Low output impedence headphone amps - Page 2

I'm OK disagreeing with him. 

I would disagree that the o2 will sound very good with all headphones. For sure it has very low distortion, low noise, and supplies a reasonably high amount of voltage and current for a portable amp. But it ignores the output impedance for headphones that prefer a high output impedance entirely. 

It should be noted that the O2 has pads to add an output resistor. It is a good fail-safe if the amps mysteriously oscillate once released into the wild (I'm not aware of any going wrong, but not really following the thread) or habitually blow output op-amps but it does offer builders/listeners some options. It would not be too hard to have added a switched resistor (like XIN used to do, and Meier does with the 2 jacks) to the amp. 

Regarding the DT880:

I'm fairly sure it is just the output impedance that was caused the change in the DT880's. Tested with an SS amp and a resistor cable so distortion should not have been significantly different from one to the other. I did volume match, but did not DBT. If its any consolation to not DBTing them, I expected it to suck with the 120 ohm cable. 

Quote:

Originally Posted by nikongod 

 

If the headphones were designed around a high output impedance they may sound pretty bad from a 0ohm output. Beyer DT880 springs to mind as the best example - with harsh and grating highs when run from an amp with a 0ohm output impedance, but they calm down and really sound quite nice driven from 120. 

 

Thanks.  I get your meaning now.
 

Quote:

Originally Posted by FSonicSmith 

 

 

I may have to re-read NWAVguy's blog, but I think this is one area where you and he apparently disagree. I believe his engineering viewpoint is that a well designed amp with between 0 and 3 ohm of output impedance can sound optimum with all headphones regardless of impedance. His "02" amp apparently is designed to sound very good with all phones (other than true statics) and from the feedback so far, he has not been proven wrong.  Are you sure there is not some other aspect of the Beyer DT880s that accounts for them sounding harsh in the higher frequencies other than it's high impedance?

It's largely a matter of perspective:  If certain headphones don't pair well with a neutral, low output impedance amp, I think NwAvGuy would point out that it's not the amp's fault.  I would agree here, since designing around such an amp is really the only way to get a stable reference point for headphone performance:  The concept of amp neutrality is objectively well-defined, but coloration spans a huge multidimensional spectrum.  Similarly, 0 ohm output impedance is well-defined, whereas banking on pretty much any other output impedance is totally arbitrary.  For the sake of standardization and keeping consumers from going crazy and broke, headphone designers should really be designing around 0 ohm output impedance amps.  If certain headphones are depending on a high output impedance amp to roll off certain frequencies that the headphones go overboard on, I'd personally consider that a design flaw in the headphones.

In a perfect world, all headphones would be designed around neutral, low output impedance amps, but this is the real world...and sometimes maybe they aren't.  Even if they are, headphones are impossible to make perfect with our current technology, so even some headphones technically designed around low output impedance amps might have flaws that some higher output impedance amps could alleviate by happenstance.  (Or maybe you just prefer muddy bass? )  At that point, you pretty much have to search for a Goldilocks zone...but what if a particular amp DOES compensate perfectly for a headphone's flaws?  In that case, the amp and headphone combination becomes much more than the sum of its parts.  Independently, I'd consider both flawed...but together, they could be a perfectly viable or formidable choice for great audio.

Ultimately, no amp will be the best choice for all headphones.  However, I think a powerful, objectively well-measuring, neutral, low output impedance amp is inherently more versatile than colored amps:  It may not compensate for any sonic flaws in the headphones, but it also won't introduce any of its own that will exacerbate them or otherwise make things worse.  Neutral amps may not sound great with ALL headphones, and saying they do would be an overstatement...but they're a good middle ground between warm and bright, and they're really the only stationary targets for designing headphones around.  The same applies to low output impedance, since the effect of high output impedance is an arbitrary sort of frequency response rolloff, which would count as a source of coloration.

That's a big reason why I went for the O2:  I'll just restrict my headphone purchases to the ones that work well with it, which means "no stats, K1000's, Sextets, or headphones that need extra coloration to sound good."  The last part means I'm sacrificing a few opportunities in favor of simplicity:  No headphones are perfect, and there may be a particular amp that matches a particular pair of headphones better than the O2 will ever match anything.  For instance, the FA-002W High Editions can be really great headphones according to LFF, but they're picky about amps, and the O2 (and presumably any other neutral amp) doesn't make the cut.  Nevertheless, I want the versatility to try (and judge) a bunch of cans without worrying about amp coloration as a variable or trying n*m combinations of headphones and amps, so the O2 is perfect for me.  I'd recommend it (or another inexpensive and neutral amp, such as The Wire) to anyone in the same boat.  If I need to tweak, I'll go for an EQ or DSP.  (It is interesting though that you could add a switched output resistor to it.  That would definitely increase the versatility aspect further.)

However, if you're set on a particular flagship headphone, you may get more mileage finding the perfect amp for that particular headphone model.  If you're a serious headphone hobbyist (deep pockets ), you may get more mileage just playing with amp options too.

Quote:

Originally Posted by nikongod

 

 

The problem with orthos is not getting output impedance "right" (by whichever definition you choose). Most orthodynamic

Look for something that can put at least 3W into 8ohms. More if you listen loud. Dont worry about output impedance. There are a few headphone amps that can do it, but mneh. I would lean towards small high quality speaker amps rather than sticking with headphone amps. older low-power krell amps, Nelson Pass/firstwatt amps, small tube amps (the leben), etc. 

I would argue that if you want to drive orthos (which are low impedance phones) then you need to drive them with a low impedance amp.

Quote:

Originally Posted by Rawrbington 

help me out here, im still learning.

i have recently sat down with a pair of 32 ohm beyers and 600 ohm beyers and played both side by side out of a head amp with an output impedance of approx. 100 ohms.

the 600 ohm sounded incredible, while the 32 ohm sounded bad and poorly controlled. 

what else would cause such a stark difference in control and sound?  im not highly educated in this area.

 

 

does this mean my Woo with high output impedance could possibly power the LCD2?

 

I would assume that the low impedance Beyers didn't like the high output impedance amp because of the almost non-existent damping factor in the combination. You said they sounded poorly controlled.

It is also possible that the high impedance amp couldn't output enough current to drive the Beyers, hard to say man, you didn't say what amp you're using.

If the Woo doesn't have enough jam to drive the Beyers, it cetainly won't drive the LSD-2, assuming the high impedance amp is the Woo?
 

Quote:

Originally Posted by SobbingWallet 

Could you explain what you mean by this?  Other than noise/hiss (due to poor design), is there a reason why a 0 ohm output impedance amp would color the signal with any headphones, on account of its low output impedance alone?  Or are you just referring to the "synergy" problem of liking/disliking the total combined frequency response coloration of amp + headphones?

 

A 0 ohm output impedance amp cannot colour the sound due to it's impedance. It would have to be something else in the design.

Which is why zero impedance (or pretty damn close to zero) is such a nice feature, you don't hvae to worry about it!
 

BTW..........SobbingWallet!   That name cracks me up!

Quote:

Originally Posted by SobbingWallet 

 

It's largely a matter of perspective:  If certain headphones don't pair well with a neutral, low output impedance amp, I think NwAvGuy would point out that it's not the amp's fault.  I would agree here, since designing around such an amp is really the only way to get a stable reference point for headphone performance:  The concept of amp neutrality is objectively well-defined, but coloration spans a huge multidimensional spectrum.  Similarly, 0 ohm output impedance is well-defined, whereas banking on pretty much any other output impedance is totally arbitrary.  For the sake of standardization and keeping consumers from going crazy and broke, headphone designers should really be designing around 0 ohm output impedance amps.  If certain headphones are depending on a high output impedance amp to roll off certain frequencies that the headphones go overboard on, I'd personally consider that a design flaw in the headphones.

 

In a perfect world, all headphones would be designed around neutral, low output impedance amps, but this is the real world...and sometimes maybe they aren't.  Even if they are, headphones are impossible to make perfect with our current technology, so even some headphones technically designed around low output impedance amps might have flaws that some higher output impedance amps could alleviate by happenstance.  (Or maybe you just prefer muddy bass? )  At that point, you pretty much have to search for a Goldilocks zone...but what if a particular amp DOES compensate perfectly for a headphone's flaws?  In that case, the amp and headphone combination becomes much more than the sum of its parts.  Independently, I'd consider both flawed...but together, they could be a perfectly viable or formidable choice for great audio.

 

Ultimately, no amp will be the best choice for all headphones.  However, I think a powerful, objectively well-measuring, neutral, low output impedance amp is inherently more versatile than colored amps:  It may not compensate for any sonic flaws in the headphones, but it also won't introduce any of its own that will exacerbate them or otherwise make things worse.  Neutral amps may not sound great with ALL headphones, and saying they do would be an overstatement...but they're a good middle ground between warm and bright, and they're really the only stationary targets for designing headphones around.  The same applies to low output impedance, since the effect of high output impedance is an arbitrary sort of frequency response rolloff, which would count as a source of coloration.

 

No headphones are perfect, and there may be a particular amp that matches a particular pair of headphones better than the O2 will ever match anything. Nevertheless, I want the versatility to try (and judge) a bunch of cans without worrying about amp coloration as a variable or trying n*m combinations of headphones and amps, so the O2 is perfect for me. If I need to tweak, I'll go for an EQ or DSP.  (It is interesting though that you could add a switched output resistor to it.  That would definitely increase the versatility aspect further.)

 

However, if you're set on a particular flagship headphone, you may get more mileage finding the perfect amp for that particular headphone model.  If you're a serious headphone hobbyist (deep pockets ), you may get more mileage just playing with amp options too.

I would say I agree with all that! Especially the part about a low output impedance head amp being a stable reference.

Having said all that, I really dig tube amps, with transformers and OTLs.

And now I have to go, Big Bang Theory is on the box tonight.........followed by Whitney.........then Person Of Interest.

BTW, how soon is Sheldon's sister going to be back on the show?

no amp:

http://www.head-fi.org/t/553094/continued-sidetrack-discussion-from-tiniest-portable-amp-i-can-build-nikongod-microtransformer-based-impedance-step-down-box

Its quite nice, and for $20 you could do much worse for IEMs, particularly ones that normally hisssss. 

Expanded to a size suitable for real headphones:

http://www.head-fi.org/t/85561/post-pics-of-your-builds/7350#post_6995689

excellent points nikongod.  
 

Quote:

Originally Posted by FSonicSmith 

 

 

I may have to re-read NWAVguy's blog, but I think this is one area where you and he apparently disagree. I believe his engineering viewpoint is that a well designed amp with between 0 and 3 ohm of output impedance can sound optimum with all headphones regardless of impedance. His "02" amp apparently is designed to sound very good with all phones (other than true statics) and from the feedback so far, he has not been proven wrong.  Are you sure there is not some other aspect of the Beyer DT880s that accounts for them sounding harsh in the higher frequencies other than it's high impedance?

well...when fronted by my Benchmark DAC1, the O2 can be a painfully harsh/bright experience when driving any of my AKGs.  if i were going to keep the O2, i would socket the output resistors and play around will the dampening factor.  with the DT990/600ohm i used to own, i had good results with increasing the amplifier's output impedance helping reducing the brightness.  if running the DT990, the O2 would would need the same treatment to be be tolerable...subjectively of course. 

Quote:

Originally Posted by FSonicSmith 

 

 

I may have to re-read NWAVguy's blog, but I think this is one area where you and he apparently disagree. I believe his engineering viewpoint is that a well designed amp with between 0 and 3 ohm of output impedance can sound optimum with all headphones regardless of impedance. His "02" amp apparently is designed to sound very good with all phones (other than true statics) and from the feedback so far, he has not been proven wrong.  Are you sure there is not some other aspect of the Beyer DT880s that accounts for them sounding harsh in the higher frequencies other than it's high impedance?

You can design a headphone to sound neutral driven by 0 ohm or 120 ohm or any other output impedance. It's designing the system as a whole and not individual components. Unfortunately headphone manufacturers don't normally specify which output impedance they designed in mind. Beyerdynamic's A1 amplifier has 100 ohm output impedance. Some Meier Audio amps have two sets of outputs: 0 ohm and 120 ohm.

You can also design a tube amp to have 0 or even negative output impedance through the use of feedback. With an output transformer and without using feedback you can create a tube amp with very low, around 2 ohm output impedance. It depends on the tube's plate impedance, transformer turns ratio and construction.

Quote:

Originally Posted by fishski13 

excellent points nikongod.  
 

 

well...when fronted by my Benchmark DAC1, the O2 can be a painfully harsh/bright experience when driving any of my AKGs.  if i were going to keep the O2, i would socket the output resistors and play around will the dampening factor.  with the DT990/600ohm i used to own, i had good results with increasing the amplifier's output impedance helping reducing the brightness.  if running the DT990, the O2 would would need the same treatment to be be tolerable...subjectively of course. 

 

 

 

 

 

This might be good to mention in the O2 thread.  As far as subjective impressions of the O2 go, the most useful ones we can get are probably comments about how well it pairs with specific cans.

Quote:

Originally Posted by Donald North 

You can design a headphone to sound neutral driven by 0 ohm or 120 ohm or any other output impedance. It's designing the system as a whole and not individual components. Unfortunately headphone manufacturers don't normally specify which output impedance they designed in mind. Beyerdynamic's A1 amplifier has 100 ohm output impedance. Some Meier Audio amps have two sets of outputs: 0 ohm and 120 ohm.

 

You can also design a tube amp to have 0 or even negative output impedance through the use of feedback. With an output transformer and without using feedback you can create a tube amp with very low, around 2 ohm output impedance. It depends on the tube's plate impedance, transformer turns ratio and construction.

 

I would assume that Beyer has designed the A1 to work with their 600 ohm 'phones...................? I find it hard to believe that Beyer would design the A1 to be used with their 250 ohm versions.

I like Meier's idea: two different outputs, two different output impedances, so you are not locked into one impedance, if that floats your boat.

There is a guy who did a large comparison of the FIIO E9 with approx. 10 'phones in this web site, (I'm sure you have probably seen it) which has two different outputs of differing impedances, he does not prefer the high Z output.

You could design a tube amp to have very low output impedance by using lots of feedback, which implies a very complex tube circuit, which makes me think.......why?  One of the beauties of the tube circuit is you can (hypothetically) design a simple circuit which sounds very good. In addition, a lot of feedback would drive the second order harmonic distortion to the vanishing point, again, you would be losing the tube sound. May as well save your money and get an SS unit.

Very ironic: the tube amp should have (relatively) high output Z, the SS amp (relatively) low output Z.      But we have Beyer charging a lot of money for a high output impedance SS amp.

It is possible to design simple SS amps that sound quite nice. I built a 1-transistor/ch amp that is pretty pimp. Nelson pass first watt amps have very few parts. the problem with simple SS amps, as with simple tube amps, is that they dont look as good as SS or tube opamps on paper. This does not mean that they sound bad, indeed they can sound GREAT. 

Tubes with output transformers can have very low output impedance, even without global feedback. Keep trying. 

Could you link to the review of the E9?

Its not really ironic that Beyer did that to their amp. they wanted it to sound the best it could with their product. Although I have not measured, I would assume that the output impedance of the amp with their head tracking system is also 100ohms. They bundle their "head-tracking" amps with the DT880/250. Nope, nothing hard to believe at all. 

In my experience with my beyer DT990 from 1990, DT911, DT931, DT880/250 and listening to the DT880/600, they all sound better to me when powered by an amp with 100-120 ohm output impedance. When driven from low/zero output impedance they sound thin and lean in the bass and bright.

Regarding tube amps, when traditionally used with output transformers you can get very low output impedance (depending on tube parameters and output transformer turns ratio and construction) with simple circuits and without feedback. To get down into the 0-3 ohm range, you need to add feedback. This doesn't mean the circuit needs to be overly complex but does require at least an additional resistor from output to input.

Feedback-less tube amps can have low distortion - it's all in the execution.
 

Quote:

Originally Posted by Chris J 

I would assume that Beyer has designed the A1 to work with their 600 ohm 'phones...................? I find it hard to believe that Beyer would design the A1 to be used with their 250 ohm versions.

 

I like Meier's idea: two different outputs, two different output impedances, so you are not locked into one impedance, if that floats your boat.

 

There is a guy who did a large comparison of the FIIO E9 with approx. 10 'phones in this web site, (I'm sure you have probably seen it) which has two different outputs of differing impedances, he does not prefer the high Z output.

 

You could design a tube amp to have very low output impedance by using lots of feedback, which implies a very complex tube circuit, which makes me think.......why?  One of the beauties of the tube circuit is you can (hypothetically) design a simple circuit which sounds very good. In addition, a lot of feedback would drive the second order harmonic distortion to the vanishing point, again, you would be losing the tube sound. May as well save your money and get an SS unit.

 

Very ironic: the tube amp should have (relatively) high output Z, the SS amp (relatively) low output Z.      But we have Beyer charging a lot of money for a high output impedance SS amp.

Quote:

Originally Posted by nikongod 

It is possible to design simple SS amps that sound quite nice. I built a 1-transistor/ch amp that is pretty pimp. Nelson pass first watt amps have very few parts. the problem with simple SS amps, as with simple tube amps, is that they dont look as good as SS or tube opamps on paper. This does not mean that they sound bad, indeed they can sound GREAT. 

 

Tubes with output transformers can have very low output impedance, even without global feedback. Keep trying. 

 

Could you link to the review of the E9?

Yeah, I like Nelson Pass's work.

Surprising how simple his latest X series is.

As for the tube amps with output transformers with lo O/P Z I was only trying to say you can get it lower with more feedback..............

The E9 link:

authored by a guy named Gwarmi:

http://www.head-fi.org/t/582916/fiio-e9-the-big-users-guide-the-10-x-headphone-round-up-how-does-yours-stack-up-with-the-e9-pictures-inside

Quote:

Originally Posted by Donald North 

In my experience with my beyer DT990 from 1990, DT911, DT931, DT880/250 and listening to the DT880/600, they all sound better to me when powered by an amp with 100-120 ohm output impedance. When driven from low/zero output impedance they sound thin and lean in the bass and bright.

 

Regarding tube amps, when traditionally used with output transformers you can get very low output impedance (depending on tube parameters and output transformer turns ratio and construction) with simple circuits and without feedback. To get down into the 0-3 ohm range, you need to add feedback. This doesn't mean the circuit needs to be overly complex but does require at least an additional resistor from output to input.

 

Feedback-less tube amps can have low distortion - it's all in the execution.

I'm probably getting a pair of DT880/600 in a few days, it will be interesting hear how they sound with a Matrix M Stage and with a 336C.

My 336C makes my old archiac Senn HD 424 phones (2000 ohms) sound not too bad, who knows, maybe the tubes fatten up the thin sound.

Assuming closed loop remains the same, if you want more feedback, you need more open loop gain which usualy works out to more gain stages, hence more complexity.

I got this old tube phono pre-amp, only 2 triodes per channel, no feedback, 20 years later it still pushes the right buttons. The designer must have done something right

An interesting article on the effect of headphone output impedance on the apparent frequency response of a headphone:

http://www.soundandvisionmag.com/blog/2011/11/14/output-impedance-show-and-tell?page=0,0

Quote:

Originally Posted by Chris J 

An interesting article on the effect of headphone output impedance on the apparent frequency response of a headphone:

http://www.soundandvisionmag.com/blog/2011/11/14/output-impedance-show-and-tell?page=0,0

 

heyo! last week called, they want you to read that article. 

The frequency response of the Phonak Audéo PFE 232 is a pretty good example of where I would assume that a high output impedance amp would improve things. the spike at 8KHZ probably trumps the dip at 10Khz. 

Quote:

Originally Posted by Chris J 

An interesting article on the effect of headphone output impedance on the apparent frequency response of a headphone:

http://www.soundandvisionmag.com/blog/2011/11/14/output-impedance-show-and-tell?page=0,0

Thanks a million for this!  Saved to favorites.