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Old 27th March 2012, 07:44 AM   #2211
mikelm is offline mikelm  England
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Quote:
Originally Posted by hahfran View Post
But I think the idea of only current amplification all over should have audible benefits .
An amp without a VAS ? you'll need very low impedance speakers !

really do not understand ur logic here.

I thought that it was well understood, in the final analysis, that BJT's are in fact voltage controlled with finite resistance whereas FETs are voltage controlled with almost infinite resistance.

You seem to be attempting to wrap up your preference for BJTs in some kind of logic - but all I'm hearing is that you have a preference for BJTs.
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Old 27th March 2012, 07:52 AM   #2212
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by mikelm View Post
An amp without a VAS ? you'll need very low impedance speakers !

really do not understand ur logic here.

I thought that it was well understood, in the final analysis, that BJT's are in fact voltage controlled with finite resistance whereas FETs are voltage controlled with almost infinite resistance.

You seem to be attempting to wrap up your preference for BJTs in some kind of logic - but all I'm hearing is that you have a preference for BJTs.
No BJTs are not voltage controlled. This is not the place to explain the physics of pn junction, though.
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Old 27th March 2012, 07:59 AM   #2213
mikelm is offline mikelm  England
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Oh ok then, must be the text book I read was wrong.
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Old 27th March 2012, 08:26 AM   #2214
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by mikelm View Post
Oh ok then, must be the text book I read was wrong.
Physics of pn junctions cannot be explained in terms of classical physics. But this cannot be a subject for DIY audio.
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Old 27th March 2012, 08:58 AM   #2215
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by mikelm View Post
An amp without a VAS ? you'll need very low impedance speakers !

really do not understand ur logic here.

I thought that it was well understood, in the final analysis, that BJT's are in fact voltage controlled with finite resistance whereas FETs are voltage controlled with almost infinite resistance.

You seem to be attempting to wrap up your preference for BJTs in some kind of logic - but all I'm hearing is that you have a preference for BJTs.
A current amp can be equated to a current controlled current source CCS.
The CCS forces a current which is a linear multiple of control current. No need for Vas.
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Old 27th March 2012, 04:37 PM   #2216
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Hi hahfran

That's completely wrong approach. All power amplifiers have to follow voltage gain linearly according to frequency. Why? Because all the speakers's sound pressure is linearized to input voltage at their terminals. Impedance curve is much more unlinear and has no correlation to sound pressure curve even at driver's resonance frequency.
Current amplifier would make a speaker sound completely wrong because SPL would follow impedance curve and that would be a real mess. We have to make amplifier's gain linear to input voltage and to have output impedance as low as possible (high damping factor). Power supply and numerous BJT output pairs enables high current capability. Basics of audio ...
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Old 27th March 2012, 05:22 PM   #2217
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by Lazy Cat View Post
Hi hahfran

That's completely wrong approach. All power amplifiers have to follow voltage gain linearly according to frequency. Why? Because all the speakers's sound pressure is linearized to input voltage at their terminals. Impedance curve is much more unlinear and has no correlation to sound pressure curve even at driver's resonance frequency.
Current amplifier would make a speaker sound completely wrong because SPL would follow impedance curve and that would be a real mess. We have to make amplifier's gain linear to input voltage and to have output impedance as low as possible (high damping factor). Power supply and numerous BJT output pairs enables high current capability. Basics of audio ...
No it is the correct approach because B*l*I= d2/dt2+ d/dt+....
that is the mechanical motion equation.
All one has to do is to feed a current amp with the output of an "analog computer" ( 3 integrators and one adder ) to cancel out all of the mechanical
constants such as mass compliance...and electrical constants such as resistance and inductivity of the voice coil. So far only swedish co ACE employs this approach. It gets a bit simpler with positive feedback from a resistors in series with the speaker.
of course the real speaker does not follow a simple second order de but it is a simple and easy to implement approach.
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Old 27th March 2012, 05:28 PM   #2218
hahfran is offline hahfran  Germany
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I am not telling anything new here. Of course one has to map the mechanical stuff onto an electrical schematic and the whole trick is to give the amp a complex output impedance which is exactly the reverse ( the mirror image in complex plane) of the speaker's electrical equivalent. It took a very long time until makers of active speakers adopted this most simple idea but now all of them do it.
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Old 27th March 2012, 06:02 PM   #2219
hahfran is offline hahfran  Germany
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Back to the roots
provided the model provided by Bob Cordell is correct and the schematic is correct
I get an op of 1.8 amps drain current .
Is that correct?
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Old 27th March 2012, 10:36 PM   #2220
maxente is offline maxente  Romania
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Hi LC !
How much slew rate does this version has?
Thanks again for this wonderful design !
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