Testing DC offset on Amp (K1000/T-Amp)
Mar 8, 2006 at 6:04 AM Thread Starter Post #1 of 9

gordie

100+ Head-Fier
Joined
Aug 13, 2001
Posts
192
Likes
18
I've seen some posts discussing the T-Amp and DC offset issues, which could lead to unhappy headphones. I've got a Super T-Amp waiting patiently for some K1000s, and don't want to fry the headphones if I have any issues with the amp.

I haven't done any electronics testing in a long time, so before I start touching leads to random junctions on the amp, I had a few questions.

Is it OK to simply connect the test probe leads from a multimeter to the one of the hot and ground pairs on the speaker outputs on the T-Amp while its on? Seems obvious, but I'm not sure if this is safe, or if there's anything else I'll need to do to test DC offset (or test for any other potential issues).

Thanks

-- Gordie
 
Mar 8, 2006 at 9:38 AM Post #3 of 9

gordie

100+ Head-Fier
Joined
Aug 13, 2001
Posts
192
Likes
18
Ed,

I'm not sure what you mean by that - for what you mention, what should I connect the two test leads (hot and ground from the multimeter) to?

I was planning on connecting the multimeter's ground lead to the negative speaker terminal, and the multimeter's hot lead to speaker positive, with the amp on, volume turned on 0, and no input signal (since I just want DC) - with some variations, like an input source connected, and maybe turning the volume control up a bit (without an actual input signal)

Thanks

-- Gordie
 
Mar 8, 2006 at 12:57 PM Post #4 of 9

Trogdor

Reviewer: Metal-Fi
Joined
Feb 1, 2004
Posts
4,141
Likes
419
gordie, that's what I did. Just to let you know, I think I might be the first reported victim of DC leakage. I'm not a 100% sure but I would be very careful using the Super T and K1K (at this point I'm putting this setup on hold until I figure out exactly how to prevent this issue).

A good friend of mine who is into power said that sometimes its not the source (amp) but rather the power source and that ina lot of buildings there could be a DC bias already present that is leaking through. Don't know...
 
Mar 8, 2006 at 5:33 PM Post #5 of 9

gordie

100+ Head-Fier
Joined
Aug 13, 2001
Posts
192
Likes
18
I'll make sure to check the amp in any location I use it (it's at work right now, will also test it when I get it home), in case the power out of the wall is different.

I'm also a bit worried now, so considering other options for amps for the K1000s...

Thanks,

-- Gordie
 
Mar 8, 2006 at 9:16 PM Post #6 of 9

Trogdor

Reviewer: Metal-Fi
Joined
Feb 1, 2004
Posts
4,141
Likes
419
Actually I'm stupified. I'm not so sure it was DC leakage that killed my AKG K1000's. Certainly as many of suggested, putting a 6 to 8 ohm resistor on the output terminals maybe a good idea for starters. Uggh, I got to figure this out.
 
Mar 9, 2006 at 2:38 AM Post #7 of 9

gordie

100+ Head-Fier
Joined
Aug 13, 2001
Posts
192
Likes
18
I measured the DC offset on my (one week new) Super T-Amp today, and it was about +50 mVolts (left) and -30mVolts (right).

So for now I'm powering my K1000s out of my Grado RA-1 (driven by my Powerbook headphone out turned up to full), which sounds surprisingly good on a variety of music as long as I don't need to really crank it.

Moral of the story is I'm afraid to use my T-Amp, so looking for something else for the K1000s...

The quest begins.
 
Mar 9, 2006 at 4:02 AM Post #8 of 9

Trogdor

Reviewer: Metal-Fi
Joined
Feb 1, 2004
Posts
4,141
Likes
419
Quote:

Originally Posted by gordie
I measured the DC offset on my (one week new) Super T-Amp today, and it was about +50 mVolts (left) and -30mVolts (right).

So for now I'm powering my K1000s out of my Grado RA-1 (driven by my Powerbook headphone out turned up to full), which sounds surprisingly good on a variety of music as long as I don't need to really crank it.

Moral of the story is I'm afraid to use my T-Amp, so looking for something else for the K1000s...

The quest begins.



Yeah well after talking to Mr Madis about the Super T and doing some math, that isn't a whole heck of a lot of bias. One idea is to simply put a 6 or 8ohm resistor on the outputs. That should allow for better impedance matching and prevent some level of RF and DC interference.

I have not given up on the Super T yet...
 
Mar 9, 2006 at 6:04 AM Post #9 of 9

Teerawit

Headphoneus Supremus
Joined
Mar 21, 2005
Posts
3,988
Likes
11
Add some coupling caps to block DC?
 

Users who are viewing this thread

Top