Audio electronics question – PSU for PC speakers

[Robin GrahamParticipant @robingraham42208]

I'm having a weed out and a pair of Creative T20 mf1545 active PC speakers has turned up. I was going to junk them, assuming they were rubbish, but a quick internet search suggested that they're actually quite good of their kind and worth passing on even if I don't use them myself.

I can't find the power supply though. The power input is marked 12V AC, but no current rating.

As far as I can discover the speakers are 14W 'nominal RMS' each. The beefiest cheap 240V to 12V~ PSU I've found so far is rated at 2.5A, 30VA. Do you reckon that would do? If not, any other suggestions?

Robin.

[Robin GrahamParticipant @robingraham42208]

[Jon LawesParticipant @jonlawes51698]

https://files.creative.com/manualdn/Manuals/TSD/9509/0x79C582A6/Creative%20GigaWorks%20T20%20Quickstart%20Multlilingual%20Front.pdf

Apparently its a 2.9A adaptor.

That would be for worst case scenario, I'd imagine for most uses you'd get away with the one you have mentioned, especially on a "freebie"

Edited By Jon Lawes on 09/07/2021 00:02:33

[Robin GrahamParticipant @robingraham42208]

Thanks – despite assiduous searching I hadn't found that. I'll take the risk with the 2.5A adapter then – if I use the speakers myself it'll only be to for TV, I won't be pushing them.

Robin

[John HaineParticipant @johnhaine32865]

Well, leaving aside just what they mean by "nominal 14W RMS", taking it at face value the total mean output power would be 28W. Assuming they are Class B with efficiency ~60% including all the drive circuits, the DC power needed would be 28/0.6 = 47 watts, so even a 2.9A adapter would be underpowered! But maybe they are Class D if recent enough so more efficient. If the adapter you get is a bit underpowered there might be a hum problem, might need an additional smoothing capacitor.

[Robin GrahamParticipant @robingraham42208]

Thanks John. I too wondered about 'nominal 14W RMS' – I think I know what RMS means but 'nominal'? I've never understood what 'Peak Music Power' means either. In the course of the weed-out I found some Panansonic speakers which which are rated 30W (Music) 15W (DIN). Presumably DIN is another standard. The great thing about standards is that there are so many of them, as some wit wisely said.

The input for these speakers is 12V AC, so smoothing the input is obviously not an option.

On further thought the work/expense to get them going just isn't worth it. I really hate junking stuff that could be repaired, but it seems that's the way of the world at the moment.

I'm going to have to steel myself for more of this – I'm lucky to have about 550 square feet of potential cellar workshop space, but at least half of it is full of rubbish.

Does anyone want a 10kg box of assorted wood screws ,or a 32 inch flat screen analogue TV weighing 17kg? Probably not.

Robin.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Robin Graham on 10/07/2021 23:02:03:

Thanks John. I too wondered about 'nominal 14W RMS' – I think I know what RMS means but 'nominal'? I've never understood what 'Peak Music Power' means either. […]

.

‘nominal’ probably means “but don’t hold us to it” !

'Peak Music Power' assumes that the signal being handled has a spectral distribution ‘typical of music signals’ rather than pure sine-waves. …

MichaelG.

.

Edit: __ That ^^^ was from memory, but Wikipedia has a page which ‘amplifies’ the topic

https://en.wikipedia.org/wiki/Audio_power

Edited By Michael Gilligan on 11/07/2021 08:00:59

[Author]

Posts