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Old 7th March 2006, 11:35 PM   #1
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Default DacMagic 2 DC Offset problem??

Hi all... whilst investigation a random sound dropping out on one channel. I started investigating the sources (clutching at straws). I found that the Cambridge Audio Dacmagic 2 line out has a DC offset of -3mV on the left and +5mV on the right. After checking all the other line sources, the 5mV is about 20 times worse than anything else!

Do these offsets seem OK? And is it possible that these offsets could be upsetting my amp?

Many thanks.
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Old 8th March 2006, 12:30 AM   #2
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-2 and +5 is not too bad, it's probaly a product of the output opamp that's being used, if it's a NE5532 they can give varying amounts of dc offset, change to a fet input opamp like the OP275 they can give close to zero or one mv, if your worried about it and you don't want to change opamps you could always put a 10 or 20 uf nonpolarized blackgate nx on the output with a 100k to ground after it. But i can hear even these in the signal path compared to direct coupling, so try some different opamps that have fet input like the OP275 (very tube like), AD825 (smd) my favourite, opa2604. That is if yours is a dual opamp.

Cheers George
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Old 8th March 2006, 10:09 AM   #3
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Thanks,

nice to know that it's not widely out and that I could easily be sorted out with a coupling cap or a possible OP-amp swap. As I was thinking of tweeking it anyhow (as it is full of cheap caps), an op- amp swap may be the long term way to go.

Thanks again and BTW it used twin AD712's.
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Old 8th March 2006, 10:33 AM   #4
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ad712's are a dual and they are fet input, but they're old school tlo72 era and from memory the dc offset could be up or down a bit, bung in a couple of OP275's they're cheap and sound great if you do'nt mind a sort of tube smoothness and a big rich sound.

Cheers George
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Old 9th March 2006, 12:39 AM   #5
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Some good pointers, when I've finished 'hacking' my amp, I'll get it socket'd up and try some different op-amps in there. Even if the offset doesn't improve, it will be nice to hear a different style of presentation. Might even calm it's slighty pushy nature.

Thx
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