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Old 15th August 2014, 05:10 PM   #1
Alex M is offline Alex M  United Kingdom
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Default Headphone amp ideas?

I am starting to put together some ideas for my next project, which is a nice little amplifier for my Sennheiser HD595 headphones. I have misplaced the user manual for these, but I am assuming that they are the more recent 50 ohm version. Iíve been using the headphone output from my otherwise-defunct Aiwa cassette deck, but I am aware of the limitations of this setup and Iím sure that a much better drive system is possible.

Having done some searching, I realise that there is a wealth of different topologies out there Ė transformer, parafeed or capacitor output, and single-ended, cathode follower, White CF or push-pull output stages and so on - but there doesnít seem to be an overwhelming preference for one or the other, either in the commercial world or the DIY community. My own prejudice is towards transformer output Ė after years of avoiding electrolytic caps in the signal circuits, I find it very hard to put a big one between the output devices and the jack socket.

I have good stocks of both 6922 (left over from my abandoned differential crossover project) and EL84/6BQ5 (spares for my Croft Series 5 amps). I would imagine a nice push-pull triode-strapped EL84 transformer-output circuit might be just what I am looking for, though I havenít yet managed to find a schematic I like. I have also seen some 6922 circuits out there too, but these all seem to be capacitor coupled outputs.

Does anyone have a recommendation for a headphone amp project?

Alex
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Old 15th August 2014, 05:33 PM   #2
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Looks like they are 50-ohm cans.

If you want to use your tube stock, you might try a single-ended design using the 6922 as input and a triode-strapped EL84 as the output. You won't need the extra power available by going push-pull. Transformer coupling sounds like it might be the way to go given the tube choices and aversion to electrolytic capacitors in the signal path, although you might get by using the 100uF Solen film caps. These might set you back as much as an acceptable transformer set, though.
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Old 15th August 2014, 05:39 PM   #3
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Designing for headphones is fun in my opinion because you don't ever really have to worry about power - there's always more that your ears can take (or, at least, mine).

A good place to start would be a fully balanced 6SN7 amp, with parafeed transformer output. Since power efficiency is not an issue, parafeed really is the way to go, unless you especially want to have expensive OT's.

I sugguest a two stage fully balanced gyrator loaded CCS tailed parafeed amp.

It would also be ok for speakers with lowish volume.
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Old 15th August 2014, 05:41 PM   #4
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Balanced topology really isn't about power - it's just an extra. But I do agree that EL84 is overkill - and furthermore the higher the heater current and the more inexperienced the builder, you're just asking for trouble building for headphone use.
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Old 15th August 2014, 06:41 PM   #5
jcx is offline jcx  United States
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OTL?
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Old 15th August 2014, 08:52 PM   #6
Koifarm is offline Koifarm  Netherlands
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My best sounding tube headphone amp was a 300B SE amp with transformer output. but best overall headphone amp and the one i use now is with a LME49600. The sound is the same as the 300B with better basscontrol.
My headphones are AKG 702, Beyer Dynamic DT770-80.
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Old 16th August 2014, 02:56 AM   #7
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That 50 Ω spec. is pretty darned low. You might be better off with a 1st class SS design.

I own a Sheldon Stokes headphone amp and find it to be highly satisfactory. As the man said, it doesn't sound like "sand".
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Old 16th August 2014, 03:38 AM   #8
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Get yourself one of these, either new or used, then search around on line for dozens of DIY modifications. Or just use it as is. Don't let the low price fool you because the sound quality is very good in stock condition. There are some even on this website. Below is a highly modded one.
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Last edited by HollowState; 16th August 2014 at 03:48 AM.
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Old 16th August 2014, 03:48 AM   #9
jcx is offline jcx  United States
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with output transformer 50 load is no problem

but OTL @ 50 mApk should reach 120 dB SPL with HD595 and should be walk in the park for those tubz, SRPP

OTL may even get plate dissipation within shouting distance of the heater power
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Old 16th August 2014, 04:03 AM   #10
BRSHiFi is offline BRSHiFi  United States
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I am thinking possibly retrofit this design with a custom wound transformer from Edcor that has a 32 ohm tap along with the 600 ohm if you want to make use of it for a line stage as well.

No Feedback Balanced Line Design

Headphones do not require tons of power to be driven to deafening volumes. You also may want the ability for the user to allow the driving of multiple pairs of phones. My friends do that with their Ipods.

Note I just came up with this design by fooling with Spice. It is by no means sound, but I do intend to try it on for size. The distortion figures in spice are always, in my experience, too good to be true. Real life variables always seem to affect this parameter. The design uses no feedback. It thus is dependent on its own linearity.
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