[gorgon_123]

I have for you folks what may amount to a stupid question - keep in mind I know nothing about DIY!

My father has a cell phone. One of those little silver Motorola numbers. It has a 3.6V Lithium Ion battery in it which lasts quite long and is, of course, the best kind of rechargeable battery out there. Would it be possible to build a DIY amp using one of these batteries? Or are you restricted to simple AA, AAA, DD etc etc???

A friend of mine has a pcdp with the built in lithium ion battery. He simply plugs the whole unit into the wall every few days for more juice and that's that. It seems like the best system out there and I hope it's easily applicable to other things.

Anyway, thx in advance! -g

 

[thomas]

Well, lithium ion batteries are insanely expensive, and you'll need at least 2-3 of those for a (decent) portable amp. Preferably 8-9 of them. So you're looking at $300 worth of battereis, minimum, much more for good performace. plus you'll need to design a charger for it, which is much more complex than a normal NiCad/NiMH chager...

Overall, lithium is a good technology, since it has the highest voltage per cell of any battery type and lightest weight, but it is too expensive and new for it to be economical. It is starting to become popular in expensive camcorders and laptops, but i think it will be a long time before you can diy with one...

and btw, to my knowlege, no CDPs use lithium batteries- in the past there were a few sharp and one sony Minidisc that used the technology, but it was too expensive and unreliable and now they all use NimH. Many of the new CDPs use fancy "gumstick" batteries, but they are still NiMH...

 

[aos]

I had a similar line of thought. For example, digital cameras use these and they can pack quite a resonable punch. I have two 7.x Volt 700mAh (I think) batteries and a charger, all together about $200 Canadian for my camera, but I would think you can get much more powerful stuff cheaper. Sony cameras have excellent batteries, so maybe buying a "spare" battery or two and just using your camera charger would give you quite a powerful (over 1Ah) battery with sufficient voltage (>10V) at quite a reasonable size and weight.

 

[gorgon_123]

Quote:

to my knowlege, no CDPs use lithium batteries

Sorry. It might have been a minidisk player, don't really remember.

Quote:

lithium ion batteries are insanely expensive

But they'll last "forever" so you only buy them ONCE. That changes the value.

Quote:

you'll need at least 2-3 of those for a (decent) portable amp. Preferably 8-9 of them.

8-9 of them? 3.6V * 8 = more than the typical 9V setup? Or can you not add up voltage like that? (I have no idea... just an ignorant fool

)

Quote:

plus you'll need to design a charger for it

Like aos says, just use the charger from the camcorder (or whatever charger goes with your specific battery)


Anyway, put on your thinking caps and let's make this happen

 

[thomas]

Well 3 of them will equal a 9V, but that is really the MINUMUM for a high-fi headphone amp. But for ideal performance, somthing like +/-15v (30V, 8 X 3.6V) would be best...

Quote:

But they'll last "forever" so you only buy them ONCE. That changes the value.

Well depends on how you look at it- Yes, they have incredibly high capacities, you could get a few times the capacity of nickle batteries for the same weight. But they can't be recharged anywhere near as many times as a nickel battery- At best you will get 100-300 charge/discharge cycles out of a lithium battery, compared with 500-2000 for a nickle battery. (though the lithium doesn't suffer from memory effect, so its a little more flexible)

I guess you could charge them in the camcorder, especially if you had multi-cell batteries like AOS. But if you use individual cells, it would take way too long to recharge all of them like that.

 

[Tomo]

Gorgon -

The batteries lasts longer if the CDP's power useage is small. This is very natural but often forgotten. It does not really matter whether if cellphones last how long. They generally are designed to use as little power as possible. I would not be surprised if they last for 5~10 hours at full output power.

Portable CDPs are also designed to have very small power expenditure. Most of them have smaller than 10mW output capability for 8 ohm headphones. The motor in the CDP is a tuned stepper motor. These use relatively low power since it does NOT require constant current to run these guys. I would not be surprised if the total power expenditure go below 300mW.

I own a CDP that lasts for continuous 20~30 hours on two 1.5V batteries (with anti-shock). I never have to recharge for at least 3 days. This was nearly 2 years ago, I assume by now new CDPs should last 30~40 hours no problem.

I guess I see no need to use lithium Ion batteries. Personally, I find Ni-Cd and Ni-HM so much more reliable due to their low cost and availability not to mention less lethal chemicals.

Tomo

P.S. Oops forget about Lead Acid Batteries. They are becoming very reliable now. Safer and smaller packaging allow portable use. Personally, I think that is the way to go if I were to grow out of Ni-Cd and Ni-HM.

 

[Joobu]

I use HD600s at 300 (?) ohms so I seem to have managed to get away with ±3V. I don't see why a true audiophile portable amp needs to have ±15V. Of course it allows you a lot of choices when it comes to topology and op-amp choices but that's just too much battery for my pocket.

Remember, a typical CDP uses 2 AA cells (3V - 2V). Mind you, they could have a switcher or a DC-DC converter. Of course, let's not forget they typically don't sound very good.

 

[Tomo]

Joobu -

You are correct on your observation. I myself have experimented with 600 ohm headphones. I used +-4.5V and I was successful in driving 600 ohm cans.

Appearently, "audiophiles" does not understand how to calculate the absolute required PSU voltage from efficiency. Given 100 dB SPL, you can do following approximated calculation for HD580.

10~20mW = VRMS ^ 2 / 300 ohms
(at 20mW of sound pressure, your ear should be about to explode)

VRMS = 1.732~2.449 Vrms

You will be able to get away with +-3V. However, it is recommended to go +-4.5V just be safe when battery voltage start to fall hours later. (Days for me!!) +-15V is not required. I would recommend against it since battery pack will be signficantly larger than +-9V. Two 9V pack. That is probably highest I would go for portable headphone amps.

Tomo