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-   -   Issues with AV123 X-amps (http://www.diyaudio.com/forums/class-d/170961-issues-av123-x-amps.html)

lennon_68 28th July 2010 06:06 PM

Issues with AV123 X-amps
 
So I bought four AV123 X-amps (monoblocks) used off of their forums, they arrived yesterday and I hooked them up. I found that one of them plays much louder with the same signal - like 10dB louder :eek: I posted on their forum but since they're all but dead in the water I'm not getting any response. I of course opened them up and looked for something that looks "adjustable" but didn't find anything - although a large section of components are enclosed in an aluminum heatsink that I didn't attempt to take apart yet.

Any ideas on what I should be looking for?

On a different note the amps come with cheater plugs as they have a bit of a "hiss". When I was hooking up the second one the backs of my fingers were rubbing on the amp below it and it felt like it was really sharp or something. I broke out the multimeter and found that the chassis - with the cheater plug in use - are carrying anywhere between 25 and 40 volts of AC? With the cheater plugs off this goes away of course. For now I'm just running them without the cheater plugs but something doesn't seem right about that? I measured all of them and they all have the AC running through them :confused:

It occurs to me now that anyone that knows this kind of thing will probably want pictures which I don't have at the moment but let me know and I can take some tonight :)

Let me know if this is the incorrect forum as well, I don't post here often but was recommended to come here on a different forum due to the many experts that post here :)

rhing 28th July 2010 10:19 PM

This is the correct forum for your amplifier; however, there might not be much support for these amps since these amps are based on Philips Class D amp modules that aren't really popular with DIYers. On top of that, AV123's implementation of those amp modules was ever changing during their short production run with some Chinese manufacturer with poor quality control. I remembered when they came out, and there were a lot of problems with ground loop hum, loose transformers, blown channels, etc. A friend of mine bought a pair and returned them after a week, because the build quality was so poor and they didn't sound that great.

lennon_68 29th July 2010 03:38 AM

Quote:

Originally Posted by rhing (Post 2256628)
This is the correct forum for your amplifier; however, there might not be much support for these amps since these amps are based on Philips Class D amp modules that aren't really popular with DIYers. On top of that, AV123's implementation of those amp modules was ever changing during their short production run with some Chinese manufacturer with poor quality control. I remembered when they came out, and there were a lot of problems with ground loop hum, loose transformers, blown channels, etc. A friend of mine bought a pair and returned them after a week, because the build quality was so poor and they didn't sound that great.

Thanks for the input. I took some pictures tonight, I'm sure they'll mean more to you guys than they do to me. I understand these aren't top of the line amps or anything... I'm not sure what they were smoking when they came out with a retail price of $299 each but I got these four for about $40 each which seems reasonable to me (but maybe not?).

The pictures are up on my photobucket here:
X-amp pictures by lennon_68 - Photobucket

The heatsink that goes over a bunch of the board is soldered in place plus some of the other components that are soldered to the board are also screwed to the heatsink which would make removing it very difficult for someone with my lack of soldering skills...

Someone on a different forum recommended using an in-line attenuator on the input which may be an option :confused:

lennon_68 29th July 2010 01:39 PM

Someone on a different forum (admittedly guessing) mentioned that there may be an op amp front end that will be gain adjusted by the resistors around it. Sound reasonable?

If so I'm guessing I should be comparing this section of the insides with the ones of the amps that do not have the problem. From what I understand QC issues ran rampant with these so it's not far-fetched to imagine one of the resistor values on this amp is wrong...

This is right where the RCA jack comes in.
http://i713.photobucket.com/albums/w...p/IMG_9634.jpg

Here's a broader view of the insides:
http://i713.photobucket.com/albums/w...p/IMG_9639.jpg


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