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Old 10th February 2007, 10:36 AM   #1
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Default Problem with amp

Sometimes my brother will stop by and we will talk audio and test various recordings with various pieces of equipment. Well one day he brought over his homemade headphone amp named Big Ugly to test it against my Technics V85a. After a few switches back and forth we both noticed that there was information missing when playing the music through my amp. I guess you could say there were symmetrical holes in the soundstage. I have made a crappy diagram to further explain the problem.

Click the image to open in full size.

Imagine the red dots as headphones and the blue arch as the soundstage.

The yellow sections are where I believe the information is lost.
It became even more apparent when I was listening to the intro to Pinball Wizard where (in this particular mastering) the acoustic guitar starts off in the right ear cup and the echo travels over to the left cup. With my amp the echo cuts in and out at those points along its travel.

Does anyone know what could be happening "under the hood" to cause this?
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Old 10th February 2007, 02:03 PM   #2
honsten is offline honsten  United Kingdom
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Location: london
sounds like it could be a capacitor issue, odds are that the "holes" were there all along and the tests that you and your bro have been doing have brought these characteristics out somewhat.obviously his headphone amp is pretty good!
anyway, back to solving your problem... try replacing the caps in the output stage with ones rated with a broader frequency range, you dont need to go all out on blackgates or know the score.
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Old 10th February 2007, 03:22 PM   #3
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Location: Sussex, UK
Hi Mox00,

I can't get see the picture
I can't tell if your comparing the headphone amp to your amp and speakers or your amp connected to headphones.

I think that you're trying to describe a soundstage problem rather than a frequency response problem so I doubt that the caps are the issue. Output caps pass all frequencies above a certain point that is related to its capacitance (and sometimes connected components such as resistors and Coils,and following equipment)

Honsten: I'm not sure what you mean by output capacitors on this amplifier. Does it even have any? Do you mean input caps?

"Ones rated with a broader frequency range" would have a larger capacitance which may only serve, if anything, to pass more low frequencies. These frequencies generally are not involved in the soundstage since they usually go to both channels (and are very hard to locate below ~200Hz in speakers).

I can't see your diagram but, and this a complete guess, it would seem that the two channels are somehow being summed together at certain frequencies and cancelling out.
I'll say it again: This is just a complete guess and I cannot see your diagram!!

As a first step I would check the wiring of your setup to make sure that nothing is out of phase: Speakers or input cabling or maybe even the headphones connector if this is what you are using. I have had problems with these connectors in the past but the symptoms have been more pronounced.

Maybe later I will be able to see the pic...... and stop guessing. Sorry about that but it is an interesting problem and I couldn't help it.

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Old 10th February 2007, 08:41 PM   #4
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Thank you for your comments

Martin, I have attached the file. Perhaps you will have better luck with it.
Attached Images
File Type: jpg untitled2uq8op.jpg (75.7 KB, 59 views)
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Old 10th February 2007, 10:01 PM   #5
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Join Date: Dec 2005
Location: Sussex, UK
Hi Mox00,
I appreciate you taking the time to repost the pic and I can see it now. Yippee!!!

Hmmm, a very strange problem. I stand by most of earlier comments as possible causes. Since you are comparing to such a good (I assume) headphone amp then maybe it is just that your amp has poor channel separation. Have you got any other headphone amps to compare with? May well be that any ordinary amp would have similar results or is it more pronounced than that?

It would be very interesting to make some test tones at different frequencies. Static and also ones that pan from side to side to hear the problem under controlled conditions? Perhaps these identical wave forms may cancel out slightly when panned across the problematic areas.
This is what I'd do but I'm no expert.

I was kind of hoping that someone else would have had this problem specifically or personal experience with this series of Technics amps. My ideas are based purely on theories.

Is it really noticeable or do you have to really listen hard to hear the differences?

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