req. info audio current (transconductance) amplifier

[sarathssca]

Hello,


Could you please provide some more information regarding audio current amplifiers especially for full range speakers (without crossover circuits)?

It seems the loud speakers are current consumers, rather then voltage. the sound from the speakers are proportional to the currents through them rather than voltage, and also they provide complex impedance to the driving amplifier rather than resistive load. So the voltage output may not be in line with the current output of the amplifier over the whole audio frequency range.

So the current (transconductance) amplifier are better for audio to driver loudspeakers rather than traditional voltage amplifier. Is it true? If its true, are the amplifiers like LM1875 does voltage or current amplification ie will the output current be same even if the impedance of the speaker changes with frequency?

thanks and regards

S Sarath

 

[diesel engine]

What exactly is in your mind? There are both voltage amplification and current amplification in power amps. LM1875 and likes are no exemption- do both. a voltage amping input stage and current amping output stage. (if you can call it current amplification! I believe there is no such thing as current amplification. I would rather call the output stage a non linear switch.)

 

[linuxguru]

There are basically four kinds of input and output summation arrangements that are possible in amplifiers - without going into too many details, they are:

1) current-in, voltage-out - normally used in I/V stages.
2) voltage-in, voltage-out - the most common, known as voltage-series feedback.
3) voltage-in, current-out - V/I stages, also known as transconductance stages.
4) current-in, current out - a pure current gain stage, which in its simplest form is simply a bipolar transistor.

There are some advantages in using a transconductance amplifier as the final gain stage in a power amplifier - this has been done for several decades, most notably by Tim da Paravinci for the Musical Fidelity A-370 in the '70s. There are several key ideas involved, which you can probably read up yourself by googling the following terms:

Howland Current Pump
MyRef
MiniRef
Composite Amplifier
Nested Feedback Amplifier

 

[kanwar]

Hello,


Could you please provide some more information regarding audio current amplifiers especially for full range speakers (without crossover circuits)?

It seems the loud speakers are current consumers, rather then voltage. the sound from the speakers are proportional to the currents through them rather than voltage, and also they provide complex impedance to the driving amplifier rather than resistive load. So the voltage output may not be in line with the current output of the amplifier over the whole audio frequency range.

So the current (transconductance) amplifier are better for audio to driver loudspeakers rather than traditional voltage amplifier. Is it true? If its true, are the amplifiers like LM1875 does voltage or current amplification ie will the output current be same even if the impedance of the speaker changes with frequency?

thanks and regards

S Sarath

What you are actually referring is to Negative Impedance amplifiers which take feedback in form of current and function as Voltage IN || Current OUT. Normally power amplifiers function as Voltage in Voltage out devices and the current draw happens inversely proportional to the impedance curve of the speaker. Sometimes this type of current amplifiers also provide constant power output.

Try THIS

 

[tnvijay]

Hi Everybody,
I am a new FM joined recently.
I recently built a miniref 1875 Using our linuxguru kit.I am extremely happy and pleased with it. It works on transconductance principle. I would request more and more inputs on this topology of gainclones.
Thanks.