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What kind of battery to replace an adaptor?

T

Tim's Dad

pfm Member
This is my first ever foray in the DIY forum! Hopefully this is the best place for my questions.

My Kingsound King electrostatic speakers were powered by walmarts - AC/DC adaptors with output rating 12V DC 250mA 3VA, tip positive.

I say "were" - my son has just managed to trip over one of the wires and rip it out of its moulded housing.

Rather than try to get it repaired or buy a (cheap) replacement, I'm thinking to use this as a prompt to get some rechargeable batteries instead, the theory being they will sound better and hopefully provide a better quality to cost ratio than a pair of high-quality expensive power supplies.

But I'm clueless on what kind of battery to buy.

Is my best option a sealed 12V car battery? I understand that the amount of time it will last is specified as Ah, but does the current rating matter, or will the speakers simply draw the current they need? In which case should I simply go for the biggest Ah I can afford (and cope with aesthetically), and safely ignore the current rating?

What kind of charger should I buy? I imagine the best solution audio-wise is to have a charger I can plug in when not using the speakers?

Can I connect the battery terminals directly to the wires of the broken walmart cable (ie do the +/- battery terminals correspond exactly to the outputs of the adapter)?

Sorry if these are stupid questions - any help is much appreciated.

Many thanks

Mark
 
Tim's Dad said:
This is my first ever foray in the DIY forum! Hopefully this is the best place for my questions.

My Kingsound King electrostatic speakers were powered by walmarts - AC/DC adaptors with output rating 12V DC 250mA 3VA, tip positive.

I say "were" - my son has just managed to trip over one of the wires and rip it out of its moulded housing.

Rather than try to get it repaired or buy a (cheap) replacement, I'm thinking to use this as a prompt to get some rechargeable batteries instead, the theory being they will sound better and hopefully provide a better quality to cost ratio than a pair of high-quality expensive power supplies.

But I'm clueless on what kind of battery to buy.

Is my best option a sealed 12V car battery? I understand that the amount of time it will last is specified as Ah, but does the current rating matter, or will the speakers simply draw the current they need? In which case should I simply go for the biggest Ah I can afford (and cope with aesthetically), and safely ignore the current rating?

What kind of charger should I buy? I imagine the best solution audio-wise is to have a charger I can plug in when not using the speakers?

Can I connect the battery terminals directly to the wires of the broken walmart cable (ie do the +/- battery terminals correspond exactly to the outputs of the adapter)?

Sorry if these are stupid questions - any help is much appreciated.

Many thanks

Mark
Click to expand...

Mark

Welcome to the DIY Room. Your questions aren't stupid.

Sealed Lead Acid batteries (YUASA are, as I recall, one of the readily available brands) are an option, being widely available in a wide range of capacities.

But batteries are not a straightforward replacement in many applications due to various factors - battery internal impedence, how noisy they might be (lead acid batteries are not brilliant in this respect), how long they take to recharge, but most importantly the exact voltage characteristics of the cell. Some batteries have a voltage that varies with charge state and some have a nominal voltage that sags under load.

Connecting a battery to your speaker should not be difficult, but by the time you buy a charger and a battery, you may as well go to Maplin and buy a regulated 12v mains power adaptor. They do a variety and anything rated for more than 250ma current draw will be fine, just as easily connected, more discreet aesthetically and free from subsequent charging faff.

Regards

Mark
 
Hi,

I would just get another adapter, you won't get any improvement is sound quality, and you will end up spending a lot of money.
There is also a safety aspect a large battery is a fire/explosion risk if you short the terminals, it needs to be fused and enclosed.

Pete
 
Thank you for the replies, Mark and Pete.

I carried on searching after creating my post and eventually found this article from Stereotimes, where a Panasonic 12v 7.2Ah "rechargeable lead battery" is found to give a slightly cleaner background. I think I must have read this a good while ago to set my thinking on the battery track.

You can also buy a pair of specially designed matching valve-based supply from VAC in the US for $1000!

It would be interesting to find out whether most of this improvement can also be gained with a more sensibly priced regulated 12v mains adapter. I had a long look at the Maplin website but couldn't find anything with that description. Do you have any specific suggestions?

Many thanks

Mark
 
Thanks Pete

It certainly is cheap. I'm not sure it will provide an improvement over my existing walmart though.

I accept your sceptism that the quality of the supply will make any difference, but would like to test this since I have to buy a new one anyway. I'm happy to spend up to maybe £100 for the pair. This is in the context of £10K (RRP) speakers after all, so a small noticeable improvement for 1% of total retail value seems to me to be worth a punt.

Many thanks

Mark
 
Well its only for the HV supply which draws an extremely low amount of current so I can't see it making any difference.
You will get more of a gain by spending the money elsewhere.

The ones I linked to are 4 times the current of your existing ones, so could be considered an upgrade.

Pete
 
If the HV bias supply runs off a small DC wallwart there has to be a small SMPS internal to the speaker, to achieve the necessary step-up to kV range (often a simple oscillator and a Cockroft multiplier or similar; Stax do the same in their electrostat headphone amps). That will make any notional improvement to be gained from an the raw DC supply rather moot. A linear regulated wallwart is a good answer I think.

NB Pete's right, once charged there is very little current drawn because electrostats essentially run as a capacitor at constant-charge, and the only loss is by conduction/corona away in the air - varies with humidity. The time constants in the HV 'ladder' are usually pretty long too - megaohms to a few nanofarads, in Quads at least anyway (which use a simple multiplier run off the mains via a transformer) and the result is more than adequate HV smoothing -even though the process looks a bit rough!

Never heard of the Kingstons Tim - can you tell us a bit more about them? Oh, and welcome!
 
If the PSU does nothing more than allow a constant charge on the diaphragm, as with Quads, the quality of the power input is going to be completely immaterial. Stick with a cheap wall-wart though use a linear version as Martin suggests. At least you'll reduce any potential impact the SMPS may have on the mains or other connected kit.

I really wouldn't use batteries in this case. Hassle and expense for no benefit.
 
I'm in the realms of ignorance here, but my impression was that the Kingsounds do not require kV in same way as eg Quads. I had assumed they worked directly with the 12v but could be wrong.

Assuming that the movement of the diaphragm is governed by an interaction of voltages, it also appears feasible to me (again in my ignorance) that a pure constant voltage will produce less audible noise than a noisy one.

I'm learning the issues though through your helpful responses. How can I tell that the wall-wart (not walmart!) is regulated?

Many thanks

Mark
 
They do need several KV of voltage but hardly any current, as Martin said the plates act as a capacitor storing the charge so you can unplug the wall-wart and still get sound out until the plates discharge, my ELS57 ran for quite some time after switching off, so nearly any supply will be o/k.

Pete
 
Tim's Dad said:
it also appears feasible to me (again in my ignorance) that a pure constant voltage will produce less audible noise than a noisy one.
Click to expand...

Welcome Tim,
Speaking in more generic supply terms It is often a misconception that batteries are more pure and have less noise than correctly designed regulators and I easily understand how this must seem so. However the is quite a learning curve to climb, your starting with the right questions and in the right place so given time you will indeed begin to understand.

Additionally not all regulators are the same neither are all batteries and not certainly not all loads. This is quite a complex subject but I find it fun to try and comprehend how, why and why not.

You may well find a completely different response should you have posted this in the audio room and probably started another audio room argument. :D

Tony
 
Tim's Dad said:
Thanks Tony

Do you have any recommendations and/or links as to what I should consider purchasing?

Mark
Click to expand...

To be honest Tim I have no experience of your speakers so would not like to comment. It does seem as though there would be a secondary switching power supply within your cabs potentially swamping any gains in the primary supply noise.

If I were to have a play myself I would trial a linear front end with perhaps 317 regulators in TPR mode but would not readily expect any reward, I may even go stupid and try some super regs but that's just me :D

I don't think I would be trying SLA batteries and the load is to high for a practical solution with other types of cell.

There again if you realy must try something SLA is simples for a dirty quick trial.
 
It seems odd that the speakers would require DC input only to convert to AC again but who knows.

Can anyone point me to for sale examples of good power supplies? (Already assembled and ready for use, I'm afraid - remember I don't really belong to the diy forum!)

Mark
 
Hi Tim,

Rapid are good for things like this.

large selection here:
http://www.rapidonline.com/Electrical-Power/Power-Supply-Units/Plug-In-Power-Supply-Units

One that seems to do what you need:
http://www.rapidonline.com/Electric...g-Regulated-Power-Supply-Unit-T3665ST-90-2635

- through to total and utter loony overkill:
http://www.rapidonline.com/Electrical-Power/8A-AC-DC-Power-supply-65046

(- I'm not seriously suggesting this, but it would work fine with two suitable cables made up to connect to the speakers. The excess current capability would be wasted / bring no benefit though)

HTH :)
 
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