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Are all amps being built wrong?

The power amplifiers that drive our loudspeakers are mostly built as a low impedance voltage source. They have always been ... but why?

Loudspeakers have a (greatly) varying impedance over the frequency range. A current drive amplifier would eliminate the issues that stem from this varying impedance, and at the same time make discussions about esoteric speaker cables that strive for optimal R, C, L superfluous. Although there still would be these un-measurable ’this (very expensive) cable sounds better’ debates and opinions ... and that’s OK, that’s part of the fun. :)

So ... why are amplifiers not built as a high impedance current source?

This is an interesting read: https://www.current-drive.info/
rudyb

Showing 9 responses by holmz

holmz's avatar
holmz
2,328 posts
 
It is proportional to current.
Just they shove it across a resistor and use voltage amplification from the microphone.

On the output side. the driver is not very linear to current.@rudy It was all cool into the cable impedence was mentioned. 
holmz's avatar
holmz
2,328 posts
 
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**As we all know our speakers suffer from very low sensitivity,,,and the music consequently is only heard in bits and pieces,,,we need alot lot more power to drive our Wilson's, Vandersteens, Thiels,. Tektonics, Magnepans**

BS…
My 100W SS and then the 100W tunes powered my Vandersteens fine.Or maybe nit the PSE died 16 years in, and the VTLs 15 years later, and the latest one and a NAD before that worked fine.
I would not trade them except for a 36 year new version. And even then maybe not.
But the OP has a point about current.
Speakers with a more uniform impedance, would get a more uniform current at a fixed voltage. Maybe there is something in it?Or
We fix wild impedance swings with a current source amp? 
holmz's avatar
holmz
2,328 posts
 
PS, db Volts is calculated this way:

db = 20 x log( V original / Voltage now) 

So doubling the amplifier voltage = 6 dB louder in both voltage and sound pressure level (SPL) so long as everything is not over driven. 

Technically dB(V) is 10log(V)
Since power is V*I… and with a constant impedance is also equivalent to V^2/R…Then we use dB(W) as 20Log(V).
(I am pretty sure of it?)
holmz's avatar
holmz
2,328 posts
 
Is a phono cartridge a current device or a voltage device?And what about a DAC?
holmz's avatar
holmz
2,328 posts
 
@atmasphere 
Running zero feedback is a nice way to insure stability. What is the output impedance of your amp?

I was talking to a fellow yesterday that said that the feedback of the Prima Luna was too high.

Do you have thoughts on that?
holmz's avatar
holmz
2,328 posts
 
If one was to use a DSP, then (I think that) all gets normalised to be right whether using a voltage or current source?


Room correction in modern systems would be doing the same thing I think.
holmz's avatar
holmz
2,328 posts
 
Speaker drivers are designed to work best when fed with a voltage source.

I am only sure that this is true is the impedance is flat.

Since the equation for magnetic flux is based upon current, then one could argue that it is the current that is producing the force in the motor.

Speakers which means drivers and crossovers are also designed to work properly with a voltage source.

There are advantages and disadvantages of driving a speaker driver with a current source or a hybrid but to make it work the overall speaker must be designed from the ground up for it.

^That^ is a statement, and sounds like an opinion.

No DSP is not a substitute. It has to happen at the driver/amp interface.
Anything that linearises and equalises the output makes for a more linear system. (Yeah it’s a tautology) However if the speaker was a constant impedance and the, then it would play flatter. You can alter the incoming signal’s voltage so that it plays flatter out of the speaker as a system. One can do this for both current source or voltage source amplifiers and end up with a flatter speaker response curve.

holmz's avatar
holmz
2,328 posts
 
The business part is that, IMO, it is unfair and unrealistic for one to think that they can sit for hours on end in a brick and mortar store, take up a salesperson's time comparing amps, ... and then not to buy something.
  • The sales people are there for that purpose.
  • And the profit margin is designed to account for that.

The alternative is to buy gear and sell it, doing the demos in one’s own home. Or just trusting the internet to provide information on what one is looking for. And that later part is bit problematic with confirmation bias.
holmz's avatar
holmz
2,328 posts
 
Thanks @bifwynne , one problem is that I am 1000-2000 miles from most shops. But I do an appointment with one in 3-1/2 weeks.


My ARC gear has also worked fine… for many decades.
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