Electronics > Repair
Audio… (Amps, THD, channel separation) with analog equipment (scopes, etc.)
Fried Chicken:
I'm calling it quits for tonight;
I'm going to put the amp back together and actually use it, b/c that's why I have it. Maybe something will change. Maybe I'm chasing a nothingburger, but if the scope is lying, the Fluke 45 is not. What a thing. It's pinpointing that ever so slight less voltage.
bdunham7:
--- Quote from: Fried Chicken on December 27, 2024, 03:56:27 am ---Surely something can be done with a normal scope? I mean the scope samples at several orders of magnitude above audio signals?
Are there no analog tricks or similar?
--- End quote ---
I missed this thread or I'd have given you the short answer first: A scope and ordinary tools are useful when testing and repairing a malfunctioning audio amplifer but are nowhere near good enough to quality-test the final product. You might aim for 0.1% THD or better, but you won't be able to even see 1% on a scope even using offset or null methods. 10% THD maybe by comparison. Have you verified that if you feed the same signals to both channels of your scope that you can adjust it so that they overlap perfectly? And if you invert one channel, you get a flat trace?
Fried Chicken:
WOW.
I THINK I FOUND THE PROBLEM.
The amp is completely anemic and shitty, not like it was before. It completely lacks power, and the reason for that, I suspect, is the amazing Elna and Nichicon filter caps I replaced with mouser p/n: 598/383LX333M050B052
I hooked up an old sony amplifier thinking maybe there's something else that could be wrong (speakers, preamp, etc.). OH BOY HOWDY WAS THE POWER BACK.
I'm pretty sure the filter caps I installed are garbage; luckily I still have the originals. Way to big to even test with my LCR meters. I could charge it and hook up a resister and find the time constant and back calculate RC whatever, but I am disinterested.
I'm just going to put the old caps back in and cry that they're NLA new... manufactured with real pride, gold cursive lettering on black with FOR AUDIO prominently displayed across the front.
Coordonnée_chromatique:
--- Quote from: Fried Chicken on December 29, 2024, 07:01:55 am ---mouser p/n: 598/383LX333M050B052
--- End quote ---
"readily handles tough switching power supply input and output circuits and motor-drive"
There are not designed for a linear PSU, do you hear an energization noise when you power up the PSU (like a soda can noise opening) ?
Haenk:
--- Quote from: Fried Chicken on December 27, 2024, 03:56:27 am ---Surely something can be done with a normal scope?
--- End quote ---
I guess, the short answer is "no", at least not as a precise measuring device.
On a budget, you could use a good external PC/USB sound card to measure the performance (200+ USD). That is probably the cheapest option.
Next step up would be COSMOS ADC+precision generator (that would be like 400+ USD) oder QuantAsylum (even more expensive, at 600USD).
Next up would be a used Audio Analyzer, depending on brand and quality, that's 1000+ USD, up to a couple of k.
If money does not matter, an "Audio Precision" would be the top of the line, at tens of k.
Those are the instruments "everyone" uses for measuring audio devices, no shortcut or cheap option there.
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