On Tue, Dec 12, 2023 at 06:55:39AM -0500, Tony Miklos via Jukebox-list wrote:
On 11/28/2023 11:47 AM, Steve Wahl wrote:
On Tue, Nov 28, 2023 at 08:16:28AM -0500, Tony Miklos wrote:
On 11/27/2023 6:55 PM, Steve Wahl wrote:
Tony: I would love to see your video if you can find it!
--> Steve
Square wave audio amplifier test vs a sine wave.
Ah, I think I get it.
The square wave has all the odd harmonics, so your 300Hz square is like simultaneously putting sine waves at 300, 900, 1500, 2100, 2700, 3300, ... (at decreasing amplitudes) through the amp.
So you're testing the amp over a wide range of frequencies at once, but also seeing if there's interferences / interactions between those frequencies within the amp.
Is that right?
--> Steve
No, the square wave input is a perfect square wave.
I think we're actually agreeing here.
I never took signals theory, but I've read about it and have played with square waves and filters, and adding sine waves together on synthesizers. Acording to theory, a square wave contains the fundamental plus all the odd harmonics. See for instance this wiki page:
https://en.wikipedia.org/wiki/Square_wave#Fourier_analysis
So, with a square wave, you would be exercising the amp's ability to operate over a wide range of frequencies simultaneously, at the fundamental frequency and all of the overtones present in the square wave. Any oddities (e.g. deficiencies in frequency response) will distort the resulting waveform, as you have said.
The problems arise when you see the ringing (up AND down in the circuit/output. This is not to be confused with a single spike which is sometimes normal with the treble turned up to max. Maybe I'll try testing an amp before rebuilding it and get a good picture of a distorted signal. Even a good signal will show different looking output than the input do to the frequency response of the amp. I had later noticed that I had the input at 300hz instead of 1K. While trouble shooting I often turn the frequency down so it doesn't make my tinnitus a lot worse than normal. (I have the tinnitus all the time but a 1K square wave will make it really bad.) I have the speakers on 100 watt L pads to turn the volume either down all the way or just very quiet so I can make the speakers quiet while the volume of the amp is turned way up.
I don't have diagnosed tinnitis, though maybe a light case of ringing that I can ignore when I'm not thinking about it. I have friends who do have it bad, and I don't envy any of you! Putting Lpads on your test speakers is a very smart thing to do, IMHO.
--> Steve