[GalaxyGuy]

Since he is quite self-contradictory, I take everything that he says with a grain of salt.

 
More to the point, though, the fact that all of his measurements differ from what Jack has published by a factor of two or more it seems that something is amiss, that's all.

 

[Sylafari]

My anti-slip glass protection pads arrived today in the mail.
 

 
I thought these were supposed to be self-adhesive but it maybe due to the weather or something but the pads were not adhesive at all as whatever adhesive was on the pad was gone once I peeled them off.
 
 

 

 
One pad for each side!
 

 
 
They seem to work even though mines aren't self-adhesive, they at least get the job done. OCD problem solved

 

[DougofTheAbaci]

^^^

Should I have a reason not to believe the measurements that he got?

Whenever someone releases anything that contradicts current information it's generally a good idea to question it, but not necessarily reject it out of hand.

I'd say this is a good time for some others to post their measurements.

 

[atomicbob]

I don't have a Rohde & Schwarz analyzer but using Fluke meters and Picoscope with distortion measurement I was able to closely match the lo-Z 1/4" jack measurements given in the link for the Rockwell site. I also had a variable resistive load so I could duplicate what I believe Jack measured. I measured 1.05W at 10% THD for a 32 ohm load. At 37.5 ohms I measured 0.777W at 5% THD. At low impedance the amp will be limited by current drive available. For high impedance it will be limited by available voltage. But however you wish to look at it, Jack has created a well designed, exemplary performing tube headphone amplifier capable of driving most headphones to ear bleed territory. The WA7 is my personal favorite for recreational listening.

 

[shigzeo]

Well said.

 

[MiniMaster]

I am currently running on a Xonar Essence STX and am looking pretty seriously at getting ext. amp and dac. The fact that there are so many choices makes it hard. I wanted to know if the WA7 would be a more worthy investment over something like a WA3 + Bifrost, considering they both come out to be around the same price. Being able to run both low and high impedance headphones is a bit of a necessity. 

 

[Kevin Brown]

Quote:

I don't have a Rohde & Schwarz analyzer but using Fluke meters and Picoscope with distortion measurement I was able to closely match the lo-Z 1/4" jack measurements given in the link for the Rockwell site. I also had a variable resistive load so I could duplicate what I believe Jack measured. I measured 1.05W at 10% THD for a 32 ohm load. At 37.5 ohms I measured 0.777W at 5% THD. At low impedance the amp will be limited by current drive available. For high impedance it will be limited by available voltage. But however you wish to look at it, Jack has created a well designed, exemplary performing tube headphone amplifier capable of driving most headphones to ear bleed territory. The WA7 is my personal favorite for recreational listening.

 
How about 1%?  Personally, I think 5% or 10% THD is too much.  At 5%, Ken got 667 mW, and you got 777 mW, and considering you're using different measurement techniques, 2 different units, etc, I don't think that your results contradict his at all.
 
(I just emailed Icon Audio to see if they will say what their power measurement conditions are.)
 
Got my WA7 yesterday.  Really like its tonality, even just right out of the box !!

 

[Taliesin]

what is the wa7  like with the HD800?

 

[atomicbob]

@Kevin Brown - a more interesting question is how much power does a given headphone need to achieve a specific sound level. Here are characteristics for a number of popular headphones:
 
 

​	​	nominal​	nominal​	100​	110​	peak​	peak​
​	​	Impedance​	Sensitivity​	dB SPL​	dB SPL​	voltage​	current​
Mfg​	Model​	Ohms​	dB SPL / mW​	mW​	mW​	volts​	mA​
Audio-Technica​	ATH-M50​	38​	99​	1.3​	12.6​	0.69​	18.20​
Audeze​	LCD-2​	50​	91​	7.9​	79.4​	1.99​	39.86​
Audeze​	LCD-3​	50​	93​	5.0​	50.1​	1.58​	31.66​
Beyerdynamic​	T1​	600​	102​	0.6​	6.3​	1.95​	3.24​
Beyerdynamic​	T90​	250​	104​	0.4​	4.0​	1.00​	3.99​
Beyerdynamic​	T5p​	32​	102​	0.6​	6.3​	0.45​	14.04​
Denon​	D7000​	25​	108​	0.2​	1.6​	0.20​	7.96​
Fostex​	TH-900​	25​	100​	1.0​	10.0​	0.50​	20.00​
Grado​	multiple​	32​	98​	1.6​	15.8​	0.71​	22.25​
Hifiman​	HE-500​	38​	89​	12.6​	125.9​	2.19​	57.56​
Sennheiser​	HD600​	300​	102​	0.6​	6.3​	1.38​	4.59​
Sennheiser​	HD650​	300​	102​	0.6​	6.3​	1.38​	4.59​
Sennheiser​	HD800​	300​	102​	0.6​	6.3​	1.38​	4.59​
Ultrasone​	Edition 8​	30​	96​	2.5​	25.1​	0.87​	28.94​

 
Note 1: Grado SR225i, RS2i, SR80i, GS1000i and PS1000 have the same nominal impedance and sensitivity.
Note 2: The last two columns are peak values related to the 110 dB SPL power column
 
One headphone jumps out as being particularly demanding, the HE-500. To power that headphone to 100 dB SPL average with peaks to 110 dB SPL (assuming the music has a crest factor of 10:1) it needs 12.6 mW avg and 125.9 mW peak.The next most demanding is the LCD-2 at 80mW peak. The rest can get by with less than 5mW avg and 50mW peak. Far less than 1W. Looking at the data at the Rockwell site link we find the HE-500 might push the WA7 to between 1 and 5% THD when driven to 110 dBSPL. For the other headphones the THD will likely be between 0.1 and 1.0% when driven so loud. It will also mostly be even order harmonic distortion rather than odd order harmonic distortion. If we keep the listening levels at 85 dB SPL with peaks to 95 dB SPL the WA7 won't even approach 0.1% THD for most headphones. And those levels are still too loud for long listening sessions if one wants to conserve their hearing long term.
 
Final note, I used different equipment but the computations are the same standard for electrical measurements. The differences are likely due to variance in tube characteristics. My points are as follows:
 
1) my measurements corroborate a select portion of the Rockwell site well enough that I tend to trust the others he published
2) my measurements also recreate what I think Jack has spec'd though he left out the 10% THD for 1W at 32 ohms - this is a common measurement for mfgs
3) The WA7 will perform exceptionally well even for the HE-500 if one listens at levels consistent with avoiding long term hearing loss
 
I use both the HE-500 and T90 with my WA7 and enjoy their respective sonic signatures very much with this amp.

 

[GalaxyGuy]

Nice post, AB!  Thanks!
 
I'm a bit surprised that the HE-500's are so much harder to drive than the LCD's.  Still, your measurements pretty much correspond to what I've heard with my own two ears.  As I said previously, I think the WA7 sounds pretty darn good with the HE-500's.  Lately my wife has been complaining about the sound leakage from my open-backed headphones, so I've picked up a T5p.  The WA7 sounds very good, indeed, with this headphone, and the comfort level of those cans is really, really high!  They don't have the same kind of soundstage that you get with open-backed cans like HD800 or HE-500, but they sound pretty fantastic to me.  I'd love to hear a pair of TH-900's some time, but I'm not sure my wallet could stand it.

 

[Kevin Brown]

Quote:

Nice post, AB!  Thanks!
 

 
+1. 

 
I would have a question: any chance you could put Grado numbers in with the other headphones you have?
 
I am on my 2nd day of listening.  Just for a data point, with older, well mastered CDs, with good dynamics and not much compression (i.e., before the loudness wars took their toll on CD mastering), I haven't pushed the vol knob up above about 11 o'clock.
 
It is a great sounding amp.  (I am still using an offboard DAC though; that testing for later).  Warm but detailed, slightly lush but without any harshness, brittleness or fatigue.  Not overly "tube-y", but accurate too.

 

[atomicbob]

Thank-you GG & KB.
 
Which Grados would be representative of commonly owned or which would you like to see added?
 
Loudness wars lowered crest factors which increases listening fatigue. Listen to a level matched pre / post hyper-compressed recording and it is so obvious. The high crest factors prior to compression allow the music to breath properly.  I realize this isn't available to most unless you are in the business or have access to a person in the mastering business.

 

[Kevin Brown]

^^^
 
I think any of the good lower end models all have the same specs.  If you could look for anything from the SR225i to the RS2i, I think the specs are all the same.

 

[atomicbob]

I was able to hear the TH-900 on my WA7 at a local head-fi meet. It reminded me of the Lawton Audio modified Denon AH-D7000, and it sounded very good for its particular sonic signature. Plenty of solid bass. I wish I could have heard a T5p side by side with the TH-900. In the end the T90 are still the cans that spend the most time on my head with the WA7. They work well with my ears.

 

[atomicbob]

Quote:

^^^
 
I think any of the good lower end models all have the same specs.  If you could look for anything from the SR225i to the RS2i, I think the specs are all the same.

I have added Grado to the table in post #279. Many models do appear to all have the same nominal impedance and sensitivity.