[doobooloo]

I've finally had some time to build myself my own META (after a few for my friends and purk here at head-fi), and for this META I decided to just run it off straight from the Elpac WM080 power supply, a 24V wallwart mentioned in Tangent's website for its clean output. For all previous METAs, I've tested them and made them for 2x 9V batteries.

The parts that I'm using are basically identical to the ones I've built previously, except that I'm using quad-stacked EL2001s instead of single EL2002s.

However, I'm noticing something that was never there before with previous METAs - background hiss (even without source connected) with my CD3000. I tried adding a 120Ohm resistor for R9, and that almost completely eliminated the hiss (still a slight, very slight audible hiss) but now it is not 0ohm output anymore...

Is this a common occurence with wallwart power supplies, (will making it battery based eliminate the hiss) or some mistake I made during construction? Oh, btw, the case is made of wood, so there's no shielding and perhaps it's the particular noisy EM surrounding at my summer house?

Oh well. The 120ohm output still sounds fantastic (I actually kind of like how it made the CD3K sound "fuller") but still I'm a little bothered by this whole hiss thing. Too bad I don't have my HD600s now to test it on those...

Any ideas? Thanks in advance!

 

[usc goose]

improper grounding, interference, flourescent lights, crt monitors... hmmm. turn everything off around it and see if that helps.

 

[fiddler]

With my META42, I get a slight hiss around my CRT monitor, and a loud buzz near fluorescent lights. Probably a shielding issue.

 

[Whit]

Is the hiss constant regardless of the volume level or does it increase as the pot is turned up?

 

[doobooloo]

i have a 21inch crt monitor that i am using my meta right next to.

the hiss is pretty much constant, except at around 80~90% volume it dips for a little bit and then at 100% it comes back up. strange.

perhaps it is a shielding issue. don't think it is a ground issue since the virtual ground is completely isolated from the PS ground (it's wood!) so... hmm perhaps i'll try wrapping the thing in like multiple layers of aluminum foil, and see... or find some metal case that i can try this in or something... eeaak

 

[Whit]

When you use the aluminum foil you must ground the foil to the virtual ground or it's shielding properties will be ineffective.

 

[Sol_Zhen]

Funny thing about mine. When I changed from battery to my Elpac AC power, it eliminated my hiss problem.

 

[usc goose]

my battery powered hisses way more than my wallwarted too. weird thing is with both of them, hiss goes away if i flip them upside down.

 

[dokebi]

All of my hissing problems disappeared when I moved to a new place which brings me to the conclusion that my old place had some nasty electricity.

 

[Rizumu]

Quote:

Originally posted by fiddler With my META42, I get a slight hiss around my CRT monitor, and a loud buzz near fluorescent lights. Probably a shielding issue.

Just tested this out on my battery powered META which hums with my main system. Put my amp closer to my monitor and it buzzed like crazy, move it away and it diminished. Still there though. My source is right next to my monitor though. No buzz with my PCDP connected to a wallwart away from my comp though. So I think this is my problem at least...

 

[orl2222]

Sounds like a ground problem. Check all your switches, rca jacks etc. Especially if your using a metal case.

 

[joe_cool]

If you have a volume control that is ungrounded (wood or plastic case, or metal case which floats from signal ground) then you should connect the metal bushing to ground with a ring lug or soldered ring of solid wire. The Alps pots are especially prone to this since the metal shaft is outside the chassis and picks up noise. I also use a 10 ohm resistor in series with the headphone outputs (R9) but I don't know if this is necessary. You shouldn't hear any significant noise with the inputs open and the volume at max.

 

[doobooloo]

the alps pot has been grounded to the virtual ground.

perhaps it is the combination of being right next to my crt, and also being enclosed in wood without any shielding...

oh well.

 

[fiddler]

After re-encasing my amp into a 1455 Hammond case, and temporarily grounding the case, I got rid of most of the buzzing/hissing. However, I haven't found a good permanent way of keeping it grounded... I need to find a nice clip or something.

 

[tangent]

You haven't really said you went and tried batteries with this amp. I know you've built other amps like it that used batteries, but that isn't the same thing. Try connecting up some batteries temporarily to see if that changes anything.

As far as output impedance goes, if you put the resistor inside the feedback loop (R9 -> R8) the output impedance of the amp as a whole will still be nearly 0 ohms, due to feedback. If this cures your problem, I would suspect that it's just due to high sensitivity in your headphones, which is a common cause of slight hissing in this kind of amp.