Squeezebox Touch Power Supply Problem or a tale of 2 PSUs

[Richard]

Hi all, I recently bought another SBT second-hand to use with the vintage system in the other room. It arrived in good condition with SBT unit, original infra red remote and correct power supply unit.

It worked fine in the system using the phone app, but the infra red remote didn't work with it, nor did my old remote which is fine with my old SBT. However, both new and old remotes worked with my other SBT, so probably not a faulty remote.

Then swapped the power supply from the old SBT to this new one and magically now both remotes and everything else works fine on the new one!

Now of course the focus fell on a failing PSU working well enough to power the SBT but for some reason not the remote control circuitry.

I cleaned the plug connector but no joy so using a multimeter I checked DC out of both PSU units and both were 5.1VDC. Switched the meter to ACmV and the good one shows 0.1mVAC but the bad one 82mVAC - nearly a thousand times worse - but - bear in mind this is with almost completely unloaded supplies. They are 3A rating and I haven't checked them loaded but am in no doubt the new one has failed and ripple under load will probably be horrendous.

They made SBT from 2009 to 2012 and the newest will be 6 or 7 years old. So I didn't even think about chasing around for an old original PSU. I've ordered a new supply from RS and will let you know how it checks with the meter and if it works with the remote and all...

This makes me wonder about building a linear supply. Can anyone point me to a design or have any exp of whether a linear supply would be better than a SMPS in this application?

[snowman_al]

That is interesting.
I have been a SB Touch user for 8 or 9 years now. The only thing I notice is the plug and socket do need cleaning from time to time, they both attract a white 'growth' over time?
I have just checked my Touch supply and it measures 5.08 volts DC and 6/7mV AC. It has been on more or less all the time since new, I only power down if I am away for a period.

I tried a linear supply quite early on (I will have to look to see which regulator IC I used), but I could not tell any difference. I know at the time (and now I expect) there were 2 camps, ''Linear is better'' and ''Linear not necessary'' due to the internal filtering in the Touch.

As an aside you have set me thinking, I have recently built a PiCore player with Squeezelite, using a standard Pi PSU, now I might just try the linear supply with that...
Alan

[snowman_al]

My regulator is an LM1084IT-5.0v. A fixed 5 volt LDO 5A type.
Pennies to try if you have a suitable transformer etc.

[Richard]

Hi Al, thanks for the info. A bit of googling seems to agree with you about no sound difference, it seems to be that the psu is good enough as the Touch has further regulation inside, makes sense I suppose.

For anyone in a similar situation, I phoned Logitech and despite the psu being shown on their website it's definitely no longer available from them. Googling the Phihong part number on the unit gets us the specs but they no longer seem to do an exact equivalent.

So I chose another psu from RS and all is working well now including the infra red remotes on both Touch set ups. That seems to confirm remote failure was due to a failing psu in this instance. Perhaps sensitive circuits are regulated inside the Touch but the remote IR sensor may be run straight off the psu, just a thought.

Anyway, I went for RS 731-6002 £15 +vat which is a direct plug-in replacement with similar ripple and regulation,

5V 4A rating (original 3A)
coax cable with ferrite choke
5.5mm x 2.5mm pin round plug

Sounds great, no difference obvious on a comparison with my good Logitech supply, but I bought 2 as they are both a few years old now.

With all working well I thought I'd investgate the failure a bit more by loading the supplies a little and checking DC and AC with the meter again. I clipped the meter leads to the ends of 100R resistor and connected them into the psu output plug. That should load the supply a modest 50mA or 0.25W, not much, but the results were interesting. I used the 2VAC range this time as the 200mV range is erratic;

Good Logitech supply 5.1VDC and 2mVAC
Bad Logitech supply 5V DC and 238mVAC(!)
New RS supply 5.2VDC and 4mVAC

These were just cold readings so don't take them as Gospel but the bad supply was certainly obvious and worth keeping an eye on an old Touch!