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I need an oscilloscope to bench test an amplifier I've building. I haven't got any.

I thought If I limit it to 20kHz, it can be used as a sound amplifier. Would simply judging by the sound be enough to diagnose just a sound amplifier? If in case it is, would there be any way to tell if it works to much higher frequencies?

I just don't want deal out that much cash right now and I've always spent very little for every single equipment/supply that I acquire.

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  • \$\begingroup\$ You are going to need to buy something I think. I can't think of any way to verify a circuit beyond audible range besides an oscilloscope. Look into USB scopes and low-cost brands like Rigol. See if your budget can afford it. \$\endgroup\$ – mkeith Mar 5 '17 at 7:59
  • \$\begingroup\$ Some volt meters might work at higher frequencies, but that can't verify the shape of the waveform if it is doing something weird. \$\endgroup\$ – mkeith Mar 5 '17 at 7:59
  • \$\begingroup\$ If it's a long term investment, then I guess I can dish out a few hundred bucks. But, I'm open to other ideas as well. \$\endgroup\$ – Dehbop Mar 5 '17 at 8:22
  • \$\begingroup\$ How about a used Tektronix scope from the 1980s. These are available for a couple of hundred dollars. \$\endgroup\$ – kiwiron Mar 5 '17 at 10:06
  • \$\begingroup\$ Brand new Rigol is also "a couple hundred dollars." Well, 329 dollars. \$\endgroup\$ – mkeith Mar 5 '17 at 17:21
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To test your amplifier at 1MHz, place some feet of wire on the input, and connect output to the screw-terminal of a standard AM/FM stereo receiver. You'll likely also need to bring over the GND of the amplifier to be the GND for the AM/FM radio. You thus examine 540---1620KHz.

You can certainly repeat this for FM, getting to 88-108MHz. If the AM is clear as you monitor several stations, and the same clarity is found for the FM stations, you have high confidence there is NO OSCILLATION in your amplifier.

And if the various stations have made it thru your amplifier, particularly in a station-dense urban environment, your distortion (at least the 3rd order, where uniformly spaced stations will trash each other) is good.

You can inject a strong audio signal while examining AM or FM clarity. Vary the audio signal frequency. If you hear no effect on AM or FM, you gots a fine amplifier. IMHO

Your garage door opener might radiate at 433MHz. Or not.

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