Tiniest Portable amp I can build

[Ikarios]

Ari, your transformer thing is very interesting. So basically it steps up what impedance the source sees from the headphones? If there's no increase in power from the transformers, how does this affect the output of the headphones? Admittedly I don't know very much about impedance/impedance matching. Is there a basic schematic for your device? (on a somewhat unrelated note I wish I could go to the Philly meet so I could hear this thing in-person and hear you explain it...)

 

[AVU]

The ibasso T3 is smaller than both the Pico Slim and the Shadow.  I've owned all three.  without the case, as I use it, the T3D is 15g.

 

[High_Q]

I see.  Next time I should attention to what I am calculating as 6.5in for width probably doesn't make sense.

  If it is that small, I can probably slide it under the amp I had earlier, the only problem is implementing a contact point to the amp so that it can be charged with the provided charger. That or, open up the battery charger and fit it into the amp, but thats adding more bulk to it.
 
Quote:

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

 

 

[High_Q]

Did you end up with T3 and why?  
 
Quote:

The ibasso T3 is smaller than both the Pico Slim and the Shadow.  I've owned all three.  without the case, as I use it, the T3D is 15g.

 

 

[nikongod]

 
Quote:

Ari, your transformer thing is very interesting. So basically it steps up what impedance the source sees from the headphones? If there's no increase in power from the transformers, how does this affect the output of the headphones? Admittedly I don't know very much about impedance/impedance matching. Is there a basic schematic for your device? (on a somewhat unrelated note I wish I could go to the Philly meet so I could hear this thing in-person and hear you explain it...)

Thanks
 
Yes, the power through a transformer is roughly constant. 1mW in gets you 1mW out. This works to your advantage with SS gear here the same way it does with a tube - the output stage of your source can probably output a little power, just not into a low impedance. By using a transformer you give the source the high impedance load it works best with and you can save a bunch of active circuitry and all the nastiness associated with that.
 
The impedances are a tricky point here. In a tube amp the output impedance of the tube makes a transformer a totally obvious solution. In SS even a junky opamp or simple circuits with 1 transistor as voltage follower can achieve a ~0ohm output impedance easily so the transformer got passed over by the world to save a few bucks. The problem is that when you MUST have an op amp driving the load (as is almost always the case in ultra-small portables where you dont have physical room or adequate battery power for a real buffer) they dont work as well into low impedance loads as high. Some do better than others, but for the troubles associated with "almost stable" ultra-fast high current op amps why bother when you dont even need gain to run IEMs or even many full size headphones?
 
Impedance matching is a weird point. Multi-driver IEM's want the source to have a very low output impedance so the crossovers work the way they were designed. Im not sure what the limits are, but since nobody has complained about certain portables with 22ohm output resistors screwing up the sound from their headphones the single digit output impedance from a transformer should be totally cool.
 
Single driver IEM's are much less critical of amplifier output impedance. I really like my Ety ER4p on my transformers. 
 
I pretty much always have the transformer with me at meets, ask the next time you see me. 

 

[Armaegis]

Quote:

I see.  Next time I should attention to what I am calculating as 6.5in for width probably doesn't make sense.

  If it is that small, I can probably slide it under the amp I had earlier, the only problem is implementing a contact point to the amp so that it can be charged with the provided charger. That or, open up the battery charger and fit it into the amp, but thats adding more bulk to it.

 
Heh, or fit the amp into the charger... http://www.google.com/products/catalog?q=nb-4l+charger&oe=utf-8&rls=org.mozilla:en-GBfficial&client=firefox-a&um=1&ie=UTF-8&cid=15662776239877331888&sa=X&ei=FZHBTbXEIcbb0QHdyLy3Cg&ved=0CGgQ8gIwAg#

 

[Ikarios]

Okay, so this is how I understand it - the transformer makes the IEMs appear to be high impedance (by whatever stepdown factor) to the PDAP, and the IEMs see the PDAP as a very low impedance source (divided by the stepdown). In terms of voltage and current, PDAPs are generally better at providing voltage swing than current. The point of the transformer is to allow the PDAP to provide a lot of voltage with not a lot of current into the transformer, which steps it down to normal voltage and adequate current. Is this right?
 
How does the transformer affect noise floor/hiss? I recently picked up an iBasso T3 but I realized a little while ago all I really want the amp for is to reduce hiss on my HTC Thunderbolt (which is present at a relatively high constant level no matter what the volume is, for all IEMs I've tried). If I turn up the volume on the Thunderbolt, the music gets louder and the hiss stays the same. Attenuating this output has the effect of making the hiss seem quieter. If the transformers had this effect I might have to make a little box...

 

[Mad Max]

Fiio E5 is still the tiniest, lol.  Pre-built to boot.

 

[batphink]

Fred_fred2004 is an evil genius when it comes to Cmoys.  You should PM him.
 

 

[High_Q]

Thats very very evil

  Fred is indeed an evil man.  Wow, looks like its all battery.  Lets try to shrink the battery down.  Any battery engineers in here?

 

[Armaegis]

Maybe a stack of watch batteries?

 

 

[nikongod]

 
Quote:

Okay, so this is how I understand it - the transformer makes the IEMs appear to be high impedance (by whatever stepdown factor) to the PDAP, and the IEMs see the PDAP as a very low impedance source (divided by the stepdown). In terms of voltage and current, PDAPs are generally better at providing voltage swing than current. The point of the transformer is to allow the PDAP to provide a lot of voltage with not a lot of current into the transformer, which steps it down to normal voltage and adequate current. Is this right?

Pretty much yes.  
 
Quote:

How does the transformer affect noise floor/hiss? I recently picked up an iBasso T3 but I realized a little while ago all I really want the amp for is to reduce hiss on my HTC Thunderbolt (which is present at a relatively high constant level no matter what the volume is, for all IEMs I've tried). If I turn up the volume on the Thunderbolt, the music gets louder and the hiss stays the same. Attenuating this output has the effect of making the hiss seem quieter. If the transformers had this effect I might have to make a little box...

The transformer DOES reduce noise floor/hiss, in an exact relationship to the actual signal. In a kind of similar way an active amp will actually do the same if it has a low enough noise floor, as it sounds like you noticed. The transformer box saves you a few batteries

 

[limpidglitch]

What about putting a pot in front of the transformers, how will that affect the whole impedance issue?

 

[nikongod]

 
Quote:

What about putting a pot in front of the transformers, how will that affect the whole impedance issue?

Im not 100% sure how that would work I have good guesses though. 
If you use a low impedance pot (like 1 or 2Kohms) Id bet this works out on the better side provided your source can drive the load
If you use a high impedance pot (10Kohms and up) I bet things start to suck. 
The source impedance not only effects output impedance of the transformer but also BANDWIDTH in many transformers. 
 
 
 
As an alternate idea: Some people (myself included) have tried using transformer & autoformer volume controls to run headphones off of. I got frustrated because none of my home sources have any digital volume controls for fine tuning. That being said, at the ferocious levels my little device ran at (it only ran at >80db with beyer T1: I normally listen in the 60's) it sounded quite good. Here is a link to my post in the "post your builds thread" post #7364 on 10/15/10
 
I think Dsavitsk has had better success, although with much more expensive parts. Check his website, where I got a bunch of ideas for these things from.  LINK to Dsavitsk

 

[High_Q]

^your transformer is not an amp.  It has no gain.  What does it do again?? Its useless object in a can that produces placebo.  Nice try nik, but you neglicted to mention its not an amp, and its a piece of crap in a tin box. You neglicted a no brainer key feature of an amp.  Its called gain...  Lets see... there is no power source.... ummm were talkin about amps here?  How is that transforer(look at the definition again) doing what I was looking for??  Do some research before you slap together some nonsensical box you think its revolutionary.  Umm there is a reason why it doesn't exist in place of an amp.  You got quite an imagination for coming up with ideas. 

 
 
 
The quality of an amplifier can be characterized by a number of specifications, listed below.  What does it do again?  Pay attention to the power ratio.

[edit]From wiki:

Gain

The gain of an amplifier is the ratio of output to input power or amplitude, and is usually measured in decibels. (When measured in decibels it islogarithmically related to the power ratio: G(dB)=10 log(P_out /(P_in)). RF amplifiers are often specified in terms of the maximum power gainobtainable, while the voltage gain of audio amplifiers and instrumentation amplifiers will be more often specified (since the amplifier's input impedance will often be much higher than the source impedance, and the load impedance higher than the amplifier's output impedance).

1. Example: an audio amplifier with a gain given as 20 dB will have a voltage gain of ten (but a power gain of 100 would only occur in the unlikely event the input and output impedances were identical).

If two equivalent amplifiers are being compared, the amplifier with higher gain settings would be more sensitive as it would take less input signal to produce a given amount of power.^[1]