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Cambridge Audio CXA81 Review (Sample 2)

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amirm

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I asked this question previously, you probably missed it. Which of the Cambridge measurements is valid, the ones in the first review or the ones in the second review. It doesn't get any simpler than that.
It doesn't get simpler but if you are not paying attention, then you won't understand the answer already given, or this one.

Company wanted me to investigate lifting the ground from USB. I had already returned the first unit so I could not. So they sent me one. In the process of evaluating this, I realized that USB cable is polluting the performance of the device in every subsystem (whether used or not). In the first review, USB was plugged in all the time. In this review, it is only connected when testing USB input. So if you are going to leave USB plugged in all the time, the first review is more representative (*). If not, then this one is.

* I say more representative but because we are talking about noise leakage from a computer, there is no way to predict what performance you see. This is the nature of this problem and cannot be dealt with.
 
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amirm

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Who said that?
He did. Are you not reading anything before commenting? He said to test the unit before clipping which means lower voltage.
 

laudio

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I think we can all chill a bit about apologies and such, I agree with that he retested, gave the opportunity to show that it's a competent unit, and gave the precision on what has changed and why. Amir have put the extra work, no apologies needed there. But still we could debate about if "It's on Cambridge":

"Issue was brought up that this is an instrumentation thing that the Audio Precision analyzer is creating a loop and ground noise that would not be there. While this is true, I explained that I have tested hundreds of DACs that don't have this problem."

So the key word here is: instrumentation issue. If a measurment shows a problem that don't exist in real life usage, we can hammer as much as we want that others don't have this "problem", but if it's only present when you connect an AP and in no other situation, if the matter is understood, and it can be demonstrated that no possibility it creeps into the audio signal when listening to music, well, it's a non issue, it's not "On Cambridge". Electronic designers need to use instrumentation of course, but they don't design to fix analysers weird behaviours. If some do, it may be by chance, it may be just different way of working the grounding scheme, or maybe they put the extra work on looking good on AP, but looking good on an AP analyser is not a design goal in itself, it's a consequence. If there is no problem, there is no problem.

This. That statement is the 2nd review pretty much says the test equipment caused the ground loop. So any other inferences about the performance of the unit (and I think it's even stated after this that there is now way to know for sure) in a real world situation (sans test equipment) is kinda meaningless. To me anyway. A dead horse it being beaten. It's the Heisenberg uncertainty principle and why I don't always rely on measurements :)
 
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amirm

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That statement is the 2nd review pretty much says the test equipment caused the ground loop.
Stunning level of reading incomprehension.....
 

firedog

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If you can't leave the USB cable connected without degrading performance that's a big negative. Can't imagine why anyone would accept that design limitation. Especially at a $1400 price point. :facepalm:o_O:D
Maybe I didn't understand something, but this seems like a huge negative. I think most people using computer audio are going to want to use the usb connection. If other companies don't have this problem, why does Cambridge?
 

laudio

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Stunning level of reading incomprehension.....

Did AP cause a ground loop or not, simple question. I think you already said it did? Guess I misread.

"Issue was brought up that this is an instrumentation thing that the Audio Precision analyzer is creating a loop and ground noise that would not be there. While this is true, I explained that I have tested hundreds of DACs that don't have this problem."
 
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amirm

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Did AP cause a ground loop or not, simple question.
I tested using AP's Toslink output which fully isolates the AP from the device. The addition of USB from the computer, lowered performance.

index.php


What you quoted was their theory before I investigated and found this issue.
 

Talisman

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Question, does the signal degrade even if the usb cable is simply connected to the usb input of the cambridge or must it be connected to a pc to give problems? would there be the same problems if a tablet was connected? (This is my use case, iPad connected with usb)
in the meantime i'm using my cxa 61 as a preamp that drives a Hypex Ncore 252 module, keeping the output below 1.5v i shouldn't degrade too much performance right?

EDIT
As not mentioned, I'm an idiot, my iPad is attached to the usb, but the topping dx3pro + not the cambridge, no problem for me, but maybe someone else is interested in knowing.
The preamp question is always valid instead
 
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sarumbear

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I think we can all chill a bit about apologies and such, I agree with that he retested, gave the opportunity to show that it's a competent unit, and gave the precision on what has changed and why. Amir have put the extra work, no apologies needed there. But still we could debate about if "It's on Cambridge":

So the key word here is: instrumentation issue. If a measurment shows a problem that don't exist in real life usage, we can hammer as much as we want that others don't have this "problem", but if it's only present when you connect an AP and in no other situation, if the matter is understood, and it can be demonstrated that no possibility it creeps into the audio signal when listening to music, well, it's a non issue, it's not "On Cambridge". Electronic designers need to use instrumentation of course, but they don't design to fix analysers weird behaviours. If some do, it may be by chance, it may be just different way of working the grounding scheme, or maybe they put the extra work on looking good on AP, but looking good on an AP analyser is not a design goal in itself, it's a consequence. If there is no problem, there is no problem.
I think you miss-understood the issue.
amirm said:
Issue was brought up that this is an instrumentation thing that the Audio Precision analyzer is creating a loop and ground noise that would not be there. While this is true, I explained that I have tested hundreds of DACs that don't have this problem.
The noise was generated when a cable is plugged into the USB socket, even if the other end of the cable is not connected anywhere. That is not instrumentation problem that only exists within @amirm's test environment. It is a situation that can exist at any owners' set-up.
 

Bryan T

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I tested using AP's Toslink output which fully isolates the AP from the device. The addition of USB from the computer, lowered performance.

index.php


What you quoted was their theory before I investigated and found this issue.

I’m confused about how this is wired. My interpretation was that your TOSLINK+USB experiment supported the ground loop hypothesis, not refuted it.
 

Bryan T

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I think you miss-understood the issue.

The noise was generated when a cable is plugged into the USB socket, even if the other end of the cable is not connected anywhere. That is not instrumentation problem that only exists within @amirm's test environment. It is a situation that can exist at any owners' set-up.
??? I thought the USB was connected to the computer, completing the loop since the AP is also connected to the computer. ???
 

F1308

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Amir, you have been warned.

Please, oh please, ground yourself every single time before start testing any other device.
One never knows.

And thank you indeed for your good testing.
 

sarumbear

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??? I thought the USB was connected to the computer, completing the loop since the AP is also connected to the computer. ???
Please read the review again.

amirm said:
We see noise intrusion reducing SINAD by a few dBs relative to TOSLINK optical. Here is a key discovery though: this is NOT due to USB input but mere connection of USB cable. You can see that noise even with Toslink when I have USB plugged in (but not used as an input):
[...]
Turns out this noise issue will proceed to corrupt the measurements of all other subsystems and was the reason why the amplifier for example did not perform well either in the first round. The impact with this second unit is lower than first sample though. This could be due to noise conditions changing on my test system (nature of computers and grounding) or something is different in the second sample.

To eliminate USB noise as a factor I continued the rest of DAC tests using Toslink so let's go through them quickly:

Notice that @amirm tested the unit using Toslink input as USB input was still noisier. Emphasis is not mine.
 

Kosimo

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I have both in two different setups and I am happy with both (topping on Kef LS50 Meta and CXA81 on Klipsch RP-8000f).
But I have to say that, at least for transients and dynamics, I find CXA81 more convincing, especially on lower sensitivity speakers.
 

Bryan T

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Please read the review again.



Notice that @amirm tested the unit using Toslink input as USB input was still noisier. Emphasis is not mine.
As I understand it, in his setup having the USB connection (regardless of whether USB is being used) completes the loop between the computer, the CXA81, and the AP. Most of us probably won’t have a loop like that.
 

sarumbear

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As I understand it, in his setup having the USB connection (regardless of whether USB is being used) completes the loop between the computer, the CXA81, and the AP. Most of us probably won’t have a loop like that.
You are simply assuming.
 

sarumbear

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I don’t understand what you mean. My first sentence or my second sentence?
You said "Most of us probably won’t have a loop like that," which is an assumption, an opinion, which adds no solid value to the argument other than as a chat.
 
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