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Old 20th September 2006, 04:24 PM   #11
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OK, I'm a total noob as fas a electronics go, However, I would like to improve my cambridge audio 640A by replacing some caps.

Is there a picture guide on doing something like that?

From the posts above I understood , the biggest improvement would be to replace the power amp input caps with some better film caps...

By noob, I mean really noob, Couldn't tell a resistor or capacitor apart....
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Old 20th September 2006, 06:45 PM   #12
jaycee is offline jaycee  United Kingdom
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With no expertise, you are really best leaving well alone or you will end up with a dead amp. Sorry to be so negative about it but I have seen plenty of people kill their gear by attempting mods they read about on the internet, but they had no experience of implementing them.
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Old 20th September 2006, 08:24 PM   #13
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Thank you for the advice, I'll just leave it as it is...
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Old 12th November 2006, 07:57 AM   #14
ricafe is offline ricafe  Malaysia
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I have the Azur 640A V2.0 and it seems that it clips easily
whenever I try to drive it volume pass 11 o'clock even I disable the clip protection cricuit (CAP5) during power up , and I can't play me Kitaro and Eagle's Live CD satisfy .

FYI, I have a pair of Mission 753 Freedom connected at the output.

Is there anyone who had try to modify the protection circuit to make it less sensitive or best still, to totally dissable it.

I need the protection section circuit and if anyone have, can please email to me at

Many thanks in advance.

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Old 12th November 2006, 08:48 AM   #15
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Why do you think there is a protection circuit ??

Modding the protection circuit should only be with great care...

Why not try to locate the reason ?
Have you measured the rail voltages during clipping ?
It could be because the power bank is to small, so the rails drop easily under load
Free Schematic and Service Manual downloads, Spare time company (just for fun):
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Old 12th November 2006, 08:51 AM   #16
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You might just be trying to push the amp too hard. I'd look at upgrading to a bigger one and speakers to match if I were you.
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
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Old 12th November 2006, 10:59 PM   #17
ricafe is offline ricafe  Malaysia
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" Why do you think there is a protection circuit ?? "

From the WEB at Cambridge Audio and the given customer operation manual, its said there is a build-in protection circuit called "CAP5" and it also taught on how to disable it.

During driven hard, you will be able to hear the relay to speaker output clips, there no sound from the speakers, and the red LED on the front panel blinks.

I played with the source direct button ON and even that it clips.

You will have to power OFF the set and restarts it again inorder to continue playing.


" You might just be trying to push the amp too hard."

NO . NO .

I have a Rotel RC-980BX pre-out connected to an Acram 8P and I try to play the same CD's with the same sound level but there's any problems.

BTW the Acram 8P only rated 50W output but the CA 640A V2.0 had 70W.

I did try to measure the rail voltage during Clipping with a digital Multimeter and it looks OK !! Only a slight drops of +- 2,3 volts during hard drive.

With the CA 640A V2.0 output, I believe that it's better than my faithful Acram 8P but real test review otherwise.

As for the sound stage, it is good with tight bass and clear at high end when play at normal volume level. .


" Modding the protection circuit should only be with great care...

That's why I would like someone who know the circuit well or have a circuit diagram to guide me on that.

Many thanks.
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Old 28th August 2008, 07:41 AM   #18
Stream is offline Stream  Russian Federation
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Hi all. Sory for getting up so old topic, but I would be pleased if anybody makes some photos of 640A for me and other...

I have an Azur340A and want to compare this two amps.
Photos of 340A you cn see here:
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Old 5th October 2008, 11:47 PM   #19
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just a standard Taiwanese circuit
This amp is infact british designed and only built in the far east.

I own A 340A SE which has 10'000uF caps per rail and its only a 45 wpc amp. I would say go with the 12'000uF per rail or possibly a tad higher if you have space.

Input buffer (preamp) mods:

Use 2.2 Film MKP types for signal path decoupling (I used Mundorf's). Upgrade the local decoupling caps (grey box types) to larger high quality caps (I used 100uF 25v Nichichon MUSE). Fit a socket and try some better opamps (I uesd LM4562). Also upgrade the local decoupling caps on the input selector chip.

Click the image to open in full size.

Im assuming the circuits are simmilar on 340,540,640A's so the following should apply too:

There are signal decoupling caps before the power stages so change these to 2.2 film types. Also in the tone circuit there are a pair each (tone and 'tone bypass') which need replacing. Again use film types. If you use the tone control then replace the ones in that circuit and try some better opamps.

PSU: Fit some good quality low ESR caps (such as Panasonic FC, Blackgate etc) inplace of the cheapo lytics - before and after the opamp regulators. I have replaced the 100uF caps on each rail -after the regs - with 220uF Blackgates. Replace the diodes on the power amp supply with hexfreds. Use Shottkey type on the preamp stage. Lastly fit some low noise regulators such as 'Spower' inplace of the 7815,7915.

Click the image to open in full size.

Click the image to open in full size.
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Old 5th October 2008, 11:53 PM   #20
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Default Well boys... have schematic for uncle Charlie? kind with your old friend here:

I am , JUST CRAZY, for this amplifier... also i will be very, very, very, very happy to watch the schematic and to assemble it in my home to listen.

This is Doctor Self last design...and they guy use to do good things... and this unit has some modifications into the bias system...some kind of dinamic biasing from A to AB. and the oposite..seems something different than usual automatic shift, something usually happens from class A to AB when we increase volume


Sorry, Brazil only to be sold... top secret ultimate schematic, not to share...encapsulated VAS:
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