a dream...real audio current amplifier.... - diyAudio
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Old 1st November 2007, 03:34 PM   #1
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Lightbulb a dream...real audio current amplifier....

Hi,i'm max from italy!and first of all sorry for my bad english.

i have 30 years old. i'm new for this fantastic site, but i have a discrete experienxe in AUDIO speaker/amplifier/cables DIY

see my site
http://arkangel-speakers.blogspot.com/


i have found a lot of information on diyaudio.com about transconductance audio amplifiers.
Very interesting informations but in reality......

i'm an AUDIO DIYer.. and i have a dream...

to built a Current Amplifier for audio applications usyng transcoductance operational amplifiers or other methods

In teory a current amplifier, is a device with an infinite output impedence. we need a big band width,,,low distortion....bla......bla...

But if we built an amplifier that convert an input voltage signal of 1-2 volts (that comes from a preamplifier for example) into a current output proportional to this signal
(for example 6 Amperes for a 2 volts input) we will make the goal in my opinion.

In this case, if we use a single speaker system or a no crossover system (my case with the arkangel speakers... ) all the current generated, go into the voice coil moving it.

But a current amplifier has an infinite output impedence (example 10-20 kohm) so is it impossible that the voice coil generate Electro Magnetic Feedback into the amplifier (introducing distortions and phase changes)

The Chain is ...open..from 20 hz (when the voice coil impedence is low) to 20 khz (when the voice coil impedence is high)....

The impedence chain from the amplifier to the voice coil is OPEN.....

In my opinion this is the nirvana for an audio system, if you use a good single speaker system or a no crossover speaker system.

in your opinion there are OTAs in the market to reach this dream?? (LM13600 or LM 13700 have low current output i think....)
there are electrical drawings with this OTAs for audio applications?

who wants to reach the goal with me?

i hope you can help me to reach this dream....

thanks
max
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Old 1st November 2007, 05:42 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

The principles and execution are relatively easy :

http://sound.westhost.com/project56.htm

/sreten.
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Old 1st November 2007, 10:46 PM   #3
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tahnks for the answers, but i think we are too far from the solution....

in that link i can't find the solution......how to realize a real constant current amplifier for audio applications.


max
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Old 1st November 2007, 11:15 PM   #4
Magura is offline Magura  Denmark
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Quote:
Originally posted by menekken
tahnks for the answers, but i think we are too far from the solution....

in that link i can't find the solution......how to realize a real constant current amplifier for audio applications.


max

Take a look at www.firstwatt.com and www.passdiy.com both has the info you're looking for.


Magura
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Old 1st November 2007, 11:24 PM   #5
Giaime is offline Giaime  Italy
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Quote:
Originally posted by menekken
in that link i can't find the solution......how to realize a real constant current amplifier for audio applications.


max
Have you got any clue to configure whatever operational amplifier (even power ones, maybe LM3886) in transconductance mode?

Basic opamp theory
http://pc31.fauser.it/operazio/operazionale.htm
http://www.etec.polimi.it/studenti/m...pAmp/index.htm
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Old 2nd November 2007, 04:02 AM   #6
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HI Gaime...anche tu qui?? (io non vado su VDH da tempo....li ci sono le solite.....).

hi gaime, yes, i understand

see this page
http://www.national.com/mpf/LM/LM3886.html
and....referring this link and your links, http://pc31.fauser.it/operazio/opera...htm#transcondu

but i have a doubt to use an LM3886 as a current amplifier (figure 21 of your link):

1) is it not the natural....use of this OPAMP
2) R2 is 20 kohm. in the case (for example) that R1 is 10 ohm,
I output is 2000 I input. If the input is 2 volt and R input is 10 kohm , Iout is 0,4 ampere......to low...
3) are you sure that in this configuration there are no oscillations?

thanks!
max
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Old 2nd November 2007, 01:40 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by menekken

in that link i can't find the solution......how to realize a
real constant current amplifier for audio applications.

max

Hmmm....... not much hope then ..... it is all there, /sreten.
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Old 2nd November 2007, 01:55 PM   #8
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thanks sreten for you help!!!
i ahve appreciate it!

Giaime say that an operational amplifier like the LM3886 or the LM4780 can be used like a current aomplifer.

in your opinion the LM4780 kit is changible in a current amplifier?

Attached to this mail there is a file with a my personal interpretation....of a current amplifier....

I don't have pspice or other software, so i don't know if this current amplifier is good...or not....

Is it possible to have an hand please???

in your opinion is it right? oscillate or not?
if is it right can you help me to determine the Output impedence, the current gain, the output current and the input impedence?


Do you like my idea?
i hope you can help me to reach this goal....

this is the original configuration (i use stereo mode)
http://www.audiosector.com/lm4780%20amp.pdf

thanks
max
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Old 2nd November 2007, 02:27 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

Download the free TinaTI circuit emulator and play with it.

http://focus.ti.com/docs/toolsw/fold...t/tina-ti.html

If you cannot manage the above you should go nowhere near
a real circuit with a soldering iron trying to change its operation.

And yes you can modify it to any output impedance you like,
including very high impedance constant current mode, as
opposed to the very low impedance constant voltage mode.

/sreten.
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Old 2nd November 2007, 07:30 PM   #10
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this is the the idea......
Attached Images
File Type: gif lm4780-current amplifier.gif (28.0 KB, 663 views)
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