On Thu 11/01/2024 22:57, Java Jive wrote:
> On 11/01/2024 20:23, Woody wrote:
>> On Thu 11/01/2024 17:05, Java Jive wrote:
>>> On 11/01/2024 14:51, Woody wrote:
>>>>
>>>> Can 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
>>> longer available, presumably because it is a superseded model:
>>> 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!
>
>> The 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.
>
>> If 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.
>
>> Most 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 :-)]
>
>> I 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.
>
>> Methinks 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!"
>
Confirm audio is switched by the KVM, and also confirm that the BT Rx
directly into the PC is as silent as the grave.

Maybe if I try Cherry I might perhaps use a little 'truth economy' per
the whole story and see how they respond. Of course the thing I haven't
look at is whether or not I can get into the KVM box and if I can then
maybe a bit of decoupling on the audio amp might have effect - I admit
the buzz level is quite low.

Failing that I will have to resort to prising the the keytops off my M$
keyboard and cleaning it out a bit - you wouldn't believe how much dust
accumulates in this house!! 8-))

Thanks for your input.