Why not batteries instead of power supplies?

There are lots of reasons to avoid the house AC if at all possible. Aside from voltage regulation there's also the issue of RFI/EMI coming in along with the voltage and current, the cost of power cords, the high cost of a good power supply especially for high power amps, ground issues, fuse issues, transformer issues (magnetic field and vibration) and the need for huge capacitors.

@geoffkait

I knew that AC could be a problem. Is there a way to hook up an amplifier to a battery pack and avoid AC altogether?

A few years back a company was showing a strong presence at RMAF that had a few components that were 100% stored DC power. Although they didn’t sound extraordinarily good, the idea was launched. For some reason it never caught on, but doesn’t PS Audio already somewhat address this with their Regenerator P5 & P10?

The negative side of battery power supplies is the supplies themselves have inherently high output impedance compared to their AC counterparts, leading to higher cross-talk, and potentially weak bass and dynamic range.

This is all theory, of course, as is the benefits of battery supplies. I’m just playing devils advocate. It's not a 100% free lunch, and has its own set of challenges.

I own the Veloce Lithio line stage, which is powered by lithium batteries;  it was a "hot" product a few years ago, and now is rarely mentioned or even on the radar. Vytas, the designer/manufacturer offered an update about a year or so ago which I recently took advantage of--one of the changes is the batteries- now much smaller than the big lithium green boxes that originally populated the unit. Despite this aspect of the design, the unit uses tubes- 6H30s, and I'm using NOS DR Reflecktors.
I have owned the unit for several years and have been very pleased with the sound. It replaced a Lamm L2 Reference line stage, which was also a very good unit. The Veloce lacks for nothing in the areas of bass or dynamics. It is also not noisy- to the contrary, using the Avantgarde Duo, a high efficiency  horn-type speaker with 104db sensitivity, the system is remarkably quiet. 

I think we'll see more of this and Powerwall is just the tip of the iceberg.

But a DC power supply will not get rid of noise problems that originate from inside your house.

@erik_squires, "The negative side of battery power supplies is the supplies themselves have inherently high output impedance compared to their AC counterparts, leading to higher cross-talk, and potentially weak bass and dynamic range."

Well, put.  Weak bass and dynamic range definitely plagues the majority of these products.

@whart, "The Veloce lacks for nothing in the areas of bass or dynamics."

Vytas is a buddy of mine, and your point is absolutely correct.  As a basshead and power focused guy in general, he would NEVER build anything that didn't meet that mark, and took a different tack than what I've encountered in many other products.  As we mentioned Erik pointing out, this really shows up as a problem for most other battery powered products

@erik_squires 

This is fascinating stuff. I must admit that I don’t understand the link between output impedance of batteries and more cross talk and dynamic range. 

You clearly know this stuff inside out. if you could give me a pointer or two to help me get it I would be totally grateful. 

Hi Defiant,

Power supplies provide a (hopefully) fixed voltage to the circuits which does work for us. Say, +15VDC, Ground and -15VDC is typical for a solid state preamp / CD player, etc.

A "perfect" power supply has no output impedance. No matter what the circuit it feeds does, the voltage remains rock-solid.

As the output impedance of the supply goes up, the voltage sags and surges as the demands go up and down respectably. So, instead of exactly 15VDC, it will start to look like 13V to 15V, tracking the output signal somewhat.  The higher the PS output impedance, the more this happens.

Once this happens, your power supply has a "copy" of the music. This is where cross-talk happens, as well as weak bass and reduced dynamics. If the L channel is moving the power supply V, the R channel will be influenced, and vice-versa.

One of the best Ideas I ever read about was a designer who would listen to his power supply. He would treat the + and - rails and hook them up to headphones or speakers, so he could literally hear the noise or cross talk in the power supply itself. Pretty brilliant.

Best,


E

@erik_squires

Awesome explanation, many thanks. I think I am beginning to get it.

Technical discussions are always fun, but it is important to keep an open ear and buy what you like to listen to.


Best,

E

defiantboomerang
 Why not batteries instead of power supplies?

Easy to do for preamps, phono stages, ect using single rail power supplies.

But to do for poweramps with positive CT negative rails is harder, back in the 80/90’s (as you can tell by the ad) Nelson Pass was said to be the designer of one for a company called N.E.W. A20.1
http://www.canuckaudiomart.com/details/649334581-new-p3-new-201/images/1459271/

Two Nelson Pass designed tow box models for memory N.E.W. DCA-66 and DCA-33 had a bank of those black rechargeable brick shaped alarm system type batteries arranged in series/parallel to give +24v 0 -24v this way you get a 0 centre tap to ground.
https://tangentsoft.net/elec/bitmaps/vgrounds/ctap-battery1.png
When working properly it did sound very good to me.
The only problem I believe with it was if there was more current draw on one side more than the other or the battery lost more charge on one side than the other, the battery rails became unbalanced with age, which then results in higher distortion and can lead to dc offset problems.

Cheers George

To add to the list, there are the folks at Definitive Audio/Living Voice in the UK that starting making full system battery supplies some years ago--covered in 6Moons, among other places. I'm sure improvements in battery technology have only helped them. Not sure if it is on their website, but they used to be set up in an Edwardian factory outside London. Long on my list for a visit. (Same folks who make those million dollar horns for your ship). They also sell stuff to lesser mortals, and seem to have a keen sense for interesting products. 

The late Gary Dodd produced some very fine electronics powered by batteries. Check out posts on the Dodd Audio and GR Research AudioCircle Forums for discussions about them.

I'm surprised nobody has brought up or suggested supercaps. Those things have insane capacity, very low internal resistance, huge voltage capacities, and charge very rapidly. A lot of you folks probably have supercaps in your digital gear already since they're replacing mounted batteries left and right. You could feed a bank of those the lumpiest, ugliest power imaginable, output those to a conventional RC filter supply, and you'd have a very clean, albeit massive power supply. 

I'm surprised nobody has brought up or suggested supercaps.

I think voltage rating is too small for them to be used as poweramp supply caps. Only 2.7v unless that's changed in the last year or so.

Cheers George

Cost!
http://www.mouser.com/Passive-Components/Capacitors/Supercapacitors-Ultracapacitors/_/N-5x76s?P=1z0x...

Wow it’s been a while, since looking at them. And you can get 48v 83 farad for a "cheap" $1,300 each you’ll need two. Great ESR as well,can you imagine the inrush current!!!!!!! No BS boutique ac voodoo fuses here, you'll need massive circuit breakers
http://www.mouser.com/ProductDetail/Maxwell-Technologies/BMOD0083-P048-B01/?qs=sGAEpiMZZMuDCPMZUZ%252bYl9uUUNJQGTDeS0ZKH5mj4e4%3d
Wonder who’s going to be the first linear amp manufacturer to start using them, my bets on Dan D’Agostino .

Cheers George

If memory recalls, I think Vinnie Rossi already uses this technique in his LIO amp, one of the reasons why it sounds so good. Two sets, one set is used while the other is charging and they switch back and forth as needed. 

I heard a system with the Veloce linestage and it sounded quite good.  I have no idea how it would compare with an otherwise identical model running off of a conventional supply.   I have also heard an ultra expensive version of a preamp that is quite similar to mine (same builder), but it ran off of a large battery pack.  It too was very nice sounding, but, it had to be recharged quite often.  It, like the Veloce, is a tube unit.  I saw pictures of a DIY tube phono stage with a battery power supply that was the size of a large refrigerator; all in the name of extremely low output impedance.

I would think that battery power would make even more sense with solid state where there would be far less draw at idle.  

Jeff Rowland Design Group offer battery powered amplification since early 90's

http://jeffrowlandgroup.com/us/preamplifiers-criterion.html

http://www.hifi-advice.com/blog/specials/jeff-rowland-company-special/jeff-rowland-battery-power-sup...

@nycjlee +1! Vinnie Rossi room was one of my fav at LA Audio Show this year!
Sutherland battery-powered phono got ditched by the man, I was really disappointed that in his interview with Stereophile he bluntly refused to answer why.
Agree with the sentiment that God is in listening: PS Audio Power Plant worked magic in my lab when we tried to make video of our efforts. When used in my "bedside" kit of Naim CDX/Lehmann h/p Amp/HD600 the benefits came at the price... Sent it back to the lab!!

No doubt supercaps are expensive as all hell, but when you're talking about $50,000 amps, is $3000 really all that insane when it comes to filtering a power supply? I'm not suggesting using them as primary supply filter caps. I'm suggesting using them as an additional filter stage between the rectifiers and the common electrolytics. If you've got even 200 Farad between the filter caps and rectifiers, are you going to even be able to measure the ripple? Sure, you'd need massive inrush current control, and the thing might take 5 minutes to charge up, but that's really about as close as you're going to get to a completely hassle free battery with practically none of the drawbacks. 

I used a capacitance multiplier circuit on a preamp once, worked very well, bit hard to do on a poweramp though.
http://electronics-diy.com/electronic_schematic.php?id=486

Cheers George 

@larryi 
The ones Mouser is selling are designed for UPS backup power supplies. The main thrust of development for supercaps is to use them are replacements for batteries. A lot of gear already uses small supercaps for memory retention and running clocks in DVD players and the like. They replace button cells. I've never tried anything with supercaps in an amp. I'm not sure my amp building skills are to that point yet. I'd want to try it on a pre-amp first. Make a board and just hang up a half dozen or so of the little 2.7V 100 Farad deals and see how that works. Those are cheap. 

As a cheap experiment born of curiosity, I tried using a a widely available commercial "online" uninterruptible UPS, which does a full AC>DC>AC conversion for all power output, here:    https://www.amazon.com/dp/B0050NZTQ2/ref=cm_sw_r_sms_tai_GYJ4zb8PJA3P1. In other words, it is NOT a stand-by power source; it is the primary source.  It has a rated output of 1500 amps, far in excess of my system's needs.  According to the included monitoring software, output, voltage and frquency were rock steady regardless of the music. 

The results were impressive, even though the nominal THD quoted for the UPS was poor.  Using a sound meter, hiss and noise at the speakers dropped 4-5 dB. Music sounded both more detailed and with greater air. Bass seems unchanged, but admittedly I am not a bass fiend. Ymmv. 

Cheers, Alex

Jeff Rowland Design Group offer battery powered amplification since early 90's

When things were linear and Class-A/B then this could have helped reduce noise ect, but with their new class-D stuff today, batteries can't solve the biggest problem they have, which is the Class-D switching noise filtering.

Cheers George

IIRC, ASR makes battery powered gear