If I put my notes here, I might be able to find them again later!
Portable headphone amplifiers
The shift of the center of gravity of the high end from component, rack systems to portable continues. Exhibit A
I've also noticed that over the last couple of years the basic blueprint for a portable headphone amplifier as defined by the Sony PHA-1 has now been taken up by all of the major Japanese audio companies.
Sony PHA-1, PHA-2, PHA-3
Denon DA-10
Onkyo DAC-HA200 and TEAC HA-P50 (variants of the same basic unit)
JVC SU-AX7 (report) (seems to be mostly Kenwood DNA)
Audio Technica AT-PHA100
and Fostex hp-p1
For all the above you are looking at a battery powered, slim-cased DAC + headphone amp typically with some sort of guard around the controls. They all feature a good variety of analog and digital inputs, offer switchable gains, and are priced over a range from $200 to nearly $1000.
You are looking at the convenience of having the DAC built in, the small size, and the rechargeable lithium battery. Its not really an area where DIY can compete, I think its better for home grown efforts to target the full-desktop, all-analog, high-end model where size and power consumption are not important considerations.
I've also noticed that over the last couple of years the basic blueprint for a portable headphone amplifier as defined by the Sony PHA-1 has now been taken up by all of the major Japanese audio companies.
Sony PHA-1, PHA-2, PHA-3
Denon DA-10
Onkyo DAC-HA200 and TEAC HA-P50 (variants of the same basic unit)
JVC SU-AX7 (report) (seems to be mostly Kenwood DNA)
Audio Technica AT-PHA100
and Fostex hp-p1
For all the above you are looking at a battery powered, slim-cased DAC + headphone amp typically with some sort of guard around the controls. They all feature a good variety of analog and digital inputs, offer switchable gains, and are priced over a range from $200 to nearly $1000.
You are looking at the convenience of having the DAC built in, the small size, and the rechargeable lithium battery. Its not really an area where DIY can compete, I think its better for home grown efforts to target the full-desktop, all-analog, high-end model where size and power consumption are not important considerations.
Total Comments 9
Comments
-
I can't help thinking that portable amps are going to be hamstrung by insufficient power supplies - as you say the size constraint is severe. Have any portable amps taken up using output transformers yet? I have an idea that with a small enough transformer, an amp could use photoflash caps which have the highest energy density of any high voltage caps (excluding supercaps). I rather suspect the trafo won't be particularly portable though.....Posted 14th January 2015 at 10:14 AM by abraxalito
-
Well, there's insufficient in power, which is a rather subjective point, and there's insufficient in voltage, which since I imagine most of these units are regenerating voltage rails using DC-DC converters should not be an insurmountable problem.
As you know, output transformers solve problems and create them. For a push-pull design they wouldn't have to be all that large, but perhaps "portable" is still a bit of a stretch.Posted 14th January 2015 at 11:53 AM by rjm
-
I have some reasonably compact ferrite trafos in my transportable Ozone DAC. For driving low impedances from opamps they're invaluable but they're at least 20mm tall so wouldn't fit into a low profile case. However I still need a much bigger volume of caps to get the best dynamics, so caps are the primary problem. Perhaps pure classA is a better solution though. When I said 'insufficient' I meant insufficiently low impedance - i.e. too saggy.Posted 15th January 2015 at 12:23 AM by abraxalito
-
It depends if your output transformers are cut for single ended use. If not you are going to have to go push pull or parafeed.
What kind of voltages are you looking at?Posted 15th January 2015 at 12:31 AM by rjm
-
I guess mine are parafeed, I just put them between the driver (normally a CFB high-drive opamp like AD8017) and the transducer, fed through an LC low-pass filter and a 'lytic to block DC. I like to run the driver IC as close to its max supply as possible, so around 10V for the AD8017. I reckon though that higher voltages will probably sound better, because that necessitates a bigger step-down ratio and hence attenuates PSU noise more. Forgot to mention - given the AD8017 is a dual, I run them anti-phase, i.e. the trafo is driven as BTL, doubling the swing.Posted 15th January 2015 at 02:01 AM by abraxalito
Updated 15th January 2015 at 02:15 AM by abraxalito -
Oh, I imagined MOSFETs running at 100-200 V. If you are just using regular op amps and normal voltages why do you even need an output transformer? Whatever you gain by the step down ratio you lose by having to increase the voltage gain of the op amp proportionately.Posted 15th January 2015 at 06:34 AM by rjm
-
Having the trafo improves the dynamics, considerably. With IEMs the swing is perhaps 1V peak, with the 10:1 trafo a 10V peak swing is downconverted to 1V, the PSU noise goes down 20dB. Or put another way, the IEMs look like 1600ohms.Posted 15th January 2015 at 03:34 PM by abraxalito
-
I don't think you get the benefit of 20 dB less noise since the op amp gain had to be increased 20 dB (relative to the direct-drive case).
The increase in load impedance seen by the op amp is the more persuasive argument. A McIntosh amp for headphones!Posted 15th January 2015 at 11:23 PM by rjm
-
Yes, I wasn't meaning 20dB less noise, rather that much reduction of PSU-induced noise. PSU noise is signal dependent and I reckon its in the main introduced by the output stage. Yes partly I was inspired to try this from learning about how dynamic McIntosh amps sound with their autoformer outputs. I was shocked how dynamic my old Sony headphones (CD3000) sounded once fed via a trafo - previously I'd figured that the fatiguing sound at higher levels was due to their age. The trafo's given them a new lease of life.Posted 15th January 2015 at 11:50 PM by abraxalito
