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
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
Hi,
The principles and execution are relatively easy :
http://sound.westhost.com/project56.htm
/sreten.
The principles and execution are relatively easy :
http://sound.westhost.com/project56.htm
/sreten.
menekken said:
Take a look at www.firstwatt.com and www.passdiy.com both has the info you're looking for.
Magura
menekken said:
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/matdid/OpAmp/index.htm
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/operazionale.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
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/operazionale.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
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 amp.pdf
thanks
max
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 amp.pdf
thanks
max
Hi,
Download the free TinaTI circuit emulator and play with it.
http://focus.ti.com/docs/toolsw/folders/print/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.
Download the free TinaTI circuit emulator and play with it.
http://focus.ti.com/docs/toolsw/folders/print/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.
sreten said:Hi,
Download the free TinaTI circuit emulator and play with it.
http://focus.ti.com/docs/toolsw/folders/print/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.
done...but there are not LM3886 or LM4780...
max
...the last mail for today, sorry.....
this is an ipothesys of implementation of transconductance amplifier using the LM4780 kit that Audiosector sell.
this is a my interpretation.....
at the end we have to put a little resistor 0,5 ohm with big power in my opinion (20 W) connecting the negative pole of the speaker with this 0,5 ohm and not directly to earht.... as in the picture.
the 22K resistor (R1/R2) must be bypassed and R3/R5 must be disconnected.
in my opinion this is a transconductance amplifier with infinite output impedence.
is it right? in your opinion is it possible that it works well?
thanks boys!
max
this is an ipothesys of implementation of transconductance amplifier using the LM4780 kit that Audiosector sell.
this is a my interpretation.....
at the end we have to put a little resistor 0,5 ohm with big power in my opinion (20 W) connecting the negative pole of the speaker with this 0,5 ohm and not directly to earht.... as in the picture.
the 22K resistor (R1/R2) must be bypassed and R3/R5 must be disconnected.
in my opinion this is a transconductance amplifier with infinite output impedence.
is it right? in your opinion is it possible that it works well?
thanks boys!
max
sreten said:Hi,
The principles and execution are relatively easy :
http://sound.westhost.com/project56.htm
at the end i think i will adopt the Elliot tecnique for transconductance amplifiers......thanks sreten!!!
i will use a 0,5 ohm impedence. The gain will be 16 on a load of 8 ohm with a constant current of 2Ampere with 1 volt input.
32 Watts on the load and 2 watt on the resistor.
With an input of 3 volts (very high input) The gain will be 16 on a load of 8 ohm with a constant current of 6Ampere.
288 Watts on the load and 18 watt on the resistor.
6 ampere is a a good current but is certainly under the LM4780 limit of 14 ampere (that's ok!)
max
Hi,
I will caution that with current drive for the loudspeaker:
Qts instead of being based on Qes and being slightly lower, will be based on Qms and be slightly lower due to a nin-infinite impedance.
What does this mean for a typical full range driver, e.g. Fostex FE166ES-R :
A pronounced treble lift, impedance should be RC'd at supersonic
frequencies to prevent pointless voltage swing. A bass boost :
Related to an effective Qts near 4.5, does not look pretty, needless
to say output impedance interaction with Qts means you need to set
it to what you can get away with, or at least add a parallel resistor.
/sreten.
I will caution that with current drive for the loudspeaker:
Qts instead of being based on Qes and being slightly lower, will be based on Qms and be slightly lower due to a nin-infinite impedance.
What does this mean for a typical full range driver, e.g. Fostex FE166ES-R :
A pronounced treble lift, impedance should be RC'd at supersonic
frequencies to prevent pointless voltage swing. A bass boost :
Related to an effective Qts near 4.5, does not look pretty, needless
to say output impedance interaction with Qts means you need to set
it to what you can get away with, or at least add a parallel resistor.
/sreten.Attachments
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