Paramounts as headphone amp for AKG K1000

[rbc3]

I've been thinking about pulling the trigger on a pair of Sennheiser HD800 when a pair of AKG K1000 came up locally for more or less the same price as a used pair of HD800, so I bit the bullet.  When I got them home after the purchase I promptly connected them to my Paramounts to have a listen.  Wow what a soundstage!  It's like listening to live music right here in my living room.  My only complaint is the bass.  It's OK that the bass isn't strong and thunderous, but I found it to be very rumbly.  For comparison, I listened through my Audeze LCD 2.2 (non Fazor) and HiFiman HE-500.  The LCD had the tightest and strongest bass but are a little too warm with the Paramount and lacked soundstage.  The HE-500 were the best balance between good bass, not warm, and decent soundstage.  My Paramounts are stock 1.1 and I was listening with WE 396A and KR VV300B.  Also, my OT is tapped at 4 Ohm for my speakers.  I wonder if the rumbly bass in the K1K would be resolved if tapped at 16 Ohm.  I bought parts to install an impedance switch so that I could easily play around with the impedance of the Paramounts for different speakers but maybe it will help with using them as a headphone amp with the K1K.

I have to admit, for listening to live recordings or audiophile recordings, there's nothing I've ever heard in a headphone quite like the K1K.  Everything sounds so real!  Has anyone else used Paramounts to drive them?  What have you done to optimize their sound?

[Doc B.]

I have been demoing with Paramounts and K1Ks for several years now, but I don't know if anyone else has used them together. To add a little intrigue to this, I like the K1Ks enough that PB and I have been working on a dedicated headphone amp that has among its requirements the ability to drive K1Ks. The proof of concept prototype has me pretty enamored so far. I don't care to share any more details yet. We hope to have a working prototype ready for a reveal at the Head Fi meet here on the 25th of the month.

Do be careful, the Paramounts put out enough power to hammer the K1K drivers if you're not paying attention. Staying with the 4 ohm tap will give you a little extra insurance against putting too much power into them.

[rbc3]

How does the power output of the Paramount 1.1 change when tapped at the different impedance of the OT?  The spec rates the amp at 8.5 watts with 300B tubes, which I presume is at 8 Ohm impedance.  So if tapped at 8 Ohms, I believe the output to the K1K is 566 mW (8.5W * 8 Ohm / 120 Ohm).  Does that calculation change if tapped at 4 Ohm or 16 Ohm?

[Paul Birkeland]

It's a little more complicated than that.  When you unload the winding (by loading it with headphones instead of a speaker), the output voltage will pop up a fair amount, as the load on the tube changes (for the better). We'll just call it 10V for the sake of argument, but I'd suspect it's much higher into 120 Ohm headphones.

So, into 120 Ohms, 10V would give you somewhere north of 800mW. 

It's good to note that the original K1000 power rating was something like 8W from a solid state amp, which halves power every time you double impedance, and thus we arrive at something around 500mW assuming that we started with a solid state amplifier that could deliver 8W into 8 Ohms.   

[rbc3]

Thanks Paul.  Does tapping at 4 Ohm, 8 Ohm, or 16 Ohm at the OT change that calculation of roughly 800mW to the 120 Ohm drivers in the K1K?  If not, what impact does tapping at the different impedance have on the headphones?  I noticed that on my 4 Ohm Tekton Design Seas Pendragon speakers, tapping at 4 Ohm tightened up the bass so that it was less flabby vs. being tapped at 8 Ohm.

[Paul Birkeland]

For loudspeakers, moving around on taps will change the loading that the 300B sees.  It's a sparsely discussed topic, but tuning an enclosure for use with SET amplifiers requires some adjustments to the T/S parameters of the driver used, and if you don't do that, the added damping from going down a tap on the output transformer will help correct the design deficiency.  (I'm going to call it that, since a high efficiency high end speaker should have this tuning to begin with)

On headphones, you're so unloaded on all the taps and the damping is high enough, that what you're actually left with is a way to control the noise floor.  While the 4 Ohm tap will provide less power into your headphones, it will do so with less background noise contributions from your amplifier.  With the K1000's, sensitivity is low enough that this doesn't really matter, but if you're really crazy and you want to drive Grados with your Paramounts, then you'd want to be on the lowest impedance tap.

-PB

[rbc3]

Thanks Paul.  Your post has triggered even more research and learning on my part.  As I'm sure you are aware from my questions, I'm new to this.  Your speaker comment has me wondering about how my speakers were designed, and if there are adjustments that can be made to them for use with SET amps.

It makes sense what you are saying about noise floor and the different output impedance taps for the K1K.  When I install the impedance switch to the Paramounts, it'll be interesting to hear the difference between the different taps with both the speakers and the K1K headphones.