2. misc-audio
  3. 132963-1209

Noise Between Receiver/Preamp and Integrated/Power

I recently picked up a used Cambridge Audio Azur 551R (receiver) and a Cambridge Audio Azur 840A v2 (integrated amplifier). My goal is to use the 551R as my home theater receiver with the 840A as the power amplifier as it has the capability to set the inputs to be fixed (i.e. home theater bypass). The problem is that I am getting quite a bit of noise through the speakers with this setup.

The 551R and 840A are both silent when being used independently. I currently have an Airport Express and DAC as the source for the 840A and an Apple TV as the source for the 551R because it allows me to feed both from my computer simultaneously.

When I’ve adjusting the fixed input level on the 840A the noise seems to mostly be eliminated around -20 dB but the end result is having to drive the volume level on the 551R significantly higher than if it was on it’s own which doesn’t make sense.

They are connected with a fairly long set of cables that I plan to replace with a much shorter set to minimize any potential interference from the next of cables (that include power cables) that is the reality of my setup. I’ll also try plugging them in differently to see if that makes any difference.

Any thoughts?

Update: I switched in a different different BJC LC-1 cable that is about half the length and swapped one of the power plugs from the power conditioner to a power strip to give them different equipment paths to the wall plug. I didn't notice any change.
mceljo
3 responses Add your response
williewonka
1,826 posts
 
@mceljo - One simple test is to get  length of wire and attach one end to a ground point - the ground pin of the power supply is perfect.
Then touch the other end on the neutral side of any phono jack on the receiver/pre/amp and see if the noise stops.

If it does you will know which component(s) is causing the issue.

The fix will be to either
- take the unit in for repair
- add a phono plug to the end of the wire and leave it plugged in to that component.

Hope that helps you track down the problem

Regards - Steve
mceljo OP
983 posts
 
Today, I was able to verify that the signal and chassis ground is the same for the 551R so I made a cable to run from one of the RCA inputs to the ground lug on my power conditioner where both the 551R and 840A are plugged in. No real change. I turned off the 551R and realized that the noise that’s part noise and part 60 Hz hum (based on an FFT app I have on my phone). 

I am in contact with Cambridge Audio and they seem to be willing to assist, but the holidays are getting in the way.

After talking to an EE friend of mine we are thinking that the 840A has some type of ground issue that will need to be repaired.  I will wait to work through whatever help Cambridge Audio provides and then will likely take it to a local shop for diagnosis and repair. 

On on its own the 840A seems to have muddy mid bass which a 60 Hz ground issue is likely to impact. 
mceljo OP
983 posts
 
By the way, thanks for the help Steve. I essentially did exactly what you said to do. It’s a slow project. 
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