[khaine1711]

Hello knowledgable head-fiers,
 
I have some questions about preamp that I hope can get answered.
 
As far as I understand; for speakers, power amps don't have a volume knob, so preamp is used for volume control (also preamp + power amp gives cleaner signal vs integrated I heard). However I know nothing about headphone preamp, so my questions are:
 
- In which case a preamp is necessary for a headphone chain?
- To my understanding, the preamp does color the sound; that's why people use tube preamp for their system, is that correct?
- I've seen that most headphone amp can be used as preamp, however the opposite isn't true; what's the (main) difference between a "dedicated preamp" and a "headphone amp as preamp"?
- How does a good headphone amp fare again a dedicated preamp in a speaker system?
 
I guess that's all for now 

 

[hodgjy]

I'd say you answered most of your own questions!
 
You don't really need a separate pre-amp for a headphone amp.  Some do add them to the chain, especially if they want to add a tube preamp to a solid state headphone amp.  I'd say the vast majority of headphone amps have volume controls, to no preamp is necessary.  They are only added to achieve the desired coloration.
 
As far as a "dedicated preamp" vs. a headphone amp with pre-outs, you can't generalize.  I'm sure some headphone amps with pre-outs are better than some dedicated preamps without headphone amplification.  You see some headphone amps with pre-outs because it simplifies setups for users wanting a premium headphone out in their 2.0 speaker system.  And, it doesn't take a whole lot to add into the headphone amplifier to install a pre-out.  It doesn't really degrade the sound, so the thought is "why not?"

 

[khaine1711]

Hmm maybe the question I really wanna ask is:
-How much does a tube headphone amp acting as preamp color the sound?
 
My guess is it would depends on the amp and circuit; however it'd be really helpful if someone can give me a glimpse of that.
 
Also hodgjy, I remember you have both the Asgard and Woo 3, this may sound silly but have you tried using the Woo 3 as a preamp for the asgard? If you did then how did it turn out?

 

[hodgjy]

I've actually never used my Woo 3 as a premap, which is unfortunate.  So, I cannot comment on how it colors the sound as it enters another amplifier.
 
However, I can speak of very basic generalities.  There is a little bit a of a misconception about tube headphone amps vs. tube power amps.  Many people equate tube with "warm, syrupy, and luscious."  This isn't always the case.  In fact, while this may be more commonplace in tube power amps, it is less common in tube headphone amps.  In fact, tube headphone amps are sometimes disappointing to the new owners of them expecting the warm and syrupy sound.  A well designed tube amp tends to be very clear and linear.  So, if tube headphone amps aren't always warm and syrupy, what's the appeal?  Many selling points.  For one, they tend to be more holographic and 3-D in their sound stage than their solid state counterparts.  Also, they really have a lot of power and have a lot more headroom to drive power-hungry and/or high impedance headphones.  They also tend to be more linear, give a little lushness in the mids, and can smooth some of the high frequencies out a little.
 
So, where am I going with this all?  As opposed to tube power amps driving speakers, tube headphone amps/pre-amps tend to sound less tubey.  They colorize the sound less.  Most of the time.  As with all gear, you can't make broad claims for all gear because there are always many exceptions.  But, people tend to pair tube pre-amps with solid state power amps to get more holographic sound staging and a touch of tube magic, but the effects are often far from overly warm and syrupy.
 

 

[mulveling]

For a "preamp" into a headphone amp:
There's no solid reasoning to ever feed one head-amp (or preamp) into another. That's called double-amping. You're summing up the gains and then throwing gobs of it away across the 2 volume controls, which has repercussions towards the noise floor. The last amp in the chain is still burdened with 100% of the hard job of driving the transducers; it gets no help from the "preamp" in this regard - unless you're gain starved, in which case you chose TWO wrong amps instead of a single appropriate amp. You're adding unnecessary coloration by adding a superfluous component. Solid-state devices color the sound too - it's just that with SS, you're usually stuck with what you get. In short, it's an incredibly inefficient and kludgy solution. If you want the optional to modify tonality, then get a well-designed tube amp with good tube rolling options. 
 
As far as using a headphone amp as a preamp:
Yes, the typical voltage amplification done by a headamp and preamp are very similar, and of course they share the requirement for a high quality volume control. Any well engineered/implemented headamp should be capable of serving as (at least) a decent preamp (given appropriate adapter cables). Where they differ is in their output impedances. Headamps are designed to drive much lower impedances (usually 32-600 ohms), which typically means that they won't degrade in performance when faced with a much higher impedance load - like those presented by a speaker amp's inputs (usually 10,000-500,000 ohms - higher impedances are easier to drive). The exception would be a transformer-coupled headamp, I believe, and other designs which are tuned to specific impedances (SRPP). On the flip side, preamps are designed for these much higher loads, and will degrade SIGNIFICANTLY (if not outright fall apart) when faced with even a 300 ohm load...so usually they suck as headphone amps.
 
Where this gets tricky is in the high-end. High end preamps can be absolutely wonderful in that application (obviously). High end headphone amps can still make great preamps, but won't quite hit that top level in a preamp application. The reason is that the requirement for a low output impedance becomes a liability at that level - the devices that they utilize to reach such a low impedance become a compromise and/or a liability in scenarios where they'll only ever face an easy load. Preamps don't need to provide such a low output impedance, and thus are free to utilize more transparent parts and designs that happen to yield higher output impedances.

 

[khaine1711]

I haven't try many tube headphone amp yet. However some tube power amp I've had the chance to listen to, they have something I'd call "ethereal"; sorta unique and I cant really describe them with my limited vocabulary. Oh well, guess I should start another thread looking for a warm and syrupy tube amp; since the solid state amp I've tried so far has solved the "neutrality" requirement for me.
Quote:

However, I can speak of very basic generalities.  There is a little bit a of a misconception about tube headphone amps vs. tube power amps.  Many people equate tube with "warm, syrupy, and luscious."  This isn't always the case.  In fact, while this may be more commonplace in tube power amps, it is less common in tube headphone amps.  In fact, tube headphone amps are sometimes disappointing to the new owners of them expecting the warm and syrupy sound.  A well designed tube amp tends to be very clear and linear.  So, if tube headphone amps aren't always warm and syrupy, what's the appeal?  Many selling points.  For one, they tend to be more holographic and 3-D in their sound stage than their solid state counterparts.  Also, they really have a lot of power and have a lot more headroom to drive power-hungry and/or high impedance headphones.  They also tend to be more linear, give a little lushness in the mids, and can smooth some of the high frequencies out a little.
 
 

Thanks for all the information. Many good points there. I didn't have the thought that preamp -> headamp will result in double amping; couple that with 2 cheap volume pot and SQ may suffer. Another question if you don't mind:
 
I see some Dac + amp combo having a switch they call "Variable" and "Fixed output". In short the fixed output disable the volume control on the unit. Is an dac/amp like that, running in fixed output mode, equivalent to a dedicated dac with no volume control? - in terms of double amping only.


Quote:

For a "preamp" into a headphone amp:
There's no solid reasoning to ever feed one head-amp (or preamp) into another. That's called double-amping. You're summing up the gains and then throwing gobs of it away across the 2 volume controls, which has repercussions towards the noise floor. The last amp in the chain is still burdened with 100% of the hard job of driving the transducers; it gets no help from the "preamp" in this regard - unless you're gain starved, in which case you chose TWO wrong amps instead of a single appropriate amp. You're adding unnecessary coloration by adding a superfluous component. Solid-state devices color the sound too - it's just that with SS, you're usually stuck with what you get. In short, it's an incredibly inefficient and kludgy solution. If you want the optional to modify tonality, then get a well-designed tube amp with good tube rolling options. 
 
As far as using a headphone amp as a preamp:
Yes, the typical voltage amplification done by a headamp and preamp are very similar, and of course they share the requirement for a high quality volume control. Any well engineered/implemented headamp should be capable of serving as (at least) a decent preamp (given appropriate adapter cables). Where they differ is in their output impedances. Headamps are designed to drive much lower impedances (usually 32-600 ohms), which typically means that they won't degrade in performance when faced with a much higher impedance load - like those presented by a speaker amp's inputs (usually 10,000-500,000 ohms - higher impedances are easier to drive). The exception would be a transformer-coupled headamp, I believe, and other designs which are tuned to specific impedances (SRPP). On the flip side, preamps are designed for these much higher loads, and will degrade SIGNIFICANTLY (if not outright fall apart) when faced with even a 300 ohm load...so usually they suck as headphone amps.
 
Where this gets tricky is in the high-end. High end preamps can be absolutely wonderful in that application (obviously). High end headphone amps can still make great preamps, but won't quite hit that top level in a preamp application. The reason is that the requirement for a low output impedance becomes a liability at that level - the devices that they utilize to reach such a low impedance become a compromise and/or a liability in scenarios where they'll only ever face an easy load. Preamps don't need to provide such a low output impedance, and thus are free to utilize more transparent parts and designs that happen to yield higher output impedances.