Hi
Until recently, I was using a DrayTek 2830 router and a pair of GS-108 switches (using the DrayTek's port based VLAN features to separate the two networks that I require, and using it's tag based VLAN feature to create the trunk to my WAP, so both networks were available to wireless devices; each network had its own SSID). Of course, everything was fed from FRIWO PSUs (principally because the existing power units were all causing radio frequency interference).
The above all worked well, but after creating yet another network, the DrayTek was starting to struggle (not enough CPU horsepower) and there was also another issue with the DrayTek's VLAN capabilities (which I'll not go into, here), so I recently revamped the entire network.
Now, I've replaced my router with a fan-less mini-PC running Sophos UTM (which is very cool) and as it uses the same CPU as Qnap TS-453, there's no lack of CPU grunt (and it actually draws less power than some routers draw, so also not an expensive device to run). I also replaced the GS-108's with a D-Link L2 managed switch (model DGS-1210-24) and everything is now behaving as it should; well, almost.
When listening to the system, it sounded less musical than I'd been used to, so I quickly connected the GS-108 to one of the DGS-1210-24 ports then connected my DS and NAS to the GS-108; it definitely sounded more musical, so that was very interesting. I'll need to do that again some time (borrowing my friend's ears to confirm the findings).
I opened up the DGS-1210-24 to have a peek inside and it has a pretty decent internal SMPS, but it does dump some rubbish back onto the mains supply and the DC side is not too bad, but certainly a little rougher than a FRIWO. The handy thing is that the internal SMPS is not a multi-rail one, but simply a 12V DC supply, so I'll see if I can find the appropriate connector (to suit the DC input on the main switch board) and then fit a DC socket onto the back panel, such that I can try feeding it from an external FRIOW SMPS.
Of course, an interesting thing to ponder is that like all these 12V fed units, it uses an on-board DC to DC converter to derive the other Voltage that the switch requires. These are not things I'd looked at as when I used to tinker with electronics, such devices were not in use. Looking at the one in my Ethernet to fibre converter (I use fibre between the switch and the Sophos UTM 'router') I see it also has a DC-DC converter, so I looked it up and found the spec sheets for it. Interestingly, there are various suggested circuit designs (it can be used to step up as well as step down) and when you look at them, most show an optional choke and capacitor output filter. Of course, in cost engineered products (so virtually all products) these are not fitted. Of course, there's typically a voltage regulator after that DC-DC converter, so perhaps that doesn't pass any trash onto the rest of the circuit (I've yet to look into all that stuff and then try measuring what's actually going on).
So, when you use a FRIWO to feed a switch (or some folks even use a linear supply) you might well be cutting down on the noise fed back into the mains (and I suspect that in some cases - particularly where the switch is located electrically close to the Hi-Fi system - that's maybe why it sounds better) and cut down on the noise fed to parts of the switches circuitry, there is also this noise generating DC-DC converter stage to ponder.
I've only just started to look into all this, but I'll open up a GS-108 to bits in a few days (one is out on loan and the other is in use elsewhere in my network, so I can't do that right away) and see what's in there, then see if I can see a spec sheet for it (to see if they've filtered its output side, though I'd be surprised if they have). I'll also take the cover off my DGS-1210-24 and see which version of DC-DC converter they have used (and again look for a spec sheet) and also take note (in both cases) of whether there's a regulator following that DC-DC converter stage.
All that aside, it will be interesting to see whether just adding a FRIWO makes any difference to my DGS-1210-24 (without changing anything else) and when I eventually get round to doing that, I'll report back with my findings.
Bri
NB For anyone interested, the spec sheet for the DC-DC converter that's used in my TP-Link fibre to Ethernet media adapter can be viewed at the following link:
https://www.sparkfun.com/datasheets/IC/MC34063A.pdf and on page 7 (the first step down variant) you can see the optional L+C output filter (that they have opted not to fit in that particular unit). It will be interesting to see which devices are used in the GS-108 and the DGS-1210-24 (and measure what - in the way of unwanted trash - is coming out from them).