RFI PC Speaker Hum

[Brian - N5BCN]

Hi all,

I'm experiencing the dreaded PC Speaker hum every time my K2 transmits, even when power is dropped to about 2 W.

The speakers are Harmon Kardon amplified speakers and they do not hum when turned off.  Per other threads, I plugged the speakers' wall wart into the same outlet as the K2 and this did improve the situation (hum dropped by about half) but did not completely eliminate it.  The computer chassis and K2 are grounded together with a ground strap.

I'm going to try some ferrite on the AC power cord, the speaker cable to the computer, and the speaker wire connecting the left and right speakers.

In an email to Fair-rite, they suggested their #31 material snap on cores.  My thought is that these would be limited in the number of turns of wire to perhaps one, maybe two turns at the most.  Would there be additional benefit from getting their toroid cores instead and wrapping several turns of wire versus using their snap on core?

Also, would it be better to use a HF low pass filter such as I.C.E.'s 420 to clean up my signal versus trying to fix my speakers?

Thanks for any suggestions!

73

N5BCN - Brian

[Ken Kopp-3]

Hi Brian,

It's a more costly solution, but I ... and others ... swear
by the COMspkr(s) from West Mountain Radio.  They
work well, and even sound pretty good when listening
internet radio stations.

73! Ken Kopp - K0PP
     [hidden email]

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[Phil LaMarche-2]

I use COM speakers with my R5000 receiver and they sound great. Use better
hifi speakers through an amplifier with my K3.  Mounted on the wall and
pointing at me.  Such a pleasure to use for SSB and general coverage.

Phil


Philip LaMarche
 
LaMarche Enterprises, Inc
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www.LaMarcheEnterprises.com
 
727-944-3226
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www.w9dvm.com
 
K3 #1605
 
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-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ken Kopp
Sent: Saturday, May 29, 2010 3:54 PM
To: Brian - N5BCN; [hidden email]
Subject: Re: [Elecraft] RFI PC Speaker Hum

Hi Brian,

It's a more costly solution, but I ... and others ... swear by the
COMspkr(s) from West Mountain Radio.  They work well, and even sound pretty
good when listening internet radio stations.

73! Ken Kopp - K0PP
     [hidden email]

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[Joe Subich, W4TV-4]

Almost any commodity computer speakers can be cleaned up
by adding a simple bypass cap across each of the speaker
leads.  The most difficult cases respond to a basic pi-
section filter at each speaker output and on each input
channel.

I cleaned up all of my computer speakers by adding a .01
or .005 uF cap from my junk box from each speaker lead to
ground on the output of the amplifier board and putting
about 6 turns of the speaker cable going to the "remote"
side (speaker with the long cable) through a .405" ID #31
"clamp on" bead.

If I had the parts, I would use pi section filters with
.01uF caps and a 1 mH choke in series with each speaker.
That should provide nearly 40 dB reduction of the voltage
on the speaker leads that gets back into the output of the
audio amplifier to be rectified causing the noise/hum.

73,

    ... Joe, W4TV

On 5/29/2010 3:54 PM, Ken Kopp wrote:
> Hi Brian,
>
> It's a more costly solution, but I ... and others ... swear by the
> COMspkr(s) from West Mountain Radio.  They work well, and even sound
> pretty good when listening internet radio stations.
>
> 73! Ken Kopp - K0PP [hidden email]
>
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[Brian - N5BCN]

Hi Joe,

I'm going to try your suggestion.

The way I understand your post is that you installed the bypass caps directly on the amplifier board, one cap for each speaker wire, each grounded to the circuit board's ground?  My speaker's circuit board is difficult to work on, could I accomplish the same thing by installing the caps across the speaker lugs themselves?

Thanks and sorry for such a novice question.

N5BCN - Brian

[Sverre Holm (LA3ZA)]

One thing that I believe has not been mentioned in this thread is a very simple solution to the hum problem. Since the K3 already has an audio power amplifier, amplified speakers are not really needed. I had an old pair of computer speakers - which hummed every time I transmitted on the K3. Then I just disconnected the amplifiers and connected the inputs directly to the speakers. Now I don't need to connect them to their power supply, and they will of course not hum.

[Jim Brown-10]

On Sat, 29 May 2010 11:10:39 -0700 (PDT), Brian - N5BCN wrote:

>Thanks for any suggestions!

W4TV has given you great advice. 99.9% of all amplified speakers have RFI
problems at some frequency, including pro products with major brand names.
The usual causes are 1) lousy shielding  2) lack of RF filtering on audio
wiring; and 3) pin 1 problems. W4TV's advice addresses #2 and #3. There's no
good solution to #1 short of a science project or a bucket.

As others have noted, you don't need amplified speakers with a K3 (or with
any ham rig I've used). Ordinary un-amplified speakers work quite well.

73,

Jim Brown K9YC



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[Brian - N5BCN]

Hi,

Just to be clear, I'm not using the speakers with the radio, I'm using them with my PC which is in the same room as the K2.

I don't know if my PC requires amplified speakers or not.

73

Brian - N5BCN

[Julian, G4ILO]

All computer speakers are amplified. Many of them have very poor immunity to RF. I have sometimes reduced RFI to acceptable levels by winding a couple of turns of the cables through snap-on suppression toroids. Winding several turns through a large ring toroid would be more effective as the snap-on suppressors are really only designed to suppress VHF.

Some computer speakers have such poor RFI immunity that they are probably beyond fixing. One pair I bought made by Logitech hummed even when placed near a cordless phone base unit that probably has an output power of a few milliwatts. The first time I pressed the PTT of my transceiver the resulting noise nearly gave me a heart attack. I gave them to a charity shop. There is a firm (I think it may be the one that makes RigBlaster interfaces) that advertises RFI-proof computer speakers, but I seem to recall the last time they were mentioned on this reflector they were out of stock.

[M0XDF]

I have Harman Kardon speakers & sub on my Mac via USB and another pair, different model, same manuf., traditional audio from headphone out, generally no poblem. Never had any RFI on the Mac ones, occasionaly get it on the others - but I have a lot of RF in the shack (something I need to fix).
73 de M0XDF, K3 #174
--
Math Anxiety: an intense lifelong fear of two trains approaching each other at speeds of 60 and 80 MPH. -Rick Bayan

On 3 Jun 2010, at 12:25, Julian, G4ILO wrote:

>
> All computer speakers are amplified. Many of them have very poor immunity to
> RF. I have sometimes reduced RFI to acceptable levels by winding a couple of
> turns of the cables through snap-on suppression toroids. Winding several
> turns through a large ring toroid would be more effective as the snap-on
> suppressors are really only designed to suppress VHF.
>
> Some computer speakers have such poor RFI immunity that they are probably
> beyond fixing. One pair I bought made by Logitech hummed even when placed
> near a cordless phone base unit that probably has an output power of a few
> milliwatts. The first time I pressed the PTT of my transceiver the resulting
> noise nearly gave me a heart attack. I gave them to a charity shop. There is
> a firm (I think it may be the one that makes RigBlaster interfaces) that
> advertises RFI-proof computer speakers, but I seem to recall the last time
> they were mentioned on this reflector they were out of stock.

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[Ken Kopp-3]

Julian, others ...

West Mountain Radio has the "COMspkr" back in stock.
I ordered a set at the Visalia DX Convention and they
were promptly shipped when the folks returned home.

They work well and I have no interference from 1KW on
HF and 600W on 6m within ten inches of the unit(s).

73! Ken Kopp - K0PP
     [hidden email]


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