Re: Modify Marantz 1050 amp to suppress mains noise

On 2008-01-28, Arny Krueger <arnyk@xxxxxxxxxx> wrote:
"Toby Newman" <google@xxxxxxxxxxx> wrote in message
news:slrnfprddo.6kv.google@xxxxxxxxxxxxxxxxxxxxxxxxxxxx

I've run my home LAN over mains using DLink's DHP-301
PowerLine HD Network Starter Kit in a bid to reduce
wires. I was very happy with
the new system until I turned on my Marantz 1050
amplifier yesterday
and found that, being a piece of hardware from the 70s,
it's picking
up the noise of the LAN. Sounds like rapid switching
between a 6kHz and 7kHz square wave.

There are other ways for noise to get into your system, besides the power
line.

It is quite possible taht a modern power amp or receiver would have the
identically same problem.

I guess the Marantz
designers didn't anticipate anything but 50Hz hum on the
power supply and didn't see fit to filter for anything
more than that.

Only a guess, and one that I would agree with the others - its a lower
probability.

The first think I'll try is putting a surge protector
between the amp and the wall.

Why? This isn't about surges, it is about EMI. Surges are defined as
relatively long-term (i.e. milliseconds) increases in the voltage at the
input to your amplifier. There's nothing inside your LAN that can produce
surges that big. I'd bet that 5 volts is the largest voltage anyplace inside
your LAN equipment, and in terms of a power line, that's a nit. The surges
that a surge protector works against are dozens or hundreds or even
thousands of volts.

The reason I will try a surge protector first is because consumer surge
protectors also often contain filtering, and are more readily available than
a mains filter. This will enable me to verify if the noise is borne on the mains
cable rather than carried through the air. If I see an attenuation I'll know that
the mains cable is the culprit.

The manufacturer says that these items must
not be used alongside the Powerline device because they
interfere with the network connection. I will try to use
this shortcoming to my favour. :)

I suspect that they are worried that a surge protector would make additional
interference.

If that fails, I'm planning to pop the case and add some
filtering inside, starting with the simple things like
ferrite rings and then moving up to adding capacitors or
a mains filter if that fails.

First thing I'd do is swap in a new cheap ($80) receiver - borrowed from a
friend or something. If it has the same problem, then look at the
possibility of interference pick up by the signal cables or other gear in
the system.

Links:
The Marantz 1050 (showing internals)
http://www.classic-audio.com/marantz/1050.html

The power transformer in equipment like this is a major barrier to power
line noise. It's got great response at 50-60 Hz and lousy high frequency
response.

That's interesting to know.

The LAN-over-mains equipment:
http://www.dlink.com/products/?sec=1&pid=533

Even the thought of this equipment is giving hams and other users of
RF-based equipment heart attacks. But its not about surges, its about RFI
and EMI.

If you want to filter out what your LAN is pumping into the power line, get
a power line filter, which may also have surge protection.

Here's some examples:

http://www.e-sonic.com/aboutus/cat/S/surge%20suppressors.pdf

anything that says it has effective line filtering built-in.

The reason why everything on the page has surge protectors is that surge
protection is cheap to add. Good line filtering can cost a little money.


--
-Toby
Add the word afiduluminag to the subject to circumvent my email filters.
.

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