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Old 8th December 2012, 09:59 PM   #361
bkercso is offline bkercso  Hungary
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Good built, nice! But I would use shielded coils in output integrators.
How does it sound (eg. vs JLH or vs 30 years old Danish "HP-Amp")?

Tripath TPA series is often used for amp and HP amp too. Here is a Muse one: link. There is a combined version (equivalent with this buit with 6.3 Jack connector in the front) but I don't find that. This is class-T, I don't know exactly what is the difference.
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Old 9th December 2012, 07:13 AM   #362
oz7aff is offline oz7aff  Denmark
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I se no reasons for shielding the coils, no hum fields inside the cabinet.

This amplifier uses a TPA3122 IC, and the sound is a little thin I think. But the amplifier is well suited for headphone amp because it has common ground at the output, some of these amplifieres does not have this and therfore need rewired headphones. That goes for the Muse also, it is not fit for headphones.

But this amplifier is cheap and very easy to work with and it also runs on a single 12V supply and deliver up to 15W class D.

2 x 15 Watt 8 Ohm Class D Audio Amplifier DIY Kit TPA3122 15W Stereo Amp | eBay
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Old 29th April 2013, 08:24 PM   #363
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Hello Miles,

I made the modifications you described and everything worked well. However
there was hum cause the Transformer was to close. I decided to put the transformer in an extra case. When I connected everything and powered up and measured voltages everything was fine. Exept that I could not measure an AC Voltage that shoud double on the both secondaries...
So I put my headphone up and there was the most terribel hum I ever noticed!
I was wondering if I have to connect the earth coming from the mains to the
both secondaries which are combined for 0V.
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Old 30th April 2013, 08:46 AM   #364
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Ok, I found out that after putting the transformer back, I mixed up secondaries connections…
how embarrassing
After the connections are back proper, there is still too much hum. Is it possibel that something got destroyed?
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Old 30th April 2013, 09:29 AM   #365
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DC offest is -31mV and 50mv
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Old 30th April 2013, 10:55 AM   #366
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Ok, all good again, I had an earth loop…still dont know why, but for the moment I am happy again
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Old 1st May 2013, 02:03 PM   #367
bkercso is offline bkercso  Hungary
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Quote:
Originally Posted by sangeet2 View Post
DC offest is -31mV and 50mv
You should measure DC offset when amp is warmed up. The offset difference between cold and warm state is about 100mV. Anyway, up to 50-100mV DC is acceptable for headphones.
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Old 1st May 2013, 05:14 PM   #368
Telstar is offline Telstar  Italy
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Quote:
Originally Posted by bkercso View Post
Anyway, up to 50-100mV DC is acceptable for headphones.
ahem I'm not so sure about that
I try to stay under 5mV for 'phones and 100mV for speakers.
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Old 1st May 2013, 05:28 PM   #369
EUVL is offline EUVL  Europe
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Take a low impedance headphone of 32 ohm (e.g. Beyerdynamic DT990-32).
Power handling of the headphone is specified at 100mW.
http://europe.beyerdynamic.com/shop/...90_DB_E_A3.pdf

100mV DC => 0.3mW. So that makes 0.3% of specified power ?


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Last edited by EUVL; 1st May 2013 at 05:31 PM.
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Old 1st May 2013, 06:52 PM   #370
bkercso is offline bkercso  Hungary
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Quote:
Originally Posted by Telstar View Post
ahem I'm not so sure about that
I try to stay under 5mV for 'phones and 100mV for speakers.
No problem with 100mV also @phones, trust me! Anyway, it is clipping when switch the amp ON/OFF. For no clipping <10-20mV is desired (depends on phone's impedance and SPL).
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