Power Supply RF EMI

[Daryle Tilroe]

I guess I could have posted this in the Elpac thread or
one of the other power supply ones; but I am only concerned
with gross EMI in the AM and FM bands, not esoteric audio
issues.

I have just hooked up an SB2 to a Tivoli Model Two for
bedroom listening. I expected some noise from the stock
switching power supply. However the amount of garbage,
particularly in the AM band, that the current supply
spews out when the SB2 is hooked up is ridiculous. AM
is virtually unlistenable and FM is affected as well.

Now I am assuming that most of this EMI is from the power
supply, not generated by the SB2 itself. Can anyone out
there with the Elpac, or other linear supply, confirm
that decent radio reception is possible with the SB2
hooked up?

Finally, are there any radio friendly switching supplies out
there? IIRC there are some techniques to quite them down
but I suspect they are rarely used on mass market, el
cheapo, ones. In any event I'm probably going to order
up an Elpac to see if I can get a setup where I don't have
to continually unplug the SB2 to listen to the radio.


--
Daryle A. Tilroe

[rme]

An additional question on this thread as well for the power experts out there...

Is there increased RFI/EMI if the dc power cable portion of the sb2 power supply is run tied to an amplifier's ac power cord or doesn't that matter? In other words, should the dc part of the cable be kept away from any other ac power cords?

[Music Machine]

This is not the test you would have done, but provides at least some comparison.

I tuned an AM radio to a station that sounded clear and strong.

Plugged in the little stock switcher, and didn't notice any change. I wasn't trying to hear small changes, just a quick test. The output of the supply was not connected to anything.

Then the radio was tuned to a weaker AM station (about half strength on the radio signal strength meter). Plugging in the stock supply caused awful noise out the radio speaker. Very annoying ticking/buzzing. Unplugged the PS and the noise went away.

Plugged in the elpac and didn't notice any difference in the sound of the weak AM station.

I also have a surplus linear supply from Hosfelt. I found out about it from a thread on Audio Circle. This one: http://audiocircle.com/circles/viewt...a43cdfe058f6ab
The last post on the first page tells you how to find it. It's about $10 less expensive than the elpac and looks like a much better design. I plugged this supply in during the AM radio test and didn't notice any problem. I've not tried this supply with the Squeezebox yet because the connector needs to be replaced. That's the nice thing about the elpac, it's plug'n play.

Hope that sheds at least a little light.

Regards,
Music Machine

[Daryle Tilroe]

Music Machine wrote:

> I also have a surplus linear supply from Hosfelt. I found out about it
> from a thread on Audio Circle. This one:
> http://audiocircle.com/circles/viewt...a43cdfe058f6ab
> The last post on the first page tells you how to find it. It's about
> $10 less expensive than the elpac and looks like a much better design.
> I plugged this supply in during the AM radio test and didn't notice any
> problem. I've not tried this supply with the Squeezebox yet because
> the connector needs to be replaced. That's the nice thing about the
> elpac, it's plug'n play.

Well I just ordered the Hosfelt 56-534 mentioned in that thread as well.
It looks like a nice heavy duty linear PS from the pics plus it's not a
wall wart. We will see in a few weeks if it does the trick.

--
Daryle A. Tilroe

[Daryle Tilroe]

Daryle A. Tilroe wrote:
> Music Machine wrote:
>
>> I also have a surplus linear supply from Hosfelt. I found out about it
>> from a thread on Audio Circle. This one:
>> http://audiocircle.com/circles/viewt...a43cdfe058f6ab
>>
>> The last post on the first page tells you how to find it. It's about
>> $10 less expensive than the elpac and looks like a much better design.
>> I plugged this supply in during the AM radio test and didn't notice any
>> problem. I've not tried this supply with the Squeezebox yet because
>> the connector needs to be replaced. That's the nice thing about the
>> elpac, it's plug'n play.
>
>
> Well I just ordered the Hosfelt 56-534 mentioned in that thread as well.
> It looks like a nice heavy duty linear PS from the pics plus it's not a
> wall wart. We will see in a few weeks if it does the trick.
>

Well I hooked up the Hosfelt supply; and what a difference. On
the AM dial all power supply interference is basically gone.
I am getting a bit of noise on some stations generated by the
SB2 itself. Could be the wireless circuitry, display, internal
switchers, etc. In any event it is much more acceptable, and
luckily the AM station I listen most to is completely quite.
Only down side is that Hosfelt hoses you on the shipping and handling.
The power supply was $7, plus a $5 handling fee, plus $15 freight
(almost *double* the actual postage of ~$8), totalling $27. Probably
still worth it though.

--
Daryle A. Tilroe

[dwc]

Hmmm... hosfelt or elpac?

Can I get a part number on the correct plug tip from a trusted online vendor (or Rat Shack ?

-Dan

p.s. ordered the hosfelt, as the price diff is too big to go elpac. Now to find tips.

positive tip/center right?

[Daryle Tilroe]

dwc wrote:

> Can I get a part number on the correct plug tip from a trusted online
> vendor (or Rat Shack ?

You could also do the job by snipping the end off an old AC
adapter with the same end that you might have hanging around
and then soldering the two wires together. That's what I did.
Between home and work I have over a dozen from defunct
electronics. They always come in handy!

> positive tip/center right?

Right. But always take your DMM and check twice with the
original and solder once. Then check again before plugging
into the SB.

--
Daryle A. Tilroe

[Daryle Tilroe]

Daryle A. Tilroe wrote:

> Well I hooked up the Hosfelt supply; and what a difference. On
> the AM dial all power supply interference is basically gone.
> I am getting a bit of noise on some stations generated by the
> SB2 itself. Could be the wireless circuitry, display, internal
> switchers, etc. In any event it is much more acceptable, and
> luckily the AM station I listen most to is completely quite.
> Only down side is that Hosfelt hoses you on the shipping and handling.
> The power supply was $7, plus a $5 handling fee, plus $15 freight
> (almost *double* the actual postage of ~$8), totalling $27. Probably
> still worth it though.

So a few other observations with the Hosfelt: You definitely
notice, as a linear power supply, it is not as efficient; the
case stays nice and warm. It has a noticeable 60 Hz hum from
that transformer; I can hear it quite distinctly up close and,
when the room is otherwise silent, from about 6 feet away.

--
Daryle A. Tilroe

[Daryle Tilroe]

Following up again.

The Hosfelt, while a lot better for EMI in the AM band/modulation than the stock switcher, turned out to be worse in the the FM band/modulation; particularly in the lower ranges of the dial. I finally got around to getting some snap on ferrite RF chokes/cores/beads for the power cable and that has cleaned up things significantly. At this point it would be nice to find a really modern, quite (RF and audible hum), ripple free, linear power supply that I could just replace all 5 of mine with. Something that had the right end and a ferrite on it already would be great. Anyone have any leads?

[TechHome]

Count me in. In fact, I don't mind replacing w/ another switcher, as long as the FM band RFI is cured. My favorite FM stations are not listenable unless I unplug the SB2 power supply, either from the back of the SB2 or from the wall.

dfrazee