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14 minutes ago, davewantsmoore said:

Voltage controlled amplifier exist for nothing more than convenience.... it is not what any smart person would go to if beginning with a blank sheet of paper.

 

Unless the person was designing an amplifier meant to work with any off-the-shelf passive loudspeaker. Or designing an active loudspeaker costing less than $20k ;)

 

 

 

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I hate to say it and I’ll say it once; “stop linking marketing BS”.    Do some research and look at how some of the most the respected designers and you’ll see how to design something that can be a “s

@JkSpinner did your original question get answered? the thread seemed to go in multiple directions...   possibly not - especially at high volumes Most of the below has been said above

That's just how you see it and wish for it to happen. Unfortunately no matter how much you wish for it, I'm quite sure that apart from perhaps some exceptional examples, won't be happening any time so

44 minutes ago, davewantsmoore said:

 

Voltage controlled amplifier exist for nothing more than convenience.... it is not what any smart person would go to if beginning with a blank sheet of paper.

 

 

Here's a comment on 'current amplifiers' from an amp designer:

 

Just about all loudspeakers which are designed for SS are set up for voltage drive, that is, a voltage source as the amp.  This accommodates the back emf which is produced by the moving magnet coil.  Pass has done some current amps, sometimes described as current source amps, but they are only suitable with specialist drivers, like Lowthers, which is pretty the same as a tube amp.  The benefit of SS amps is damping factor - so control over bass, with prodigious power.

 

You can design a SS amp to measure current for fb and such an amp is designed for balalaika amp guitars.  It is done to simulate a tube amp, particularly with a very high impedance tube like a pentode.  Such amps give a very tubey sound, delicate, but no sense of real power.  In truth, most people would not like perfect current feedback because it is 'wimpy' and the balalaika guitar amp uses a combination of current and conventional voltage fb.  Current amps need to use a very stiff, low compliance voice coil/cone to sound good, to maintain mechanical control over the excursion because the amp does not have a low impedance, that is, it does not have a high DF.

 

I bolded what sprung out at me as the vital issues.  :)

 

Andy

 

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Basically you need a matched pair of current amp with the speakers it was designed for in mind. Excepting the case of active speakers, why would any manufacturer make an amp that only suits one speaker and vice versa? Voltage drive is here to stay.

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1 hour ago, davewantsmoore said:

Correct.

 

 

Sorry OP - Most people will consider this off topic  (it's very related to impedance.... but a bit far out from the question which was being asked)  :) 

 

My loose interpretation of it is, simply an extension of what Bruno has said loudly for a long time.   Feedback isn't bad..... unless it is used poorly (it's a powerful tool, with great responsibility, etc).    The whole simple argument of "current drive" is the question of what is it that we are trying to control.    The voltage?  No (it's borderline irrelevant) .....  the current is what is relevant.

 

Well designed voltage feedback... is great and all (better than badly designed)..... but trying to control the wrong thing is quite daft.

 

Voltage controlled amplifier exist for nothing more than convenience.... it is not what any smart person would go to if beginning with a blank sheet of paper.

So if I was (hypothetically) designing a DIY active speaker with off the shelf components, where would I get a current drive amp and how would I ensure it worked well with the speakers?

 

 

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22 hours ago, Steffen said:

Unless the person was designing an amplifier meant to work with any off-the-shelf passive loudspeaker.

That's precisely what I mean by "convenience".    So amplifier designers and speaker designers can be different people.   Daft.

 

22 hours ago, Steffen said:

Or designing an active loudspeaker costing less than $20k ;)

Cost has nothing to do with it.     The $1 speaker in your mobile phone is just as applicable.

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21 hours ago, sir sanders zingmore said:

So if I was (hypothetically) designing a DIY active speaker with off the shelf components, where would I get a current drive amp and how would I ensure it worked well with the speakers?

 

There are few I know of "off the shelf"....  having it "work well" with the speakers is not different to "normal".  In that you EQ drivers to your target responses (regardless of whether using filters before or after the amplifier).

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22 minutes ago, davewantsmoore said:

That's precisely what I mean by "convenience".    So amplifier designers and speaker designers can be different people.   Daft.

 

They can be the same people if they want, it doesn’t really matter. Customers want to mix and match components, so there have to be (more or less) standardised interfaces between them. Those interfaces happen to be defined in terms of voltage, and response to voltage signals. You can get proprietary all-in-one solutions that don’t care about these interface conventions, or even mention speaker and amplifier specifications. BlueTooth speakers, or Apple Homepods, for example. But see below. They don’t play in the same ballpark. 

 

24 minutes ago, davewantsmoore said:

Cost has nothing to do with it.     The $1 speaker in your mobile phone is just as applicable.

 

Are we still talking about home stereo? Because in a home stereo setting, a $1 mobile phone speaker will sound like $1, at best.

 

The idea of all-in-one lock-in doesn’t seem to be palatable to most people investing in a home stereo setup, unless the gamble is worth it by promising huge advances in sound quality. Hence the Kii-style $20k+ price tags.

 

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22 hours ago, andyr said:

  It is done to simulate a tube amp, particularly with a very high impedance tube like a pentode.  Such amps give a very tubey sound,

 

Off topic, but these days I believe the way to go is modelling with a good DSP.    The best sounding replacement for a Fender Twin Reverb tube amp  is done this way in my Mustang GT.   Bonus, I can switch in a Showman's JBL speakers, or a Vibraverb amp circuit  and much more, at will.  I can also adjust the bias on the fly, and even tweak the power supply sag.

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41 minutes ago, davewantsmoore said:

 

There are few I know of "off the shelf"....  having it "work well" with the speakers is not different to "normal".  In that you EQ drivers to your target responses (regardless of whether using filters before or after the amplifier).

I find it difficult to understand where you can say "few I know of" and "normal" in the same sentence WRT this.

 

22 hours ago, sir sanders zingmore said:

So if I was (hypothetically) designing a DIY active speaker with off the shelf components, where would I get a current drive amp and how would I ensure it worked well with the speakers?

Either you can easily buy off-the-shelf current amps for a project like this, or you can't. As far as I'm aware, you can't - so at this point, off-the-shelf voltage drive is the only option.

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18 minutes ago, Cloth Ears said:

"normal"

Normal with respect to how you would normally design a speaker (the question was how would I get my DIY speaker to work well with a "current source" amplifier).   You measure the driver responses, and correct them to your target.

 

18 minutes ago, Cloth Ears said:

Either you can easily buy off-the-shelf current amps for a project like this, or you can't. As far as I'm aware, you can't - so at this point, off-the-shelf voltage drive is the only option.

Yes, that's right.

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36 minutes ago, Steffen said:

Customers want to mix and match components

Yes.... I don't think it's a good idea.

 

36 minutes ago, Steffen said:

Are we still talking about home stereo? Because in a home stereo setting, a $1 mobile phone speaker will sound like $1, at best.

Of course.

 

You made the point that someone would (be smart to) use "voltage drive" in an active speaker which cost < 20K.    My point is that speakers at any price point could be "current drive".     Cost has nothing to do with it.

 

Replace my comment about "TV/mobile" with "$2000 active loudspeaker"....  same difference.

 

36 minutes ago, Steffen said:

The idea of all-in-one lock-in doesn’t seem to be palatable to most people investing in a home stereo setup

Indeed....  that doesn't mean it's smart, of course.

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27 minutes ago, Cloth Ears said:

off-the-shelf voltage drive is the only option.

 

6 minutes ago, davewantsmoore said:

Yes, that's right.

 

 

So where's the problem? :)    It's not as if the result cannot be a fantastic sounding system.

 

 

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23 hours ago, andyr said:

This accommodates the back emf which is produced by the moving magnet coil.

?

LOL

 

This is precisely the point of why one would want to avoid voltage drive.

 

23 hours ago, andyr said:

 Pass has done some current amps, sometimes described as current source amps, but they are only suitable with specialist drivers, like Lowthers

Not really.   The work with such drivers with out any type of filter (ie. no XO filter etc, like in a typical speaker)...... but they can work with any drivers with the appropriate crossover filter (which is no different from "voltage drive")

 

 

23 hours ago, andyr said:

The benefit of SS amps is damping factor - so control over bass

Nonsense.

 

 

23 hours ago, andyr said:

You can design a SS amp to measure current for fb and such an amp is designed for balalaika amp guitars.  It is done to simulate a tube amp, particularly with a very high impedance tube like a pentode.  Such amps give a very tubey sound, delicate, but no sense of real power.

 

Yes... you don't have to design a current source amplifier to "sound different" in this way.

 

 

23 hours ago, andyr said:

In truth, most people would not like perfect current feedback because it is 'wimpy'

 

Nonsense.

 

23 hours ago, andyr said:

Current amps need to use a very stiff, low compliance voice coil/cone to sound good, to maintain mechanical control over the excursion because the amp does not have a low impedance, that is, it does not have a high DF.

 

This assume that no other method in the speaker is used to give a "flat" response.

 

It is correct to say that if a "voltage source" and a "current source" amp is the only difference in the system.... then they will have a different frequency response.   The CS will have more output around the speaker resonance, providing the "illusion" of less "control".

 

Methods must be taken in the system design to correct for this.

 

One way (a daft way) to try to do that would be to use a driver with low cms (compliance).

 

23 hours ago, andyr said:

I bolded what sprung out at me as the vital issues.  :)

 

In short, the bits you highlighted are basically false.

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13 minutes ago, aussievintage said:

So where's the problem? :)    It's not as if the result cannot be a fantastic sounding system.

 

I'm not sure I understand?

 

Are you asking something like ....."if voltage drive can result in a fantastic sounding system, then why not just use it?"

 

If so.... "because you can do it much better... and not unsurprisingly it sounds significantly better".

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5 minutes ago, davewantsmoore said:

Are you asking something like ....."if voltage drive can result in a fantastic sounding system, then why not just use it?"

 

If so.... "because you can do it much better... and not unsurprisingly it sounds significantly better".

 

But then, why aren’t we seeing that? I.e. significantly better sound at a comparable price?

 

All I can see is significantly worse sound at a budget, or great sound for a price that, if I may say so, excludes the majority of HiFi lovers.

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8 minutes ago, davewantsmoore said:

 

I'm not sure I understand?

 

Are you asking something like ....."if voltage drive can result in a fantastic sounding system, then why not just use it?"

 

If so.... "because you can do it much better... and not unsurprisingly it sounds significantly better".

 

 

So, you are saying current source amplifiers are (in general) always better sounding?

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9 minutes ago, Steffen said:

 

But then, why aren’t we seeing that? I.e. significantly better sound at a comparable price?

 

 

 

To some extent we are seeing that - think SGRs or KIIs

 

As to why it's not more prevalent, I suspect that has less to do with actual sound quality and more to do with sales and distribution (all-in-one speakers destroy the additional margin that comes from selling amps, preamps, dacs and all the associated cabling)

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1 minute ago, aussievintage said:

So, you are saying current source amplifiers are (in general) always better sounding?

 

Yes..... in general.   There is systemic distortion that is part of "voltage drive" which can be avoided.   If we look at a moving coil loudspeakers electrical properties while it is moving ....... it becomes obvious that using the coil as a "voltage to current converter" to recover the music signal, is a crazy-bad idea.

 

But like many/most things this is an "all else being equal" type of thing.    Without dramatically changing the speaker design, then a VS vs a CS amplifier will sound strikingly different as the speaker won't have the same frequency response.

 

Depending on the speaker, switching to a CS amp (without changing anything) might sound better or worse, if you "like" the  specific change in the frequency response.  Typical modern multiway speakers have an electrical impedance rise at low frequencies, sometimes high frequencies, and at the crossover points .... so the FR could get quite lumpy.

 

 

It's not all roses of course .... not everything can be magically fixed  (the electrical impedance of the driver still fluctuates) .... but by taking control of the signal (the current) via feedback, it can be a marked improvement.

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I reckon that if we see a broad adoption of integrated active solutions then this will not be by transitioning from controlling voltage to controlling current. I think we’ll skip right over that and go to controlling membrane position.

 

This has been done for decades, to a certain extent and with varying success. Designing an automatic controller to keep the instantaneous position of the membrane linked to the instantaneous amplitude of the input signal is almost trivial, but the implementation isn’t. With high-speed digital processing and sufficient power and bandwidth this will eventually be possible.

 

Until then, we’ll have to concern ourselves with things like speaker impedance :)

 

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39 minutes ago, sir sanders zingmore said:

 

To some extent we are seeing that - think SGRs or KIIs

 

 

Sure, if money is no object. But can you take a typical, say, $3k+$6k amp+speaker combination, and replace it with a current control setup that costs the same but sounds better? No. One that sounds the same but costs less? No.

 

In other words, the prevailing voltage control approach is not daft, it is simply the most cost effective approach in the price regions that are of interest to the majority of customers.

 

 

Edited by Steffen
clarity
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5 minutes ago, davewantsmoore said:

There is systemic distortion that is part of "voltage drive" which can be avoided.   If we look at a moving coil loudspeakers electrical properties while it is moving ....... it becomes obvious that using the coil as a "voltage to current converter" to recover the music signal, is a crazy-bad idea.

 

 

"crazy-bad" implies an awful impact on the sound quality, is it really that bad in practice?

If you have a voltage drive amp that can respond to the changing electrical properties of moving speakers, why wouldn't this be "good enough"?

 

Or put another way, what improvements does current drive provide to the sound that ultimately comes out of the speaker (is it lower distortion, flatter FR etc?) 

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28 minutes ago, Steffen said:

But then, why aren’t we seeing that? I.e. significantly better sound at a comparable price?

 

That's a complex question.....  but point was only that such an amplifier costs no more or less to build.... and uses the same speaker drivers, etc .... so there is no need for it to cost more  (aside from business 101 = sell product for as much $ as the market will bear).

 

28 minutes ago, Steffen said:

significantly worse sound at a budget

I'm not sure why you say that.

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4 minutes ago, Steffen said:

 

Sure, if money is no object. But can you take a typical, say, $3k+$6k amp+speaker combination, and replace it with a current control setup that costs the same but sounds better? No. One that sounds the same but costs less? No.

 

In other words, the current voltage control approach is not daft, it is simply the most cost effective approach in the price regions that are of interest to the majority of customers.

 

I guess it's a chicken and egg thing, we are seeing current drive coming in at the expensive end and also at the very cheap non-audiophile end, perhaps the tech will trickle down/up to the middle of that range.

 

Having said that, there are still precious few current-drive systems at the high end. I still reckon a big reason for that is the lack of profit margins and tweak-ability

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13 minutes ago, davewantsmoore said:

Without dramatically changing the speaker design, then a VS vs a CS amplifier will sound strikingly different

 

13 minutes ago, davewantsmoore said:

Depending on the speaker, switching to a CS amp (without changing anything) might sound better or worse,

 

14 minutes ago, davewantsmoore said:

It's not all roses of course .... not everything can be magically fixed  (the electrical impedance of the driver still fluctuates) .... but by taking control of the signal (the current) via feedback, it can be a marked improvement.

 

I am seeing it as -  the best of the best comparison between the two types would lean towards the current drive.  Other than that, it is pretty much a case of maybe.

 

Combos of voltage drive amps and speakers that are known to work well, always seems to me to be the best bet.  Of course that would be true for current drive, but they a much less common and much less well known.

 

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4 minutes ago, sir sanders zingmore said:

"crazy-bad" implies an awful impact on the sound quality, is it really that bad in practice?

 

Circa 20dB of non-linear distortion....    but it depends a lot on the amplifier and drivers in question.

 

On one hand there are things much more audible (eg. linear distortion).... and NLD can be quite benign when below certain levels.

 

... but I think we find that this type of voltage-drive distortion is more audible than expected as it is not constant (ie. it's related to cone velocity) ..... kinda insidious in a way, like "jitter".

 

 

4 minutes ago, sir sanders zingmore said:

Or put another way, what improvements does current drive provide to the sound that ultimately comes out of the speaker (is it lower distortion, flatter FR etc?) 

 

It's lower non-linear distortion.

 

It's also lower linear distortion due to temperature effects (ie. frequency response doesn't change due to changes in VC resistance) .... but for hifi this is usually a corner case.

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5 minutes ago, sir sanders zingmore said:

 

I guess it's a chicken and egg thing, we are seeing current drive coming in at the expensive end and also at the very cheap non-audiophile end, perhaps the tech will trickle down/up to the middle of that range.

 

Maybe... as was already mentioned.   Not while we have people mixing and matching systems.... and loudspeaker designers who want to make a speaker which can be driven by any amplifier (for many reasons, either they may not understand the issue, or they may think it's what the "market wants", or both, etc).

 

5 minutes ago, sir sanders zingmore said:

I still reckon a big reason for that is the lack of profit margins and tweak-ability

 

Yes.... and many players in the high-end are exclusively either amplifier OR speaker manufacturers.

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