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Old 23rd August 2007, 12:31 AM   #11
arnoldc is offline arnoldc  Philippines
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Hi,

My 45 (driven by choke-loaded 5842) uses Tamura F-475 and I derived a headphone out from the 16 ohm tap. Sounds very good, but the amp is big for a headphone amp!

ps.

If you are interested, and inspired by Kevin's article, I made a 417A/5842 headphone amp, that spells simplicity and great sound.
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Old 23rd August 2007, 02:26 AM   #12
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I assume that the thread starter is the same person that emailed me asking the same question. If not, the info still applies.

I just got back from a 3000 mile road trip (I picked up a few hundred pounds of tubes), and finally caught up on most everything. The email asked about modifying a TubelabSE for headphone use.

There is a page on my web site that details the extreme modifications that were done to a TubelabSE to build a custom amplifier for a very particular (and well financed) customer. He had previously purchased a TubelabSE amplifier with 45's for use with speakers. I added a headphone jack and a switch that put the headphones in parallel with a 10 ohm resistor across the output of an otherwise unmodified amplifier (5842 driving a 45), while disconnecting the speakers. I feel that this worked very well, but it could not get very loud with his high impedance (600 ohm) phones. The owner wanted another amp to add to his already large collection. He wanted it only for phones, and since he already had several DHT based amplifiers and this one would only need to make 1/4 watt at most, I suggested to try some tubes smaller than the 45 like the 30, 31 and the 01A.

I set up a TubelabSE board on a bench power supply, and tried several different tubes and transformers. The customer made a 500 mile trip (twice) to listen to each combination with his personal headphone collection that spanned from 32 to 600 ohms. He reached his personal audio nirvana with 01A tubes and multi tapped UTC LS57 OPT's that were meant for a 20 watt P-P amp.

Were these modifications really necessary? In this customers mind, they were. These were extreme modifications for an extreme customer, but they are easilly duplicated by an experienced builder. The details are here:

http://www.tubelab.com/Headphone.htm

Many TubelabSE users have used their unmodified amps with headphones. I have recommended a 10 ohm resistor in parallel with the headphones just to keep the 45 operating with its intended load, but many users simply connect their phones to the speaker terminals.

Keep in mind that the amp must be really quiet for use in this manner since the phones are far more efficient than speakers, and your ears are really close to them! I recommend using a choke and a supplemental capacitor in the power supply. All filaments should operate on DC. The layout and lead dress should be optimized to reduce hum.

I think that any of the designs mentioned here would produce satisfying results. If I was building a headphone amp using a triode wired pentode (6W6) I would give some consideration to the 6V6GT. It sounds really sweet in triode mode. At the power levels used with headphones transformer saturation is not a problem, so there is no need for huge OPT's, which may actually cost in the detail department. The $19 Edcor XSE15-8-5K transformers might just be ideal. I have built an amp like this using a SimpleSE board. It sounds real good with speakers, and with my (cheap) Sony headphones. I have been known to listen to the amp with the phones and the speakers hooked up at the same time. The phones provide most of the sound, while the speakers provide bass enhancement, and some vibratory realism.
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