crossover! Hope this clears a bit.
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Old 21st November 2002, 07:19 PM   #6
halojoy is offline halojoy  Sweden
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Thanks, Havoc
it is time for me to do some studying again
to increase knowledge
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