[binkgle]

Hey all, 
 
It's been a VERY long time since I last visited head-fi. I have a xin supermini 3 amp that I haven't used in ages since it produces a lot of noise and, unless I squeeze the input and output cables towards each other while music is playing, it seems to be picking up a talk radio signal of some sort. This started years back when I tripped over a cable and one of the cables was wrenched out of the amp very fast. 
 
I'm guessing that there's a grounding mechanism that's out. I'll post an image of the inside of the amp when I get home later. Does anyone have a diagram of the amp, or know where the ground would be? I have a soldering iron, I just need to know what needs doing. 
 
Thanks, 
Jack

 

[Mad Max]

Have you checked the input/output jacks?  Do all of their tabs make good contact with whatever you plug into the amp?  If not, carefully bend them in a little bit with a needle, pin, or the like and test again.
Hope this helps. =]

 

[Jester]

As an aside I love this amp and hope you're able to resolve the problem. Best of luck!

 

[binkgle]

Look at the socket on the left, where the computer-to-amp cable goes. Half of it has broken off, and while all the pins are there, it seems that the jack loses connection with one of those gold connectors (the one on the right, I think). I get a beautiful signal if I push the cable jack up away from the table while it's in the socket, so the part nearest the edge of the amp hits that connector. 
 
So, how can I fix this? 
 
Also, I still get that radio signal. It happens when there is no music playing but the amp is plugged into the computer, and the amp volume is turned all the way up. There's always a lot of computer noise when no music is playing, but the radio only happens with the amp volume all the way up. 
 
 


 
 

 

[Mad Max]

What I said before, plus check that the damaged socket is still properly soldered to the circuit board.
 
The radio signal sounds like a problem with your USB cable.  You hadn't noticed it before or it began after the accident?  You may have to get a USB cable with ferrite cores or put ferrite cores on that USB cable.

 

[binkgle]

It does seem solidly attached, no wobble, but I'll look again once I can find a magnifier of some sort, just in case. 
 
I'm not sure whether the radio signal was always there or not, it's been such a long time since I've even tried fixing this. It's not a usb cable, though, just 1/8" to 1/8". Do you mean a shielded cable of some sort? Can you suggest one? I'm using a very cheap one at the moment. 

 

[Mad Max]

Because I saw the USB cable in the back.
 
Hmm, I really don't know what the problem could be then as far as the interference.  It does look like your amp's case is metal, is it grounded?
 
Try asking in the DIY forum.

 

[qusp]

nah the cases are plastic as far as I know. a hard plastic, but still plastic. wow AD8397 and looks like a bypassed buffer.OK well sorry distracted there lol. OK well the ground terminal is the one closest to the panel edge, where you have broken it. I would say the central grounding point (star ground) is at the ground wire of the first power supply cap or the ground of the charger input. you could test for continuity between those points. but by the look of your damage there, your problem is that when you ripped it out and broke that piece off, you destroyed the part that was holding the ground ring in place.
 
I can see that the ground terminal seems to be further out/looser than the other jack, you could try just bending it back in so it causes better contact. do this while the case is open and music is playing, just take care not to short anything. otherwise you could find out what type of jack it is and replace it. also if there isnt contact to ground from that terminal, you could even do a quick and nasty fix/test, by connecting a wire from the input jack ground to the output jack ground, they are probably one in the same anyway. my guess its more a mechanical connection issue rather than an electrical connection issue. most likely even when you think you are getting a good connection, its slightly marginal because of the ground ring not being held firmly in place, allowing the radio frequency to sneak into the ground. or its just been there all along; as by the sounds of it you have to have the amp up way louder than you use it to hear it. since its quite a low power amp and with a plastic case, it wouldnt be that hard for noise to be coupled into the signal
 
 
hope that helps

 

[binkgle]

Sorry for the delay in my response. 
 
Qusp, you are right that it's a mechanical issue, but there doesn't seem to be a way to bend the pins enough to fully solve the issue, as the plastic ring the jack fits into is also broken, allowing the jack to move a bit. 
 
So, does anybody know what the make and model of these audio jacks is? If I could buy one, I could replace this bad one. 
 
Thanks, 
Jack

 

[binkgle]

Does anyone know where I can buy a replacement audio jack for my amp?

 

[HiFlight]

As those amps were made in California, it likely uses off-the-shelf parts that you could probably find by checking with DigiKey or Mouser. 
I would go by pictures and datasheet information that you can find after you have done a search for 1/8" jacks on their websites. 
 
Once you track it down, it should be an easy fix.