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Old 10th May 2007, 05:52 PM   #1
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Default Help with mis-behaving Cambridge 540A

I just pulled my Cambridge Audio Azur 540A out after 4 months of non-use. It has developed a nasty channel imbalance. I have verified that the source and speakers are not the culprits. It sounds pretty good when I adjust the balance knob but I believe part of the output stage has become damaged.

I'm a third year EE student and have built some DIY projects such as headphone amps, DACs and regulated power supplies and this amp is out of warranty so I figured I'd see if I could fix it.

I have been unable to locate a service manual online, does anyone know where I can find one?

Also, does anyone have a suggestion what specific parts may be bad?

Thank you,
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Old 10th May 2007, 05:59 PM   #2
sreten is offline sreten  United Kingdom
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Damaged power amplifiers tend to not work at all.

I'd check switches, potentiometers and connections first.

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Old 10th May 2007, 07:04 PM   #3
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Yeah I was trying to think what would just cause a channel imbalance. I've switched inputs to verify that it wasn't a problem with just my CD input. I've switched over to the B speaker outs, though that doesn't help much since they are internally connected to the same point.

How should I check the pot? Just test the resistance across it is equal for both channels?
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Old 11th May 2007, 05:40 AM   #4
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Test the signal coming from the pre-out socket for the same imbalance. If it's imbalanced there, the fault is in the pre-amp stage, and the most likely culprit is the pot.

You are correct - simply check the resistance measurements on both tracks of the pot.
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Old 11th May 2007, 07:30 AM   #5
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I just got the serivce manual from cambridge, maybe this will shed some light.
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Old 11th May 2007, 07:30 AM   #6
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Looks like the problem is the pot. I tested the pot resistance on both channels. At first I only noticed a small difference, but then I remembered it was an audio-taper pot so small difference at normal levels can be bad.

I picked a data point right around normal listening level to test:
At 9 o-clock on the dial, the right channel resistance measured 17.13 k-ohms and the left channel resistance was 17.01 k-ohms. It seemed close enough to me, but then I realized that I needed to increase the volume to about 11:30 to get the right channel resistance down to the value the left channel had at 9 o-clock.
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Old 21st August 2011, 11:05 PM   #7
sasha70 is offline sasha70  United Kingdom
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Hi I'm looking for service manual for my Cambridge Audio 540A integrated amplifier.
I have service manual for for 540A v2, but need for 540A.
Planning to upgrade OP AMS, potentiometers and caps, same way as I have done on 640C v2, have a manual if any body interesting.
Hope for your advice.
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Old 23rd August 2011, 05:55 PM   #8
sasha70 is offline sasha70  United Kingdom
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Hi I have downloaded service manual for CA 640A and so far this look exactly same as CA 540A, can't see any differences. Price?
Looking for advice:
Double capacitors 47U and 10N in parallel in signal path, what is the reason for them?
Can I bypass them with a piece of wire?
Regards. Sasha.
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File Type: jpg Signal path capacitors.JPG (46.4 KB, 265 views)
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Old 24th August 2011, 12:03 AM   #9
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Reason is to block any DC offset from the NE5532 opamps. If you use low offset output opamps such as something FET based like OPA2134, you can bypass them.
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Old 20th September 2011, 08:06 PM   #10
kevinkr is offline kevinkr  United States
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Kjozsi - the material you posted was clearly marked as copyrighted, complete with a statement that the material may not be copied, retransmitted, or otherwise disseminated without the permission of Cambridge Audio. Such materials may not be posted here.

You may hand copy the original schematics or redraw them, and post your interpretation of their instructions with questions. Note any quotes.

Please do not do this again. (Next time will get you an infraction)
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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