[Sinbios]

My new elpac got in the door today, and when I plugged it into my Pimeta, there's a buzz coming out of it. Not too serious, but very annoying when the pot's turned more than halfway. Now, when I touch my finger to the DC jack, it goes instantly away. However, when I grounded the jack to ground in the amp itself, and then to real ground from my power strip, the buzz remains. How would I go about fixing this?

 

[cetoole]

DC jack is supposed to be isolated from the case.

 

[robzy]

Quote:

Originally Posted by cetoole DC jack is supposed to be isolated from the case.

As above, the ground of the power pack should have NOTHING to do with the amps signal ground, which is created by the TLE

Rob.

 

[Sinbios]

It doesn't - it's in a plastic Serpac case.

 

[kin0kin]

edit.....sorry....mistake here

 

[Sinbios]

But would that not introduce it into the ground channel? Or do you mean the PG hole?

 

[kin0kin]

Wait, My mistake. Don't tie the DC fround to input ground.....sorry about that. Try to isolate everything, including your jacks.

 

[Sinbios]

Everything has been isolated, since it's a plastic case. I find it interesting that touching the jack would make the noise go away, but grounding it won't... any insight in that?

 

[kin0kin]

Do you know if the metal barrel you are touching is V-/V+, or neither? if it's neither, ground it to PG/IG and check if the buzzing is still there. btw, remove al your opamps and check the supply pins before turning it on with the opamps.

 

[Sinbios]

I hooked the plug to be tip positive, so the barrel is V-.

 

[kin0kin]

(oh btw, i'm talking bout the jack's barrel....the hum goes away when you touch the jack's outer barrel, no?) not neccessarily, that's why I asked you to check it out

my walwart has a +ve at outer barrel, and -ve middle pin. when connected to the jack, I measured the outer barrel of the jack to -ve, and there is no continuity. Although it is metal, it could be isolated

it's the same thing as some pots, the housing may be metal, but it is not tied to the pot's ground. Since it is so close to the signal, it may cause some interference. Therefore grounding it may solve the problem.

Now take out your MM and double check it

if't it's neither, ground it to IG/IP and the hum should go away. But still, remove the opamps and take measurement on the power pins first....sh1t happens.

 

[USER NAME:]

I've ordered about 200 Elpacs this year and had about 5 defective units. The defective units all caused a hum in an otherwise functional amplifier. You may have a defective unit.

 

[Sinbios]

Quote:

Originally Posted by kin0kin (oh btw, i'm talking bout the jack's barrel....the hum goes away when you touch the jack's outer barrel, no?) not neccessarily, that's why I asked you to check it out my walwart has a +ve at outer barrel, and -ve middle pin. when connected to the jack, I measured the outer barrel of the jack to -ve, and there is no continuity. Although it is metal, it could be isolated it's the same thing as some pots, the housing may be metal, but it is not tied to the pot's ground. Since it is so close to the signal, it may cause some interference. Therefore grounding it may solve the problem. Now take out your MM and double check it if't it's neither, ground it to IG/IP and the hum should go away. But still, remove the opamps and take measurement on the power pins first....sh1t happens.

Oh, I just realized I didn't mention that the amp does work, there's just a noticeable buzz when I turn the volume high, so it's not oscillation. It disappears when I turn the pot about halfway down, but it's quite annoying when I need to get any kind of volume, and apparently easily dampable.

I know the barrel is V- because when I insert the + probe into the center and -probe on the barrel, the voltage reading is positive. Also, when I tried connecting the barrel to ground, the wire sparked a bit and tried to weld itself to the pot...

 

[kin0kin]

Quote:

Originally Posted by Sinbios Oh, I just realized I didn't mention that the amp does work, there's just a noticeable buzz when I turn the volume high, so it's not oscillation. It disappears when I turn the pot about halfway down, but it's quite annoying when I need to get any kind of volume, and apparently easily dampable. I know the barrel is V- because when I insert the + probe into the center and -probe on the barrel, the voltage reading is positive. Also, when I tried connecting the barrel to ground, the wire sparked a bit and tried to weld itself to the pot...

Maybe I wasn't clear. Anyway, just to cofirm things:
1) Picture 2 is what you are getting, mid pin +ve, outer barrel -ve.
2) when you plug it into the jack. Assuming (2) is middle pin. Putting your -ve probe on (1) and +ve probe on (2) gives you a voltage reading? or nothing?

And to my understanding, when you touch on (1) with your hand the hum goes away, is that right?

if measuring (1) to (2) doesn't give you a reading, try doing what I said in post 11. And Hopefully, your pot's housing is grounded to PG.

 

[Sinbios]

I have this fancy closed circuit jack here:

http://www.cui.com/adtemplate.asp?in...116&subcatky3=

Which pins do I measure? I already forgot how they're hooked up