[ishtob]

I saw Xin's super-micro was able to use just 1 AAA battery to power the opamps, and also claims its boosted to 5.5v. I was wondering how this was done and is it possible to adapt this design to my DIY cmoy. I would love to have a tiny Cmoy that could fit on the back of a ipod nano.

 

[xmokshax]

a boost converter, or DC step-up converter, is what was probably used in the super micro. you could probably do it, but i'm not sure how much battery life you'd get. you'd have to do a bit of calculating.

 

[ishtob]

how do I make a boost converter?

 

[ericj]

There are a LOT of pwm step-up converter controller chips available. The parts from Maxim and Linear are probably your best bet. See their websites, read the datasheets, implement the recommended circuits.

 

[ishtob]

ok, will do, thanks alot.

 

[ishtob]

Sorry, a bit of a noob when it comes to reading schematics for IC's I have no idea how the chip should work or how to use it. Every site seems to have it's own application and slightly different design.

can someone give me a simple schematic to build a step-up booster?

 

[NelsonVandal]

Some screwd up ideas

:

Can't you just use 3 AAA's and a low voltage opamp like AD8656 or AD823? They aren't that much bigger than one AA, and you save yourself from a lot of trouble

, and you can make the amp thinner.

Is it possible to tap some voltage from the Nano?

Why not buy the cheapest cellphone and use it as a charger. The LiIon batteries are typical 3.7 V and have a very high capacity like 500 - 1000 mA. Use AD8656, AD823 or AD8397.

 

[ishtob]

the ipod outline has a 3.3v output for accessories, I guess I could try that . But wouldnt the virtual ground split the voltage and make it around 1.7v ?

 

[FallenAngel]

You can take a look at the RUNT headphone amp by Paragon on this Korean site. Use Google Translator if you want, but the schematic is in english anyway. It will be TINY and mostly likely needs a PCB of some sort, trust me I've tried to deadbug it, it's very hard with a chip so tiny.

Also take a look at Sijosae's implementation of that LM2664 in his 1.2V and 2.5V TDA1308A amps. Very similar to the RUNT, but you also get a photo of the PCB. How he does them, I don't think anybody will ever know, they're fantastic.

About the IPod 3.3V output, I've tried using this exact design on it, unfortunately with little success, but if you get it working, do show it! Try using this LM2664 chip, it should give you a -3.3V rail from the single supply.

 

[threepointone]

yeah, you're probably better off trying to work off of a tested design--switching power supplies are harder to design well than the good old linear stuff.

You also have to consider that there's a lot more noise from a boost converter, and that (by audiophile standards) will affect sound quality. (might not be audible if designed properly)

 

[ishtob]

hm.. noise... that's not good

 

[villekille]

yes the noise is a problem but I guess it depends..the Ipod Shuffle 1Gen has somekind of boost converter and it has some noise which is so loud that it makes it impossible to use it with my etymotic er-6i IEMs but that's only because they are so sensitive..I can't hear the noise with higher impedance phones.

 

[ericj]

the 1st gen shuffle also has a switchmode headphone amp in it - but i hear that it performs very well.

The actual switching noise of the pwm converter becomes less of an issue the faster you switch. If you're switching at 50khz you might offend some bats and mosquitos but you'll never hear it.

But maintaining that switching rate while providing enough current for the job requires some careful selection of capacitors, and the "bigger is better" rules of linear power supply design do not apply.

Couldn't tell you how to do it, personally.

Edit: check the diy forum on headwize - a guy posted a schematic for an eensy opa551-based headphone amp that runs off a cell phone battery with a maxim pwm stepup controller and fits in an Altoids Smalls tin.

 

[jcx]

newer single cell boost regulators can be fairly safely built without much deep understanding if you can get application note or demo board layouts and parts list and carefully copy them

but just soldering some leadless packages/backside power pad and tiny, low inductance chip Caps is going to be tough for a hobbyist

 

[joneeboi]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif the 1st gen shuffle also has a switchmode headphone amp in it - but i hear that it performs very well.

Someone correct me if I'm wrong, but I believe the shuffle 1G was lamented as being the only iPod without a screen but having the best headphone jack SQ.