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-   -   Class A voltage amplifier circuit w/o caps or inductors (http://www.diyaudio.com/forums/solid-state/186306-class-voltage-amplifier-circuit-w-o-caps-inductors.html)

cuallito 2nd April 2011 09:01 PM

Class A voltage amplifier circuit w/o caps or inductors
 
Hi, I'm designing a "minimalist" amp and I need some sort of circuit that will amplify voltage for the input stage without nasty coupling capacitors and operates in class A mode. No current will be flowing out of the circuit.

Tried a simple common emitter circuit but seems like you need the input capacitor for it to work properly.

I know I could use a class AB push-pull configuration but darn it I want it pure class A.

nigelwright7557 2nd April 2011 09:54 PM

You can do it (or get close) if you use a split level power supply.

DF96 2nd April 2011 10:17 PM

You could try using nice coupling capacitors. Or, as it will be running with no output load (so no output current), just don't bother to attach the input signal.

You could use an op-amp with a split supply, and accept any DC offset it produces. That way, at least all those nasty Cs and Ls will be hidden away in the PSU.

cuallito 3rd April 2011 02:34 AM

Don't attach the input signal?

djk 3rd April 2011 04:33 AM

You're not going to draw any output current, why would you need an input signal?

MiiB 3rd April 2011 06:26 AM

The funny this is that there's is no design that excludes capacitors...If you don't use them as coupling in the input and out put (input cap can sometimes be omitted), then the PSU caps are right in the signal path...as they support the GND end of the signal...

Mooly 3rd April 2011 07:11 AM

Quote:

Originally Posted by cuallito (Post 2525453)
Hi, I'm designing a "minimalist" amp and I need some sort of circuit that will amplify voltage for the input stage without nasty coupling capacitors and operates in class A mode. No current will be flowing out of the circuit.

Tried a simple common emitter circuit but seems like you need the input capacitor for it to work properly.

I know I could use a class AB push-pull configuration but darn it I want it pure class A.

I don't understand "no current will be flowing out of the circuit" !

So what do you want this amp to drive ?

Elvee 3rd April 2011 08:35 AM

1 Attachment(s)
Here is a 20dB class A amplifier, without inductors or capacitors:

djk 3rd April 2011 08:58 AM

The CD4069UB looks like it is class B above 0.25A at 25C.

http://focus.ti.com/lit/ds/symlink/cd4069ub.pdf

Elvee 3rd April 2011 10:44 AM

Quote:

Originally Posted by djk (Post 2525857)
The CD4069UB looks like it is class B above 0.25A at 25C.

http://focus.ti.com/lit/ds/symlink/cd4069ub.pdf

Where did you see that?

From the characteristics, I see that output stage remains class A from 2.5 to 7.5V for 10V supply.
And the output current can also reach 1.5mA without too much difficulty.


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