[ziv]

Hi,

I recently bought an AVP-18 / MCA-18 combo to replace an integrated Marantz AV receiver. The first thing I noticed (beside it sounds really well on both music and home-cinema) was a background hiss on all channels coming from the MCA-18 (I had it even when the AVP-18 was off) when there was no music or at low listening levels. My room feels much quieter when I switch off the amp at the end of the day, that's how it is annoying...

I immediately contacted my reseller who said he had an MCA-20 at home and did not notice any hiss on it.

He was kind enough to let me try another copy of the MCA-18, that has the same issue, so I guess this has to do with the model (and its low SNR, at 89dB, while my previous amp was rated at 105dB?), not my particular copy. However, he also said that none of his other customers reported anything.

So, if there are some MCA-18 users, did you notice that and does it bother you?

For me, it's a deal breaker and I am in the process of changing the amp for another brand, while keeping the AVP-18 which sounds very good.

[Steven Stone]

I never heard any hiss from my sample. Usually hiss is a result of a sensitivity mismatch, such as when you try using 110 dB + sensitivity headphones with a normal or high gain amplifier.

[ziv]

Well, I am using Tannoy M3/M2/MC speakers which have a sensitivity rating of 89dB, which is not unusually high.

[Steven Stone]

Sound's like the speaker sensitivity is not the issue, but what about your power amplifier? 26 dB is the usual gain increase for most amplifiers. Also have you tried connecting the MCP-18 directly with no AVP-18 in the system? I suspect that something in your system is boosting gain. To trouble shoot I would take apart and rebuild the system is different ways to see when and where the hiss enters the picture.

[ziv]

I have the hiss even if the AVP-18 is not connected/powered-up. Note that it is a constant volume background noise, not heard at normal day-time listening levels (around 30 or above on the AVP-18) but that can be heard when it is getting a little late and I have to limit my listening level to respect my neighbors...

[John Casler]

I have the hiss even if the AVP-18 is not connected/powered-up. Note that it is a constant volume background noise, not heard at normal day-time listening levels (around 30 or above on the AVP-18) but that can be heard when it is getting a little late and I have to limit my listening level to respect my neighbors...

It could also be a Powerline issue.  Is the amp plugged straight into the wall?  or a Power Conditioner of some sort?

I have quite a few MCA 20 and MCP 18 amps in the field, and none seem to have that issue.

While rare, it could be Powerline induced, made evident by the amps sensitivity.

And the other possible situation, is that you have VERY sensitive hearing in the frequency range of the hiss (all electronics have some level of it) and this allows you to be sensitive to it where others either don't hear it, or don't notice it.

[ziv]

No, there is no power conditioner on the line, just some power strips. However, the ground is not connected and it would require major electrical works to bring it where the amp is connected. My previous amp (a Marantz integrated AV receiver) did not require ground connection and did not have any issue with background noise.

My father, which is more than 60 years old now and not as audiophile as I can be also heard this noise so I believe I am not that sensitive. However, my listening room is quite small (about 10m²) and I am about 2 meters from the speakers (which may not be that close).

[ricardojoa]

Interesting,
i have the same issue but with the STA 100 and i have 85 db speakers.
The hiss can be heard wth no RCA connected.
I dont think the hiss has to do with gain but rather Signal to noise ratial, which i think the STA isnt that high.

[John Casler]

Before changing amps try this:

I contacted Bob at NuFORCE Tech Support and he said to try the following:

John,
 
He should connect the ground on the amp to the earth/safety ground of the AC outlet. This should be done for safety's sake, let alone any noise issues. With all of the internal HF switching going on inside the amp chassis (particularly the SMPS power supply), if that energy has nowhere to go (i.e., "ground") it is likely to get into the signal path and be amplified as hiss. Grounding may not completely get rid of it, but it should help.
 
Furthermore, once the amp has been properly earth grounded, then the customer can "lift" the AC power ground on the rest of the equipment. At that point all other components in the system will be connected to earth/safety ground through their various interconnect cables and on through the MCA's power cord to earth ground. That is called "end of chain" grounding and should help to reduce any noise even further - not to mention eliminate any ground-loops.
 
Although, in his case he says he doesn't have an earth ground available at all. So... if he could just get the MCA grounded, then there would be nothing else for him to do with regards to the other equipment as apparently... they already have no earth ground connection to begin with.
 
Thanks,
-Bob

The above would explain why a couple have mentioned a hiss, and others have none.

The Marantz used earlier was likely not of the same amp topology, and thus might not be as susceptible to a lack of grounding.  And since this has only been reported in 2 incidents (but over 3 total amps) it is possible that it is a manufacturing defect in those particular samples, as all the others I have placed in the field have not needed to be grounded, and have no hiss.

Hope that helps. 

[ziv]

Thank you for these explanations. However, I still do not want to engage electrical works to bring the ground to my living room without any guarantee that it will completely eliminate the noise source.

However, one difference between the MCA-18 and the two AV receivers I have used before that (a Marantz and a Sony before that) was that they did not require to be grounded. Even more, the power outlet had no ground wire at all, so I guess their internal architecture allowed to be shielded from noise and protected from electrical defects without any ground connection.

One side note is that I found other testimonies about background noise on a French forum. However, it does not seem to bother these people so much, so it depends from person to person.

[ziv]

I finally replaced the MCA-18 by a Marantz amp (while keeping the AVP-18). Absolutely no hiss (even when listening near the speaker) and it works fine with the AVP-18.

Too bad for Nuforce