Need some help with findin a suitable power supply for a sound system.

legend474 · 19 Oct 2013 at 18:42

So I got this Tevion/Medion Aktives 5.1 Soundsystem MD 42491 but I don't have the power supply for it. It states that it needs a 25V 2.2A 50Hz AC power.

I tried with a 16V from my other system to test it and it works, but I need to find a power supply now. I tried the manufacturers but the system is too old and they can't help me find one.

I found some on ebay, but they are 24V 3A. I know the amperage is fine since it doesn't matter if it's higher than needed, but I don't know if 24V will be "ok". Also that one on ebay is DC 24V but the system needs AC power.

So I need your help in deciding what to do.

lucid · 19 Oct 2013 at 19:04

Your system would be very unusual if it needed 24V AC. I think it's more likely that you're mixing up the input and output specs on the tranformer.

The bit that connects to the wall runs on 220V-240V AC 50Hz and at a faily low current of about 0.3 Amps.

The DC side is the part that powers the speakers. The transformer converts AC to DC. The DC output is 25V 2.2 Amps which gives about 55 Watts. There won't be a frequency because DC doesn't oscillate the way AC does.

So, you're looking for a transformer with a DC output of 25V with a current rating on 2.2 Amp (2200 mA) or more.

legend474 · 19 Oct 2013 at 20:47

Well I was going on with the specs that I have infront of me.

Since I don't have the original power supply, I have no way of knowing if the stuff on the manual or the printed numbers on the back are actually AC or DC.

Pics from manual:

The manual is in German, but we can see the numbers.

My original question stands, would the risk of the system dying be big if I put a 24V DC with 2.2A or greater, considering it requires 25V AC 2.2A or greater (unless they meant to say DC on the manual?

).

Thanks in advance.

Kei · 19 Oct 2013 at 21:09

Easiest way to find out whether it really needs to be AC in would be to dismantle the unit and see if it has a bridge rectifier (a 4 diode bridge, sometimes discrete, sometimes a chip with two ~ symbols and a + & -) built in, as amplifier gain stages require + & - DC rail voltages. A transformer does not convert AC to DC, it is merely the means to stepping voltage up or down, The diode bridge is what converts, and even then you have some different types. (full wave rectification and half wave rectification) There should be some large can capacitors near to the bridge as these are needed to smooth out the ripple.

legend474 · 19 Oct 2013 at 21:46

Ok I will dismantle it later on see what I can find. If unsure, I will prob post pics again. Thanks

lurkio · 19 Oct 2013 at 23:10

Yep , you are reading it correctly , 25V AC @ 2.2A

legend474 · 19 Oct 2013 at 23:10

Ok looks like it has a bridge rectifier. I see 4 diodes and a big capacitor next to them.

According to what you said, this sound system needs an AC adapter for real.

I doubt I can find such an adapter anywhere (unless custom build?), so if I hook this up with a 24V DC, what would actually happen and will it survive for a long period of time.

Here's a pic just in case:

Kei · 20 Oct 2013 at 10:22

A custom build using a 55VA 24V transformer and a box to house it should work provided you wire it up right.

legend474 · 20 Oct 2013 at 13:34

Kei said:
A custom build using a 55VA 24V transformer and a box to house it should work provided you wire it up right.

Just had a quick look on google and such transformers go for more than 20 quid which is not worth it in my case as the sound system is probably worth 10

Can you tell me if this would work Ebay link. If not I guess I will just get some second hand system from ebay.

Tealc · 20 Oct 2013 at 14:12

If you have some old bulb type external christmas lights you may find they have a 24v 2A transformer or something similar. I know that a couple of sets of my old lights had such a transformer which I scavenged when it was time to throw the lights out. I don't see a regulator in that image so I don't suppose it would matter too much if you got 1vAC less.

legend474 · 20 Oct 2013 at 14:23

Tealc said:
If you have some old bulb type external christmas lights you may find they have a 24v 2A transformer or something similar. I know that a couple of sets of my old lights had such a transformer which I scavenged when it was time to throw the lights out. I don't see a regulator in that image so I don't suppose it would matter too much if you got 1vAC less.

Very interesting. I will have a look in the loft. Thanks

EDIT: I doubt I will have the bulb type ones but, worth a look

Tealc · 20 Oct 2013 at 17:30

Regarding the DC question.

You will find that the rectified voltage from an AC supply when rectified to DC will be larger than just 25V. You should get around 35V DC with some ripple. The power supply of this device seems to be single rail given that it has just the one large reservoir cap (4700uF 50v as a guess). The chip amps may have internal voltage splitters or something, or one is acting as a splitter for the power.