Electronics > Repair
Audio… (Amps, THD, channel separation) with analog equipment (scopes, etc.)
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Tation:
I think that, in order to measure THD using a reasonable amount of money, the best solution goes thru an external (USB) sound card. Focusrite seems to be one of the preferred brands, but there are many others, and people have reported good results with more affordable brands, like Behringer.

DIYAudio site maybe of interest for the OP.
bdunham7:

--- Quote from: Fried Chicken on December 29, 2024, 07:01:55 am ---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.

--- End quote ---

The filter caps are 33000µF?  And only 50V?  What is the power supply voltage and what is the rated power of this amplifier?

If there's a clearly audible problem then you should be able to track it down--with some help and guidance perhaps--using the tools you have plus a pair of 8R power resistors as test loads.  If you recapped it and the problem started then, you've probably made an error somewhere.  I doubt it is the filter caps, but if you suspect them or some power supply issue then put your scope on the power rails and look at them when you load the amplifier.  With a signal into a test resistor at higher volume you'll see a sawtooth pattern with an inverse of your signal superimposed on it.  As long as the rail doesn't drop too much everything is OK.
Fried Chicken:

--- Quote from: bdunham7 on December 29, 2024, 02:52:01 pm ---
--- Quote from: Fried Chicken on December 29, 2024, 07:01:55 am ---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.

--- End quote ---

The filter caps are 33000µF?  And only 50V?  What is the power supply voltage and what is the rated power of this amplifier?

If there's a clearly audible problem then you should be able to track it down--with some help and guidance perhaps--using the tools you have plus a pair of 8R power resistors as test loads.  If you recapped it and the problem started then, you've probably made an error somewhere.  I doubt it is the filter caps, but if you suspect them or some power supply issue then put your scope on the power rails and look at them when you load the amplifier.  With a signal into a test resistor at higher volume you'll see a sawtooth pattern with an inverse of your signal superimposed on it.  As long as the rail doesn't drop too much everything is OK.

--- End quote ---

I have two 8Ω power resistors that I've been running all these tests on.
Yes the originals were 50v and 35v Nichicon and Elna.

The Amp was working, but something was off and it got progressively worse after the recap (that included the filter caps)... that I didn't notice until I hooked up the Sony and realized what real sound is.  It's textbook not enough power... I also have a hard time believing the filter caps would go bad and cause that, but that's my immediate instinct
CaptDon:
120vac line voltage is around 340vpp.  As to your amplifier 120vpp equal 60 vp x .707 = 42.5vrms and that becomes 225 watts rms with no head room or around 22.5 watts with 10dB of head room all assuming an 8 ohm load.
Fried Chicken:

--- Quote from: CaptDon on December 29, 2024, 05:36:34 pm ---120vac line voltage is around 340vpp.  As to your amplifier 120vpp equal 60 vp x .707 = 42.5vrms and that becomes 225 watts rms with no head room or around 22.5 watts with 10dB of head room all assuming an 8 ohm load.

--- End quote ---

ok?
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