[IBPhoenix09]

  It should be fine. The one concern would be if the amp's output impedance is greater than a couple ohms, but even then it wouldn't damage the 25 ohm headphones (it just would not necessarily drive them without audible artifacts/changes to the sound).

I see, so even if the amp doesn't damage the headphones it may not be the best match in terms of sound quality. Additionally does using a balanced connection versus single ended change impedance matching concerns? Or is that a non issue?

 

[cjl]

That depends on the design of the amp. If the balanced is identical circuitry to the single ended, just with 2 amps bridged, the balanced will have twice the output impedance (and therefore be worse for low impedance headphones). If the balanced topology is different though, it's difficult to say, and it'll depend on the specifics of the amp.

 

[IBPhoenix09]

  That depends on the design of the amp. If the balanced is identical circuitry to the single ended, just with 2 amps bridged, the balanced will have twice the output impedance (and therefore be worse for low impedance headphones). If the balanced topology is different though, it's difficult to say, and it'll depend on the specifics of the amp.

Ah I see, Thank you for the explanation. I'm having a hard time with this search for an amp to go with them. I guess its a good thing it isn't an immediate purchase.

 

[mindbomb]

What do measurements of phase tell you? Just that you might need more power than you expect?

 

[proton007]

  What do measurements of phase tell you? Just that you might need more power than you expect?

 
Hmm... my knowledge is limited in this respect, but I believe phase measurements are reflective of the Inductance properties of the coil. As much as the coil works with an outside voltage source, its own emf will oppose this change.
So yeah, in some cases, more power may be needed because you'll have to overcome the reverse emf. This may be related to the damping factor.

 

[waflet]

Hideeho
 
I am very new to the whole hifi thing, so I am trying to do a lot of reading to get an understanding of how things work. Currently I am having trouble wrapping my head around tube amps. Before I get to my hang up, what I am looking for is a nice tube amp for my HiFiMan HE-400i’s. I started with an SMSL M3 from www.Massdrop.com, but have found its few short comings (it is VERY bright). I am interested in a tube amp to get a more full sound & to play with tube rolling. I want to stay under $200 butdon’t have a problem waiting an extra paycheck or 2 if I need to go over. I have been looking at the Darkvoice 336se, Little Dot MKII, Little Dot I+, Schiit vali2, & Gemtune APPJ. I have been advised that the Darkvoice & Little Dot MKII would not be a good match for my 400i because they are OTL amps.
 
That is where I am running into an inability to grasp the issue. I had never heard of an OTL amp, so I did some reading on the subject. From what I read OTL amp means Output TransformerLess. By my understanding an amp uses a transformer to convert the 110v input from the wall to whatever the tubes want to see & then uses something else (another transformer or capacitors) to convert to what the headphone wants to see or drives directly from the tube to the headphone (OCL amp). If there is a 2nd transformer to convert the tube output it is a standard amp. If there are capacitors or it drives directly from the tubes it is an OTL amp. Standard amps tend to be either more expensive or cheaper (nice transformers are EXPENSIVE, but cheap ones are very cheap).
 
Of all the amps I mentioned only the Gemtune has (what I assume is) a transformer in it at all. Are these not all OTL amps? Something like the Schiit lyr2 has 2 transformers in it, so I assume it is not an OTL amp. The reports of the Darkvoice not being perfect for the 400i are fairly universal. The MKII gets some bad marks with the 400i, but there are not as many people reporting so I take that with a much larger grain of salt. The only difference I can see is the recommended headphone impedance listed (which is why I’m posting this question here). Both the Darkvoice & the MKII start listing at 32ohm, while the rest start at either 8ohm or 12ohm. The 400i is listed at 35ohm but I have seen several tests pegging it as high as 40ohm. Would this be the real reason the Darkvoice & MKII aren’t as popular with the 400i crowd? Might this be something like footroom (as opposed to headroom on the top end ) allowing better sound in low impedance headphones? Are some of these OCL?

 

[Krutsch]

  Hideeho
 
I am very new to the whole hifi thing, so I am trying to do a lot of reading to get an understanding of how things work. Currently I am having trouble wrapping my head around tube amps. Before I get to my hang up, what I am looking for is a nice tube amp for my HiFiMan HE-400i’s. 
 
...

 
I've listened to an HE-400i and they are nice cans, but low impedance (35 ohm). OTL amps do best with high impedance cans, like 150, 300 and above (e.g. Sennheiser HD-650). Low impedance cans will distort at higher volume (e.g. my Grado or AQ NightHawk).
 
I think the 400i 'phones were designed to work right out of portable devices. Doesn't mean they won't sound better with more power, but you want a tube amp that works well with low Z cans (i.e. not an OTL).

 

[waflet]

Hideeho
Thank you very much for making the effort to reply, but you did not answer any of the questions I asked or impart any information or knowledge I did not state in the op.
 
Do you or does anyone else have an explanation of why the Darkvoice & MKII would not be suitable while the Vali2 & I+ would be even though they all seem to be OTL amps?

 

[Ruben123]

Hideeho
Thank you very much for making the effort to reply, but you did not answer any of the questions I asked or impart any information or knowledge I did not state in the op.

Do you or does anyone else have an explanation of why the Darkvoice & MKII would not be suitable while the Vali2 & I+ would be even though they all seem to be OTL amps?

Do you even need an amp? And if so, get one that doesn't colour the sound.

 

[waflet]

Do you even need an amp? And if so, get one that doesn't colour the sound.

Hideeho
Thank you for taking the time to respond as well.
Need? No, but then again I don’t NEED $400 plannar magnetic headphones & could get by with $10 inked headphones.
The whole point of tube amps in this day & age is specifically to color the sound. If I didn’t want to color the sound I would be looking for a solid state amp & the impedance would not be an issue.

 

[pinnahertz]

  Hideeho
Thank you for taking the time to respond as well.
Need? No, but then again I don’t NEED $400 plannar magnetic headphones & could get by with $10 inked headphones.
The whole point of tube amps in this day & age is specifically to color the sound. If I didn’t want to color the sound I would be looking for a solid state amp & the impedance would not be an issue.

There are other, more flexible, and better ways to color the sound, if that's what you want to do.  What you are essentially doing here is trying to choose an "equalizer" in the form of a tube amp that you will be paying a lot of money for and want to live with for a long time.  Times change, tastes change, different music benefits from different...um...color...so why would to lock into a particular tube amp?  Or will you get lots of tube amps and pick the one you like for a particular situation?  
 
The whole thing seems a bit like closing your eyes and shooting an arrow at a target that is moving.  You could, for example, get a really good SS amp, then insert resistors between it and your phones.  Resistors cost a few cents, even the really good ones, so you could get a couple hundred different ones to play with and end up with your own boutique sound using only passive components.  Pick out a few favorites, mount them on gold connectors, insert as desired.  Label them "dark", "open", "airy", "vaporous", "glassy", "solid", etc.  Now, doesn't that sound like fun?  And you be the only one with just exactly those combinations.  
 
Passive...it's such a nice sounding word, isn't it?   

 

[waflet]

  There are other, more flexible, and better ways to color the sound, if that's what you want to do.  What you are essentially doing here is trying to choose an "equalizer" in the form of a tube amp that you will be paying a lot of money for and want to live with for a long time.  Times change, tastes change, different music benefits from different...um...color...so why would to lock into a particular tube amp?  Or will you get lots of tube amps and pick the one you like for a particular situation?  
 
The whole thing seems a bit like closing your eyes and shooting an arrow at a target that is moving.  You could, for example, get a really good SS amp, then insert resistors between it and your phones.  Resistors cost a few cents, even the really good ones, so you could get a couple hundred different ones to play with and end up with your own boutique sound using only passive components.  Pick out a few favorites, mount them on gold connectors, insert as desired.  Label them "dark", "open", "airy", "vaporous", "glassy", "solid", etc.  Now, doesn't that sound like fun?  And you be the only one with just exactly those combinations.  
 
Passive...it's such a nice sounding word, isn't it?   

Hideeho
What you suggest does sound like fun, but I have to have something to waste my money on. I'm choosing tubes rather than pot or lsd or alcohol (although some in moderation is not too bad of a thing, unless you have to take a drug test for work...) . Honestly tube rolling sounds interesting, so I am trying to learn the hows & whys of it. My op was not meant to be a debate on what amp I need to buy (even out of the ones mentioned), I was looking for information about OTL vs standard amps vs other OTL amps. I am trying to gain some knowledge so I can make a more informed guess as to what amp will best punch the most buttons for me.

 

[pinnahertz]

 
Hideeho
What you suggest does sound like fun, but I have to have something to waste my money on. I'm choosing tubes rather than pot or lsd or alcohol (although some in moderation is not too bad of a thing, unless you have to take a drug test for work...) . Honestly tube rolling sounds interesting, so I am trying to learn the hows & whys of it. My op was meant to be a debate on what amp I need to buy (even out of the ones mentioned), I was looking for information about OTL vs standard amps vs other OTL amps. I am trying to gain some knowledge so I can make a more informed guess as to what amp will best punch the most buttons for me.

I doubt you'll get any useful help.  You're asking for a recommendation that satisfies your current personal preferences.  We don't know them, and they will change.  Research has shown a strong preference for uncolored, neutral sound across a wide population segment.  
 
You're also into this for the entertainment value of the hardware.  Well, someone might help you there, but their opinion now mesh with yours.  And now you want to go tube rolling?  Our goals are SO different.  I want the best, most accurate, undistorted sound possible. You're asking for something completely different and out of my world.  Probably most other in Sound Science.
 
You already have the technical and performance differences between general topologies.  Other than that, it's all biases and opinions.  All I could suggest is buy several with return possibility, audition them all, pick your favorite...if you can narrow it down to one.  Personally, I've heard a few very nice tube amps, but never one that offered any advantage over a good SS amp, and what qualities it had, for better or worse, could be obtained better in other ways.  
 
Oh, and BTW, my name is not Hideeho. 

 

[waflet]

  I doubt you'll get any useful help.  You're asking for a recommendation that satisfies your current personal preferences.  We don't know them, and they will change.  Research has shown a strong preference for uncolored, neutral sound across a wide population segment.  
 
You're also into this for the entertainment value of the hardware.  Well, someone might help you there, but their opinion now mesh with yours.  And now you want to go tube rolling?  Our goals are SO different.  I want the best, most accurate, undistorted sound possible. You're asking for something completely different and out of my world.  Probably most other in Sound Science.
 
You already have the technical and performance differences between general topologies.  Other than that, it's all biases and opinions.  All I could suggest is buy several with return possibility, audition them all, pick your favorite...if you can narrow it down to one.  Personally, I've heard a few very nice tube amps, but never one that offered any advantage over a good SS amp, and what qualities it had, for better or worse, could be obtained better in other ways.  
 
Oh, and BTW, my name is not Hideeho. 

Hideeho
My apologies, I left out a very important word in my last post. It should have read "My op was NOT meant to be a debate on what amp I need to buy...". That changes the whole sentence completely. My mistake, sorry.
 
Yes, Pinnahertz, I know your name, hideeho is my greeting. Like hello, or hi, or hideeho neighbor (although I was saw it LONG before Tim Allen had a show).

 

[pinnahertz]

 
Hideeho
My apologies, I left out a very important word in my last post. It should have read "My op was NOT meant to be a debate on what amp I need to buy...". That changes the whole sentence completely. My mistake, sorry.
 
Yes, Pinnahertz, I know your name, hideeho is my greeting. Like hello, or hi, or hideeho neighbor (although I was saw it LONG before Tim Allen had a show).

Doesn't change your position or mine.  

I had to stop re-greeting people every time I had something to say in a conversation because I got too many odd looks.