Looking for simple Schematic of 2A3 or 45 or 26 Headphone Amp SE OTL ? anyone ? - diyAudio
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Old 14th February 2011, 05:18 AM   #1
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Default Looking for simple Schematic of 2A3 or 45 or 26 Headphone Amp SE OTL ? anyone ?

I want to build Headphone amp using one of these tube... 2A3, 26, 45.
does anyone ever built one or any recommendation ?

I just need SE OTL and simple schematic.

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Old 14th February 2011, 08:04 AM   #2
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Wouldn't any of the normal amp schematics work just fine, but with an output transformer with the appropriate secondary tap(s)?
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Old 14th February 2011, 10:15 AM   #3
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mastodon is right. And if you have headphones such as AKG 601, the appropriate secondary tap would be 4 ohms.

I would recommend you build a Darling amp - it has more than enough of power to fully drive headphones - and you can drive speakers too, with the same amp. This is the setup I have at the moment, and it works brilliantly. The 1626 is considerably cheaper and easier to work with than those tubes you mentioned.

With headphones, the biggest hassle is the noise. You need sub millivolt B+ ripple, preferably no more than 500V. With those DHT's you mentioned, the only possible alternative is to use battery as filament source.
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Old 14th February 2011, 10:26 AM   #4
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Quote:
the only possible alternative is to use battery as filament source.
...or Rod Colemans filament supply as discussed here.
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Old 15th February 2011, 08:09 AM   #5
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I'm thinking without using Output Transformer.

I prefer 2A3 or 26 or 45 tube rather than mini tube like darling use.

looks like there is no 2a3 headphone tube amp around.
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Old 15th February 2011, 08:29 AM   #6
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2A3 or similar OTL is going to be a challenge. You could put lots of triodes in parallel, but of course, that would be huge overkill for headphone use. I'm not aware of any OTL 2A3 designs for any kind of purpose.

More realistically, you could adapt one of John Broskie's designs (or something else based on an SRPP, totempole or Aikido-like topology) for your use, or simply build them as outlined in one of his blogs. See e.g. here Aikido PCB & Broskie OTL & Feesforward Shunt Regulator updates

Or build a simple resistor-loaded cathode follower output stage and couple the output with a huge cap to your load and simply accept the still phenomenal impedance mismatch, horrible inefficiency and the use of an electrolytic for audio purposes. Or be weird and consider a circlotron design. Broskie's done some articles on that as well, see e.g. Circlotron Amplifiers Once Again

I'm dealing with a similar challenge, only with a (completely) different tube complement. I'd like to design something for headphones in an OTL topology using ECL84's (6DX8) with the pentode strapped as a triode, preferably with one tube per channel (one triode and one triode strapped pentode). There simply is no really efficient way to solve that puzzle, and any resulting design will be highly compromised in one way or another.

In short, driving relatively low impedance headphones with regular output tubes with their high impedances is a game of compromises. If you insist on using one of the triodes you mentioned and you're looking for really good performance and sound quality, OTL simply isn't very realistic for the average DIY-er (or for anyone else, for that matter). One of the Headwize OTL tube projects (all using triodes, albeit smaller ones than you mentioned!) or one of John Broskie's designs are the only options I'm aware of that will lead to reasonable success without too much frustration.
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Old 15th February 2011, 08:48 AM   #7
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well the reason I like 2a3 is the sound, compare to other mini tubes or even 300B.

I'm not good at electrical design or anything, but I love building kits with Schematic already there.
I don;t think I can modify any tube amp schematic for headphone amp, even the simple thing like you guys said.

I just like 2A3 and trying to find schematic which already working, well ... with OT then .. and I can not find one.

why you are using ECL84 for your design ? not a bigger tube ? sounds better to me with bigger tube.
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Old 15th February 2011, 09:06 AM   #8
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If you really want to use the 2A3, then I'd recommend using one of the tried and tested designs and trying to find an OPT that has a secondary tap that matches your headphone's impedance. Or better yet: the other way around; try to find an OPT, and then find the matching schematic. But OPT's with headphone taps are pretty rare to begin with, I must say. What impedance do your phones have anyway? If they're 32Ohms (as most of the cheaper ones are these days), you're pretty close to speaker impedance and you could add a resistor network to match in your headphone. That will cause some power loss, but for the average set of headphones, you won't need all the power of a 2A3 anyway.

Quote:
why you are using ECL84 for your design ? not a bigger tube ? sounds better to me with bigger tube.
Hah, well, this is not exactly an example of good practice in high-end audio engineering, but still... I got a few of those tubes lying around; actually they're the Russian version 6Phi4Pi, and I somehow like the idea of building an amp with a minimal number of tubes. The combination of a triode and a 'power' pentode in one package is therefore appealing. The second requirement of the project is that it should be _cheap_. So no 'proper' OPT's will be bought, not even cheapish ones. I experimented a bit with using small power trannies for OPT's using a parafeed design, but the frequency response is just crappy every which way I turn it; either lacking lows or highs. So OTL is the only way to go, but that leaves the impedance matching problem. Wavebourn designed a headphone amp that uses a cathode follower of the output stage using an ECL84, and I built something along those lines in a breadboard setup. It works pretty nicely in the sense that it has a good frequency response (pretty much flat out up to about 100kHz, and even higher with some optimization), but power is a bit lacking at 15mW. Mind you, 15mW is sufficient for most reasonably efficient headphones and for 'normal' (not ear-shattering) listening, but I'd really like to have a design that will go up to about 100mW in order to have some headroom. That won't drive any of the less efficient headphones, but there are plenty decent phones in the $100 range that will put out more than decent SPL's with that kind of power.
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Old 15th February 2011, 09:17 AM   #9
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yes I was thinking like you said, get the OT that match the impedance of my headphone for the secondary.
and yes it;s hard to find, my headphone is 50 Ohms, I know I can use resistor but I don;t want to loose a tiny bit from 2A3, it's because I want as muuch power and pure (NO RESISTOR).

I 'm thinking high end tube amp headphone.
but using as little komponent as possible.
I know OT is a must now .

I have tried many solidstate amp for headphone, I like "overkill" power for headphone but they usually not sounds good.
I found little power but sound good, that's a pity.

OT is very important for tube amp, I don;t think I can find OT that has 50Oohms output. well never seen one.
Tamura, Tanggo is one of the best OT I think.
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Old 15th February 2011, 09:32 AM   #10
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Don't worry about the power loss when using some resistors to match impedance. I bet you won't need more than 500mW for your headphones to begin with. Take an OT with a 16Ohm secondary tap and put a 22Ohm 5W resistor in parallel with your headphones and you've got a pretty decent impedance match. Suppose your amp is capable of putting out 3.5Wrms, then you'll still have about 1 to 1.5Wrms left for your phones. Which is probably enough to destroy them and your ears in the process as well.
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