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DC 9v replacement

Cheeks

Jun 19, 2019
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Hi, I have a wireless, outdoor Brookstone speaker with an aux transmitter. It's the old model - at least 10 years old.

The transmitter has a power cord that says DC 9V.
The manual says the speaker also came with one that is DC 9V (if 8 D batteries are not available).
Unfortunately, I have misplaced the power cord for the speaker. The company was unable to help me locate a replacement. I tried the transmitter power cord in the speaker and it does not fit.

So, what can I use to replace this? It says DC but does that actually mean AC to DC? Is that the same as AC/DC? If I found another DC 9V in the house is it safe to use it? Thank you for any help and information!
 

Bluejets

Oct 5, 2014
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You will need the nameplate current rating details from the system or a link to your model specs or manual.
Just any old 9v plugpack you might have laying around simply will not do.
 

Cheeks

Jun 19, 2019
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Thank you for your reply! I've attached the manual, but I'm not seeing any specs that might be on the nameplate. I suppose I could try contacting Brookstone again, although all they did last time was send me the manual for the newer model.
 

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dave9

Mar 5, 2017
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It can't use much current at only 9V. I'd seek a 1A @ 9V supply. The other factor is the connector, does it use a typical DC barrel socket for power input? If you don't find a power supply with a mating connector then you'll need to buy a connector separately and solder it on.

The two most common size barrel connectors (if that's what it is) are both 5.5mm O.D. and one has 2.5mm I.D. but the other is 2.1mm I.D.

https://www.ebay.com/sch/i.html?_fr...V+1A+adapter.TRS0&_nkw=9V+1A+adapter&_sacat=0
 

BobK

Jan 5, 2010
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8 D cells makes 12V. Are you sure the adapter is 9?

Bob
 

duke37

Jan 9, 2011
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You can make a couple of wooden batteries and fix some thin tinplate at the end to make a connection. Solder a wire to the tinplate and feed with 9V of the correct polarity. Note that 8 batteries will give more like 12V.
 

dave9

Mar 5, 2017
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8 D cells makes 12V. Are you sure the adapter is 9?

Bob
I'd imagine it's set up that way so it still functions at the end of the discharge curve for 8 series cells, closer to 8V.

On the other hand, this also means it is 12V tolerant and would have higher output power at 12V, as well as 12V brick AC/DC adapters being more common... he might even have one lying around the house. Just make sure it's a regulated switching supply not something that floats closer to 16V at low load, which could be measured with a multimeter before plugging it into the speaker.

It does make you wonder why they spec'd 9V, perhaps it gets on the hot side and depends on voltage droop from the 8 series cells to limit power and stay within thermal margins.
 

duke37

Jan 9, 2011
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There will be plenty of room inside the battery compartment to fit a 9V or 10V regulator.
I was asked to repair a US 120V ghetto blaster which had been run on 240V. I fitted a 9V regulator in the battery compartment. This was a 7805 with the reference pin raised with a red led. It worked but would not respond to the zapper. I may rewind the mains transformer in the next decade or two.
 

Audioguru

Sep 24, 2016
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When you shop for an AC/DC adapter, the very important polarity of the jack on the receiver shown in the manual must be matched by the plug on the adapter.
 

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Cheeks

Jun 19, 2019
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Thank you for all the replies, this is really helpful.
Dave9: yes, it is a barrel socket for power input. I've attached a picture which shows that it is the 5.5mm size.

BobK: The picture notes 9V and there are definitely 8 D batteries in there.

I appreciate the ideas of soldering or making wooden batteries (is that a thing?) or inserting regulators, or using a multimeter. These are all things that are beyond my abilities or that I don't have the tools to do.

AudioGuru: I'll definitely make sure it has that picture on it, which matches the diagram in my picture below.
So aside from that i'll look for something with a 5.5MM barrel, 9v, 1Amp power cord? Does W matter? This one is 12W, what do you think? https://www.amazon.com/Belker-Unive...ord+1a+dc&qid=1561031854&s=electronics&sr=1-4


20190620_074155.jpg
 

BobK

Jan 5, 2010
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1A might not be sufficient. Do the speakers have a power rating?

Bob
 

Audioguru

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Stereo was not mentioned, I assume the speaker is mono.

With a 9V supply and one linear single ended amplifier feeding an 8 ohms speaker, the power output is 1W and the heating is an additional 1W so the total is 2W. A 9V/0.25A adapter or even more current is fine. If the speaker is 4 ohms then a 0.5A adapter is fine.

Who knows if the speaker uses a bridged amplifier that produces 4W into an 8 ohm speaker? 8W into a 4 ohm speaker and they guess that nobody would overload it by playing full power tones continuously?
 

Alec_t

Jul 7, 2015
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At least you have a polarity marking on the plastic. The centre pin of the barrel connector is +ve.
 

dave9

Mar 5, 2017
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The one you linked should work. You'd just be paying a few dollars more for the voltage adjustment feature and extra tips, though having both the 2.1mm and 2.5mm I.D. tips, eliminates the need to guesstimate which it is... though from the picture I'd guess it's 2.1mm.

Sometimes I guess these things wrong so I prefer to try plugging in a random adapter I have lying around, a 2.1mm adapter's plug first to see if it fits.

At the same time if you'd find the adjustable feature and multiple tips handy to power other things in the future, they also sell a 30W version for only a couple dollars more:

https://www.amazon.com/Belker-Universal-Adapter-Household-Electronics/dp/B078LSVVTB
 
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Audioguru

Sep 24, 2016
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Having an adjustable voltage on an adapter is asking for something to be blown up by it.
 

dave9

Mar 5, 2017
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^ Perhaps, but they don't discriminate different voltage adapters with different barrel plug sizes in any standardized way so there's always been a risk to use the wrong voltage for a device when you mix and match using a different PSU than what came with the device.
 

BobK

Jan 5, 2010
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I would be very surprised if an outdoor speaker produced only 1W of output. You would barely be able to hear it.

Bob
 

Audioguru

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I would be very surprised if an outdoor speaker produced only 1W of output. You would barely be able to hear it.

Bob
I figured that an amplifier powered from only 9VDC has a maximum output swing of 8V peak-to-peak if it is good, which is 2.83V RMS. Then the power in an 8 ohms speaker is exactly 1W. If the amplifier is bridged then its output is 3W to 4W into 8 ohms.
A little LM386 amplifier IC produces only 6V p-p into 8 ohms when powered from 9VDC. Then its output power is only 0.56W.
 

BobK

Jan 5, 2010
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Based pm what Brookstone stuff costs, I would expect a bridged class D amp.

Bob
 
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