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Old 14th November 2002, 06:57 AM   #1
Rarkov is offline Rarkov  England
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Default Any advantage to Current Amplifiers?

Hi,
Before I really got into DIY audio and gained more knowledge about it, I saw a website shouting the pros of current amplifiers. I have not re-read the site, now I have more understanding but was wondering if there really any advantages to current amplifers?

What are your views?

Edit:
I forgot to leave the URL...Here it is: Current Amplifers

Thanks,
Gaz
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Old 14th November 2002, 07:09 AM   #2
halojoy is offline halojoy  Sweden
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Thanks Rarkov for the Link, it was new to me.
I will have look at what Gary Novak
has to give.
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Old 14th November 2002, 07:20 AM   #3
halojoy is offline halojoy  Sweden
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Default A current buffer Output Stage

this is what he uses
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File Type: gif current_buffer1.gif (4.2 KB, 409 views)
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Old 14th November 2002, 09:25 AM   #4
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Default Current etc

It should be clear that this is a voltage amplifier, because of the 100% local feedback in the output stage. Gain should be close to 1.

Whether there is any advantage in current-drive of speakers has been discussed elsewhere on this board.

But since this guy apparently doesn't know the difference between voltage and current amps anyway, I wonder about the usefullness of the rest of his arguments.

Jan Didden
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Old 14th November 2002, 10:57 AM   #5
Rarkov is offline Rarkov  England
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I wasn't able to find the thread you mention. Did it spawn off another topic as they so often do?!

Thanks,
Gaz
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Old 14th November 2002, 11:03 AM   #6
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Default Current drive

Jeez, not off the top of my head, I think it was in relation to damping factor and control of speaker drivers. I'll see if I can find it back.

Jan Didden
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Old 14th November 2002, 03:52 PM   #7
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"But since this guy apparently doesn't know the difference between voltage and current amps anyway"

It looks like a current amplifier to me, in the sense that the output current will be some multiple of the input current. In the same way that a BJT is a current amplifier.

I think what you are saying is that the input Z is all over the place. If this circuit were driven by a high Z current source then it would behave like a current amp.

On the subject of whether it matters whether it is best to control the output voltage to the speaker or output current, it is obvious the voltage must be controlled because of the way speakers are designed. Driving a speaker with a current proportional to the input voltage will not sound right. I know, I've done it.
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Old 14th November 2002, 04:14 PM   #8
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Jan, Gaz,

This is, I think, the thread Jan is referring to. Unfortunately it is a bit Gromanized. Thatís how it went from damping factor to output drive topologies. You can take a look if you want.

info on amplifier damping factor

Have fun,
Rodd Yamashita
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Old 14th November 2002, 08:59 PM   #9
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Quote:
Originally posted by traderbam
"But since this guy apparently doesn't know the difference between voltage and current amps anyway"

It looks like a current amplifier to me, in the sense that the output current will be some multiple of the input current. In the same way that a BJT is a current amplifier.

I think what you are saying is that the input Z is all over the place. If this circuit were driven by a high Z current source then it would behave like a current amp.
[snip]
Well, to me it is clear. This thing puts out (almost) exactly the same output voltage as the input voltage. Moreover, it does so irrespective of the load (within reason, of course). 10 Ohms, 100 Ohms, 100k Ohms, doesn't make any difference. This is the definition of a voltage source.

The output current is definitely NOT related to the input current in any way, but is only dependent on the load (and input voltage of course). Again, this is the definition of a voltage source.

The input Z is not all over the place, but is reasonably independent of the load. Vo=Vi means there is 100% feedback, so all the transistor gains are used to make the output voltage independent of the load -> voltage source. With a fixed input voltage, the output current will be whatever is necessary to maintain the same voltage at the output.

I don't see by what stretch of the imagination one could call this a current source.

Jan Didden

PS Someone above used the term "current buffer", which of course it is. But the designer specifically talked about "current drive of speakers", and that cannot be done with this circuit.
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