Cheap Mosfet amps popping up on ebay for song. Any input???Please Comment - Page 2

Westerp · 28th April 2009, 03:29 PM

Another one and for 14 euro's I would not even expect it to work

I might even order one just for fun.

spirod · 29th April 2009, 04:12 PM

Hi all,
managed to get a few minutes and hooked up the amp for some testing.
The pictures are quite poor sorry about that.
Also see pictures attached the crossover distortion is actually worse IRL, the pictures make is look smoother for some reason.

any how I've added a picture at 1khz one at 20khz and a picture of the top and bottom of the board, if any one is interested.

Overall apart from the crossover distortion, the responce was better than I expected, I have not listened to the sound yet at all as it is late so I will post again when I do get a chance to play some tunes thru it.

FYI PSU is a 25-0-25 toroid. and nothing on the board got hot at all during the 10 minutes of testing, testing was done at low power (2-3 watts) out one channel only. Load was only 12 ohms.

spirod · 29th April 2009, 04:14 PM

output at 20khz, about 15v peak to peak approx 5v RMS

spirod · 29th April 2009, 04:18 PM

Bottom of PCB

spirod · 29th April 2009, 04:20 PM

TOP of PCB

Westerp · 29th April 2009, 04:27 PM

At 2 watts into 12 ohm hmmmm.....

wg_ski · 29th April 2009, 05:53 PM

Quote:

Originally posted by spirod
Overall apart from the crossover distortion, the responce was better than I expected, I have not listened to the sound yet at all as it is late so I will post again when I do get a chance to play some tunes thru it.

The 20k crossover distortion is pretty scary. It's what you'd expect with zero bias in the outputs. That's one sure way to completely avoid thermal runaway - even without bias compensation.

Quote:

FYI PSU is a 25-0-25 toroid. and nothing on the board got hot at all during the 10 minutes of testing, testing was done at low power (2-3 watts) out one channel only. Load was only 12 ohms.

It would take 8 at full power, maybe even 4 if you didn't run it till spit boils on the heatsink. With a +/-35 supply you can run 2N3055 outputs without failure so fakes won't really hurt anything. And you'll only get about 50W.

They are definitely fakes. They're using the Fairchild type package, Sanken-style laser marking, and calling them "Toshiba".

CBS240 · 29th April 2009, 06:25 PM

I suspected class B bias is the case.

Try loading it with 4 Ohms, then output a few volts into it. A square wave test (including different values of cap loading) might be interesting. Look for instability in the crossover region.

Gabdx1 · 29th April 2009, 06:27 PM

I wanne buy

CBS240 · 29th April 2009, 07:18 PM

Really?

One could easily out do this circuit, even with a "blameless" circuit on vero-board. There is more than enough knowledge on this site to suit.

28th April 2009, 03:29 PM	#11
Westerp diyAudio Member Join Date: Jan 2006 Location: Amsterdam	Another one and for 14 euro's I would not even expect it to work I might even order one just for fun. __________________ http://tda1541a.com The Final List

29th April 2009, 04:27 PM	#16
Westerp diyAudio Member Join Date: Jan 2006 Location: Amsterdam	At 2 watts into 12 ohm hmmmm..... __________________ http://tda1541a.com The Final List

29th April 2009, 06:25 PM	#18
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	I suspected class B bias is the case. Try loading it with 4 Ohms, then output a few volts into it. A square wave test (including different values of cap loading) might be interesting. Look for instability in the crossover region. __________________ All the trouble I've ever been in started out as fun......

29th April 2009, 07:18 PM	#20
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Really? One could easily out do this circuit, even with a "blameless" circuit on vero-board. There is more than enough knowledge on this site to suit. __________________ All the trouble I've ever been in started out as fun......

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29th April 2009, 06:27 PM	#19
Gabdx1 diyAudio Member Join Date: Jan 2009	I wanne buy

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