Post by WoodyPost by Java JivePost by WoodyCan anyone recommend me a KM or KVM switch with USB on board please?
I have recently changed from a M$ Desktop (wireless mouse and
keyboard) to a Cherry Gentix equivalent and have just discovered that
the USB Bluetooth receiver plugged into my existing KVM switch is
generating a low level buzz on the audio feed to my speakers. This
never happened with the M$ kit but the keyboard was becoming
intermittent so I had no option - the M$ Desktop that I had is no
longer made it seems.)
After much pratting about I have discovered that if the BT Rx is
plugged directly into my main PC there is no buzz and audio is
reproduced perfectly. However if I plug the BT Rx into the KVM switch
I get the buzz.
I have two desktop PCs, one that is rarely used running XPSP3, and my
normal PC running W10Pro. As my (latest) monitor has two inputs (HDMI
and DisplayPort) I no longer need the video switching capability but
it is useful to have soft control of the keyboard and mouse should I
need to use the XP machine.
I have tried a longish USB extension cable on the BT Rx with three
turns passed through a ferrite bead but it makes no difference, the
buzz is still present.
I have tried everything in terms of hum loops etc but this is not a
50Hz or 100Hz hum, more a buzz which sounds like USB clock getting
onto the supply wires in the cables. Using the soft switch to change
over to the XP3 machine (switched off but connected to main) kills
the buzz.
If anyone has polite suggestions of a cure, or a reasonably priced KM
or KVM HDMI switch I would be most obliged.
If you can find an alternative PSU of the same rating and polarity for
the KVM, try swapping that in to see if that fixes the hash.
I use two KVMs, one in normal use, the other as a backup ...
The one currently in normal use is a Belkin OmniView PRO3 16-Port KVM
Switch, USB/PS2 + VGA, which I bought second-hand/used for £25 inc
p&p, a lucky find on eBay.
Previously I paid £40 + surcharge of £7 p&p* for 2 x Belkin OmniView
PRO2 + 1 x Belkin OmniView PRO3, all 4-port, + an assortment of
cables. One of the PRO2 was an older model, PS2 only, and was faulty
(magenta output, so green channel broken), the other I used to have
daisy-chained to the PRO3 for my old tower W2k machines, but it became
redundant when my monitor caught fire (literally, black smoke rising
out of the back of it, I used welding gloves to carry it outside at
arms' length). The PRO3 worked for many years after but died in a
thunderstorm last summer.
The backup system is a 4-port USB-powered one with analog video, for
around £10 excluding cables from eBay, but I can't find the original
sale item now.
Previous to all the above, I had a Belkin SOHo 4-Port model number now
forgotten.
All of the above have been in use with a Logitech MK520 wireless
keyboard & mouse set, the keyboard model number seems to be K540, the
mouse model number M310. I still have an Amazon link, but it's no
https://www.amazon.co.uk/dp/B003ZWL9G4/ref=pe_217191_31005151_3p_M3_dp_1
None of the above combinations have caused me any interference on
sound, and I play a lot of music through a Terratec USB sound-card on
the end of a long USB lead to take it to the stereo the other side of
this room.
* Something to which I wouldn't normally agree - I'm on the
mainland, no ferries involved, so no more remote than some areas of
Wales or Galloway in southern Scotland, which AFAIK don't incur extra
charges for delivering there.
Rereading your OP and restated comments below, I missed that, I think,
you're also switching analog audio output from the PCs via the KVM? Pls
confirm, as otherwise I'm way off mark. The PRO models I described
above don't have the connections to allow that, and, although the SOHo
model did, I never actually did this except once to see if it actually
worked, which of course it did. However, I've never wanted to do this
on a permanent basis, because if I have media playing on one PC, I
wouldn't want the sound to be interrupted while working on another.
However, as always, your own needs are allowed to differ from mine!
Post by WoodyThe KVM switch that I have is powered from the PCs through USB, there is
no separate power supply. If I switch to the XP PC when it is unpowered
but still connected to the mains lead the buzz disappears.
If my assumption above is correct, that is presumably because the XP
machine, being switched off, is not acting as an audio source into the KVM.
Post by WoodyIf I unplug
the audio input or output of the switch whilst selected on the W10
machine the buzz disappears.
Again because, like the XP machine being switched off, there is no audio
coming into the KVM.
Post by WoodyMost significantly if I unplug the BT
receiver (mini USB) the buzz also disappears.
Ergo I conclude that the receiver is radiating interference onto the USB
connection to the W10 PC.
No, I don't think so, surely it's much more likely that hash is leaking
directly onto the audio connection through the KVM? To test this, try
plugging the audio directly into your main PC without it being switched
by the KVM, and without letting the audio leads come anywhere near the
KVM &/or BT Rec'r. My guess is that doing so will remove the hash.
[If not, I can't imagine how all this would be happening given the tests
that you've already described, so I won't bother to think about that
possibility until you've actually done a test to show that such a
rethink is actually necessary :-)]
Post by WoodyI thought it could be a radiation issue so
fitted an extension USB cable and wound three turns of it into a
substantial ferrite tube but it made no difference.
My previous M$ Desktop 2000 was connected in exactly the same
configuration and was never a problem.
I wonder what would happen if you did that to the audio output cable?
It would probably mess with the FR of the sound, and wouldn't be ideal
as a permanent arrangement, but might be interesting as a test, to see
if & how it alters the sound being produced? Also, if my theory is
correct and if you tried it on both the audio input and output in turn,
putting it on the input should make little or no difference to the sound
of the hash itself, but putting it on the output should change its sound
somehow.
Post by WoodyMethinks an email to Cherry might be appropriate?
If plugging the audio directly into the PC removes it, then it's more of
a KVM problem that has only just come to light because of the change of
hardware attached to it, so maybe is not really the fault of the
keyboard & mouse. However, I suppose they could be partly to blame, in
that their receiver could be causing the USB input circuit in the KVM to
misbehave somehow, so you could try emailing Cherry to see what they
say. I suspect they would probably reply, at least initially, blaming
the KVM, and saying:
"Sorry, but not our problem!"
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