Need Amp for K240DF

[RamblinE]

I thought my Headroom Micro Amp would be more than enough when I purchased my DF. However I was wrong. Headroom never appeared to publish specs for this amp. My DF drives it into clipping. It was enough of an amp when my primary concern was just driving my K701, but not anymore.

These are the closest I can find to specs for the DF

Volts RMS required to reach 90dB SPL: 0.792 Vrms
Impedance @ 1kHz: 613 Ohms
Power Needed for 90d BSPL 1.02 mW
Broadband Isolation in dB (100Hz to 10kHz): -7 dBr

I've narrowed a purchase time down to July or August, a budget of $350, and a willingness to start selling some extra speakers and headphones to begin raising a fund.

My front runners are, the Schiit Valhalla 2 and the Musical Paradise MP-301.

The Schiit appears to be the best OTL in my price range, and as far as OTL tube amps go, if I buy something cheaper than the Valhalla, I'll probably be left wondering what gains I'm missing. http://schiit.com/products/valhalla-2

But the MP-301 appears to be a better all-in-one solution. Why's that matter? The MP-301 represents a direction I want to begin steering my systems in and I think it would make a great first step into the world of all-tube amplification. I also believe it will be just fine driving my modified Dayton B652 AIRs or AR Holo Image M.5's, neither of which are all that sensitive. http://www.musicalparadise.ca/store/index.php?route=product/product&product_id=54

But, and back to the possibility of missing something...

The one big thing that's bothering me is, what will I be missing if I "COMPROMISE" and buy the MP-301 vs. buying the Schiit Valhalla 2 and continuing to run the pre-out into my silly, plastic, Stellar Labs T-amp.

Take that $350 and put it all towards a headphone amp or take that $350 and put it towards a speaker amp that can also double as a headphone amp?

What would YOU do and why?

 

[ericj]

People seem to like that schiit. I've personally never been near one.

With efficient speakers, 7W could be good for near-field listening. May be basically as good as your T-Amp but you would want to check that it can drive 4-ohm speakers, if that's what you've got.

 

[SoNic67]

Yeah, the K701 have 62 ohms and they are slightly harder to drive than the 32 ohm crowd. I got away with the K701 by just modding the output of my DAC.
But the 240DF have 600 ohms! Those are made for plugging in directly into consoles. Not worth for daily drivers IMO, becaue you have to add a really good headamp.
I was in the "tube" crowd for a while, but lately I realized it was just a preference, not based on real audio quality. You get used to a certain type of distortion...
Personally think that Schiit Magni 2 Uber are a much better alternative, much better than the price suggests. See the THD and IMD numbers...
Or, if you want to spend a little more, Asgard 2 is the other choice. I actually would love to listen it too, because of their claim of class A with limited/no feedback.

 

[xero-D-hero]

Those specifications are somewhat deceptive in that they leave out things like the max amount of power they K240DF can handle.
And that's night & day to what ^^^^ those ^^^^ specs tell you is needed to get that 90db SPL w/just 1.02mW.

The K240DF can handle like 11V max,and that's like 220mW or so I believe.
Heck my NAD 106 puts out > 8V into 600 ohms and IIRC that's like 106.6mW & I've yet to come anywhere close to clipping that 106 preamp's headphone section.
You would likely risk serious hearing damage by the time that would happen (yeah they get THAT loud,,,LOL...).
Yet the K240DF's SQ is still crystal clear at those levels.

So that 1.02mW spec is'nt very telling of where one stands when trying to drive a pair of these K240DF to levels that really let them sound their best.
JMO here if one is trying to drive these cans with just 1.02 mW or so,well they're very likely to end up being quite unhappy with their performance.

There was a thread a while back where some of this stuff was tossed around a bit,and some comparisons were made for the sake of that brief side discussion,and I felt compelled to compare my NAD 106 preamp's headphone section specs with that of a seriously high end (and high $$$$ too) Audio Technica headphone amp (IIRC the AT-HA5000) and that AT headamp specs stated it was capable of putting out something like 65mW > 600 ohms.

So yeah we need to understand that the "sweet spot" for driving these K240DF well is gonna require a pretty stout headamp.

As another FYI sorta example here:
Note that my Sound Blaster Zx ACM (audio control module) is rated to drive 600 ohm cans and that soundcard puts out like 80mW.
And I can speak from experience when I say that 80mW struggled significantly to power my 600 ohm AKG's (not just the K240DF either).
I would have to have the volume control pretty much maxed out just to get a decent listening SPL.
So that was when it became perfectly clear to me these puppies needed some serious muscle to sound their best.

So I'd say pick the head-amp who's highest max output is at least half that max,and if the manufacturerer wont give you those specs,move on.

So for comparisons sake:
Schiit Magni2 = 130mW > 600ohms.
Asgard2 = 190mW > 600ohms.
Valhala2 = 450mW > 600ohms.

So one could make a solid point that the Valhala2 would be a bit of overkill for the K240DF,and that either the Magni2 -or- the Asgard2 would be more than adequate.
So I guess that all tends to agree with Sonic67's comments...

But should one want those tubes,then by all means they can have them as the Valhala should easily be able to drive the K240DF.
Just know that they can max out the K240DF if pushed hard,but again you would likely be stone deaf before that happens.

The Musical Paradise MP-301 specs state 2w into the headphone section,though they dont state into what ohms that is,so I dunno what to say 'bout that unit ???
Near as I can figure that HAS to be into 32ohms as were it going into 600ohms that would be a CRAZY amount of power into that sorta load.
(If I'm doing this right 2w into 32ohms = something like 8V vs. 2w into 600ohms = something like 34V !!!)

Maybe we need someone better versed in all these electrical conversions to fill us in on that unit's specs (MP-301)...

I'll just say at this I'd be leaning towards the Schiit headamps myself...

Whew...

HTH

Bret P.

 

[xero-D-hero]

Oh,BTW which version of that MP-301 unit are you looking at ???
I mention that as I came across something like three different versions...

Anyhow during a quick search I found some 600ohm specs for the MkII version & those specs stated it was something like 80mW into 600ohms.
So IME that would be on the weak side of things for those K240DF.

But I dunno really,the MkIII version may do better than that,though I cant say for sure as I have'nt run across any 600ohm specs for the MkIII.
But I believe ^^^^ that ^^^^ MkII info mostly jives with that 2W > 32ohms spec listed for the MkIII unit on the Co.s website.

So you can compare those MP-301 numbers to the numbers in my post above and see that MP-301 headamp aint got nearly the @ss that the Schiit headamps have.

FWIW

Bret P.

 

[SoNic67]

Power requirements don't change with impedance, only the voltage and current needed for that power. IMO, 100mW should be enough for ANY modern headphone, that has a decent efficiency (95dB). 200mW is maximum rated for many headphones and that can yeld some 115dB audio. It's a lot!
1000mW (1W) is where instantaneous hearing damage occurs.
Now, the 200mW power is achieved at different voltage levels, depending of the impedance:
2.53V for 32 ohm
3.58V for 64 ohm
4.90V for 120 ohm
10.95V for 600 ohm

Usually the maximum output voltage of an amplifier is a fixed, limited value, and that provides various levels of maximum power, depending on the impedance.

 

[RamblinE]

Great stuff guys! This is why I asked!

People seem to like that schiit. I've personally never been near one.

With efficient speakers, 7W could be good for near-field listening. May be basically as good as your T-Amp but you would want to check that it can drive 4-ohm speakers, if that's what you've got.

6-ohm load. My office is the room that the landlord had listed as the half bedroom. It's quite small. I shouldn't need to worry about overhead in there.

Yeah, the K701 have 62 ohms and they are slightly harder to drive than the 32 ohm crowd. I got away with the K701 by just modding the output of my DAC.
But the 240DF have 600 ohms! Those are made for plugging in directly into consoles. Not worth for daily drivers IMO, becaue you have to add a really good headamp.
I was in the "tube" crowd for a while, but lately I realized it was just a preference, not based on real audio quality. You get used to a certain type of distortion...
Personally think that Schiit Magni 2 Uber are a much better alternative, much better than the price suggests. See the THD and IMD numbers...
Or, if you want to spend a little more, Asgard 2 is the other choice. I actually would love to listen it too, because of their claim of class A with limited/no feedback.

I built a tube amp kit in '10 and really enjoyed it for a few years. I'm looking for a return to that kind of sound. And as far as the 600 ohm headphones go? A lot of the vintage AKG's are 600 ohm, and I really enjoy the detail and transparency that the DF offers. For me that makes them worth driving them daily. The Asgard is also an option and cheaper than the Valhalla. I have not read any reviews on it and probably should.

Oh,BTW which version of that MP-301 unit are you looking at ???
I mention that as I came across something like three different versions...

Anyhow during a quick search I found some 600ohm specs for the MkII version & those specs stated it was something like 80mW into 600ohms.
So IME that would be on the weak side of things for those K240DF.

But I dunno really,the MkIII version may do better than that,though I cant say for sure as I have'nt run across any 600ohm specs for the MkIII.
But I believe ^^^^ that ^^^^ MkII info mostly jives with that 2W > 32ohms spec listed for the MkIII unit on the Co.s website.

So you can compare those MP-301 numbers to the numbers in my post above and see that MP-301 headamp aint got nearly the @ss that the Schiit headamps have.

FWIW

Bret P.

Yeah I want to email Gary at Musical Paradise and ask him how much power into 600ohms the 301 MK III puts out. The MkIII had enhancements in the headphone section to kill hum so we probably can't go by the specs from the MkII. How much power @600ohms do you have available for your DFs? I only have a chinese tube/mosfet amp available to drive mine. And while it does so, I can't find any specs for it and have no idea how much power it's using when I'm listening.

Anyway everybody, other than power requirements, what else would a Valhalla or an Asgard bring to the table for strictly headphone listening that the MP-301 might not necessarily offer? There was lots of talk in another thread about the output on receivers and integrated amps missing some of the detail and transient response of dedicated amps. Assuming the MP-301 is a similar setup, something like a padded resistor, is this a valid concern?

 

[SoNic67]

It is. You are pushing the power up trough the EL84's (audio pentodes) just to dissipate it right away. Doesn't this seem prone to adding more distortions?

 

[RamblinE]

It is. You are pushing the power up trough the EL84's (audio pentodes) just to dissipate it right away. Doesn't this seem prone to adding more distortions?

That's the thing, I don't really know enough to say.

 

[SoNic67]

I forgot to add... I have a feeling that those dropping resistors will be calculated for 32 ohms, so you will end up needing to modify them for the 600 ohms.

While the Schiit amps are already designed for a bigger range (lower output impedance).

 

[xero-D-hero]

How much power @600ohms do you have available for your DFs?

Well,I'll simplify what I said in above post(s).

My Sound Blaster Zx is supposed to be able to provide 80mW > 600ohms & that was BARELY enough to provide acceptable listening levels (at least for me it was).
And in doing so one would have to have the volume control on the ACM maxed out (in addition to maxing out the volume level setting in the player).
Also the SQ was less than stellar,listenable yeah sure I guess,but still not what I had expected based on the K240DF's reputation for superior SQ.

On the other hand my NAD 106 preamp can provide at least 106.6mW > 600ohms & that is significantly better than the SB Zx's 80mW was.
With this unit the preamp's volume control barely ever needs to be higher then half way,beyond that it's just flat out too d@mn loud.
And with the NAD preamp,SQ is about as good as I can imagine it being,all I can say is my headphone needs are 100% complete & I'm done chasing this dragon for good.

So my takeaway from said practical experience is that the SB Zx specs are likely a bit on the optimistic side & the NAD 106's specs are a bit on the conservative side.
And like I said above I'd want at least half the maximum mW that the K240DF can handle as a good starting point w/the expectations of achieving decent SQ from these.

Providing the main concern here is driving the K240DF properly,my $$$$ would likely be going to Schiit.

FWIW

Bret P.

 

[RamblinE]

Well the Valhalla 2 sounds like it would probably be the better bet. I have previously looked at the Magni 2 and thought "yeah, that could probably do it" but I want to go in on the tube experience.

And who knows. Maybe I'd get the Valhalla and decide within the 15 day window to exchange it for an Asgard?

What are the feelings on OTL Valhalla vs. SS Asgard? Found a relevant thread on Steve Hoffman http://forums.stevehoffman.tv/threads/schiit-headphone-amp-advice-valhalla-2-or-asgard-2.487964/ but I'd still love to hear what you all have to say as well!

 

[xero-D-hero]

Me,,,I dunno jack about tubes,,,sorry...
Strictly SS stuff here.

Bret P.

 

[ericj]

For the record, way back in the day, i hand-built Cavalli's SOHA hybrid amp. Perfboard and improvised layout. 12au7 at iirc 100v (ish) plate voltage through a voltage multiplier, +/-15v for an opamp buffer in unity gain.

The LM4562 opamp was new that year, so of course, i had to try it. The datasheet proudly proclaimed "Able to drive 600ohm loads easily" or something.

And it did. It did a fantastic job of driving my K240DF. An RCA black plate 5963 and an LM4562 did a great job.

 

[xero-D-hero]

Op-Amp for the headphone section of that SB Zx is a JRC2114 which I'm willing to bet aint nothing special @ all (I'm not an Op-Amp guru at all folks,LOL).

I say that as the one(s) driving the analog outs (JRC4556A) are'nt doing this soundcard any favors either,,,ie: the analog outs on this card suck b!g t!me...
Hence I currently use the Zx's optical outs into external DAC's w/better Op-Amps (obviously ???).

DAC in the Zx soundcard is a CS4398-C22 IIRC...
External DAC's I'm using are a Parasound D/AC-1000 for the headphone/nearfield system and a Schiit Optimodi for the main BR system.

Have considered doing some Op-Amp rolling on that Zx soundcard as they're supposedly replaceable,but I just have'nt gotten around to doing so yet.
That's largely because I have no idea what I should try out in there to achieve a given desired affect,like I said earlier this aint my strongest area folks.

Anyhow I'll hafta dig around and see what the headphone circuit of that NAD preamp is using.
I recall the fella in that other thread saying that it had a NJM2043D headphone amp IC / board in it.
Beyond that I dunno,never really needed to know more (LOL) other than it does the job well enough for my needs.

HTH

Bret P.

 

[SoNic67]

The sound cards on PC just don't have the necessary supply voltage to drive 600 ohms, I don't care what they claim. For an OpAmp to drive 600ohms loads it's easy, it just needs +/- 15V on the supply rails (30V total).

 

[RamblinE]

Response from Gary at Musical Paradise:

Hi Evan,
The headphone output of the MP-301 also goes through power tubes and output transformers. MP-301 can drive 600ohm headphones well, no clipping. The max output power for 600ohm is 95mW.

To unpack that real quick, 95mW is close enough to half of the headphones max power. He says the output goes through the power tubes and the output transformers?

 

[ericj]

Op-Amp for the headphone section of that SB Zx is a JRC2114 which I'm willing to bet aint nothing special @ all (I'm not an Op-Amp guru at all folks,LOL).

I say that as the one(s) driving the analog outs (JRC4556A) are'nt doing this soundcard any favors either,,,ie: the analog outs on this card suck b!g t!me...
Hence I currently use the Zx's optical outs into external DAC's w/better Op-Amps (obviously ???).

DAC in the Zx soundcard is a CS4398-C22 IIRC...
External DAC's I'm using are a Parasound D/AC-1000 for the headphone/nearfield system and a Schiit Optimodi for the main BR system.

Have considered doing some Op-Amp rolling on that Zx soundcard as they're supposedly replaceable,but I just have'nt gotten around to doing so yet.
That's largely because I have no idea what I should try out in there to achieve a given desired affect,like I said earlier this aint my strongest area folks.

Anyhow I'll hafta dig around and see what the headphone circuit of that NAD preamp is using.
I recall the fella in that other thread saying that it had a NJM2043D headphone amp IC / board in it.
Beyond that I dunno,never really needed to know more (LOL) other than it does the job well enough for my needs.

The jrc2114 is sort of dry sounding i agree. The 4556 is actually a very capable chip but dependent on how it is implemented. The Grado RA-1 is based on this chip. The Objective2 headphone amp uses it for the power stage by default.

Looks like the headphone output opamps on that card are socketed precisely so that you can roll other chips.

The sound cards on PC just don't have the necessary supply voltage to drive 600 ohms, I don't care what they claim. For an OpAmp to drive 600ohms loads it's easy, it just needs +/- 15V on the supply rails (30V total).

That really depends. The -12v power rail isn't available on a pcie slot, but a true rail to rail part with a virtual ground between +12v and gnd should be able to put 240mW into 600 ohms.

 

[SoNic67]

By the time you clean up that dirty power you will have left some 10V. That's only +/- 5V with median ground.
That's exactly 80mW on a 600 ohm load.

 

[ericj]

By the time you clean up that dirty power you will have left some 10V. That's only +/- 5V with median ground.
That's exactly 80mW on a 600 ohm load.

You're forgetting that +/-5v delivers current on both sides of the virtual ground. So it's twice that. For a true RTR part.