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Help needed with LD mkV and low impedance headphones

post #1 of 75
Thread Starter 

I just picked up a set of Beyer dt48 that are 25ohms. I think the LD mkV was designed for higher impedance headphones. I have a 300ohm impedance adapter a friend made for me. The dt48 definitely has better bass when I use the adapter as opposed to just plugging into the mkV. Does anyone know what the output impedance of the mkV is? My friend can change the values of the resisters in the adapter if necessary to get better synergy with the amp. Any advice would be much appreciated!

post #2 of 75
Thread Starter 

Anyone know the output impedance of this? I can't find the Little Dot website....if they even have one.

post #3 of 75

Regarding your preference of the 300ohm cable VS running the headphones straight off of the amp... I also prefer Beyer headphones when driven from a high output impedance source (what you are doing). 

 

If you care: the "official standard" for output impedance for headphone amps used to be 120 ohms (although it changed over to "whatever the MFR wants"). It is somewhat a matter of taste exactly what to use, and even when it was "official" 120ohms wasnt really the final word - headphone jack output impedances were allllll over the map... If you can try a few values (or have your friend build a little box with a 500ohm potentiometer in it, with 1/2 in series with the headphones...) do it! experimentation often yields better results than quoting numbers.

 

 

 

Anyways, the LD forum dosnt seem to give the output impedance. 

 

link

 

I would not worry about it. The amp is all SS, with a substantial looking SS buffer (its got a headsink!) enclosed in an op amp's feedback loop. The output impedance of that amp is probably in the low single digit ranges, if its even that high. 

 

PS: You should work on your google-fu. I googled "Little Dot V" with no quotes and that was the 5'th answer.

post #4 of 75
Thread Starter 

Very helpful...thanks! I'll have to run your comments by my friend. He's already planning one that's transformer based. I think 600ohms. Your idea sounds even better since I can play with the impedance value. He thinks I'll get better highs as well as bass.

post #5 of 75

I would be very careful about using a transformer designed for a 600ohm load with a 25ohm headphone. Things start to get weird quickly. OTOH, if he has them on hand, and dosnt mind experimentation go for it! It may work well if thats how the headphones work.

 

Regarding the output impedance & the headphones:

The "best" way is indeed a little tuning. I think beyers driven from a 0-ohm output tend towards being a little bright/harsh in the highs, but they become quite well behaved when driven by something with a high output impedance.

post #6 of 75
Thread Starter 

My mistake. I didn't explain it properly...but I'm totally electronically challenged, so I couldn't quite get a handle on what exactly my friend is cooking up for me. I think he told me it has an output impedance of 8ohms. Anyhow, I will try it and see what happens. Nothing to lose. If I have to eventually get a better amp for them I probably will...maybe starving student if that would work well with low impedance cans.

post #7 of 75

Ari, how would using a 300 ohm adapter make the sound of a low impedence can better? It was always my understanding that the amp's output impedance should be lower than the headphone's impedance. With the 300 ohm adapter wouldn't the damping factor be 0.083? I'm not really sure what damping factor is, but I'm told it's important.
 


Edited by tvrboy - 7/22/10 at 11:14am
post #8 of 75

 

Quote:
Originally Posted by tvrboy View Post

Ari, how would using a 300 ohm adapter make the sound of a low impedence can better? It was always my understanding that the amp's output impedance should be lower than the headphone's impedance. With the 300 ohm adapter wouldn't the damping factor be 0.083? I'm not really sure what damping factor is, but I'm told it's important.
 

 

Damping factor is the ratio of the amplifier's output impedance to the driver's impedance. It is important (or important not to do it :p) because of the way this interacts with the actual impedance VS frequency of the driver. 

 

The first thing to look at is that very few drivers have a truly flat impedance VS frequency curve. Some do, most dont. There are peaks and dips in the impedance VS frequency.

 

If you have a very high damping factor (typically given as 10 or more per rule of thumb, IE amps output impedance<1/10 headphone impedance) dips and peaks in the impedance VS frequency have basically no effect on the frequency response of the headphone. As you start reducing damping factor, the dips and peaks in the headphone's impedance VS frequency causes the frequency response to change at those places. If everything lines up this can be used to your advantage. What we are looking for here is "the right kind of wrong."

 

Take a hypothetical headphone whose impedance increases pretty steadily below 100hz but has obviously rolled off bass when driven from an amp that has a high damping factor. When driven from an amp with a low damping factor, the interaction of the output impedance and load impedance there causes a bass boost, but without the funkyness of more junk in the signal path to force that to happen. So by getting the damping factor set to " the right kind of wrong" you have picked up some bass. The headphones that had sucky bass extension now have better extension for the sonic penalty of a resistor.

 

With headphones we have an easy life because we dont typically have crossovers. Single driver speakers without passive notch filters can also see VERY strong benefits from getting damping factor "the right kind of wrong."

 

In speakers things get MUCH harder if passive crossovers or notch filters are used. The problem with crossovers & damping factors is that the crossovers must be designed/tuned around a particular source impedance from the amplifier. If you start mucking about with the output impedance from the amp with a speaker with passive crossovers you are now shooting at many many targets at once. Inevitably the crossovers stop lining up with each other correctly and your speakers which sounded great driven by your amps with a 0.0001ohm output impedance turn into little heaps of day old poop.

 

This above bit, with speakers with passive crossovers is the reason that damping factor is soooooo strongly ingrained in the hi-fi culture. Its not that high damping factor is necessary for good sound, in fact its easy to show that there are cases where its better that you have a low damping factor, its just that its easy to give 1 rule and stick to it. As long as everyone follows the same rule things work out OK. The problem is that the people making the rules are the people building high power amps & HUGE multi-way speakers, which only work if you get the damping factor right, by their definition anyways.

post #9 of 75

Thanks for the info, you're a helpful guy.

post #10 of 75

Very good summary indeed,

 

I struggled with similar problems (see http://www.head-fi.org/forum/thread/504573/homemade-headphone-amp-sounds-great-but-need-some-advice ), but probably a magnitude worse, due to 2-way earphones.

 

To give a more precise interpretation there are 2 things which immediately come to my mind.

- One is the fact that a dynamic speaker should produce a linear frequency response when driven with a constant voltage. That means electrically, the impedance from the voice coil will reduce the current flowing with rising frequency (Yes, there are bass resonances of the mechanical system visible in the impedance curve, but one might neglect them in this moment).

- Second is the damping factor. Usually, the output of the amp is much lower than the impedance of the speakers or phones. A lot of people used to argue the damping factor influence rather in a way of electro-mechanical damping of unwanted enclosure resonances. 

But when the output impedance of the amp is much higher than the one of the speaker, then we end up with unwanted frequency response (see the UE value in my thread).

 

As stated before, things get really complicated with multi-way phones, because manufacturer might use a defined measuring environment with a significant output impedance, compared to the phones impedance.

But there is one argument, which is the very low impedance of the phones at low frequencies, which should forbid the manufacturer to drive a phone with high impedance, because then the bass performance will go really bad.

So I would expect that a good brand manufacturer tests and rates his phones also at very low impedance, i.e. my best guess is to drive them always with lowest possible output impedance...

post #11 of 75

Bookedmarked. Great stuff.

 

I always thought this graph was amusing: the Fitear 333 (Japanese 3-driver custom IEM) out of the WooAudio 3 (OTL tube), from shigzeo's Woo3 review:

 

4607425603_a5d0b537df_o.png


Edited by Ypoknons - 7/30/10 at 1:04am
post #12 of 75

Reminds my of my

 

UE Super.fi 5 Pro´s transfer diagram (taken from UE´s site) - Though not too linear, still sounding well.

I bet, due to the custom molds I am using, the curve is different now. Subjective impression is a dip around 5KHz now, and coming up earlier again (than the 16KHz dip in the diagram).

Anyway, what a difference to an open system like a Beyerdynamics DT880 or Grado´s SR325, but definitely not limiting the fun with the UE´s, they are simply well made for another use case...the only thing is that they require a good headphone amp to play out their advantages...

 

 

UESuperfi5Pro transfer function.jpg

post #13 of 75
Quote:
Originally Posted by Ypoknons View Post

Bookedmarked. Great stuff.

 

I always thought this graph was amusing: the Fitear 333 (Japanese 3-driver custom IEM) out of the WooAudio 3 (OTL tube), from shigzeo's Woo3 review:

 

4607425603_a5d0b537df_o.png


That is an RMAA measurement of the output of the amp, and not frequency response of the transducer, which is what we are concerned with. Even though that graph shows a VERY skiewed output, it does not say anything about the actual sound of the headphone. Id bet it sucks, but maybe it dosnt.

 

The only thing that graph shows is that the output impedance of the Woo3 cant drive a low impedance load that varies a lot. Those headphones could sound GREAT driven from a low output impedance source.

post #14 of 75
Thread Starter 

To put the question it in practical terms... does all the above point to the fact that the LD mkV won't give decent bass performance from low impedance phones like the dt48 25ohm? That appears to be the case from my own experience anyhow. And, if that's so, what amp would be recommended for them....for someone on a 'starving student' budget? Any suggestions?

post #15 of 75

Yes, now it makes sense to me!

 

Similar results I obtained, when driving the UEs via a (240Ohms) series resitor and measuring the voltage across the earphones.

The WooAudio 3 (OTL tube) must have quite a significant output impedance, since they recommend it only for headphones from 30Ohms upwards....let me guess, sthg around 10-20Ohms?

 

Wonder how the Woo would sound with my old Beyerdynamics DT880s...(600Ohms, if I remember correctly)

Actually this brings me back almost 2 decades, when I upgraded my ´83 Yamaha A-960 amp (sometimes still in use!) with a voltage divider in front of the headphone jack (removed the unfortunately high series resistor), primarily to reduce the the residual noise of the amp, when the first CD-players became affordable...think I did choose sthg like 39/15Ohms...which worked well for the DT880s, and giving them a better damping factor as well.

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