Headphone amp for Planar Magnetic headphones

[Frihed89]

I know Bottlehead can't cover every niche, but it would be nice to know if DOC or Paul have given any thought to putting together a mod or a new kit for a DHT headphone amp that will drive these current-hungry types of cans: 50 Ohms, 91 dB for the Audeze LCD-2 I own.

Here's a brief snippet from the mfr of my Audeze LCD-2 head phones, when I asked how much power and current production i would need:

"Assuming your amp can produce 5W very clean power into 50 Ohms load (LCD-2 has impedance around 50 ohms), THD less than 1%. This corresponds to driving voltage of 16V RMS and current of 0.316A RMS into 50 Ohms load.  Maximum recommended peak power with less than 10% distortion should be 10W, 22V peak voltage, 0.45A peak current.  5W RMS will produce 127dB SPL in a midrange which approaches dangerous levels. Extra power is not to play loud all the time but to preserve the power for high dynamics in music.  "

[Doc B.]

They seem very difficult to drive to get their best performance and I have yet to hear an amp that seems to do everything right with them. At some point I will try the Paramounts with them ( hint - that would be the next time someone brings a pair to the office). I think that might be the only amp we have that could get everything right. It's what I use with my K-1000s, which are also notorious for being difficult to drive. Works very, very well.

[Paul Joppa]

...
"Assuming your amp can produce 5W very clean power into 50 Ohms load (LCD-2 has impedance around 50 ohms), THD less than 1%. This corresponds to driving voltage of 16V RMS and current of 0.316A RMS into 50 Ohms load.  Maximum recommended peak power with less than 10% distortion should be 10W, 22V peak voltage, 0.45A peak current.  5W RMS will produce 127dB SPL in a midrange which approaches dangerous levels. Extra power is not to play loud all the time but to preserve the power for high dynamics in music.  "...

This is a little bizarre, to me. 91dB per mW means it takes 12.5mW to get 102dB per can - that's 105dB for both, which is the requirement for a THX-qualified movie theater. Why you would need four hundred times as much power is beyond me, unless you are profoundly deaf!

In any case, we have only two DHT amps, the Stereomour integrated 2A3/45 and the Paramount monoblock 300B/2A3. The Paramount has DC filaments which reduces the hum to where it can work with most headphones; the Stereomour has AC filament power and is not usually recommended for headphones - though if it is used with low sensitivity 'phones, it could be pretty good. The Stereomour can make 3.5 watts, which is less than 2dB below 5 watts; Paramount of course is 8 watts.

I can see some possibilities for making a 45-based headphone amp derived from the Stereomour. Once we get the current raft of new ideas built and tested, and if interest is strong, we might try that.

[ironbut]

I'm not so sure that the "smoke has cleared" on the new wave of planar headphones. I've listened to many of the iterations of the Audeze as well as the HeadDirect planers and they've steadily evolved.
I think that HeadDirect is onto something with their newest design (it sounded very good during a meet a few months back) which is much more efficient.
I would guess that Audeze is working on designs to achieve the same efficiency with their headphones.

[Frihed89]

Paul, I was thinking the same thing about the 45. But would a DC amp (parafeed or something like the Electraprint DRD) be quiet enough, even with DC heaters?  I just don't know enough. 

Ironbut.  I am not sure either.  The LCD-2s are sort of an enigma to me.  Right now they are too dark and not very "musical" and I find myself gravitating back to my K-701s, which seem to get to the heart of the music in the way they connect the notes.  I have 2 nice headphone amps: an old SinglePower MPX3 (OTL), which I have customized and a Blue Circle model (SS) with a custom power supply that work well with 701s.

But I imagine that the 701s would sound even better, driven by a DHT amp.

[Doc B.]

My experience with the LCD-2s has been that only one amp could get the bass right. That was a Benchmark One. Tubes amps have sounded much, much better in the mids and highs to me and some have really opened the LCD-2s up on top. But the bass is way too soft and wooly. I was thinking at first that it might be a need for an amp with a high damping factor, but I am leaning more and more toward the idea that they just might need a lot (for a headphone) of power to sound controlled, similar to a lot of planar speakers.

[Jim R.]

I wonder if something like a quiet 45/2a3 amp followed by a an impedance converting current buffer amp -- such as a firstwatt F4 wuldn't be a great combination.  You can buildthe F4 with fewer output devices and thus bring the total power down somewhat, and I know some folks have built the F4 with fewer devices and lower supply voltage to make it into a headphone amp.  Of course this is that naughty SS stuff, but the F4 is very good at passing the sound signature of the tube amp on to the load.

 Just an idea as I'vee never done it myself, but know of a few folks who have built F4s and used them with a nice SET amp drivving them and thus were able to easily drive speakers that the SET amp alon would never be able to handle.

-- Jim

[Frihed89]

I wonder if something like a quiet 45/2a3 amp followed by a an impedance converting current buffer amp -- such as a firstwatt F4 wuldn't be a great combination. 
-- Jim

"impedance converting current buffer amp" ?  In language I understand, would this be something like a DC coupled DHT-JFET hybrid?  Or is that just as confusing to you as your term is to me?  Some DHT-lovers and builders have suggested to me that a JFET output stage is the way to go with these types of headphones (LCD-2).  On the other hand, the same people have told me that the recently released hybrid with a JFET output stage, claiming to deliver 6W into 32 ohms for $449 is not the answer either.

I think I'll wait until/if I can hear Doc's new headphone amp and the new 2A3 amp being built by Eddie Current.

I am beginning to think these LCD-2s are really enigmatic and all the acclaim on head-fi is hype from people with more money than experience. 

[mrarroyo]

Hi Friehed, hope you are doing well. I have the HiFiMAN HE-500 and they sound superb out any amp I have, from receivers using the speaker tabs to Musical Fidelity X-Can V2 to Red Wine Audio Isabella or the 30.2. They scale very well as you move up to the better amps but small amps can drive them very well. Even my old Xin Reference and the iBasso Toucan drive it nicely. BTW, the Singlepower MPX3 SE Slam makes them sound superb!

[Jim R.]

Hi Frihed89,

Yes, close enough, but the output devices can be either mosfets or power jfets, the amp runs in class A, single-ended, but is a current amp, not a voltage amp, so it depens on the tube  stage for all the voltage gain and then the SS device is the current buffer.  There is a 6 moons review on the firstwatt F4 that will give some more background and details on what I'm talking about.

Again, this is just me speculating as I have no idea if this has been tried or not.

I'm actually starting to wonder about the planar magnetic thing myself and like the room speaker cousins, not sure they would be my thing, while some people love them and think that lots of amps can drive them nicely, and others say that hardly any amps candrive them correctly.  The Senn HD-800s are still at the top of my wish list in headphones and I know they will work superbly with the gear I already have and am building.

HTH,

Jim

[Grainger49]

I have to ask here, weren't the Yamaha HP-1 headsets planar magnetic?  I sold them and didn't buy a pair.  I did get my brother a pair which he still has today and dearly loves.

[ironbut]

Hey Grainger,

Yup, I had a pair of the lower range Yamaha's (can't remember the model but it was only $35 IIRC). They sounded great and driving them was never an issue. That was in the late 70's and for the limited amount of headphone listening I was doing at that time, I was pretty darn happy.

[Grainger49]

Steve,

Thanks.  I reread my post and edited the model number.  My brother has HP-1 headphones and they were the top of the line at about $80 for then.  It was the mid 70s IIRC.