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Naim CD5i problem - opamps
Naim CD5i problem - opamps
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Old 11th July 2012, 09:28 AM   #1
wiland1 is offline wiland1
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Location: Leatherhead, UK
Default Naim CD5i problem - opamps


I need some help on a problem which has me baffled: i replaced the 2 x OPA604 output opamps in my Naim CD5i with 2 x OPA827 on Browndog adapters. I liked the sound, which improved over the course of a few weeks as they burned-in, so decided to replace the other 4 x OPA604's (the i/V stage?) with 4 x OIPA827's on Browndogs. I then powered up and can hear only the left channel.

I've covered the basic problem solving steps:
  • Continuity checked the signal path from the first Opamp, through to the socket on the back of the player.
  • Swapped Browndogs for new ones and replaced the 2 x OPA827's in the faulty channel.
  • Checked for any shorts on the pins of the opamps and adapters
  • Replaced the Reed relay on the output.
  • Switched interconnect cables and checked my amp input with another CD source.
Still no joy - oddly, the right channel does work very briefly for ~1-sec, after a disc has been playing for ~20-secs, then it goes again for good.

I was wondering if the OPA827 is simply not a good drop-in replacement for the OPA604 in the i/V stage? But then why would the left channel work and not the right? Perhaps it's operating on the limit of its spec. Can anybody help guide me on this, because i've run out of ideas! (other than replacing the 827's with 604's, which i've not done yet)

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Old 11th July 2012, 10:58 AM   #2
Mooly is offline Mooly  United Kingdom
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Join Date: Sep 2007
Naim CD5i problem - opamps
The most likely cause is something physical such as broken or open print or a solder blob somewhere.

Careful voltage measurement should reveal the problem. Check the DC voltage on the output of all the opamps. Usually (but not always so compare left and right) this will be around the zero volt region.

It is just possible the opamps could be unstable for some reason and is something that should be checked as a matter of course. The symptom of it working for a second and then not could possibly suggest a floating input and the bias voltage just happens to "float" through a window where it works.
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Old 11th July 2012, 11:12 AM   #3
analog_sa is offline analog_sa  Europe
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Location: Cascais
Buy a scope. Learn how to use it.
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Old 11th July 2012, 02:40 PM   #4
wiland1 is offline wiland1
diyAudio Member
Join Date: Dec 2011
Location: Leatherhead, UK
Thanks Mooly - that gives me another angle to work with. I did check voltage on the outputs and it moves above and below 0V by a few points, but i'll do it again with a more critical eye.

As for the scope - you're right - I was looking at them the other day! More a question of funds right now, than the desire to own one, hence the reason i didn't want to chuck more money at this issue...

BTW - i had excellent audio results with the OPA1641/2/4 series in my VDac-2 - now they've burned in, they are really musical. I put another post up on here about that.

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