I would like to build an amplifier to boost test signals generated in software. Specifically, low frequency sine waves or other basic waveshapes.

The circuit should operate on 12VDC, connect to one channel of my PC headphone jack, and output approx 12Vpp of direct coupled unidirectional current at around 2A. The intended loads are non-inductive.

The likelihood that some of the signals will be subaudio, and the requirement for unidirectional current, rules out any type of stock audio amp. I just need something simple and robust I can build into a black box for regular reliable use.

This old standby is what I am considering, with10uF, 2K2 and TP41/42, but any suggestions for improvement would be geatly appreciated. The sound card output will be bipolar, but I am assuming this will be removed by the input caps.

 

That circuit needs either a bipolar supply or a coupling capacitor on the output. And it has no voltage gain.

Bob

 

Thank you for pointing that out. I could possibly add a class A driver as below.

R1 22K, R2 10K, RL 22R, RE SOT, C1 2.2uF, C2 22uF

Or an op amp with fixed 10x gain LM358, etc. Or a power op amp such as the LM675.

Which of the three would be "better" for my generic bench-type application?

Is there any way to dispense with the output coupling cap and still use a single supply? I am concerned it may affect any subaudio signals.

 

You need to explain exactly what You are trying to accomplish,
not what Circuit, or Amplifier type, that You are thinking about trying.

Your request is not understandable,
You can't have an Amplifier with a 12-Volt "Peak to Peak" Output that's powered by 12-Volts.
12-Volts "Peak to Peak" requires in excess of ~24-Volts, and is certainly not "uni-directional".

What is "Direct-Coupled" "unidirectional" Current ?
It sounds like You want a DC-Output,
but Your Computer only supplies an AC Signal.
.
.
.

 

I think he wants a sine wave with DC offset equal to the peak voltage. In this case a 6V peak sine with 6V DC offset, so varying between 0V and 12V.

Didn’t we already di a kong thread about this?

Bob

 

What current do you need at the output? An opamp can easily do this, and there are high power opamps if you need more than the 20-30 mA a normal opamp can output.

Bob

 

What exactly is the input voltage to, and the output voltage and current from the amp, that you want?
You seem to be bouncing around on that.

 

What frequency range?

 

To address the points raised.

I would like a single rail 12VDC powered amp with as much voltage out as possible.

Op amp best solution? I did mention the LM675. But I believe the biasing required at the input to produce the 6V offset at output will change with the peak input voltage. If possible I would prefer not to make this adjustment with each use.

Input voltage is the normal range provided by sound card out. About 2V max. Output as close to rail as possible, given fixed gain at actual input volts. Current up to 2A.

Thank you for asking.

 

If all you have is +12V and you want a 0 to 12V signal, there is a problem. You need a R-R output amplifier.
I would use a audio amplifier. No audio amp (that I know about) is R-R output.

I looked for a 2A R-R output amp and found this one. But it will not work at 12V.

What are you driving with this signal?

 

As close to 0-12V swing as I can get. Not exact. That amp IC is nice but would be push-pull out I believe, and low voltage as you mention.

I will probably need to build something and therefore looking for the simplest workable option within the specs already given. Maybe just an LM358 with NPN emitter follower similar to this. Comments?

 

I would suggest an LM675. Minimum supply voltage is 16V. You would have to try it at 12V and see how it performs.

 

As close to 0-12V swing as I can get.

You don't care about the pull down? When the signal gets close to zero there will be no current. How many watts will you burn in R5?

 

Right. LM675 minimum 16V supply. I seem to recall running one on 12V. Will need to check.

How could I fix the pull-down in my attached op amp circuit?

R6 is the "load".

 

If you want close to a 12V swing with a 12V supply, your best bet is a class D amp.

Bob

 

Again ... I am not expecting exactly 12V swing. Give me some credit ;-)

 

Again ... I am not expecting exactly 12V swing. Give me some credit ;-)

Sure, if by 12V you mean 8V. Because a push pull stage like you show typically loses 2V on each side.

Bob

 

Then about 2V total with emitter follower. Look on the bright side.

Based upon the responses so far, I think will go with the single supply op and and follower. Offers gain and least voltage drop with a few basic parts.

Still wondering how to add the "pull down" Ron mentioned.

 

 

Thanks Ron. This inspires confidence. I will build this week. Substitute trusty LM358 for LT part which I do not have on hand. I assume R2 is 1K as well. Very much looking forward to it.