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In Reply to: RE: Building an SLA battery powered supply posted by Steve Eddy on July 13, 2010 at 15:02:47
So if I am going to design or redesign some existing circuitry, to make sure I put the caps on the equipment side and then have the power supply connector to go to either a battery power unit or an ac/dc unit. Sounds like a plan.
I am really hoping to avoid all ac entirely, but that may be for headphone listening. I am just tired of having to postpone listening to off-hours when power-line grudge is not as much a problem.
Thanks.
Follow Ups:
Well... if you are seeking isolation from the line you can't do better than batteries. And, since they can source DC all of the time, you don't get the music modulate noise generation in the diodes and the pulsating noise coupling to the line from the current gulps that were mentioned by Steve.
Theoretically that should be a good thing but from some of the comments in this thread I wonder if one can become habituated to that distortion/interference. Sort like a snare drum built into your power supply, you notice the difference if the snares are removed.
Another issue is the isolation itself. I would expect the sound to change a little, indeed improve if I isolate a component, that's the plan after all. However since you listen to the whole system, not just a component, other pieces like interconnects and grounding schemes that were optimized with the line powered piece may need to be revisited when using a battery for it. The end result however should be an improvement.
Rick
You can obtain a high level of isolation from an ac/dc ps as well.
The battery supplies I've had experience with, both diy and commercial, have been less than impressive. In real world use they're practical for only low level, low powered equipment, eg, phono pres. where, IMO, they don't sound good.
I just don't believe they have the brickwalled voltage and instantaneous current demand you need with dynamic music.
Never attribute to malice that which can be adequately explained by stupidity.
I just don't believe they have the brickwalled voltage and instantaneous current demand you need with dynamic music.
And in a typical AC power supply, that comes exclusively from the reservoir capacitors.
For the majority of the time, everything upstream from the rectifier bridge is out of the circuit and therefore doesn't contribute any current, let alone instantaneous current.
se
C1 must be large enough to keep the rail voltage up.
C1 must be large enough to keep the rail voltage up.
Right.
The more current drawn by the load, the larger the capacitance needs to be to keep ripple voltage to a minimum.
Though that's rather less of a concern when paralleled with a battery since the battery is always there providing the hold up voltage and the cap's voltage isn't being drawn down while it waits for the next refresh cycle from the AC supply.
se
"I just don't believe they have the brickwalled voltage and instantaneous current demand you need with dynamic music."
Those are the precise attributes that AC power DOESN'T have for transient loads. As others have posted their whole claim to being a transient voltage source relies on the filter capacitors and post regulators. In the long term however AC is a better voltage sources because the battery will go dead.
And no power supply can touch them for isolation although I believe that they can provide plenty if done well. Sound wise who knows, there's too many variables. I don't question what you hear, your preferences or solutions. And yes I agree that batteries are most appropriate for small signal application. All I'm suggesting is that the attributes that you value using an AC supply may not be caused by what you think.
The main thing is that you've found what works best in your system for your usage and push comes to shove it doesn't get better than that. I don't use batteries in my stereo either but I sure do if I'm doing work with very tiny signals.
Rick
Agreed, however, the AC is turned into DC so the point is moot.
If you're starting the comparison from after the rectifiers I still believe I have valid points, one being current supply.
I'm just stating my experience, I've talked to others that have reached the same conclusions. There are many opinions online both pro and con.
Never attribute to malice that which can be adequately explained by stupidity.
Instead of those cheap SLAs, get some top-quality higher AH Odyssey deep-cycle batteries with internal impedance on the order 2-20 milliohms, parallel small electrolytics to around 30,000uf between the batteries and the component, and add a good 5uf-10uf film cap inside the component chassis. Now you will have low noise, low ESR, and fast dynamics. It's not cheap to do it right.
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