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Old 10th February 2003, 11:37 PM   #1
Nisbeth is offline Nisbeth  Denmark
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Default Regulated SLA/battery supply?

(Moderators, Not sure if this is the right forum. Feel free to move the thread to where it belongs if it isn't. )

Question: If I want to use two 12 volt SLA's as a symmetrical PSU for an op-amp based preamp, would it be better to regulate the voltage from the batteries to a lower, stable voltage or to just leave it "as is" and let the voltage fluctuate as the batteries are charged and discharged? (I hope the meaning of the question is clear )

Maybe someone with experience in battery-PSU's can help?

/U.
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Old 14th February 2003, 02:05 AM   #2
mb is offline mb
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I'll share the little experience I have... I've used precisely 2x12V SLAs to power a opamp buffered attenuator. Results have been way beyond expectation. and several DIY tube diehards have been quite complementary about it.

1) "SLA's as a symmetrical PSU". I decided not to leave GND to fate, and use a TLE2426 precision voltage splitter to define a ground between the 24V+/- terminals. All other grounds (reservoir caps, signal in, signal out) reference to this GND.

2) Sound: dead silent, smooth, rock solid. Any variations perceived between freshly charged batteries and 50% discharged are most likely in my mind. I've also driven the same preamp with 2x9V rechargeables, which are puny compared to the SLAs. Sound was essentially the same.

3) There is much potential to tune the preamp with good bypass caps right next to the opamp. I use 220-470uF per side as "main" caps, which aren't that critical; a good film cap (0.1-1.0uF) will influence the sound a lot.

Imho, adding regulators to a battery PSU is a step backwards, unless the opamp specifically needs a precise voltage value. The headphone amp community (headwize.com) should offer a lot of insight into battery powered designs. It will take a lot to convince me to move away from batteries; more of my friends are seriously looking at battery supplies for preamps and DACs.

mb
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Old 14th February 2003, 03:26 AM   #3
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Default Re: Regulated SLA/battery supply?

Quote:
Originally posted by Nisbeth
Question: If I want to use two 12 volt SLA's as a symmetrical PSU for an op-amp based preamp, would it be better to regulate the voltage from the batteries to a lower, stable voltage or to just leave it "as is" and let the voltage fluctuate as the batteries are charged and discharged? (I hope the meaning of the question is clear )
No real need at all for regulators. The beauty part about batteries is that they don't have a bunch of ripple voltage like non-regulated AC supplies do. 'Bout the only thing a regulator would be helpful for in a battery situation is perhaps providing a bit lower source impedance from the batteries, which, unless you're using dry cells or something, isn't going to be terribly high to begin with.

se
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Old 14th February 2003, 03:33 AM   #4
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Quote:
Originally posted by mb
1) "SLA's as a symmetrical PSU". I decided not to leave GND to fate, and use a TLE2426 precision voltage splitter to define a ground between the 24V+/- terminals. All other grounds (reservoir caps, signal in, signal out) reference to this GND.
Leave GND to fate? You already have a perfectly good ground reference with your two SLAs. "Rail splitters" like the TLE2426 are just kludges to be used to provide a virtual ground when a split supply isn't available. A pair of SLAs is already a perfectly good split supply. Why turn them into a single supply and then use a kludged virtual ground reference instead of a real ground reference?

se
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Old 14th February 2003, 01:19 PM   #5
Nisbeth is offline Nisbeth  Denmark
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First of all thank you to all of you for the replies. I think I know what to do now.
I plan to use two 12V SLAs to power an opamp-based preamp with the centerpoint as ground. Should I bypass the rails with low-impedance caps as well or is it unnecessary?
Thanks again!

/U.
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Old 14th February 2003, 02:42 PM   #6
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Quote:
Originally posted by Nisbeth
First of all thank you to all of you for the replies. I think I know what to do now.
You're welcome. Good luck! And remember:

<center>
<img src="http://www.q-audio.com/images/noac2.jpg">
</center>

Quote:
I plan to use two 12V SLAs to power an opamp-based preamp with the centerpoint as ground. Should I bypass the rails with low-impedance caps as well or is it unnecessary?

That would be prudent. Using batteries doesn't change anything in that regard. The issue with bypass caps is inductance in the power supply lines. The (usually) internal compesnation capacitor references one of the supplies and if there's too much inductance, then at high frequencies the signal can be fed back to positively to the output stage by way of supply line modulation and the compesnation capacitor which can result in instability.

se
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Old 15th February 2003, 12:16 AM   #7
mb is offline mb
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Quote:
Originally posted by Steve Eddy


Leave GND to fate? You already have a perfectly good ground reference with your two SLAs. &quot;Rail splitters&quot; like the TLE2426 are just kludges to be used to provide a virtual ground when a split supply isn't available. A pair of SLAs is already a perfectly good split supply. Why turn them into a single supply and then use a kludged virtual ground reference instead of a real ground reference?

se
Agreed. Thing is, on occasion I use a single +/- supply (eg. 9V for portable use), in which case I must have some sort of rail splitter.
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Old 15th February 2003, 07:26 AM   #8
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Quote:
Originally posted by mb
Agreed. Thing is, on occasion I use a single +/- supply (eg. 9V for portable use), in which case I must have some sort of rail splitter.
----------------------------

Why not just take 12V from a single unit?

Does anyone have a good auto charging circuit. My probelm with lead batteries is leaving the units on and discharging/ruining the whole thing. This is inspite of using 18Ah ones. The sound using batteries is much better.
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Old 15th February 2003, 08:46 AM   #9
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Quote:
Originally posted by fmak
Does anyone have a good auto charging circuit.
Why not use a multi-pole switch and use it to switch the batteries between the unit in question and the charger? It's not automatic, but...

se
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Old 15th February 2003, 09:38 AM   #10
sangram is offline sangram  India
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Rod Elliot has one on his site - fully automatic.
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