Hashimoto HL-20K-6 Line Output Transformers

[nuhor68]

Hello,

I would like to build a high-end tube amplifier for headphones. Could somebody please recommend me which headphones are of the best choice for these transformers? Maybe schematics, etc. Thank you in advance.

[Stixx]

Hi Riga,

there was a thread just a few days ago about an highend headphone amplifier on diyaudio
--> http://www.diyaudio.com/forums/showthread.php?s=&threadid=134603 .
Though this one uses different output transformers at a different ratio.

You could also ask dsavitsk who responded on this thread and has MANY headphone amps on his site (transformer coupled).

[dsavitsk]

Because these transformers are 20K:150, you will want to use headphones with a high impedance, relatively speaking. You are right in between several, as Audio Technica seem to be in the 80 ohm range, while Sennheiser, Beyer Dynamic, and a few others are in the 300 ohm range. For the Sennheisers, you can run these 10K:300. I would think that either can be made to work with the right tube. Grados, at 32 ohm, are likely too low Z.

However, the difference in sound (not to mention comfort) between different phones is much larger than between different transformers or amp designs. I think I would pick the headphones you like, then pick the amp to go with them. And, indeed, while I like transformer coupling for low impedance headphones, for the high impedance designs, it may not be necessary, or even desirable.

[JoshK]

How much gain or watts is typically necessary for say Senn HD600's? I have zip for experience with phones, but I have a pair of HD600s.

I guess I could ask how efficient they are instead but I don't know what typical listening volume is, since your ear is so darn close to the transducer.

[rdf]

The max input power into my AKG K 701's impedance of 62 ohms is 200 mW, which works out to roughly 3.5 volts RMS. At the rated 105 dB for 1 mW that's 128 dB at the ear. Headphones are insanely efficient.
The same max voltage at the output of a regular tube OPT is less than 2 watts into 8 ohms.

[HollowState]

I use Sennheiser 580s which are similar to your 600s. I find that all CD players with a headphone jack have enough drive for them to play louder then I should ever use. Even my cheap 32 ohm phones play loud from them. Lacking any headphone output, only modest amplification is necessary from line level.

[JoshK]

Then I guess I don't really understand the need for so much gain that many of these headphone amps provide.

I was thinking of using my planned 801 preamp (parafeed, 10K:500) for a HP amp as well. The 500 is a bit high for 300ohm headphones but worth a try.

[Stixx]

The 500 is a bit high for 300ohm headphones but worth a try.

Not that much of a mismatch... With headphones as a load tubes are quite forgiving.

[HollowState]

Originally posted by JoshK
Then I guess I don't really understand the need for so much gain that many of these headphone amps provide.

Indeed, many HP amp have too much output to be truly safe for ones ears. But it's more then that. Most all players that provide a headphone output feed it from a SS large scale intergrated circuit. These LSICs probably don't have the best quality sound. So a small external tube HP amp driven from the line output is a nice thing to listen through as well as being fun to build. It should be more about fidelity then power.

[dsavitsk]

Originally posted by HollowState
I use Sennheiser 580s which are similar to your 600s. I find that all CD players with a headphone jack have enough drive for them to play louder then I should ever use. Even my cheap 32 ohm phones play loud from them. Lacking any headphone output, only modest amplification is necessary from line level.

The higher the impedance of the headphones, the more voltage you need.

Originally posted by JoshK
Then I guess I don't really understand the need for so much gain that many of these headphone amps provide.

Most people who have tried unity gain amps for high impedance phones have found that there is something lacking. These phones do seem to need a little gain.

I did some measurements on what Grado (32 ohm) headphones need in terms of voltage which can be found at http://www.ecp.cc/less-pressivo-plus-plus.html