clarification about using power amp as headphone amp

[thomas2015]

This is a bit convoluted
 
Im using Chinese valve headphone amp – Rhyme RD801 http://www.avbuzz.com/audio-video/201501/Rhyme-RD801-2/0-gb.htm
 
I like the sound although its underpowered compared to the 6 watt at 8 ohm chip amp i was using before, so I was reading about using power amps to directly run the headphones
 
the headphones are yamaha orthodynamic HP-3’s and HP-50A -
 
Im thinking of using the tripath amp as a power amp and the valve headphone amp as a preamp
 
headphones rated Input – 1 watt at 150 ohms
http://wiki.faust3d.com/wiki/index.php?title=Yamaha_HP-3
 
So from what i understand by this charts on this page
https://diyaudioheaven.wordpress.com/tutorials/power-amp-adapter/
 
if you run them off a tripath amp (already modified the headphones with separate wires to each headphone speaker – due to tripath amps not having a common ground - i read that somewhere not sure if its correct, but did it anyway in case)
 
a tripath amp that is 8 – 10 watts at 8 ohms will be around about .3 or a 3rd of a watt at 150 ohms
 
though Im not sure as the chart is saying volts not watts
 
would a tripath amp run ok with a 150 ohm load or do you need 10 ohm resistor on the speaker outs?
 
Also is it safe to use a tripath amp into an srd-7 stax amp adapter, I think i read somewhere its ok as the stax doesnt use a common ground, though Im not sure
 
as Im thinking of running my sr3 stax with the tripath amp and attach the orthodymic headphones directly to the srd7 speaker outs - am i missing anything obvious?

 

[KeithEmo]

Interesting project you've got going.....
 
Tripath amps tend to sound very good - but they are a bit fussy about their load (in the sense that the load will affect the way they sound). A Tripath amp is sort of like a DAC... it's output is a switched digital waveform, which is then passed through an "output reconstruction filter". As such, the frequency response of the amp, and how it sounds, is affected significantly by the load impedance. In short, it would probably work with a 150 ohm load, but it might sound different than it does with an 8 ohm load or a 16 ohm load (it might be harsh or very bright because the output filter that it's using, designed for loads between 4 ohms and 8 ohms, may not work as well with a 150 ohm load).
 
I would suggest trying it with just the 'phones, then with a 47 ohm load, and a 16 ohm load, and see which sounds better (or if they do sound different with the particular one you have).
 
All the smaller Tripath amps (based on the TA2024 and the TA2020) are bridged amps, so you MUST avoid common grounds. The amp WILL go into overheat/protect or fault if you try to common the outputs - and it will distort badly while it's on the way there. The TA2024 chip does about 6-8 watts/channel (into 8 ohms), and the TA2020 does about twice that, but some people say the 2024 is quieter (there are lots of different versions of each).
 
Also, since the Tripath amp is a digital switching device, DO NOT waste a lot of effort on fancy linear power supplies for it. Tripath amps actually seem to usually work BETTER with a switch-mode regulated supply (like the 12v power bricks used for computer monitors and USB hard drives).
 
You're also talking about 150 ohm headphones there.... you should bear in mind that, with high impedance phones like that, the output of most amps is limited by VOLTAGE rather than current. A Tripath amp that runs on +12V will put out as much POWER into a pair of 150 ohm cans as a regular reasonably powerful headphone amp that runs on +/- 12V (say one that uses a BUF634 output chip). This will be a worthwhile step-up from low-powered headphone amps - but possibly not as much more power as you might think. It would also be very worthwhile with low-impedance planars that need a lot of power; but it would be a waste to use a small Tripath amp with VERY high impedance phones - it won't deliver any more power into 600 ohms than an op amp running on +/- 12V.
 
 

 

[thomas2015]

the one i have is a TA2020A chip
 
http://www.diyaudio.com/forums/gallery/showphoto.php/photo/6134
 
Ive taken out the volume, bass and treble section and done the tweaks recommended online (replaced a couple of capacitors etc)
 
I did try another one with various power supplies and settled on the type you are referring too. a 12 volt 2.5 amp power supply from an external hard drive, has no background noise and doesnt clip at full volume, not that i can tell
 
I might rethink using it to run the yamaha headphones, though will try what you suggested and say how it went.
 
thanks for the help

 

[thomas2015]

just for the record, Ive tried the 2020a tripath amp running the orthodynamic headphones - the valve preamp and running the stax headphones through a srd-7 adapter.
 
I mostly listen to music while on the computer working, so I can change the headphones depending on what type of music Im listening too
 
Ive owned various  combinations of gear since the 70s when i became interested in hq hifi, valve and transistor
 
the orthodynamics through the tripath amp is just awesome, one of the limitations of chip amps to me is they can be a little harsh, i was thinking the the valve preamp could filter out some of the harshness and it has, through the valve preamp cymbals sound like cymbals again, heavy (in a good way)  controlled bass, mids very clear and valve like.
 
the stax headphones - the stax are headphones for listening not so much for background music, I cant believe what I am hearing its like I have a different collection of music or at least its mixed totally differently, the stax do things Ive never heard before - the orthodynamics are excellent in thier own way, though dont have the depth of the stax, so basically for the record, after much careful testing and listening, Ive concluded its a successful combination. the best of both worlds.
 
BTW I dont notice any issue with the tripath running 150 ohm headphones as far as any distortion etc goes,  though will try a 8ohm dummy load to see if anything changes, cant see how as I cant fault the sound.

 

[thomas2015]

fyi - google TDA7297 Amp if you arent familiar with it, much better all round than the tripath, tripath sounds distorted in comparison, sounds very valve like, i thought the tripath was clear b4
not as harsh either, just replaced the power cap and no other modifications.
made for the stax
tried 2 8 ohm dummy load resistors so the orthodynamic head phone side of it, made no difference in sound at all
TDA7297 is an A/B amp not a D class, no background noise to speak of