Amplifying Audio to +/- 5V?

[things]

Hey guys,
I am currently building a laser projector using 20K galvonometers. The problem I have, is I need to have a ILDA interface. Using a slightly modified sound card is a very cheap and easy way to do so, so i'm going to attempt it. Basically, the galvo's require a 5V +/- signal into their amps. Using just +5v will work too, but the pattern would be smaller, as the potential is less. Does anyone know how I can amplify the output of a standard USB sound card to 5V? It needs to be as noise free as possible, otherwise I could get interference in the output, and at a speed of 20K, it shows up badly.

Any help appreciated

 

[things]

BTW, I realise I wouldnt get TTL yet, but once I can figure out the 5v amp, then TTL modulation will be easy.

Thanks

 

[RadioRon]

You need simply add an audio amplifier that is capable of putting out 2 watts or more. Have any old stereo amplifiers lying around? Any old junker receiver would be able to do the job.

 

[Speakerguy]

Agree with using an old junk receiver. Easiest way by far. Question though: Why does he need 2 watts of output?

 

[RadioRon]

Agree with using an old junk receiver. Easiest way by far. Question though: Why does he need 2 watts of output?

He doesn't need 2 watts, but he wants a voltage swing of +/- 5 volts peak. If the amp were designed to produce barely just this amount, it would do so into 8 ohms. 5 volts peak is 3.54 Volts rms. The amount of power delivered into 8 ohms with 3.54 Vrms is 1.56 watts. I just rounded up to 2 watts for convenience. Since most audio amps deliver voltage to any load presented, with a source resistance that is typically very low, then an amp rated at 1.56 watts or more will deliver +/- 5 volts into any resistance of 8 ohms or more.

 

[Speakerguy]

Oh OK. If he builds a simple op amp amplifier, he shouldn't need more than a mA of current though, should he?

 

[Sceadwian]

What RadioRon is trying to say is that any cheap powered PC speakers should do it just fine, as long as it can handle 2 watts output into 8ohm speakers. Why build a circuit when you don't have to?

 

[Mikebits]

I found this circuit for driving a Galvo.
Gordon McComb's Gadgeteers Goldmine ... - Google Book Search

 

[Speakerguy]

That's a real common circuit for headphone amps - a push/pull emitter follower transistor pair enclosed in the feedback loop of the opamp. That schematic is the simplest version. The performance/fidelity can be increased by biasing the transistors with diode/resistor pairs (D1, D2, R5, R6 with 100uF caps just to stabilize the voltage across the diodes) and putting in emitter resistors:

**broken link removed**

It also blocks amplification of DC by putting an electrolytic in the feedback network. This only does 1.5W into 8 ohms off 15V supplies, but some beefier transistors would probably help. If he only needs voltage gain then this is moot. I don't know what it takes to drive a galvo.

 

[Mikebits]

This does not answer any of your questions, but since your into lasers, I thoght I would share a little project I built with a laser. Simply a laser tube, power supply and 3 motors with mirrors mounted. Regular mirrors do not work. You need the kind used in laser stuff (I can't remember the name).

 

[mneary]

(I can't remember the name)

First (or front) surface.

 

[Mikebits]

First (or front) surface.

That sounds about right. They were also made from silver I think. The rear coated mirrors simply do not work. Too much diffraction in the glass. Laser light ends up looking like fuzz.

Kinda expensive too.