Availability of "current-drive" amplifiers as commercial products

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#1
Availability of "current-drive" amplifiers as commercial products

Hi Everyone,

As a newcomer to audio, I wish to take on my first project (subject to the availability of time and resources, because, I am ambitious but, the project may turn out to be impractical). I have in mind a 2.1-channel system comprising:
  • 1 x subwoofer (the x.1 channel)
and

  • two main channels, with each channel being a 3-way sub-system with separate drivers/transducers for the bass, mid-range and high-end (tweeter) frequency bands.
Thus, altogether, seven (7) drivers/transducers are required.

Each speaker-driver may have its own dedicated enclosure but will definitely have its own dedicated amplifier. In other words, each of the two main channels is a 3-way and tri-amped system, without any passive cross-overs. Hence, seven (7) amplifiers are required altogether.

To give an idea of the overall system size (in terms of electrical power), I envisage a total of ~ 3 kW for the whole system, with at least 1 kW for the subwoofer and the remainder split (equally) between the two main channels (2 x ~1 kW).

Importantly, I wish all of the seven amplifiers (each feeding its own dedicated driver/transducer) to be "current-drive" (i.e. not "voltage-drive") amplifiers.

The main requirement for all these "current-drive" amplifiers is that:

they should work with standard commercially-available speaker driver/transducer units. More explicitly, the amplifiers should not necessitate any modifications to drivers/transducers (e.g. custom-made units), nor require an (electrical/mechanical/acoustic) feedback signal from a driver/transducer.
​
The latter is simply because incorporation of a feedback device such as a sense-coil or an accelerometer means that a modification has to be made to a standard driver/transducer, e.g. a custom-made unit, which is already ruled out. The "current-drive" amplifiers may have their own internal feedback loops, including sensing of the voltage or current supplied to the speaker-driver, but each amplifier should be connected to its driver/transducer by a 2-wire cable only, i.e. no extra wires for any external feedback from the driver/transducer unit. The latter is despite the possibility of co-locating an amplifier and its driver/transducer within the same enclosure.

Firstly,

Question 1) Do you think that such an "all current-drive" system is possible or implementable in practice?

Secondly, I have been looking around for standard "current-drive" amplifiers available as ready-made commercial products. I can hardly find any.

Question 2) Do you know of any commercially-available "current-drive" amplifier that satisfies the main requirement above? [Note that separate amplifiers are needed for the bass, mid-range and high-end (tweeter) frequency bands.]

Any thoughts, advice or suggestions will be greatly appreciated.

Thanks in advance.
 
#4
'Current-drive' amplifiers require one and only one of the following:
1. a speaker specifically designed with sufficient mechanical damping that no electrical damping is needed - note that such a speaker would not work too well with a conventional voltage-drive amplifier so would have a very limited market.
2. some form of transducer feedback from the speaker - so again a special speaker is needed
3. voltage feedback from the speaker via a sense wire, thus turning the so-called 'current drive' into normal voltage drive (whatever people choose to call it)
4. a listener who enjoys a bass boost at the speaker bass resonance, and regards this significant frequency response error as normal and desirable

All of these are seen 'in the wild' in different 'habitats'. You choose which of these you prefer - I can't think of any other options.
 
#5
DF96 said:
'Current-drive' amplifiers require one and only one of the following:
1. a speaker specifically designed with sufficient mechanical damping that no electrical damping is needed - note that such a speaker would not work too well with a conventional voltage-drive amplifier so would have a very limited market.
2. some form of transducer feedback from the speaker - so again a special speaker is needed
3. voltage feedback from the speaker via a sense wire, thus turning the so-called 'current drive' into normal voltage drive (whatever people choose to call it)
4. a listener who enjoys a bass boost at the speaker bass resonance, and regards this significant frequency response error as normal and desirable

All of these are seen 'in the wild' in different 'habitats'. You choose which of these you prefer - I can't think of any other options.
Click to expand...

An impedance compensation network can be crafted to make the speaker impedance curve flat. No need to tolerate the bass boost and treble boost from the naked speaker impedance curve.

http://users.ece.gatech.edu/mleach/ece4445/downloads/zobel.pdf
 
#6
inventor said:
Availability of "current-drive" amplifiers as commercial products



Question 2) Do you know of any commercially-available "current-drive" amplifier that satisfies the main requirement above?
Click to expand...

I could not find one. I did a fairly exhaustive search. The closest thing you will find is what is called an Inductive Loop Amplifier. They are used for the hearing impaired. A loop of wire is run around a room perimeter. The amp drives the loop. Receivers are used in the room that pick up the transmission.

Most of these amps are somewhat expensive and most do not have freq resp and distortion specs you would call audiophile grade.
 
#7
woofertester said:
An impedance compensation network can be crafted to make the speaker impedance curve flat. No need to tolerate the bass boost and treble boost from the naked speaker impedance curve.
Click to expand...
It is not the impedance curve which causes the resonance sound boost; indeed with a conventional voltage-driven amplifier the impedance curve helps flatten the audible response. It is the resonance which causes both the sound boost and the impedance peak. Current-drive makes this worse, so flattening the impedance curve will merely reduce but not eliminate the problem. You have to damp the resonance itself to get rid of the problem; that is why special speakers are needed with extra mechanical damping.
 
#8
DF96 said:
It is not the impedance curve which causes the resonance sound boost; indeed with a conventional voltage-driven amplifier the impedance curve helps flatten the audible response. It is the resonance which causes both the sound boost and the impedance peak. Current-drive makes this worse, so flattening the impedance curve will merely reduce but not eliminate the problem. You have to damp the resonance itself to get rid of the problem; that is why special speakers are needed with extra mechanical damping.
Click to expand...

Good point. A flat impedance gets you half way. For constant current you would want the impedance curve to be the reflection of what it is normally about the frequency axis.

You could probably create an FIR filter with this characteristic and use a DSP.

I wonder if there is some other clever way to invert the impedance curve and still use current drive........
 
#9
inventor said:
Availability of "current-drive" amplifiers as commercial products

Hi Everyone,

As a newcomer to audio, I wish to take on my first project (subject to the availability of time and resources, because,
I am ambitious but, the project may turn out to be impractical). I have in mind a 2.1-channel system comprising:
Click to expand...

Hi,

Your requirements are essentially pretentious nonsense.

No-one can write good requirements about anything
they simply do not understand well, all they can do
is illustrate their ignorance of the subject in question.

Here the ignorance is fundamental regarding the basics.

rgds, sreten.
 
Last edited:
#11
Thanks to everyone who replied so far. I will soon respond to your comments as best as I can. Firstly, please allow me to reply to our friend sreten (message #9). This will also be a chance to give everyone an idea about the background of my opening message.

sreten said:
Hi,

Your requirements are essentially pretentious nonsense.

My requirements may be "nonsense", but I believe that neither I nor my requirements (i.e. my wishes) are pretentious.

No-one can write good requirements about anything they simply do not understand well,

I fully agree with that statement.

However, I do not claim my requirements to be "good". Nor did I write a list of technical requirements or any required (albeit provisional) specifications e.g. for a product I want to purchase or a sales contract I'd like to enter. I simply tried to describe the system I presently envisage as something nice to have.

Anyone can and should read my message as a "wish list", simply because that is what it is: a wish list. My wishes may be nonsensical; I am aware of that (as evident from my original message) and I am happy with that. Who on earth has never had a nonsensical wish in his or her life? 🙂

I do not pretend that I "understand well" the present topic, let alone having a deep understanding of most other topics in the audio field. As I said in my message, I am new in this field, and there is as yet quite a lot for me to learn.

all they can do is illustrate their ignorance of the subject in question.

I don't mind showing or illustrating my ignorance (in the sense of 'lack of knowledge'). I do not pretend to be knowledgeable even in the areas of my background experience. Besides, I never ignore (in the sense of 'disregard') any human being, however ignorant (in the sense of 'uninformed') he or she may seem to be in a particular topic. [The message I am writing now may be an indication of that.]

During my past professional life, I have often found that the worst case is when an ignorant person believes that he or she is not ignorant.

Here the ignorance is fundamental regarding the basics.

I know that, by "fundamental", you do not mean 'essential'. 🙂

But, regarding "the basics", why don't you contribute something useful and/or pertinent to the present topic? At least at its "basics". If I can learn something from you, I will sincerely appreciate it and thank you for it.

rgds, sreten.
Click to expand...

Dear Sreten; Regardless of all that above, thank you for your message and I look forward to your contributions.

----------------

Now a general note:

I am not a proponent of "current drive" per se. I wish to find out more about it and, if it seems to be the right way forward, I want to experiment with it. I am looking for new challenges; hence this 'envisaged' project. However, I cannot fiddle with the electronics of a DIY kind of amplifier, nor can I modify the inner construction of an existing speaker-driver. This is why I am looking for ready-made commercially-available "current-drive" amplifiers.

What I basically want is: get things, put them together, and listen. If this is not possible for the system I have in mind, please do not hold back your comments.
 
#12
Current drive is easy enough to play with. I have had two products on the
market, and the schematics are available and they are easily made. You can
scale up the power simply enough.

Also Rod Elliot has schematics for using feedback to create these effects, and
as has been pointed out, you can always put a resistor in series with a bigger
power amp with almost no effort.

In any case, you don't want to insist on current drive a priori, it's just
another tool.

😎
 
#13
jacques antoine said:
Is this for your car ?
Click to expand...

No, it is not for my car. It is intended for home/personal usage (and possibly for occasional use in the assembly hall of our local primary school). The main aim is for me to learn by doing/making. (I have no intention like eventually showing off a hi-fi system to impress others - such as girl-friends in the car or visitors/friends in the house. Smile 🙂 )

Owing to residential usage, the amplifiers will be powered from standard AC mains supply (230V, 50Hz in Europe). I wish to make my own AC-to-DC power supplies, and that's why I am looking only for amplifier 'modules'. I thought, "why not get all amplifiers to be 'current-drive' (rather than 'voltage-drive') amplifiers".

The ultimate point is that I am trying to set a challenge to myself (in the form of a project that should contain something new or novel in concept, technology or product). Considering my own lack of experience in audio, I thought I may get some advice or suggestions from the diyAudio community.
 
#14
I think you you need to ponder why professionals are almost universally negative about "current drive". For one thing, the concept draws newbs like moths to a flame and that flame is a lot of time and money spent to come the same realisation that experimeters for decades before them have.

A nice idea - nice, but not thought through. Read that ESP article suggested by Nelson Pass for an introduction to the type of amplification required. That will save a lot of Q&A here and move you on to where you have a better basis for your project ideas. I have to say though, a 3 kW output audio system in the home would be quite something. Just hope your neighbours agree. 😱
 
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