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Old 30th May 2012, 12:37 AM   #1
Beranga is offline Beranga  Mexico
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Question Balanced to unbalanced schematic, is this one good?

Would you say the balanced input of this amplifier has better noise rejection or any advantage over its RCA input? I understand the amp is not fully balanced, but my preamp is, so what do you think?

Thanks in advance.
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Old 30th May 2012, 01:12 AM   #2
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I'd think a balanced input will always reject more common mode noise/hum than unbalanced. That said, I've never seen a problem with standard single ended pre and amp connections. It may not be a universal law like gravity, but I also think there's an inherent internal noise penalty with a differential input because you've got another channel of active devices. The only way around that would be the use of a transformer, which should have near zero noise contribution. So, if you need differential, use it, otherwise single ended will most likely beat it for self generated noise and THD.
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Old 30th May 2012, 11:07 PM   #3
Beranga is offline Beranga  Mexico
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Thank you for your response. I understand and agree with you in general. My question was about this specific design, as I've read about some circuits that lower the noise by only 20 dB and others that can do much better.

I've also read about transformers being the best way to ´unbalance´ a signal, but this is a supposedly good amplifier (Cambridge 840W) and was wondering if the balanced input was also well designed, on the opinion of the knowledgeable people around here.

Thanks again.
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Old 31st May 2012, 12:44 AM   #4
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I would first ask why pins 8 and 2 were left floating
rather than 52K returns from the output? Has some
mission critical information about this "terrapin" been
left out?
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Old 31st May 2012, 02:36 AM   #5
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Default Balanced to unbalanced schematic, is this one good?

Beranga,


The Cambridge Azur 840W power amplifier has balanced line level, signal splitting transformers on its inputs to allow its use in numerous ways beyond most other audiophile brands and models, moreover like that found on pro AV gear (signal looping, for one example), although with much lower distortion. The matching Cambridge preamp utilizes balanced line level output transformers. This combination allows simple worry-less connectivity without the chance of stray AC or DC offset being introduced into the signal chain.

Sorry to say, the preamp schematic you posted is of far less signal caliber than the Cambridge amplifier. The 840W amplifier is probably best matched - connected to the 840E preamplifier. The engineers seriously designed these units to work very well together especially via their balanced connections.


Best Regards,

Rich
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Old 31st May 2012, 02:56 AM   #6
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Quote:
Originally Posted by Beranga View Post
Would you say the balanced input of this amplifier has better noise rejection or any advantage over its RCA input? I understand the amp is not fully balanced, but my preamp is, so what do you think?

Thanks in advance.
No.

The shield is connected to signal earth and therefore all external interference/noise is directly injected into the audio path.
What you want is a separate path for the interference/noise as is described in the AES48 standard. Iaw shield to the chassis!
aes48-2005-f
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Old 31st May 2012, 02:59 AM   #7
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Default Balanced to unbalanced schematic, is this one good?

Beranga,

I should have said that I realize that the preamp schematic is by Cambridge. It's design capability is simply not on par with the latest 840E preamplifier and 840W power amplifier.


These units work very well together especially via their balanced connections.


Best Regards,

Rich
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Old 31st May 2012, 03:46 AM   #8
Beranga is offline Beranga  Mexico
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Quote:
Originally Posted by Dirk95100 View Post
No.

The shield is connected to signal earth and therefore all external interference/noise is directly injected into the audio path.
What you want is a separate path for the interference/noise as is described in the AES48 standard. Iaw shield to the chassis!
aes48-2005-f
Thank you Dirk, I will have a look at that paper.
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Old 31st May 2012, 03:51 AM   #9
Beranga is offline Beranga  Mexico
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Quote:
Originally Posted by RBorkowski View Post
Beranga,

I should have said that I realize that the preamp schematic is by Cambridge. It's design capability is simply not on par with the latest 840E preamplifier and 840W power amplifier.


These units work very well together especially via their balanced connections.


Best Regards,

Rich
Rich:

Thank you for your response. Actually, what I posted is the schematic for a 840W amplifier, straight out the service manual. I posted it without the title to make the file smaller, but here it is complete:
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File Type: jpg 840W Sch.jpg (753.2 KB, 337 views)

Last edited by Beranga; 31st May 2012 at 03:56 AM.
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Old 31st May 2012, 03:53 AM   #10
Beranga is offline Beranga  Mexico
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Quote:
Originally Posted by kenpeter View Post
I would first ask why pins 8 and 2 were left floating
rather than 52K returns from the output? Has some
mission critical information about this "terrapin" been
left out?
Kenpeter, thanks for your input, but at what pins are you referring?

Edit: Never mind, I found the pins you talked about. Thanks

Last edited by Beranga; 31st May 2012 at 04:07 AM.
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