[eric343]

D'oh, I guess I should have been more clear. I'm talking about the OUTPUT section...

AFAIK the input and voltage gain stages are exactly the same for the line-out and headphone section; however the output (current) gain sections are quite different. To quote Carlos, who's done some VERY extensive modding of his Melos and has a schematic of the Melos... :
(emphasis added) Quote:

there's been some speculation that the headphone amplification and the preamp amplification stages are the same on the amp. they're not. the four yellow topped caps in the rear are the output caps off the preamp, basically everything north of the top ground trace is preamp stuff. the headphone stage is a fet connected to another fet emitter to gate (the name of which escapes me at the moment).

 

[markl]

eric,
I wish that meant more to me! I'd really love to understand this stuff better. In another life...

But, if I read it correctly, the "pre-amp" section is the same whther the signal is passed out through the pre-outs, or handed off to the headphone jack-- it's the actual headphone "amp" section that is additional through the headphone section. So, there's an extra "stage" the signal passes through when the headphone jack is activated. Is that approx. right?

If so, that essentially verifies what I've been saying. If you have a $1K "pre-amp" section connected to a typical receiver's $30 head "amp" section, how can you gaurantee you're better off with a $30 dollar "pre-amp" section and a $200 head "amp" stage in some of the lower cost amps?

My point, which I know I'm not articulating clearly is that maybe we are wrong to advise folks with expensive pre-amps/HT amps that have above average "pre-amp" sections and (possibly) below average "head amp" sections to buy a cheapie dedicated headamp? Yes, the actual "amp" section may be better than what you have, but the "pre-amp" part can be vastly inferior. Am I making any sense?

Mark

 

[eric343]

Quote:

Originally posted by markl eric, I wish that meant more to me! I'd really love to understand this stuff better. In another life... But, if I read it correctly, the "pre-amp" section is the same whther the signal is passed out through the pre-outs, or handed off to the headphone jack-- it's the actual headphone "amp" section that is additional through the headphone section. So, there's an extra "stage" the signal passes through when the headphone jack is activated. Is that approx. right?

Yep.

Quote:

If so, that essentially verifies what I've been saying. If you have a $1K "pre-amp" section connected to a typical receiver's $30 head "amp" section, how can you gaurantee you're better off with a $30 dollar "pre-amp" section and a $200 head "amp" stage in some of the lower cost amps?

I don't get it. How can we guarantee we're better off with both a $30 pre-amp headphone section and a $200 headphone-amp section?

Quote:

My point, which I know I'm not articulating clearly is that maybe we are wrong to advise folks with expensive pre-amps/HT amps that have above average "pre-amp" sections and (possibly) below average "head amp" sections to buy a cheapie dedicated headamp?

I don't quite follow, either. Where has anyone with a pricey preamp ever been advised to get a Total Airhead or whatever? Generally they're the types for Supremes/Cosmics/MOH(R)/Max/Maxed Out META42/Sugden HM/Melos/RKV/Whatever.

Quote:

Yes, the actual "amp" section may be better than what you have, but the "pre-amp" part can be vastly inferior. Am I making any sense? Mark [/B]

Not really...

 

[markl]

Quote:

I don't quite follow, either. Where has anyone with a pricey preamp ever been advised to get a Total Airhead or whatever? Generally they're the types for Supremes/Cosmics/MOH(R)/Max/Maxed Out META42/Sugden HM/Melos/RKV/Whatever.

I think this happens all the time. We never bother to ask if they already have a decent pre-amp or a better quality HT receiver and go straight to recommending a head amp for them. I'm saying this may not be appropriate unless they're willing to spend as much on a head-amp as they did on their existing pre-amp, HT receiver with headphone jack.

Quote:

I don't get it. How can we guarantee we're better off with both a $30 pre-amp headphone section and a $200 headphone-amp section?

This is what I'm saying. My hypothesis is that a "typical" head-amp may, in many cases, have a weaker and less robust, and lower-quality "pre-amp" section than what you already have, although the actual "head amplifier" section in your "typical" head amp may be better than that in the typical HT receiver/pre-amp.

So, in order to gain a better "amplifier" section for your headphones, you are foregoing a much better "pre-amp" section. How do we know which section has more impact on the sound? I'd be willing to bet it's the pre-amp section, but of course, I'm just speculating as a layman.

Mark

 

[eric343]

Well, the thing is, a headphone amp's preamp section consits of the volume control.

That's it.

You want to hook a headphone amp up to the output section of your preamp, just take out the volume pot.

 

[puppyslugg]

If a pre-amp/int. amp. has a dedicated hp amp, the signal to hp amp should originate from the source selector(tape loop). And not from the pre-amp out. That is the cleanest path to the hp amp.

To hook-up an external hp amp, I would use the tape loop; no pre-amp output stage involved. Just source to hp amp. By-passing the entire output stage. Can't get much cleaner than that.

 

[tangent]

A headphone amp is in that blur of the line between a preamp and a power amp. Like a preamp, it deals with relatively low voltages, and it usually has very little overall gain after accounting for the volume control. Like a power amp, it's designed to drive difficult loads: relatively low impedance that varies with frequency.

You can have a preamp that makes a poor headphone amp, usually because it works well only into a high impedance load.

Likewise, a headphone amp might make a poor preamp. If it has no source switching, it's going to be of limited use. Or, it might rely on having to drive a low impedance load, because this brings up the current output requirements, which may make the output section components sound better. I know this is true with transistors, at least -- the harder they're working, the more linear they become.

As for the price issue, there are a number of things that can bring up the cost of a preamp: source switching components, lots of input and loopthrough jacks, a large enclosure, a phono section, a dedicated headphone amp section... A headphone amp doesn't really reqiure any of this, especially since you can always hook a heaphone amp to a preamp to get these features if you want them. A good preamp may cost $1000, but that doesn't mean that a headphone amp under $1000 isn't any good. It may mean that it won't be able to
act as a good preamp, though.

 

[daycart1]

So Markl, are you wondering whether those with nice preamps (lacking a headphone jack) should get an ASL UHC, or DIY the impedence adjustment, or????

 

[KShaft]

my cary sei 300 sure doesnt cut it let me tell ya!!!

BWUAHAHAHAHAHAHAH!!!

 

[acs236]

Quote:

Originally posted by markl I'm saying that when you look at what a head-amp has to do to the audio signal vs. what a pre-amp has to do with the signal, it's virtually if not entirely identical. Maybe a better analogy, which actually strengthens my argument, is that a head-amp is functionally equivalent to an "integrated amp" in the speaker world. It provides gain and the ability to amplify the signal. Some people have expensive integrateds or HT amps yet are encouraged to buy Total Airheads and such for their headphones. I question whether they really get any benefit. Perhaps the TA or a mini-META or Penguin or whatever can produce more power than the standard HT receiver jack, but isn't that counterbalanced by the superiority of the "pre-amp" portion of the HT reveiver? Mark

An intergrated amp is merely a pre-amp and an amplifier in one box -- if you were to add a tuner, you could call it a receiver -- so it would seem obvious that the a headphone amplifier is essentially an integrated amp. Both take a source signal and prepare it for listening whether it be through headphones or speakers. I guess I'm missing the point of your analogy. Please help me out.

 

[Budgie]

It varies with the equipment- some recievers or integrated amps have an opamp to drive the headphones, some just have a resistor to current limit, some even have an opamp with a current limit resistor on it's output.
Some preamps can output enough current to drive a headphone directly, some won't. You need to consider the efficency and impedence of the phones too. There are no hard and fast generalities that will apply.

 

[markl]

"It varies with the equipment- some recievers or integrated amps have an opamp to drive the headphones, some just have a resistor to current limit, some even have an opamp with a current limit resistor on it's output.
Some preamps can output enough current to drive a headphone directly, some won't. You need to consider the efficency and impedence of the phones too. There are no hard and fast generalities that will apply."

I don't know how to make it any more clear.

You've essentially repeated what I just said.

I'll try one last time-- in the thread I linked to earlier in this discussion, my topic was "A headamp is nothing but a limited function pre-amp. Discuss" Maybe a better way to put it is "A headamp is nothing but a limited function integrated amp".

But that's not really a fair analogy either, because an integrated for speakers is going to have huge torroids and all kinds of other expensive parts to provide the amplification, whereas a pre-amp is more in line with a head-amp on a part for part basis. In other words, I don't need 150 Krell-sized watts to power my Senn HD600.

Anyway, as an example, the headphone jack on my Denon 5800 HT receiver (a $3.5 K behemoth) is probably going to be (and in fact IS) a lot better than the "typical" $300 headamp. Why? because the "pre-amp" section of the Denon is top-notch. Yes, the "amp" part of the Denon's headamp may not be as beefy as that on the $300 headamp (although I can't verify that either), but its "pre-amp" section is vastly better (this has been noted by measurements and by using the Denon as a pre/pro on a more expensive amp), more than cancelling out the $300 headamp's advantage in that area.

So, I'm saying we may be recomending "cheap" headamps to people who would be better served by simply plugging their phones into their existing halfway-decent integrated amp and/or HT receiver. Maybe there is more here we need to know before we can help choose an appropriate headamp for a given person.

Mark

 

[carlo]

hey, just wanted to clarify this part:
Quote:

But, if I read it correctly, the "pre-amp" section is the same whther the signal is passed out through the pre-outs, or handed off to the headphone jack-- it's the actual headphone "amp" section that is additional through the headphone section. So, there's an extra "stage" the signal passes through when the headphone jack is activated. Is that approx. right? -markl, re: melos

mark, as far as your melos is concerned input stage (which includes the tubes) is the same for both headphone and preamp outputs. the headphone out doesn't pass through "an extra stage", its a completely different stage.

think of it this way: the signal goes through the tubes then goes to two different places - preamp output and headphone output. they're seperate (one isn't after the other, the only thing they share, besides the power supply, is the input stage).

to put it yet another way: changing the headphone output stage does nothing for the preamp, changing the preamp output stage doesn't do anything for the headphone output. changing the input stage affects both.

best,
carlo.

 

[Budgie]

"I don't know how to make it any more clear. You've essentially repeated what I just said."

I did?

My bad, then.

 

[markl]

I give up!

I know what I mean at least...

Mark