[CTY]

Hi guys,


My PIMETA arrived this morning. Unfortunately, I have some annoying issues with it.

First issue, I believe the pot is to blame. Sometimes when I turn the amp on, it's working flawless. Then sometimes when I turn it on, only the left channel is working and it's silent on the right one, except from when I turn the pot. Then i can hear static in the right channel, but not in the left where the music is still playing. Third case is, I don't hear anything at all in both channels, but when I crank the volume up, I hear some _very_ distorted parts of the music.
Normally powering off and powering up the amp again several times helps to solve these issues, but that's of course not the way it's meant to be.

Another issue, I think my poor power supply is to blame. I got this one with my veery old laptop. It outputs 20.4VDC, I think this okay for the Pimeta?
Whenever I plug it in a socket near to the one where my PC is plugged in, I get heavy humming. Same when my halogen lamp is running, just the sort of humming differs

I believe a line filter might help?

I hope someone can help me to solve this issue.

Greetings
CTY

 

[heatmizer]

Open it up and post pictures.
Note down what opamps are being used.
Clean the pot.
Does it have a tread or some such inside
Do not use a switching power supply. Switching power supply can screw up the ground reference between Vground and Line Ground .Use a transformer based with linear power supply AKA Tread.

 

[CTY]

Unfortunately, I do not own a digicam. But here's a pic the seller took, the look didn't change, of course

Opamps are OPA637AP, buffers BUF634P.

No tread inside, but I plan on building one for use with a big torodial transformer I have lying around, because the SMPS sucks. By the way, how likely is it for the SMPS to blow up caps or something when using it? I have nothing else at the moment.

And how do I clean the pot? The sticker on the back side is already in part ripped away, so I can see the the pot turning.

 

[tomb]

If you are not mistaken about an OPA637 in Gnd, that may be your whole problem. That looks like a quality build, though, so I doubt the builder would've made that mistake. (OPA637 is not unity gain stable and will not work in the PIMETA's Gnd.)

I tend to agree with Heatmizer: the laptop switching power supply may be the issue. It's possible that it may have a different polarity than center-positive, too.

The 24VDC @ 500ma, linear-regulated walwart at Jameco works well for a quick fix: http://www.jameco.com/webapp/wcs/sto...oductId=174879.

Maybe you can find something similar in Germany.

 

[MisterX]

Quote:

And how do I clean the pot?

Don't even try.

I can assure you the problem is the power supply not the pot.

 

[CTY]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif Don't even try. I can assure you the problem is the power supply not the pot.

You built this amp, so you do know best

You mean, all of the issues I have are related to the PS? I'm likely to build up a dedicated power supply for the amp, as mentioned before, so it should work flawless from then on. Or I'm gonna buy one of the wall warts like the one tomb posted, if they're linear and regulated, they should be as good as a TREAD, right? (Or at least, comparable. I believe building a TREAD is simpler than buying the finished product)

Another Question to MisterX: How do I operate the crossfeed? Set both switches in upper position and cf is enabled?

 

[MisterX]

Quote:

How do I operate the crossfeed?

 

[CTY]

Perfect

Mind giving me some hints regarding my other questions?

 

[Soymilk]

tomb told me in another thread where he also suggested that jameco wall wart to me that it sounds just as good as using a tread for the pimeta. unless you want to build the tread for fun, i'd say just get the jameco one.

 

[MisterX]

The only question left unanswered is one asking for a comparison between a Tread and some random AC adapter.
How are we supposed to be able to answer that?

 

[CTY]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif The only question left unanswered is one asking for a comparison between a Tread and some random AC adapter. How are we supposed to be able to answer that?

No, I meant the question about the issues I had with the Pimeta. If you're clearly saying that the PS is to blame, I will of course believe you. I just wanted you to make that clear again to me before I buy a new wall wart or whatever type of power supply

 

[MisterX]

Quote:

I just wanted you to make that clear again to me before I buy a new wall wart or whatever type of power supply

http://www.head-fi.org/forums/showpo...82&postcount=5

There you go.

 

[CTY]

Hi again,

I finally managed to throw together a simple power supply (just transformer, rectifier and regulator) and the Pimeta works like a charm with that

There is still some humming hearable, but that is totally related to my crappy ps...

Thanks to you all for hinting me to the problem

 

[FallenAngel]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif http://www.head-fi.org/forums/showpo...82&postcount=5 There you go.

Funny buddy.

CTY - nice that you got it solved, grab a TREAD kit from Tangent or make one yourself, it's a very nice cheap PSU that works very well.

 

[TzeYang]

i know this isnt the right time.

but what model number is this case?

I recently planned a tight portable amp which measures about 120mmx50mm. Needs to accomodate 2x 9V batteries, 1x RK097 (air wired) and 2x 1/8 Jacks.