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Active Speakers Powering

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Active Speakers Powering

Postby tannaroo » Fri Nov 02, 2018 7:14 pm

Hi all,

I've got an old Sony Personal Component System (Sony PMC-205L) which has 2 speakers one of which are active speakers and connects to the main unit (which has a tape deck, CD).

I have successfully connected a Chromecast Audio via the Signal Input to the active speaker and everything works, so long as I power the whole unit via the main unit and therein lies my question.

I want to get rid of the main unit but then I lose the power switch to power up the speakers.

Is there a simple way to attach a power switch to the active speaker of better still, it is always on when plugged into the power outlet?

This way I can throw away the main unit.

Many thanks
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Re: Active Speakers Powering

Postby Sam Spoons » Fri Nov 02, 2018 9:31 pm

It looks as if the mains PSU is in the active speaker with low(ish) DC voltage being passed to the main unit, switched, and returned to the active speaker via the 4 conductor cable so you'd probably need to connect two of the 4 conductors to bypass the switch in the main unit. It would be unlikely to harm the speakers if you switched them on and off at the wall socket.
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Re: Active Speakers Powering

Postby tannaroo » Fri Nov 02, 2018 10:12 pm

Thanks Sam.When you say connect 2 of the 4 conductors, where am I connecting them?
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Re: Active Speakers Powering

Postby Sam Spoons » Fri Nov 02, 2018 10:28 pm

I can't say for sure, no schematic I can find. I doubt they'll be carrying 230 volts (that would definitely not conform to the regs) so you need a multimeter to check which conductors are doing what. Given that they're are 4 conductors I'd guess one will be DC+ another DC- and the others switched DC+ and DC- but without a schematic or hands on with a meter I can't say.
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Re: Active Speakers Powering

Postby ef37a » Sat Nov 03, 2018 10:13 am

Might this be another suitable case for a wireless mains switch with RF remote?

They are also MOST handy for kit that needs the occasional "hard reset" and I have a couple of those!

They also "fail safe" i.e.off in the event of a power cut.

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Re: Active Speakers Powering

Postby tannaroo » Sat Nov 03, 2018 7:56 pm

I've not come across those before. A quick search on google brought up lots of products. Do you have a link please of a specific type that your refer to? And how do they work please?
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Re: Active Speakers Powering

Postby Sam Spoons » Sat Nov 03, 2018 9:46 pm

Don't forget yo will need to work out the means of switching the DC power in the active speaker (by bypassing the switch in the main unit). Have you enough electrical knowledge to do that (i.e. can you use a multi meter and trace what each of the four wires are doing)? Given a schematic we could probably help you even if you are a novice but without (and Sony are notoriously secretive in such matters) probably not.
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Re: Active Speakers Powering

Postby ef37a » Sun Nov 04, 2018 7:57 am

https://www.homebase.co.uk/remote-contr ... -2_p682609

I actually got a 3 pack there for about £20. You can find cheaper version and I have two sets and they seem fine. The Homebase ones do seem a little sturdier though.

I have wondered if a similar switch device existed but with say 2 pole changeover contacts and rat powered so that it could be used for wireless low voltage switching, even audio?

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Re: Active Speakers Powering

Postby tannaroo » Sun Nov 04, 2018 10:52 am

Thanks guys for the replies.

@Sam - yes I am a novice so not sure I would be confident enough to trace DC power, so I think the remote control option might work.

@ef37a (Dave): I'm not 100% sure how these might work in my situation. Do I connect the whole unit (main unit + speakers) into a wall socket and control the unit through the remote control?

I was looking a ditching the main unit and just place the speakers on my wall connected to a power source without the main unit, if possible. Or else, I would have to hide the main unit in a cupboard but would still require a longer cable to connect the speakers to the unit and rely on the remotes possibly.
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Re: Active Speakers Powering

Postby ef37a » Sun Nov 04, 2018 11:03 am

tannaroo wrote:Thanks guys for the replies.

@Sam - yes I am a novice so not sure I would be confident enough to trace DC power, so I think the remote control option might work.

@ef37a (Dave): I'm not 100% sure how these might work in my situation. Do I connect the whole unit (main unit + speakers) into a wall socket and control the unit through the remote control?

I was looking a ditching the main unit and just place the speakers on my wall connected to a power source without the main unit, if possible. Or else, I would have to hide the main unit in a cupboard but would still require a longer cable to connect the speakers to the unit and rely on the remotes possibly.

I am not 100% sure either! I just reasoned..Switch DC power. DC must come from mains unit. Switch mains unit?

Why do you have to hide anything?

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Re: Active Speakers Powering

Postby Sam Spoons » Sun Nov 04, 2018 2:59 pm

The mains supply is connected to the active speaker and low voltage DC power supplied to the main unit via the four conductor cable. I'm guessing that then goes via the power switch and back to the active speaker's DC rails. To get the speakers to work without the main unit the switch needs to be bypassed. Again I'm guessing that that would be possible by shorting some of the wires in the 4 conducted cable but which ones? Connecting the wrong ones may result in a fried PSU but without a schematic or getting hands on with a multimeter there is no way of knowing. What do you think Dave, am I wildly off track or does that make sense?

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Re: Active Speakers Powering

Postby ef37a » Sun Nov 04, 2018 3:43 pm

Now I am not TELLING you to do this! Just a suggestion!

Get some 5 amp "choc-block" connector strip (buy good stuff from Wickes/H'base etc)

Remove the 4way cable and cut and separate the wires for a good 50-60mm. Cut and strip each one and insert into the c'block and make certain to keep the order correct (piccies, piccies,piccies) .

Once you are sure you have it right you can now dive in and identify each wire with a test meter. N.B. I would diss the whole lot, plug up "off" then see if any of the wires goes to an earth*, e,g, an RCA outer? If so that gives you a ref for the other voltages.

*On Ohms, should have said.

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Re: Active Speakers Powering

Postby Wonks » Sun Nov 04, 2018 4:29 pm

I presume that the OP has tried the speaker with a phono input from another source (CD player, phone etc.) with no power lead to the central unit? The speaker may remain powered all the time and just go into a standby mode with no audio input detected.

The trouble with just using voltage to determine what the switched line is (if there is one) is that the return switched signal line may not be be easily discernable from 0v, and if the other two lines are at say +5v and +12v, then which one is used to send a voltage back to the speaker amp PSU? Very hard without taking the units to pieces, which is probably outside the OP's comfort zone.
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Re: Active Speakers Powering

Postby Sam Spoons » Sun Nov 04, 2018 5:49 pm

Mark the wires first, then it should be possible to identify which ones are the switched pairs (if that is how it works) by testing the main unit side of the cut, a simple continuity tester would be sufficient to do that (a battery and a bulb even). Then short the switched pairs at the speaker end.

Always assuming that Wonks supposition is not correct ;)
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Re: Active Speakers Powering

Postby tannaroo » Mon Nov 05, 2018 9:48 am

Wonks wrote:I presume that the OP has tried the speaker with a phono input from another source (CD player, phone etc.) with no power lead to the central unit? The speaker may remain powered all the time and just go into a standby mode with no audio input detected.


Yes I did try with a phono input with no power lead to the central unit but it does seem the speakers go into standby mode.

Guys I really appreciate all of your suggestions but it does seem beyond the scope of my abilities/comfort zone!
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Re: Active Speakers Powering

Postby Sam Spoons » Mon Nov 05, 2018 10:11 am

Just a thought, how valuable/precious is this device? If it was destined for landfill before you found a use for it then the consequences of getting it wrong are small (little or no danger to life or limb, some danger of killing the speakers). A little time understanding basic electrical circuits (at little more than light switch level) would prove useful in the future for a musician/DJ/sound guy?
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Re: Active Speakers Powering

Postby tannaroo » Mon Nov 05, 2018 1:46 pm

Well its not precious but I'm still not sure of the end result. For example, even if I was to identify each wire in the 4 way connector to the main unit , would it just a case of connecting say a wire (lets call it 1) with another wire (lets call it 2) and likewise with the remaining 2 wires, thereby creating a loop back to the active speaker unit?
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Re: Active Speakers Powering

Postby Sam Spoons » Mon Nov 05, 2018 2:12 pm

Yes, that's pretty much it :thumbup: Twisting them together and taping the bare ends will work, choccy block connecters is a little more elegant.....

Connect the wrong ones together and theres a reasonable chance you'll destroy the PSU and they become a bin job but there is no actual danger (other than, possibly, the bang as the magic blue smoke escapes making you jump). Back me up on this Dave, those wires can't possibly be carrying 230VAC can they......
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