[fewtch]

Made a sort of "frankenstein" battery pack this morning, since I have a Meta42 coming in soon... what I did was took a small Radio Shack project enclosure I had lying around, the male plug + a few feet of wire from an old AC adapter, and a couple 9v battery clips I also had lying around.

Wired the clips up in series (+18VDC, more or less), charged up a couple NiMH 9v batteries (which I also had lying around luckily). Put the cover back on the enclosure and presto -- quickie 9v battery pack that... well, I guess it ain't really "frankenstein" cuz it looks like a mini battery pack.

Just for the fun of it, tried hooking it to my Creek OBH-11 (normally runs on 24vdc with a wall wart) to see what it sounded like:

Oh my goodness... a very large jump in sound quality there over the Elpac WM080 it was using, noticeable immediately. I think I'm a new convert to battery power! Gonna have to make another of these quick & dirty battery packs for when my Meta42 comes in the mail -- I may even have more of the right parts kicking around and have to buy nothing whatsoever. The SQ improvement with the Creek is just amazing.

Anyway... as you can see by my ordering a Meta42 rather than building one I'm not normally much of a DIYer (more like a hack who owns a soldering iron & cheap multimeter), but this was a project I could handle...

Question: Will alkaline batteries perform as well as NiMH for powering amps? Not sure I want to buy another two Plainview 9v batteries if I can get away with cheap 9v alkalines, and they last long enough.

 

[Steve Eddy]

Quote:

Originally posted by fewtch I think I'm a new convert to battery power!

Welcome aboard.

I was rather surprised at how few headphone amps utilized battery power. I mean, this is a perfect application. Not like you're needing 100 watts of power, which of course would make battery power rather more inconvenient.

Quote:

Question: Will alkaline batteries perform as well as NiMH for powering amps? Not sure I want to buy another two Plainview 9v batteries if I can get away with cheap 9v alkalines, and they last long enough.

Well, from an environmental point of view, I'd recommend the NiMHs. And if you want to really be green, use a solar-powered charger.

se

 

[jeffreyj]

Quote:

Originally posted by fewtch ... Question: Will alkaline batteries perform as well as NiMH for powering amps? Not sure I want to buy another two Plainview 9v batteries if I can get away with cheap 9v alkalines, and they last long enough.

The internal resistance of a typical NiMH cell is 0.1 ohm - on par with a regulated power supply connected by several inches of wire - while alkalines range from 0.5 to 10 ohms per cell, depending on the size and where along the discharge curve the cell is at. This tends to increase the amount of ripple that shows up on the power rails from variations in current being drawn from it. On the plus side... ahem... alkalines typically deliver 4-5x more amp-hours of capacity for a given cell size, though not if said alkalines are rechargeable (perhaps 1-2x the capacity of a NiMH).

 

[fewtch]

Thanks jeffreyj, I'll probably pick up another couple 9v NiMH batteries in that case -- got the charger, might as well. BTW, turns out I have enough parts junking around to make at least one more "battery pack" like this without spending a penny on anything (but batteries). One nice thing about "projects" like this... cheapo parts are fine

.
Quote:

Originally posted by Koyaan I. Sqatsi Welcome aboard. I was rather surprised at how few headphone amps utilized battery power. I mean, this is a perfect application. Not like you're needing 100 watts of power, which of course would make battery power rather more inconvenient.

Thanks... I've been a "battery avoider" for a long time (not sure why, maybe because of the inconvenience) but I'm getting such a blacker, more solid background + better dynamics with the Creek -- it really is a sweet improvement in such an inexpensive amp. I was gonna sell it but this puts it back in the running, at least for something like bedside use -- one of the few cheap amps I've found that really synergizes well somehow with Sennheiser HD600s.

 

[CarlJF]

One thing you can do, instead of using 9V batteries, is to use a AA-cells battery holder (see DigiKey BH48AAL to see what I mean). NiMh AA batteries have much more current reserver than 9V. Typically, they show a rating of at least 1500 mAh. I even found some which have 1700 mAh and rated at 1.25V. Whith those, using 2 eight cells holder will give you 20V DC with a 1700 mAh reserve. If you take the more general 1.2V batteries, you get 19.2V with 1500 mAh reserve.

The main drawback being that that recharging 16 batteries isn't that fun...

 

[Steve Eddy]

Quote:

Originally posted by fewtch Thanks... I've been a "battery avoider" for a long time (not sure why, maybe because of the inconvenience) but I'm getting such a blacker, more solid background + better dynamics with the Creek -- it really is a sweet improvement in such an inexpensive amp. I was gonna sell it but this puts it back in the running, at least for something like bedside use.

Yeah, it helps not to have the amp's ground referenced to another AC supply. Helps keep interchassis currents down.

Oh, and you might also try adding some capacitance across the batteries. Say 1,000 uF across each rail.

se

 

[fewtch]

Quote:

Originally posted by Koyaan I. Sqatsi Yeah, it helps not to have the amp's ground referenced to another AC supply. Helps keep interchassis currents down. Oh, and you might also try adding some capacitance across the batteries. Say 1,000 uF across each rail. se

What sort of capacitor(s), and what kind of effect would that have? Would it make more difference with alkaline batteries vs. NiMH, or would it not matter. Thanks...

 

[Voodoochile]

Especially compared to a wall wart. A nice linear supply is not the same as a battery by any means, but it is a significant upgrade from even a nice wallwart.

IMHO, at least.

 

[fewtch]

Quote:

Originally posted by Voodoochile Especially compared to a wall wart. A nice linear supply is not the same as a battery by any means, but it is a significant upgrade from even a nice wallwart. IMHO, at least.

Agreed... I heard a big gain in SQ when switching from the crappy OBH-1 wall wart to an Elpac WM080... and then another gain when switching to batteries (possibly even bigger in the latter case).

The Creek appears extremely sensitive to power issues -- I started a thread on this awhile ago (complete with measurements):

http://www4.head-fi.org/forums/showt...threadid=43771

Not sure if the Meta42 design is as sensitive... would you happen to know?

 

[Steve Eddy]

Quote:

Originally posted by fewtch What sort of capacitor(s), and what kind of effect would that have? Would it make more difference with alkaline batteries vs. NiMH, or would it not matter. Thanks...

Electrolytics. Basically they work to help reduce some the electrochemical noise of the batteries. Which is really rather benign in the first place but since one's fairly likely to have some caps around those values laying around it's pretty easy to give a try.

This gal I knew who worked at Woods Hole said they used those high capacity carbon areogel capacitors in some of their sonar systems to keep the battery noise down.

se

 

[Voodoochile]

Quote:

Originally posted by fewtch Not sure if the Meta42 design is as sensitive... would you happen to know?

In my opinion, yes. It is very sensitive to PSU type. I like a dual voltage linear with the META- omitting the V ground circuit. Big improvement. I haven't built the PIMETA yet, but have the parts for it. Obviously it will have better channel separation than the META, which the dual PSU does help in the META, so it will be interesting to see how sensitive it is otherwise. The PPA does not seem to be nearly as sensitive to the PSU as the META is.

A good wallwart is okay, but I think people often only compare batteries to wallwart-AC when they do these comparisons.

I'm biased though... I just don't like wallwarts, even for the form factor- performance aside!

 

[puppyslugg]

fewtch:

Aerogel 1-FARAD 5V caps can be purchased at Digikey. Wire four in series(for voltage), you'll end up with 250,000uf! I read on audioasylum that someone replaced all of his Blackgates with aerogel caps.

VC:

With the Meta, I always felt the ps played a big role, as well. I think the same questions will apply to the PPA. Though the PPA may be less prone to ps variations, PPL obviously thinks the ps makes a difference, witnessed by his own(PPA) offerings.

 

[Steve Eddy]

Quote:

Originally posted by puppyslugg Aerogel 1-FARAD 5V caps can be purchased at Digikey. Wire four in series(for voltage), you'll end up with 250,00uf!

Yeah, but if you want to keep the ESR the same, you'll need to take those four in series and parallel them with three more sets of four in series. In other words, 16 caps total.

se

 

[puppyslugg]

Quote:

Originally posted by Koyaan I. Sqatsi Yeah, but if you want to keep the ESR the same, you'll need to take those four in series and parallel them with three more sets of four in series. In other words, 16 caps total. se

Wiring 4 in series, the esr couldn't be worse than a Pana. FC(?).

 

[Steve Eddy]

Quote:

Originally posted by puppyslugg Wiring 4 in series, the esr couldn't be worse than a Pana. FC(?).

Wasn't making so much of a comparative statement just that as you put the capacitors in series, their ESRs will add, and that if you want to get it back down to what it would be with just the single capacitor, you'll need to do a 4 x 4 array.

So basically you get four times the capacity of the single capacitor, but the same ESR.

If the capacity and ESR of four in series is good enough for a particular user, there's no reason to do anything more.

se