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Best DIY tube headphone amp or DAC?

post #1 of 37
2/20/12 at 12:27pm
Thread Starter 

I'm looking to build a tube-based headphone amp, as I already have enough solid state amps. The Beta 22 is often cited as the "best" DIY solid-state amp, is there any sort of consensus as to the "best" tube amp?

 

Right now I'm looking at the Bottlehead Smack WOT. I also saw the Mapletree Audio Design Ear+ HD kit, but right now I'm leaning toward the Smack. Any others I should be considering? Information on DIY tube amps seems to be tough to come by.

 

With regard to the Smack, I noticed that it has balanced outputs, but no balanced inputs (confirmed by Bottlehead). Can anyone tell me why a tube amp with balanced outputs would not necessarily nead balanced inputs, whereas a solid state amp would? Or is there no good reason at all? Obviously you can drive headphones balanced without balanced inputs, but I thought you lose most of the benefit of a balanced amp that way?

 

I'm also interested in advice on a good DIY DAC with balanced outputs. Right now I'm looking at the Opus from Twisted Pear. Any other suggestions?

 

I should add that I'm not looking to design my own amp or DAC, nor am I looking to modify or experiment with any designs. I don't have any technical knowledge in this area and would quickly get in over my head. I'm just looking for an existing design that I can build in a relatively straightfoward manner.

 

Thanks!

Adam

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post #2 of 37
2/20/12 at 12:36pm

Do you have a preference between OTL or Transformer coupled? 

 

The Bijou amp looks great, as does the hybrid EHHA - the MAD Ear + is also way up there. Of these, I know for sure the Bijou and EHHA can be built balanced. 

 

You could also get two Crack kits, and build them onto the same chassis and run them as a balanced OTL if you don't want to use the output transformer set up in the Smack. 


Edited by liamstrain - 2/20/12 at 12:42pm
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post #3 of 37
2/20/12 at 1:16pm
Thread Starter 

Like I said, I don't have any real technical knowledge here, so I can't really say whether I have a preference between OTL and transformer-coupled. My very simplistic understanding was that tube amps tend to have higher output impedances, and therefore aren't ideal for low-impedance headphones unless - like the Bottlehead Smack WOT -- they have an output transformer. My headphones run the gamut:

 

Denon AH-D5000

Grado SR225i (woodied)

Alessandro MS2

Ultrasone Pro 2900

Sennheiser HD600

Sennheisder HD650

HiFiMAN HE-400

 

So I've got a pretty broad mixture in terms of impedance (25 Ohms - 300 Ohms) and sensitivity (92-106 dB). I am also considering picking up a pair of 600 Ohm Beyerdynamics or a pair of HE-500s with a sensitivity of 89 dB at some point. Still, other than the Senns, my cans have pretty low impedance (<40 Ohms) and most are also pretty sensitive (with the HE-400s being the primary exception).

 

What is the benefit of an OTL design?

 

Also, I hate to keep repeating myself, but I really need to know: is there any reason why tube amps with balanced outputs don't necessarily need balanced inputs to get the best results?

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post #4 of 37
2/20/12 at 7:14pm
Quote:
Originally Posted by amcananey View Post

Like I said, I don't have any real technical knowledge here, so I can't really say whether I have a preference between OTL and transformer-coupled. My very simplistic understanding was that tube amps tend to have higher output impedances, and therefore aren't ideal for low-impedance headphones unless - like the Bottlehead Smack WOT -- they have an output transformer. My headphones run the gamut:

 

Denon AH-D5000

Grado SR225i (woodied)

Alessandro MS2

Ultrasone Pro 2900

Sennheiser HD600

Sennheisder HD650

HiFiMAN HE-400

 

So I've got a pretty broad mixture in terms of impedance (25 Ohms - 300 Ohms) and sensitivity (92-106 dB). I am also considering picking up a pair of 600 Ohm Beyerdynamics or a pair of HE-500s with a sensitivity of 89 dB at some point. Still, other than the Senns, my cans have pretty low impedance (<40 Ohms) and most are also pretty sensitive (with the HE-400s being the primary exception).

 

What is the benefit of an OTL design?

 

Also, I hate to keep repeating myself, but I really need to know: is there any reason why tube amps with balanced outputs don't necessarily need balanced inputs to get the best results?

The benefit of an OTL design (Output Transformer-Less) is that it doesn't use output transformers.wink.gif  I'm not trying to be a smarty-pants, but seriously - that's the benefit.  Transformers can be very expensive to sound very good.  Very often, you need them custom-wound for best results for a wide range of headphones.  So, an OTL amp removes the entire issue (except for the power transformer and those are not directly in the signal path).

 

The down side of an OTL design is that the output impedance can be quite high and output current can be very limited.  IOW, not necessarily an ideal topology for low-impedance headphones.  If the headphones are low impedance, but highly efficient, then they may do OK.  I have heard a Denon D2000 on a Bijou and it sounded quite good, but as mentioned, the Denon may be low impedance, but it is very efficient.  (The 5000 just adds wood for good looks).  On the other hand, the HE-400 would not be such a good choice with OTL designs.  I believe HiFiman mostly recommends tube hybrids, with the ability to supply decent amounts of current.

 

I can't help you with the balanced question, it would seem self-defeating to not have balanced inputs if there are balanced outputs, but I'm not an expert on it.

 

 

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post #5 of 37
2/20/12 at 7:57pm
Thread Starter 

Thanks, I knew what OTL meant, and I knew that output transformers are expensive, but didn't realise that doing away with them also reduces the output current. Not knowing how output transformers work, I actually would have guessed that amps without output transformers would be MORE powerful, not less. I'm certainly glad you cleared that up! It sounds like what I'm interested in is a transformer-coupled amp. Is the Smack my best bet, or are there other highly regarded DIY tube amps with output transformers?

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post #6 of 37
2/20/12 at 7:58pm
Thread Starter 

And for anyone else who is following this thread, any input on the balanced tube amp question would be appreciated. 

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post #7 of 37
2/20/12 at 9:26pm

The Bottlehead "Smack" WOT would be an excellent choice. You'll not only end up with a great amp, you'll receive an education in the construction process and have a sense of pride and acomplishment that cannot be duplicated by simply buying an off-the-shelf product.

 

I'm not sure, but I imagine the "balanced" outputs of the "Smack" are simply the results of the output transformer secondary winding configuration. This is not true "balanced" operation, but will give you the ability to run headphones in balanced configuration. Nothing at all wrong with this.

 

At this stage of your headphone journey it's best to forget about the whole concept of "balanced" operation. It's kind of an article of "cult" faith here on H.F., but many think it's a complete waste of time and resources. There are of course plenty of threads that say otherwise. Best to research, listen, and make up your own mind.

'

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post #8 of 37
2/20/12 at 9:28pm
Quote:
Originally Posted by amcananey View Post

And for anyone else who is following this thread, any input on the balanced tube amp question would be appreciated. 



That amp doesn't need a balanced input because the input on the amp is a phase splitter. 

 

which means you could put a balanced input on it, but the only thing you'd gain from doing that is a lower noise floor on the connection between the source and the amp. (Edit: provided that the cable and connectors are wired properly, which is not guaranteed.)


Edited by ericj - 2/20/12 at 9:32pm
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post #9 of 37
2/20/12 at 9:34pm

Also, I like my Bijou a great deal, so i vote for that. An all-out build with 6H30-PIs and whatnot could do you quite well. 

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post #10 of 37
2/21/12 at 6:52am
Thread Starter 

Eric,

 

Thanks for your response. I assume the Bijou is output transformerless? What is the output impedance of the Bijou? Have you used your Bijou with anything like Denons or Grados? If so, was there any hum or other problems compared to the sound quality when using higher impedance cans? And have you tried your Bijou with anything like a set of HiFiMAN's planars?

 

Sorry for all the follow-up questions!

Adam

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post #11 of 37
2/21/12 at 7:02am
Thread Starter 

Thanks, Frank. I suspect that I will indeed wind up with the Smack WOT, for all of the reasons discussed.

 

As for balanced vs. unbalanced operation, I'm fairly confident that there aren't any real sonic benefits, but I'm also fairly confident that until I try it, I will always be curious. But it seems to me that the only way to really be sure that there isn't any sonic benefit is to try a system that is "fully" balanced. From Eric's response I can't quite tell whether the Smack would be considered "fully" balanced, but intuitively, it seems that the answer should be "yes". It seems to me that it shouldn't matter whether the audio signal is split and inverted in the DAC, then passed to the amp for amplification in two separate channels, or whether the unbalanced signal from the DAC is sent to the amp, which does its own split and inversion before amping the signals separately.

 

But maybe I'm way off base with my understanding of how this works...

Adam

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post #12 of 37
2/21/12 at 7:09am
Thread Starter 

Eric,

 

I just read your "for sale" post and perused your headphone and amp collection. Very interesting! I'm amazed at how much gear you have and how completely different it is from my stuff. Different tastes and whatnot....I really enjoyed that. Out of curiosity, what are your favorite AKGs?

 

Also, I probably should have put this into my original response to you, but please see my note in my previous post, responding to Frank. Is my understanding correct?

 

Regards,

Adam

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post #13 of 37
2/21/12 at 8:37am
Quote:
Originally Posted by amcananey View Post

As for balanced vs. unbalanced operation, I'm fairly confident that there aren't any real sonic benefits, but I'm also fairly confident that until I try it, I will always be curious. But it seems to me that the only way to really be sure that there isn't any sonic benefit is to try a system that is "fully" balanced. From Eric's response I can't quite tell whether the Smack would be considered "fully" balanced, but intuitively, it seems that the answer should be "yes". It seems to me that it shouldn't matter whether the audio signal is split and inverted in the DAC, then passed to the amp for amplification in two separate channels, or whether the unbalanced signal from the DAC is sent to the amp, which does its own split and inversion before amping the signals separately.

 


 

I would not take such a certain stance...

 

The problem is that different amps work differently. The rule of thumb that applies to some amps does not apply to others. 

 

On your typical op amp based amp with very low measurable distortion, at least 40db of global negative feedback, nearly-zero-ohm output impedance, and at least 20db voltage and current overhead I strongly doubt that there is ANY audible difference between balanced and SE operation that could not be explained by the source. 

In amps without global feedback, real world distortion numbers, significant output impedance, and/or limited voltage or current the differences can be huge. Lets just call these amps "simple" amps - I'm not really sure of a better description.

 

Things get kind of dicey comparing "simple" single ended and balanced amps because of how many variables there are - before people make significant changes to the circuit! The common practice in op amp based amps of dropping 4 boards in a box and calling it balanced is rarely done in "simple" tubes/SS. Part of this freedom comes from the trend to build these amps point-to-point, where more complicated amps are almost always built on a PCB. When you build point to point you have LOTS of freedom to do lots of things differently to benefit balanced operation. 

 

 

 

The SMACK is single ended from end to end, but if you are OK working with the voltages involved I would join the others in suggesting it as a first HV tube amp project. The way the output transformer is set up looks very nice, and the bottlehead kits are very well documented. 

 

Why do I say its SE:

Most importantly: The amp has only 2triodes/ch - one is a shunt regulator, the other handles signal. you need at least 2 triodes handling signal for balanced. 

Less importantly: The description on the Bottlehead website does not actually say that its balanced anywhere "it can drive balanced cables" does not mean balanced... 

If you look closely the XLR plugs in the back are hooked up to the TRS jack in the front. 

None of it matters, its just nit picking. If the amp sounds good it sounds good. 

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post #14 of 37
2/21/12 at 9:08am
Thread Starter 

nikongod,

 

Thanks for your input. (BTW, I have a very extensive collection of Nikon cameras and lenses.) I think I'll go ahead with the Smack (though I look forward to hearing Eric's feedback on his Bijou amp). Out of curiosity, are there any documented DIY balanced tube amps out there? It doesn't sound like something I should tackle until I have more experience, but I am curious.

 

Best regards,

Adam

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post #15 of 37
2/21/12 at 9:48am
Thread Starter 

Aha! I knew that I had seen something somewhere about why (at least in some cases) balanced tube amps don't need balanced inputs:

 

 

Some comments about balanced headphone drive

I am frequently asked why the balanced output version does not include balanced inputs. This is because balanced inputs are not necessary to provide balanced headphone drive. Being a single ended amplifier, all it needs for input is a single ended (unbalanced) signal. The Sonett operates single ended triode with transformer loading the plate of the 6H30 amplification tube. The secondary windings on the output transformers are center tapped (and grounded for safety), thereby providing a true, differential, balanced output. Thus, you get balanced drive without the complexity from additional balanced input circuitry or input transformers. Again, the simpler - the better.


This is from the DNA Sonett website. I find the language a little confusing. For example where he says "thereby providing a true, differential, balanced output" - Talking about a "true" balanced output, while technically correct (I think) seems a bit confusing, since "true balanced output" almost sounds like the amp is "fully balanced", which I believe is not the case. Of course elsewhere he includes language that technically shows the amp is single-ended and "only" provides balanced drive.

 

I guess the best way to respond is to say: everything in the excerpt above is true, but it doesn't necessarily respond to the question of "why no balanced inputs" in a transparent way. The simplest, most direct response, would be something like: "The balanced version does not include balanced inputs because it is a single-ended amplier, not a "fully" balanced system. Because the secondary windings on the output transformers are center tapped (and grounded for safety), the amp is, however, capable of differential balanced drive. Thus, you get balanced drive without the complexity from additional balanced input circuitry or input transformers."

 

Is that a fair summary, with regard to both the Smack WOT and the balanced version of th DNA Sonett?

 

Regards,

Adam

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