[SinnerG]

Yes, newbie alert. I'm on leave ... it's boring leave. I've been thinking of doing a DIY portable amp. Another warning: electronics knowledge is horrendous.

I looked at the PINT circuit and the old thread on headwize and it looked simple enough, but seems many have had issues with it.

A portable pimeta looks sweet ... yet the parts selection section had my head spinning a bit.

Would anyone say the portable pimeta is a good spot to start and quite easy to build by an amateur?

Would one also be able to provide power from a li-ion setup using a 3.7V battery and charger setup feeding to a boost converter to take the voltage up to say 9V? I'm looking at using a power source like that for something else which would go in the same box.

N00b going to sleep now.

 

[cobaltmute]

the Pimeta is a decent build due the fact that it has a PCB. It was my second build behind a CMOY.

For a cool idea about what could be done with charger, battery etc in one box : http://www.head-fi.org/forums/f6/tri...rickle+Charger

I built my pimeta in a similar way, but I used 12xAAA instead of the 9V's (this meant that I had to put my power jack on the side). It give a bit lower voltage swing, but longer lifetime.

 

[Nemo de Monet]

I've built a couple Pimetas, and for the most part they're quite straightforward; the only tricky bits would be the buffers, if you choose to use a surface-mount part. Otherwise, unless you're so inept that you're not allowed near sharp or pointy objects, I wouldn't expect you to run into any problems. One of the many great things about the Pimeta is that there's very little to fiddle with - no trimpots to adjust, no high voltages to adjust, et cetera.

I personally would recommend against trying to use a 3.7v li-ion battery to power a Pimeta; the Pimeta needs voltage more than current, and I think by switching to li-ions you'd either wind up with an unnecessarily large battery, or poorer runtime than a comparable volume of ni-mh cells or batteries... or both.

Obviously, your idea of "portable" might be different than mine, so if you wanted to use, say, a battery pack of four or five 18650 cells, that'd be a different story, but IMO it'd still be easier to just use a bunch of ni-mh cells like everyone else does. Besides, I like to have absolute certainty that my electronic devices aren't going to explode or burst into flames that cannot be extinguished... but I'm strange that way.

 

[SinnerG]

Thanks folks. It sounds reassuring.

And, uhm, yes, I'm inept enough to sometimes be banned from sharp or pointy objects.

I won't be considering any SMT parts.

The thing with the li-ion is that I understand they don't usually blow up unless they really get an abusive charge current, etc. These things usually have a voltage range limiter built in anyway. But then again, DIY li-ion is not to be trusted.

I'm not even sure if I'd have to design a charger circuit for 3-4 18650 cells running in series, which is why I was kinda looking at the flat pack li-ion cells.

Perhaps I should explain how I got to the idea of the li-ion packs. I was looking at a LOD build for an ipod, but figured to add an extended battery for much longer run times. I can get 2000mAh extenders on ebay, but it seemed more fun to construct one myself. Let alone the fact the ipod would now start getting longer and longer with a battery extender and a LOD on it.

This led me to Lady Ada's MintyBoost which creates a USB charge circuit for the ipod. That's another tin to lug around. I thought it'd be good to have it changed to have a charging port which could charge the 2xAA batteries as well as run the ipod while that was happening. This adds another wall-wart to the "portable" package, or if not that then more batteries as well.

So why not build an amp package which used some low-profile high capacity batteries which contained both a amp circuit and the USB charge circuit running off a single battery source in one box. Then I'd only need to lug one wallwart around.

Sparkfun already have a charging circuit for a li-ion battery and sell both a single-cell 2000mAh and a triple-cell 6Ah li-ion battery pack. With that it seemed like a good idea to get both the extended current for the ipod and amp at the same time, but needing to boost converters to raise the voltages.

12xAA cells would measure around 38mm tall, 45mm wide and some 84mm wide. The li-ion 3-cell would be 19mm x 54mm x 54mm and then some space for the charging board (with that case already looking like it is out of space, that'd be a problem). The 3-cell weighs around 110g while judging the weight of a single AA would probably mean 12 would weigh more. There's another option I've found of a +- 11V li-ion pack also with high current capacity, yet this would mean me trying to rework a charge circuit for it and then we're definitely going to see a fire hazard.

To top it off, one could then just use a normal dock to USB cable to gather both the line-out and the charge pins for the ipod, no need for an extra line-out dock. Use a USB plug where the line-in would be.

Does that all sound too bizzare? The low current capacity of the 9V units is what really had me looking at the li-ion batteries for running a ipod battery extender/charger circuit.

But if I think about it now, a 3-cell li-ion gives 6Ah, but 12xAA cells could have 2400mAh each or 28.8Ah total which would probably run everything for a decade.

I guess then I'd just need a 5V regulator setup to do my idea of a battery feed to the ipod instead of doing the boost converter. Or, perhaps better yet, regulate it 12V instead and hook it to the firewire pins instead as I understand it is the devices responsibility to regulate its own power when feed by firewire (which has a range of 8V-30V).

I considered constructing the small PINT amp layout or a CMOY tiny enough to get an amp circuit and the charge circuit onto a small-ish board, but trying to figure out which CMOY design was the one to go for was becoming tedious. As with the rest, it all meant having to bump up that voltage from the cells. It looked promising when I found the HPDAC which used the amp section of the PINT and was powered off just USB with a 5V-9V boost converter, but further reading showed that there were issues with the boost converter going bang when the input plug was mistakingly shorted out (jack being inserted).

Does the idea of a portable amp with a built-in battery extender for the source seem like a really daft idea?

Right, let me start by looking at a normal pimeta with some AA rechargables and take the whole silly idea of a battery extender on later.

cobaltmute, how heavy is your pimeta which those 12 AA batteries? I assume you have them hooked up in series to get a +- 15-18V (1.2V-1.5V per cell) to the pimeta board.

 

[SinnerG]

I must be a real newb to ask about this... but are there still DIP16AMP out there? Last post on them was back in 2005. Looks like a nice place to start messing around on the cheap as opposed to blowing up something more expensive. What do people think? Looks like a RA-1 clone of sorts.

 

[SinnerG]

What's the average cost of a pimeta build?

 

[SinnerG]

Reality check for me: think I'll start with a cmoy.

tangent's site has tons of interesting info to follow on from.

 

[SinnerG]

I just popped open my C&C XO amp. It has a MAXIM MAX733EWE step-up regulator. It looks like it uses 2 Li-ion batteries in series, probably making 7.4V. The MAX733EWE must take this to 15V and provide 200mA and then that must split for a virtual ground circuit somewhere. The XO is running a AD832 opamp in what looks strangely like a CMOY layout. I read tangent's site and this is a low voltage op-amp. Seems like the route for me to take on a cmoy.

Does that sound like a fair plan for a power supply to avoid lugging over 300g of battery around?

Since the XO is a bastardly loud amp on my low-impedance ATH900s, I'm wondering if that voltage range is perhaps way too high.

I can't see a buffer chip in there, but the XO runs my ATs fine.