Direct Path on Test

[Mackie 0]

Voltage = Current x Resistance. I reckon Fish meant the signal out of XLR output carries higher voltage and current than RCA ones.

[fishball79 0]

Isn't Watt = Voltage x Current?

 

Higher the voltage rating, the more current there is on tap as with a pot between the cans and cd player output, voltage is reduced.

Edited September 2, 2003 by fishball79

[Rameish 0]

So Mackie, what you're saying is the XLR output on CDP equipped with them should output both higher volatge AND higher current right?

 

 

 

[Mackie 0]

Roger that Rameish.

[fishball79 0]

XLR standard is 4.5v if i remember...

[Rameish 0]

Hmm..will try with Lengcm's 1.1

[lengcm 0]

Hmm..will try with Lengcm's 1.1

You sure you want to? It does not have BG in it....

[eccentric 0]

Rameish,

Voltage doesnt equal current

Current is the measure of amps which = 1 coulomb per second

Voltage is the measure of volts which = 1 joule per coulomb

Just some basic physics.. Power(watts) = amps x voltage

Hope that answered ur question in more detail =)

Edited September 2, 2003 by eccentric

[eccentric 0]

Voltage = Current x Resistance. I reckon Fish meant the signal out of XLR output carries higher voltage and current than RCA ones.

Resistance (ohms) = Voltage / Current

[jtfoo 0]

higher voltage doesn't guarantee the required current. Most opamps aren't high in current output.

Higher voltage means higher voltage swing which mean potentially the driver in the headphone could move further, hence louder. But to move the drivers further, esp at low frquency, the load could be high i.e. impedance would dropped thus require more current. This more current will be limited by the spec of the opamps CD player using.

Edited September 2, 2003 by jtfoo

[Rameish 0]

hello eccentric,

 

Nice to hear from you ;-).

 

I know current isn't equal to voltage hence it was my question to Fish. However it has been clarified by both Mackie and Fish that it was in reference to the XLR output of CDP that have both higher voltage and current.

[Firefox 0]

The only viable candidate i know of was my old Denon as it uses 2 opamps per channel for buffering. I was reccomended by a friend who owned the same player to use a passive pre you see...

 

So basically only cdplayers that output MORE than the standard 2v got chance...

The Rotel does use 2 opamps per channel. Each channel uses a DUAL OPAMP IC. Some units go overkill. Like my NAD. It has a Dual OPAMP for each channel which is further buffered with JFETS.

[eccentric 0]

hello eccentric,

 

Nice to hear from you ;-).

 

I know current isn't equal to voltage hence it was my question to Fish. However it has been clarified by both Mackie and Fish that it was in reference to the XLR output of CDP that have both higher voltage and current.

I know.. just trying to provide more detail on the technical side

[fishball79 0]

Mmm everybody learns

 

Sounds like no passive pot for cans...

[JaZZ 0]

Yeah, what went wrong...?

 

First of all: rule number one has been disregarded: choose a DAC/CDP line out with a low output impedance! I think 100 ohm should be seen as an upper limit - the more so as the indispensable passive attenuator will add even more resistance. As already mentioned in an earlier thread below, it looks like the majority of common players have line-out impedances of 200 ohm and above. Don't waste your time which such players! They're not suitable for direct-path purposes.

 

Rameish, you have tried several different op amps with the Rotel player. How is the output impedance with them? The 600 ohm you first mentioned is way too much! Imagine the drastically reduced damping factor and its impact on the frequency response, in the form of a huge hump around the resonance frequency - even more so with 32-ohm headphones! Hence your «muffled sound». You didn't mention the attenuator, but it looks like you were using a potentiometer. With which value? It's very important for the resulting sound. 500 ohm has turned out to be ideal, 1000 ohm will work too, but sounds slightly more «muffled». I even wonder if you had to attenuate the signal at all when I think of the high output impedance...

 

A scientific, systematic approach for this «test» would have been to choose an appropriate source which fulfills the main criterion instead of a random player which turns out to be unsuitable. Furthermore, to evaluate the accuracy of the direct-path sound merely based on personal esthetic measures doesn't make sense. My goal was to detect the impact from the low and complex load represented by a headphone on the output signal (because - as you stated - it is in fact «not designed» to drive other loads than amp inputs), and with my corresponding test configuration and my equipment I came to the result that it hadn't any, so the direct path could be seen as a virtually perfect signal transfer from the source to the headphones' voice coils with no perceivable sound alteration - as would happen with additional electronics in the signal path.

 

It wasn't my main intention to achieve a better sound; I just wanted to know how the source signal really sounds, in the awareness of the unignorable sound alterations caused by all amps. In your case it seems logical that what you get has little in common with the original source sound and at the same time lacks a lot with esthetics. My experience is that in terms of esthetics the direct path has no advantage over the classic amplifier-based operation. I have described this in the earlier thread. The reason isn't clear, but what's clear is that amps add some convenient euphonic colors to the sound - and thus may mask some deficits with the source signal (keyword «digital artifacts»).

 

You may be tempted to jump on the conservative bandwagon and simply state: «Line-out amps are not designed to drive headphones.» This doesn't prove anything. But you can test the impact of a headphone as a load on its signal accuracy (like I've already described earlier): Listen to some music through a headphone amp. Then switch an additional headphone in parallel to the amp's input (thus to the source) and try to detect if this makes a difference to the sound. I bet it doesn't. So the only remaining criterion is: to what extent does the serial resistance (output impedance and attenuator) between source and headphone affect the signal? If you use a source with very low output impedance and a 500-ohm potentiometer, the average effective serial resistance will be in the same range as OTL tube amps - thus absolutely practicable.

 

Just look at the thousands of people who have their headphones plugged into their soundcards' line outs! This works really fine if your soundcard doesn't have a dedicated headphone jack, and in most cases it even sounds better - and even louder! - than the headphone output. Obviously line outs of soundcards usually have low output impedances. The great advantage here: you don't need a passive attenuator, the computer software will do it. Or there's a guy on Head-Fi called aos. He builds portable DACs with a built-in headphone amp - which in fact is a line-out stage! Who says line-out amps can't drive low impedances! This may apply to some of them because of current supply limitations, but the main criterion seems to be their output impedance.

 

Well, strictly speaking the term «direct path» isn't really accurate, I agree. There can be no direct path at all in sound reproduction; the whole signal chain consists of dozens of processes, from the microphone over the mixing console to the A/D converter... etc. I use it in the sense of «as direct as possible». And there are indeed some superfluous stages: the preamp is by nature completely senseless for normal line-level sources, except for some critical cases (long cables, capacitance issues...). The headphone amp can be renounced if the source's line-out amp has a low enough output impedance and is capable to supply the relatively high currents needed for headphones. An additional amplification stage would inevitably make the sound less accurate.

 

This is the theoretical basis. Nevertheless your ears may tell you that the additional amplification stage makes the sound more beautiful and musical anyway. After all that's what counts and the reason why I mostly use an amp, too.

 

BTW: The usual 2 volt of a CDP is more than enough to drive both power amps and headphones.