Class A voltage amplifier circuit w/o caps or inductors

cuallito · 2nd April 2011, 09:01 PM

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

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

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 0.25µA at 25°C.

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

Elvee · 3rd April 2011, 10:44 AM

Quote:

Originally Posted by djk

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

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.

2nd April 2011, 09:01 PM	#1
cuallito diyAudio Member Join Date: Apr 2004 Location: Milky Way	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.

2nd April 2011, 09:54 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	You can do it (or get close) if you use a split level power supply. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

3rd April 2011, 04:33 AM	#5
djk diyAudio Member Join Date: Feb 2001 Location: USA	You're not going to draw any output current, why would you need an input signal? __________________ Candidates for the Darwin Award should not read this author.

3rd April 2011, 08:58 AM	#9
djk diyAudio Member Join Date: Feb 2001 Location: USA	The CD4069UB looks like it is class B above 0.25µA at 25°C. http://focus.ti.com/lit/ds/symlink/cd4069ub.pdf __________________ Candidates for the Darwin Award should not read this author.

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2nd April 2011, 10:17 PM	#3
DF96 diyAudio Member Join Date: May 2007	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.

3rd April 2011, 02:34 AM	#4
cuallito diyAudio Member Join Date: Apr 2004 Location: Milky Way	Don't attach the input signal?

3rd April 2011, 06:26 AM	#6
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	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...

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