Question of Noise

[drumace]

Hey guys,

I wasn't sure where to put this post so I hope those who can help will notice it.
I'm using Marantz AV8801 pre-pro to feed my XPA-1Ls which are hooked to GoldenEar T1 speakers.
The Marantz is plugged to the wall (shared with many other AV components) using a step-down transformer (to match the local voltage).
When there's no audio signal played, I can hear a "hiss" sound from the speakers (about 5-6 feet away from them). The noise is not related volume level (can be heard even when the volume is all the way down).
If I turn the pre-pro off and leave the XPA-1Ls turned on, the "hiss" sound disappears but then I can hear a slight hum coming from the midrange drivers.
Then, if I switch from "balanced" to "unbalanced" on the XPA-1L, the hum disappears.

Please help me understand -

1. Does the "hiss" I hear in this case means there's an issue with the Marantz pre-pro or is it the expected result (maybe due to a design less optimal and noisier)?
2. Do you think replacing the Marantz pre-pro with another pre-pro (e.g. XMC-1, AV8802A) or a stereo preamp (e.g. XSP-1) will solve this issue?
3. Do you think adding a power filter (e.g. CMX-2 or CMX-6, still trying to figure out the difference between them) will solve these issues?
4. What do you think is the root cause of the slight hum I hear (only from the front channels)?

Please advise what I should do to clean up the background noise.

Thanks in advance!

[Ex_Vintage]

"using a step-down transformer (to match the local voltage)" - what does this mean? Is there a ground in the system?

[drumace]

Nov 21, 2018 7:32:54 GMT -5 Ex_Vintage said:

"using a step-down transformer (to match the local voltage)" - what does this mean? Is there a ground in the system?

Hi,
The XPA-1Ls are grounded (have 3-pin plugs).
The step-down transformer also has 3-pin plug to the wall.
Other components are not grounded.

[Ex_Vintage]

Is the secondary of the transformer grounded? The 3 pin plug on the xfrmr is on the primary. If the secondary is not grounded and the XPA's are plugged into the secondary of the xfrmr, then they are floating (subject to noise).

[drumace]

Nov 21, 2018 8:40:10 GMT -5 Ex_Vintage said:

Is the secondary of the transformer grounded? The 3 pin plug on the xfrmr is on the primary. If the secondary is not grounded and the XPA's are plugged into the secondary of the xfrmr, then they are floating (subject to noise).

Hi,
The secondary of the transformer is not grounded because the AV8801 has only 2-pin plug so even if the cable has 3-pin end, the ground pin is not connected at the AV8801 side.

[bluemeanies]

I would start from scratch. Unplug everything and then re-introduce each device turning them on.
You will quickly find the culprit and may have to plug that device in another outlet.
My 2cents.

[Ex_Vintage]

It appears as though the XPA amps are not grounded. The 3 pin plugs have no reference point on the secondary of the transformer. Why are you using a transformer? The amps should be good for 220 or 120 VAC.

[drumace]

Nov 22, 2018 14:23:47 GMT -5 Ex_Vintage said:

It appears as though the XPA amps are not grounded. The 3 pin plugs have no reference point on the secondary of the transformer. Why are you using a transformer? The amps should be good for 220 or 120 VAC.

The step down transformer is for the AV8801 which works only on 110V.