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Making a headphone amplifier from a T-amp

post #1 of 9
Thread Starter 

Hi fellow Head-Fi'ers! Greetings from a long time lurker :beerchug:

 

I just got a TA2021 T-amp from Indeed hi-fi lab. http://www.aliexpress.com/item/Indeed-Audiophiles-Grade-Class-T-Amp-TA2021S-Mini-Cute-Hi-Fi-Amplifier-25WX2-Tripath-12V-5A/1111032656.html

 

I want to turn it into a dedicated headphone amp. The result might be suboptimal, but I still want to try it.

 

Resistor network or output transformers? :confused:  I would like to go with output transformers. I'm thankful for any input here :bigsmile_face:

 

Oh, and I know it can't be bridged, so I will design it for balanced output only.

post #2 of 9
Thread Starter 

First try: I led the amp's output through an Audio-Technica ATH-7 Electret Transformer connected in reverse to get "step down" instead of "step up.

 

http://www.audiocircuit.com/A-Images/AA-Brands/A/Audio_Technica-AIP/ATH-7_______-F-001-911-AIP.jpg

 

The output voltage gets about a tenth of the input voltage through this box.

 

Observations: The sound is too bright and quiet harsh. Bottom end is lacking. Also, the transformers start to distort at louder volumes (they do that through my Fiio E9 too).


Edited by marcswede - 10/26/13 at 6:03am
post #3 of 9
Thread Starter 

Second try: I added two 15ohm/11W resistors per channel in parallel to the amps output stage.

 

Sound: much better! Bass goes deeper and evolves effortlessly. Highs are tamed.

More details and more decided bass than from Fiio E9. However, the E9 still wins in the mids department with a smoother sound.

 

I only have a couple of hours on The T-amp and the sound has already improved a lot. I think those 2 x 10.000uF capacitors will need some time to mature. I will keep this arrangement for a few days now.

 

Btw: After adding the resistors and contemplating that the amp sees a very big load (a few thousands Ohms?) from the transformers, I decided to try i with unbalanced headphones. That is to say: I bridged the negative outputs in the last stage after the transformers... Seems to work fine (fingers crossed).

 

Actually, listening to Fourplay's "Blues Force" right now, I feel I prefer the sound of the Indeed amp to the Fiio E9 :) But for electronic music and bad masterings I would still go to the E9.


Edited by marcswede - 10/25/13 at 2:40pm
post #4 of 9

Very interesting.

Sadly all the other threads asking similar questions seem to be dominated by replies along the lines of 'don't bother, Tripath amps aren't designed to do this'.

 

I see several third party anecdotal mentions of people using t-amps to drive 'phones, but they usually mention difficult to drive models like the AKG K100's or ortho's.

 

The only 'first party' account that goes 'I did this, and it sounded like this' was a short article regarding the Sonic Impact t-amp being used to drive Stax 'phones:

 

http://www.tnt-audio.com/ampli/t-amp_morsiani_e.html

 

But it's never made clear whether the Stax are being driven directly from the speaker taps of the amp, or via a Stax 'adaptor'.

 

 

In all honesty all this stuff goes over my head, but in case you haven't already seen these threads ill link to them here:

 

http://www.head-fi.org/t/167555/t-amp-as-headphone-amplifier

 

http://www.head-fi.org/t/180226/tripath-class-t-class-d-headphone-amp

 

http://www.head-fi.org/t/618443/why-cant-a-t-amp-drive-headphones

 

http://www.diyaudio.com/forums/headphone-systems/81797-t-amp-headphone-amp.html

 

Some of the discussions may be out of date as I believe even a big manuf' like Sony plans to use a D-class amp in their 35th anniversary flagship DAP.

 

Hope they're of some help, or at least interest?

post #5 of 9

Fun!  I made a headphone amp out of a Charlize a few years ago, it worked fantastically... don't recall the resistors i wired in parallel to the output, but using a transformer might be quite a bit of fun too! 

post #6 of 9

Don't suppose you documented this process or posted details for the edification of the 'electronically challenged' ( me ) ?

post #7 of 9
Thread Starter 
Quote:
Originally Posted by Q Mass View Post
 

Don't suppose you documented this process or posted details for the edification of the 'electronically challenged' ( me ) ?

 

I'm very happy if other people have a go on this. The price/performance ratio is so good for T-amps:darthsmile:

 

I could actually keep my current design because I'm very happy with the sound. Still, there must be other things that can be done to improve the performance.

 

I'm thinking of getting some real tube output transformers to replace the small ATH-7 ones. Or maybe a loudspeaker attenuator with constant 8 ohm resistance to replace the resistors?

 

Hm...  Ebay, here I come!


Edited by marcswede - 10/26/13 at 6:40am
post #8 of 9
Thread Starter 
Quote:
Originally Posted by El_Doug View Post
 

Fun!  I made a headphone amp out of a Charlize a few years ago, it worked fantastically... don't recall the resistors i wired in parallel to the output, but using a transformer might be quite a bit of fun too! 


Thanks! I've been kinda viewing Charlize as a 'role model' for T-amps. When I found the Indeed (which also has air-core inductors) I decided to push the button.

 

post #9 of 9
Thread Starter 

Here I could really need some advice: Speaking in terms of wattage ratings, are bigger transformers always better?

 

Or is there a risk of undersaturation with too big transformers? I will only need a couple of hundred mW at most, so what is the best choice? :confused: 

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