Thoughts on using Hafler power amp with HD580s?
Jun 6, 2007 at 6:05 AM Thread Starter Post #1 of 13

ofajen

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Hi, folks. This is my first post. This place is a handy source of way more info than I'll probably ever need on headphones. Very cool! I'll post a bit of my history here to get started and more later in the headphones forum, but right now I'm thinking about amps.

I've mainly been using a pair of HD540s for the last twenty-some years. Most of my listening is to my original recordings here in my studio, though honestly, my recordings are always mixed on my monitors, not headphones. Headphones are mainly so I can get at least something done when it needs to be quiet, but I still want them to be accurate and high resolution, just like my monitors and monitoring space.

Up until about a year ago, my music was all tracked and mixed on wide-track analog tape machines (3M M-56, M-79 and now I'm rehabbing a 45 year old M-23 2-track machine.) Now I do a fair amount of 24 bit digital recording, usually at 44.1 KHz, though I may start doing more at 88.2K.

Anyway, it's a familiar story, the HD540s now have an intermittent connection to one capsule. It isn't the cable as it stays with the capsule when I swap the cable connections. I should post pics of the things just for amusement sake. The thin layer on the cushions wore into nothingness decades ago, as did the foam layer over the drivers. Anyway, rather than try to buy another capsule and keep this ancient rig alive, I just bought rocktboy's modded HD580s at about the going rate for such a rig.

So, being the heretic that I am, that's most of the money I'm willing to put into this rig right now, but I'm thinking that my M-Audio interface's headphone outputs might be a tad challenged by all these high-impedance Sennheiser headphones and that a more substantial amp would tighten up the sound on signal peaks, if nothing else.

I happen to have an extra Halfer DH-200 power amp just lying around (doesn't everyone?) It's the same type of amp I use with my full-range main monitors. Rated at 100 watts per channel average into 8 ohms, 20-20K. I plan to rig up a little box to power the HD580s using this bad boy.

In the DH-200 manual it says "Headhpones are normally operated from the loudspeaker outputs, but are usually connected through a junction box which provides switching from phones to speakers. Such a box usually provides some added resistance to reduce the sensitivity of the phones, and thus minimize the likelihood of hearing component noise, because of the low setting required at the volume control..."

Later it says "some headphones, such as electrostatic types, are less sensitive and may need little or no resistance in series for normal operation. These could be easily interchanged with speakers through the use of double banana plugs."

Now, I don't need to worry about speakers, since this is a spare amp. I'm just wondering if anyone here has experience driving high impedance phones like the Senns (or electostats) with speaker outputs and whether component noise was a problem and added series resistance was required.

I don't see a sensitivity spec on the HD580s on the Sennheiser site, but the Hafler can swing a 10 KHz 60 volt peak to peak square wave with about a 3V input signal, and I assume I'll have to attenuate the signal either before the amp input using a stepped attenuator or after the amp output using a pair of big power resistors inline.

Any thoughts would be appreciated.

Cheers,

Otto
 
Jun 6, 2007 at 6:34 AM Post #2 of 13

Sinwerm

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How much you figure it is gonna cost to "rig up a little box" to drop the output from the power amp ? If you have the parts and the know how and it sure seems you do I guess not much. The sensitivity of the 580s should be 97dB the max load should be 200mW. I would also suggest you try the DIY links here for better info but it looks like you will need some really high value resistors. http://www.sennheiserusa.com/newsite/pdfs/hd580.pdf
http://www.head-fi.org/forums/forumd...p?s=&forumid=6

Sounds like a very cool thing to do but I would be afraid of frying my 580s also you will love the sound of them a very nice phone.
 
Jun 6, 2007 at 7:04 AM Post #3 of 13

ofajen

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Quote:

Originally Posted by Sinwerm /img/forum/go_quote.gif
How much you figure it is gonna cost to "rig up a little box" to drop the output from the power amp ? If you have the parts and the know how and it sure seems you do I guess not much. The sensitivity of the 580s should be 97dB the max load should be 200mW. I would also suggest you try the DIY links here for better info but it looks like you will need some really high value resistors. http://www.sennheiserusa.com/newsite/pdfs/hd580.pdf
http://www.head-fi.org/forums/forumd...p?s=&forumid=6

Sounds like a very cool thing to do but I would be afraid of frying my 580s also you will love the sound of them a very nice phone.



Thanks for the figures. Building up a little box with inline power resistors should be cheap: banana plugs for the speaker outs, 16 GA wire and 1/4" plugs I have; $6 for a box if there isn't one here in a spare parts box; 1/4" jacks for the box inputs I have, might need a 1/4" TRS jack for the headphone to plug into and then a pair of power resistors in series. I doubt I'll need more than 2W resistors and they would be maybe a few bucks each.

Based on 200mW load and 600 ohms, I could still be swinging 10V P-P, so I figure I'll start with attenuating the output voltage by a factor of 6. If I can find power resistors up around 3K ohms, that should do it. Probably buy some 1500 ohm resistors, too, in case 3K is too much.

Thanks!

Otto
 
Jun 6, 2007 at 7:13 AM Post #4 of 13

ofajen

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Quote:

Originally Posted by ofajen /img/forum/go_quote.gif
Based on 200mW load and 600 ohms, I could still be swinging 10V P-P, so I figure I'll start with attenuating the output voltage by a factor of 6. If I can find power resistors up around 3K ohms, that should do it. Probably buy some 1500 ohm resistors, too, in case 3K is too much.


Oops! That's 300 ohms nominal load for the HD580s. 8 V across the phones at max load, so 2 Kohm power resistors should be enough to tame the power amp.

Thanks!

Otto
 
Jun 6, 2007 at 7:24 AM Post #5 of 13

JadeEast

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100 watt amp for headphones is such over kill its not
even funny how much heat are those resistors going
to have to dissipate? I really think that using that
amp and trying to get a high resolution headphone
signal out of it is going to be like trying to get
a cool drink of water from a fire-hose. There has
go to be a better way like sell the amp for a few
bucks and buy a dedicated headphone amp you
can get a 4channel behringer rackmount amp for
about $120 bucks. Its not that your idea won't
work it just doesn't seem to fit the bill. Anyways
thats just my 2-cents YMMv.
 
Jun 6, 2007 at 8:23 AM Post #6 of 13

Sinwerm

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I think it would be better just to get his 540s refitted and fixed. Seems the easy solution.
 
Jun 6, 2007 at 10:03 AM Post #7 of 13

amb

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Using an inline resistor to attenuate the voltage is not a good thing. That resistor forms a voltage divider with the headphone impedance, which for the HD580 is nominally 300 ohms. However, the headphone impedance is not linear with respect to frequency, so the amount of attenuation will vary with frequency, causing frequency response aberrations.

Here is the impedance graph for the HD580, from HeadRoom's website (under "Technical information -> Product measurements -> Build a graph"):

attachment.php


As you can see, if you used a resistor in series with this "300 ohm" load, you'd get a very poor voltage divider.
 
Jun 6, 2007 at 10:29 AM Post #8 of 13

Gradofan2

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Get some K1000's...

AKG says they need a minimum of 30 watts per channel into 8 ohms out of a speaker amplifier to perform well.

Otherwise... it's probably best to scrap the Halfer and get a good head amp.
 
Jun 6, 2007 at 1:18 PM Post #9 of 13

ofajen

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Quote:

Originally Posted by amb /img/forum/go_quote.gif
Using an inline resistor to attenuate the voltage is not a good thing. That resistor forms a voltage divider with the headphone impedance, which for the HD580 is nominally 300 ohms. However, the headphone impedance is not linear with respect to frequency, so the amount of attenuation will vary with frequency, causing frequency response aberrations....

As you can see, if you used a resistor in series with this "300 ohm" load, you'd get a very poor voltage divider.




Quite right of course. I was beginning to ponder that problem. Also, the HD580s don't need nearly that much power. Better to save the DH-200 for other jobs around the studio!

However, I think I will stick with the HD580s for a while. I was happy with the HD540s for over 20 years but they're pretty run down. If anyone has an old pair and wants to sell them, I could use the extra capsule and have a second set of good phones, which is useful around here when I'm tracking with several people.

In the mean time, I think I'll look for a headphone amp. I'm rather partial to SoundDevices gear and I know they make a nice portable headphone amp with three outputs for about $300.

Cheers,

Otto
 
Jun 8, 2007 at 6:36 PM Post #10 of 13

ofajen

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Quote:

Originally Posted by Sinwerm /img/forum/go_quote.gif
I think it would be better just to get his 540s refitted and fixed. Seems the easy solution.


Thanks. I thought of that, but it's not so easy. Sennheiser USA can't get replacements. Headphonesdirect is a site they referred me to in the UK, but their site says there is no replacement and no alternative for any of the HD540 series. About the only hope is to snag an old pair off eBay and pull a capsule, which could take a while.

Cheers,

Otto
 
Jun 8, 2007 at 6:47 PM Post #11 of 13

ofajen

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Quote:

Originally Posted by Gradofan2 /img/forum/go_quote.gif
Get some K1000's...

AKG says they need a minimum of 30 watts per channel into 8 ohms out of a speaker amplifier to perform well.

Otherwise... it's probably best to scrap the Halfer and get a good head amp.



Someday I may get K1000s but the cost is more than I can justify now and they aren't that easy to find, either. I have a long history with Sennheiser phones, so I think I'll stick with the HD580s.

As far as the DH-200, it is a very high-functioning power amp already that is sometimes useful around the studio, so I'm not about to sell it. Plus, it's a classic audiophile amp and there are several high-end rebuilds available to turn it into a really high-end performer at a reasonable cost (less than $1K).

I will probably get a headphone amp in the near future. Most likely one designed as a high quality, studio headphone distribution amp with three or four outputs. Presonus, Rane and Furman all make them, but I really like Sound Devices gear, so I may get their HX-3 headphone amp, which can run off AA batteries or an AC adapter and is quite rugged for portable use. They really put a lot of emphasis on the quality of their headphone outputs. I have their MixPre 2 channel field mixer and it has a really clean, powerful headphone amp built in, but it's not very convenient to use that other than when using that field mixer to monitor live when recording.

Cheers,

Otto
 
Jun 8, 2007 at 7:44 PM Post #12 of 13

MaloS

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Why did you not get something like akg k240m or equation rp21? They are headphones designed for studio use, and will do a much better job at that >.<
 
Jun 8, 2007 at 8:28 PM Post #13 of 13

ofajen

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Quote:

Originally Posted by MaloS /img/forum/go_quote.gif
Why did you not get something like akg k240m or equation rp21? They are headphones designed for studio use, and will do a much better job at that >.<


Much of the time I prefer to use open headphones, not closed, because they sound so much better without that shell resonance. I probably will get a pair or two of the Equation headphones at some point, but I only use that kind when I really need to minimize bleed and increase isolation, which is only some of the time when I'm tracking and none of the critical listening time.

Cheers,

Otto
 

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