Woo Audio WA6 SE Review and Measurements

Here are the measured gain levels from the high Z and low Z outputs. The gain is pretty darn high for headphones. 27db and 33db for low and high Z outputs respectively. This is moderate to low efficiency speaker gain. This highish gain is usable for Sennheiser HD6**, Mysphere, modded T50RP, but not so much for Grados or AD2000s. The large volume knob helps with adjusting volume.

Woo WA6 SE

 

Here is a Grado HF-3 use case (or why it's not a good idea to use Grados). It's mainly hum.

• Volume control used to attenuate
• 32-ohms load
• Output of 1kHz signal set to approximately -23dbU that translates into 90db SPL 1kHz peak for 0dbFS output for Grado HF-3

Another look, graph normalized to 0dbFS


Yup, hum will just be audible if we listen for it, at least for Grados. When music is playing, the hum won't be. It will be masked. Note that results may vary depending upon tubes, the time of day, etc.

Not necessarily. I didn't have any trouble with any of other non-cryo tubes.
I'd say socket saver if you want to listen to tubes all day instead of music. Otherwise don't bother. I already know I like the Sovtek with the Sylvanias and will stick with this. Life is too short.

I kept making changes, so I just provided one graph.

 

For the remaining measurements, unless otherwise indicated, I will concentrate on using a 300-ohm load, the low Z (still 20-ohms Zout) and typical levels for HD6** since this is where the WA6 SE excels from a sonics perspective. Before providing measurements, I will of course provide the disclaimer that tube amps tend to have high amounts of distortion and that SET tend to have a specific pattern of distortion.

Before one goes measurement extremist or fascist, it should be noted that even trained listeners among us may not necessarily hear distortion even as bad as 45db SINAD, or at least such levels of distortion would not necessarily correlate to "bad" sound. - read here: https://www.superbestaudiofriends.o...audio-science-review-review.9827/#post-316076

Here is another realistic look at harmonic distortion in general: https://www.superbestaudiofriends.o...ically-incorrect-audio-blog.7261/#post-249242

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Woo WA6 SE
FFT 1kHz
300-ohm load
0dbU output (around 0.775Vrms)
Low Z out (20-ohms ZOut)


The AC mains is still evident, but now it's 75db down and unlikely to be audible since our ears are not as sensitive in the lows. The distortion pattern is that of SET. We have high 2nd order (-46db) with successive lower harmonics in right triangle pattern.

Let's see what happens next as we decrease output. The higher harmonics slowly disappear with the 2nd being dominant but going down i level.

Woo WA6 SE
FFT 1kHz
300-ohm load
-10dbU output


Woo WA6 SE
FFT 1kHz
300-ohm load
-20dbU output


Woo WA6 SE
THND vs input levels (+27dBu, the gain, to get output level)
1kHz into 300-ohms
Low Z output


I will be honest, the measurements from a strictly SINAD perspective are not spectacular. However again, it should be noted that folks don't seem to complain about the distortion from the class D amp in the "highly regarded" JBL LSR305. The distortion pattern from amp in the JBL can be argued as actually "worse" since it emphasize the odd harmonics.

 

So back to rectifiers. I put three on the tester and they all came back with similar results in respect to voltage drop. The Shuguang 274B (middle) had a few volts less drop than the others. Oh well, I guess we won't learn anything here.





From a THD+N POV, it's too close to call:


I still stand by that the rectifiers sound different from each other and would be certain in blind test that I could tell the difference. At least we have established that the voltage drop from the tube tester and THD+N don't correlate my subjective impressions.

I hate it when this happens (having a theory, but going nowhere with the measurements). However, limited sets of measurements should not subject us to confirmation bias.

 

A few more measurements. Some roll-off on the high-end, moreso for 32-ohm loads. This is expect somewhat. Output transformers that are flat from 20Hz to 20kHz are difficult to find, especially at this price point.

Woo WA6 SE
Frequency Response
300-ohms
Low Z output


Woo WA6 SE
Frequency Response
32-ohms
Low Z output

 

Finally for transformer coupled amps, we want to take a look at the bass distortion. It's always going to get progressively worse as we head towards DC, and at higher levels. Note there are also some 60Hz and harmonics from AC. 25Hz and 50Hz distortion is worse (compared to 1kHz) with the 2nd harmonic at -37db (instead of -47db) for the 0dBu signal. I wouldn't say bass is the best from SET type amps. It would be most interesting to compare with other SET amps. The measurements are here for future reference.

Woo WA6 SE
FFT 50Hz
300-ohm load
0dbU output


Woo WA6 SE
FFT 25Hz
300-ohm load
0dbU output

 

These TV triodes are all similar to 6SL7 and 2A3/300B in the sense in that the first is super high gain and high plate resistance, and the second is low gain and low plate resistance ~1k-ohms.

 

OK, so sure I get why Jude hates me and has been telling every other vendor (and random people at small meets) he bumps into that I am a measurement fascist and that SBAF is dangerous and will poo on their stuff. Well, he's partially right. If a piece of gear is simply so damn awful, we will point it out. It a piece of gear that may be intended for IEMs has a 45-ohm output impedance, we will point that out. If something measures (and likewise sounds) egregiously off, we will make it know.

So WTF does he hate, like hate @zerofeedex's guys? (BTW, I get all this stuff second hand from people who I cannot name, some quite close to Jude). Well it's because of this: the King Jude postcard.

 

That's King Jude with Currawong / Amos at his side and Mike Mercer in the back. For the record, I like Amos and Mike. I've talked with them at meets in the past. They are good guys, but I do know that their gear reviews have resulted in groans from the Changstar crowd. Heck, here's a unsolicited plug for Amos' YouTube channel: https://www.youtube.com/channel/UCn4Y6OtD4lUEetb1CtpzURA

Jude I'm ambivalent about. I don't hate him at all. I am somewhat frustrated that my Head-Fi account isn't officially banned, but silently banned with its posting and PM privileges revoked. But that's about it. I do love pushing his buttons and hearing the industry reports that he went off to a vendor about me for several hours. We're talking lots of giggles and shits when this stuff comes back to me, which it inevitably does.

 

So why would Jude be all upset for @zerodeefex for creating such a postcard? I mean, folks who hate me post photos of my nipples sticking out from my t-shirts and I could care less.

BTW, the image above is not the original photochop. The original has been lost. I happened upon a small batch of postcards on the shelf last night (call it providence). I then proceeded to scan one of the prints to recreate the original as much as possible. The problem with prints is that they are essentially a bunch of small colored dots, so I had to reduce the size of the scan to eliminate the dots. AI-based up-sampling software was used to scale up to a usable size without the annoying scanned dots. Cool!

Anyway getting back on track. At a Bay Area CanJam, I think it was 2013, @zerodeefex printed out a million of these postcards. Seriously, we had a stack that probably went several feet high. Sometime in the afternoon, we started dropping, by the half dozen, these postcards at all the tables. We dumped a few at strategic locations like the bathrooms, water dispenser tables, lounge chairs and tables. We even went outside to the parking lot and put a postcard on every car.

I can't explain the feeling, but it was golden when we saw meet attendees pick up the postcards and giggle. Jude's agents picked up what was happening, so they proceeded to confiscate them wherever they saw them. @zerodeefex and I, having ample stock, simply resupplied where needed. I am not sure if Jude actually knew if I was involved as I flat out denied it in bold face lie to one of Jude's people. Haha. I will however confirm that @CEE TEE is completely innocent of this.

You have to understand that one of the reasons @zerodeefex and I are friends is because deep inside we are eight year olds who love to play practical jokes (there are more stories here not related to audio).

Well, the idea was to start a series of X-mas postcards every year. Someone sent this to me the other day:


So that's that. A short story this time.

 

HE1000 SE has lowish impedance, around 35-ohms. Planars such as these will sound a bit soft on the WA6 SE which has around 20-ohms Zout. I experienced similar with EC ZDS with similar Zout of 20-ohms. Certain things will sound great, particularly the mids. However the bass will not be as controlled as amps with near zero or single-digit Zout.

 

Yes, same for the DNA amps. I am pretty sure SJR Zout is well below 3-ohms. A design consideration behind that was so that it could run the 4-ohm woofers on the JBL Cabaret 4698/9.

In general, dynamics are best from the WA6 with exceptions of high Z planars. I even felt the Fostex T50RP variants and mods (they are 50-ohms) were a bit soft in the bass and on attacks.