Speaker amps for headphones - Page 3

Prego!  Buona fortuna per ottenere un suono eccellente. La musica e' il vero obiettivo.

(So folks don't get offended and inform me that his is an English speaking forum: You are welcome, Good luck obtaining good sound.  Music is the true goal.)

I think this is so often forgotten in high end audio.  I have the impression that Head-Fiers are more into the music.  Certainly more people mention the music than traditional 2 channel high enders.     

I am assuming you are unhooking your speakers...otherwise you would be listening to the speakers and headphones at the same time.

So, if the speakers are unhooked and the amp is just playing the cans through the Headtap, you are using the device in a way it is not intended.  There is no parallel resistor across the amp leads so the amp will be playing into a high impedance load.  A apeaker amp is not intended to do this so results will vary and potential for oscillation will vary.  

This device uses the monitor speakers as the lower impedance load the amp would like to see, and you are just tapping off to play your headpones: the load on the amp would remain  nearly identical to what it was, it would not know there was a high impedance load tapped off.  

The more I think about it, some good thinking went into the volatage divider that Calibro linked.  This divider, through manipulation of the resistor values, would allow the amp to see a low impedance, the headpone see a higher impedance, with the desired attenuation achieved by changing the second parallel resistor.  The advantage over my setup would be that I could get my attenuation without having the headphones looking back at such a high impedance.  That may result in better sound, it may not.  But it offers the advantage of knowing.  

A simpler way of saying it is that with the linked voltage divider 3 variables can be set at any value one wants: load impedance on the amp, source impedance the cans see, and attenuation. 

I do not agree with his stated resistive choices as he has the amp looking at a higher than typical load impedance and the cans looking at a lower than typical source impedance.  However, the concept is nice and one can just choose different values to make the amp and cans happy.    

Despite above concerns by other posters, the cans are safe as I am using the same volume settings as with my speakers due to the parallel and series resistance network I am using for the cans.

As for the damping factor, this is a bit overblown and misunderstood.  The q of the speakes and entire system ties together with the damping factor to make damping factor alone an unpredictable thing.  For instance, I have heard a high impedance amp with low impredance speaker (damping factor = 2) have phenomenal dynamics in the bass while a very low output impedance ss amp with the same speakers be a sound soft and flat in dynamics in the bass.  It really depends on the driver, what it wants to see from the amp, and the amp and what it wants to see in the driver, and damping factor is one small thing.  Certainly this combination using the big speaker amp is so dynamic and tight on impactful bass that it puts the highly regarded headphone amps to shame in this regard.   High end 2 channel audio went through this same thing with damping factors and slew rates, finally it all fell away as it never really predicted the sonic aspects it was supposed to.

Regarding the Stax SRD-7 that a prior poster asked about, you need to do nothing when using on a speaker amp.  It is made for speaker amps.  

In the near future I'll take some input transformer impedance readings with an impedance bridge, we'll see what AC impedance load it is.      

Quote:

Originally Posted by Argybargy 

Interesting topic.

I'm thinking of building a Millet DCPP Engineers Tube Amp which is a 18 wpc into 8 ohm speaker amp (transformer coupled output).

Output impedance is about 2.5 ohms.

I want to use the following 4 different headphones with this:

Denon D7000 25 ohm 108dB sensitivity

Audio Technica ATH w3000anv 40 ohm 102dB sensitivity

Audeze LCD2 50 ohm 91dB sensitivity

Hifiman HE500 45 ohm 89dB sensitivity
 

1) Would I need to set up some kind of "impedance switch" that switches between various resistors?

2) Or would an "averaged" value single resistor work?

3) Or should I set one resistor value for the most sensitive headphones that are most likely to pick up background hiss/noise and just use more volume pot movement for the other headphones?

You may not need any parallel resistor at the amp terminals as these are all relatively low impedance headphones.  With the lower sensitivity headphones you would be throwing a lot of energy away through a parallel resistor.

However, that is a wide range in sensitivities.  Especially for those real efficient cans you may need a series resistor at the amp, a parallel resistor after that, and another series resistor before the headphones, like that voltage divider circuit a prior poster gave a link to.  I'd be careful with those 102 and especially 108db cans, not to blow them up with a speaker amp.  I personally would not be hooking them up without resistive loading.