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Tiniest Portable amp I can build

post #1 of 91
Thread Starter 

I'm amp making a setup for the current nano, and an amp.  I want to build something that is tiny and drive IEMs well.

post #2 of 91

buy a headamp pico slim. You cant build anything anywhere near as small.

post #3 of 91
Quote:
Originally Posted by nikongod View Post

buy a headamp pico slim. You cant build anything anywhere near as small.


The RSA Shadow is smallertongue.gif


http://www.headfonia.com/the-usual-suspects-12-portable-amps-compared/

post #4 of 91
Quote:
Originally Posted by cifani090 View Post




The RSA Shadow is smallertongue.gif


http://www.headfonia.com/the-usual-suspects-12-portable-amps-compared/


only in one dimension :P the pico slim has the best "small" form factor, IMO. Thick is not good for pocketability.

 

As for DIY... there's not a whole lot of kittable portable amps... really only the mini^3 comes to mind, unless you want to do a sijosae build (good luck!). Without an intricate knowledge of how to work a circuit you probably won't be able to do much better than to buy a portable amp at a premium.

 

post #5 of 91

I've seen people build some pretty tiny stuff in here...

The battery, I/O Jacks and Volume Pot seem to be

the limiting factor in how small it can get, oh, and

of course your skill at building things. What is

your skill level?

post #6 of 91
Quote:
Originally Posted by Aflac View Post




only in one dimension :P the pico slim has the best "small" form factor, IMO. Thick is not good for pocketability.

 

As for DIY... there's not a whole lot of kittable portable amps... really only the mini^3 comes to mind, unless you want to do a sijosae build (good luck!). Without an intricate knowledge of how to work a circuit you probably won't be able to do much better than to buy a portable amp at a premium.

 


rolleyes.gif, for the iPod Classic (FYI if you will be upgrading, or for the people reading this thread) i will be going with the TTVJ Slim which fits the iPod Perfectly.

 

post #7 of 91

Build a smd cmoy using a camera battery for power?

post #8 of 91

Use a radio shack headphone transformer, and claim it is an active amplifier :D  Those things are uber tiny

post #9 of 91

 

Quote:
Originally Posted by El_Doug View Post

Use a radio shack headphone transformer, and claim it is an active amplifier :D  Those things are uber tiny


If I dont tell people they would never have known...The whole thing could fit inside a 35mm film canister (and probably smaller) if you dont get fancy with switching stuff. OTOH the fact that people think its an actual "amp" makes it sound better. so the builder is left with a difficult decision. 

 

adsc_0006.jpg

 

Transformers that look very similar made by Xicon are available from mouser. They have a whole load of different winding ratios so there are tons of interesting options. The radio-shack units are 1Kct:8ohms, but other reasonable ratios should work.

post #10 of 91
Thread Starter 

I don't understand.  Transformers steps up/down AC voltage.  Its a passive component from the definition that I know.  How is this am amp?

http://en.wikipedia.org/wiki/Transformer

 

post #11 of 91
Quote:
Originally Posted by Armaegis View Post

Build a smd cmoy using a camera battery for power?



Does anyone know what kind of current those skinny digital camery batteries can push out? Something like this:

http://www.amazon.com/Canon-Battery-SD1400IS-SD940IS-SD960IS/dp/B00065L5SU

Most of them are 3.7V and have pretty good capacity. Seems like they might make a decent choice for those wanting to build a skinny cmoy style amp.

post #12 of 91
Thread Starter 

^9v is smaller by volume.

post #13 of 91
Thread Starter 

I think this is what I may build.

CMOY-5.jpg

post #14 of 91

Why do you need an amp for tiny little IEMs? OK, so there is the current thing, but why voltage gain?

 

Lets take an amp with voltage gain of 2.5 (+8db) but with a volume control in front at-46db. In the end your amplifier has an output signal -46+8=-32db Thats 32db LOWER than the input signal. Thats a far cry from amplification. 

 

Try it for yourself: take the attenuation of your potentiometer and compare it with the gain of your amp. If they dont break even (or leave you with a SANE amount of overhead just in case - 16-24db lets say), you dont need as much gain as you have. Round things off - every third of the pot is ~16-20db. Dont forget to include any digital attenuation which may be applied. Whether digital or analog attenuation is better is a topic for another thread, but it all adds up and I think everyone on both sides of that argument will agree that -30db digitally and another -40db analog is nothing but terrible gain structure.

 

So, I think I have fairly established that a lot of headphones dont need voltage gain this brings around the current question. 

 

You are sort of correct: transformers DO change AC voltages, BUT you have neglected that they also change AC currents and impedances which is very important here.

 

The voltage stepdown (or stepup) of a transformer is pretty much exactly matched by its current stepup (or stepdown) {ignoring losses}

In other words a transformer that steps voltage down 10:1 steps current up 1:10 

 

Impedances run on the squares of the voltage (or current) ratio, so the 10:1 transformer has an output impedance (1/100 * the source impedance on the primary) + whatever the DC resistance of the secondary is = generally a few ohms. The nifty thing after that is the load to the source (DAC or ipod or whatever) is ALSO reflected on the square of the transformer - 12ohm headphones on a 10:1 transformer looks like 1.2Kohms to the poopy little op amp trying to drive this whole mess. 1.2Kohms is a very easy load for most op amps you will find in output stages.

 

As an added bonus: a transformer will have a TRULY minimal effect on your noise floor. 

 

Double bonus round: no batteries.

 

I guess the third bonus is that the Radio shack transformers cost like $3 each. The Xicon ones at mouser were about the same if I recall. Less than some op amps! So the good news is you can build one of these for like $12 if you skip the totally un-necessary switches & LED. The bad news is that nobody will ever buy it second hand (I normally sell my old projects to fund new ones) but then the whole project should cost about the same as a new CD.

 

Will it work for *you* ? maybe. It really depends how loud you listen. At worst its a cheap experiment that didn't work for you and at best your happy enough with it that you stop tinkering with portables and shift your efforts to real amps.

post #15 of 91
Quote:
Originally Posted by High_Q View Post

^9v is smaller by volume.


Were you looking at the package size instead of the battery size?

9V: 48x25x15mm - http://en.wikipedia.org/wiki/Nine-volt_battery

NB-4L: 40.4x35.4x5.9mm - http://www.digitalcamerabattery.org/digital-camera-battery/canon-nb-4l.htm

 

The camera battery is less than half the volume, and almost a third the thickness


Edited by Armaegis - 5/3/11 at 11:02pm
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