I would like an amplifier that can amplify AC (a square wave at ~50-100kHz) and DC. I would like to get a stereo audio amplifier and have each channel drive a different coil (one for the AC, one for DC).

The input (for the dc amp) will come from an a/d converter and vary from 0-3v at a max of ~30hz (although random not sinusoidal) and I'd like the output to go up to about 24 volts 1amp. I have 12v & 24v power supplies but am happy to get more.

Can an audio amplifier do this or be modified to do this? If yes, is there a specific type I should get?

I was originally planning to use an op amp, but mine can only do about 10W and an audio amplifier would be so much more convenient.

  • \$\begingroup\$ 10W for an op-amp is pretty amazing. I think you need to lay out a better question, namely try to provide schematics, what is your voltage supply, what level is the input signal and what level do you want it amplified to. Audio is inherently an AC signal, and they will have DC blocking/bias capacitors everywhere. You could probably try removing the DC input blocking capacitors, have you tried this before? \$\endgroup\$ – KyranF Nov 19 '15 at 0:02
  • \$\begingroup\$ I think you need to give some examples of what you are talking about. \$\endgroup\$ – Fizz Nov 19 '15 at 1:25
  • \$\begingroup\$ @KyranF I've edited it to try to answer most of your questions. I don't have schematics because the input comes from an arduino a/d converter and there isn't much else to this circuit. I haven't tried removing blocking capacitors. Is there type (like btl, etc) of amp that would be a good candidate to try that on? \$\endgroup\$ – Caleb Nov 19 '15 at 1:34
  • \$\begingroup\$ @Respawned Fluff I added some more details. Not sure you commented before my edit or after. \$\endgroup\$ – Caleb Nov 19 '15 at 1:36
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    \$\begingroup\$ I was looking at this amp on amazon. I'm on my phone right now so I can't find the op amp I have but it was something sort of like this but higher voltage. \$\endgroup\$ – Caleb Nov 19 '15 at 2:01

Can an audio amplifier amplify DC?

Yes, I still have (and use) one, the Mitsubishi DA-A15DC (alt link) that I purchased in the early '80s and it's certainly not the only example of one.

It is a Direct Coupled amplifier (hence the DC in the model number) which means it allows DC/0Hz signals and doesn't have coupling capacitors.

I would like an amplifier that can amplify AC (a square wave at ~50-100kHz)

To produce a reasonable square wave at 100kHz requires relatively flat frequency response out to at least 1MHz (probably higher) and that is far higher than any audio amplifier that I'm familiar with. So, this seems to be the show stopper.

  • \$\begingroup\$ Oh! look who is here! tooo long haven't seen you here! I miss you. Welcome back! \$\endgroup\$ – Roh Nov 19 '15 at 8:07
  • \$\begingroup\$ Great answer! Too bad direct coupled amps are so rare. I may need to put some op amps in parallel. I don't care what the square wave looks like. \$\endgroup\$ – Caleb Nov 20 '15 at 4:04

Some amps have response to DC, but in general the response rolls off below about 20 Hz. If this doesn't happen, DC in the preamp causes the speaker to have a bias, which limits its response at high amplitudes (causes clipping).

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    \$\begingroup\$ Most amps filter DC not just because bias causes clipping, but also because many speakers have a DC resistance which is lower than their nominal impedance, and a bias voltage sitting on the speaker may thus produce a lot of heat for no useful purpose. \$\endgroup\$ – supercat Nov 19 '15 at 0:32

Usually, an audio amplifier will be capacitively-coupled at the input, which explicitly blocks DC.

What you would typically use to drive 10 watts with a 50-100 kHz square wave is usually a LOT different from what you'd use to amplify audio (nominally 20 Hz to 20 kHz).

We need to know a lot more about your proposed application.


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