Woo Audio WA6
- Thread starter Zing
- Start date
In another thread, Soundhound just mentioned the magic word - Class A - which reminded me that I never got an answer or explanation to a query about amplifier topologies. Forgive me for bringing it up again.
It was my original intention to buy the Woo WA3 for a number of reasons, not the least of which were its claimed SNR (95dB) and THD (0.08%) specs. Surprisingly, the more expensive WA6 has a lower SNR (93dB) and a higher THD (0.3%). Aside from those, the only differences are single-ended OTL vs. single-ended triode.
I'm sure most of us remember Altec constantly extolling the virtues of single-ended triode amps and, quite franky, it was that virtue extolling that ultimately tipped the scales in favor of the WA6 over the WA3. With this preamble out of the way...
...if SET is superior to SE OTL, why wouldn't its specs concur? In other words, why would a superior topology have inferior specs?
It was my original intention to buy the Woo WA3 for a number of reasons, not the least of which were its claimed SNR (95dB) and THD (0.08%) specs. Surprisingly, the more expensive WA6 has a lower SNR (93dB) and a higher THD (0.3%). Aside from those, the only differences are single-ended OTL vs. single-ended triode.
I'm sure most of us remember Altec constantly extolling the virtues of single-ended triode amps and, quite franky, it was that virtue extolling that ultimately tipped the scales in favor of the WA6 over the WA3. With this preamble out of the way...
...if SET is superior to SE OTL, why wouldn't its specs concur? In other words, why would a superior topology have inferior specs?
soundhound
Well-Known Member
The very short answer is that with tube gear, distortion specs do not really matter (within reason of course), and should not be used to judge the quality of an amp. Actually in solid state amps too, the numerical distortion spec does not really matter - what is more important in both SS and tube amps is the spectral distribution of the distortion components.
A SET amplifier's distortion spectra ends basically at the 5th harmonic, unless the amp is overdriven into clipping. Harmonics at the 5th and below are benign to the ear, and it takes really large amounts of this distortion (several percent) to be audible at all as "distortion". The even harmonics especially, the 2nd and 4th, are particularly benign, being even octave multiples of the fundamental.
A SE OTL (output transformerless) amp's distortion spectra is more likely to be more polluted with harmonics above the 5th (this amp probably uses global negative feedback where the SET does not, but that's just a guess - negative feedback reduces distortion usually at the expense of a "dirtier" distortion spectra).
In transistor amplifiers, the distortion spectra usually goes way up past the 10th harmonic, and even very small amounts of this high order harmonic distortion (like .01% or less) can degrade the sound of the amp and make it sound "hard" or "sterile".
Noise measurements are also useless unless they state the weighting factor (A-Weighted, No weighting etc), and most importantly what the number is referenced to. Without those qualifiers, the S/N number is truly useless. Even with qualifiers, these numbers can be fudged in many ways.
So, in a nutshell, specs (within reason again) are basically useless indicators for how something will sound.
A SET amplifier's distortion spectra ends basically at the 5th harmonic, unless the amp is overdriven into clipping. Harmonics at the 5th and below are benign to the ear, and it takes really large amounts of this distortion (several percent) to be audible at all as "distortion". The even harmonics especially, the 2nd and 4th, are particularly benign, being even octave multiples of the fundamental.
A SE OTL (output transformerless) amp's distortion spectra is more likely to be more polluted with harmonics above the 5th (this amp probably uses global negative feedback where the SET does not, but that's just a guess - negative feedback reduces distortion usually at the expense of a "dirtier" distortion spectra).
In transistor amplifiers, the distortion spectra usually goes way up past the 10th harmonic, and even very small amounts of this high order harmonic distortion (like .01% or less) can degrade the sound of the amp and make it sound "hard" or "sterile".
Noise measurements are also useless unless they state the weighting factor (A-Weighted, No weighting etc), and most importantly what the number is referenced to. Without those qualifiers, the S/N number is truly useless. Even with qualifiers, these numbers can be fudged in many ways.
So, in a nutshell, specs (within reason again) are basically useless indicators for how something will sound.
soundhound
Well-Known Member
Zing said:
don't worry, you bought the better of those two amps :text-imsorry:
soundhound
Well-Known Member
GreatDane said:
Sorry - I meant to say Partials :teasing-tease:
Do different tubes actually sound different?
I have a birthday coming up and I'm thinking about throwing out some hints for the Sophia Princess Mesh Plate 274B. Woo is selling it for $150 but their description reads like bullshit marketing hyperbole. Then again, I know dick about tubes.
If nothing else, I like the glow of this tube but I wouldn't ask my family to spend $150 so I can enjoy looking at it. However, if there are sonic gains to be had, that's another story entirely.
I have a birthday coming up and I'm thinking about throwing out some hints for the Sophia Princess Mesh Plate 274B. Woo is selling it for $150 but their description reads like bullshit marketing hyperbole. Then again, I know dick about tubes.
If nothing else, I like the glow of this tube but I wouldn't ask my family to spend $150 so I can enjoy looking at it. However, if there are sonic gains to be had, that's another story entirely.
I did notice some difference between tubes in my Jade amp. Both the preamp (small) and power (large) tube had an affect on the sound. It was pretty subtle, and required some careful analytical listening, but the difference was there. But my tubes were not so pricey, I think ~$80 was about the most I paid for any tube, and most were a lot less.
soundhound
Well-Known Member
Since tubes are mechanical things, there is going to be small variances in the geometry of the grid, anode, cathode etc. This cannot help but cause small variances of how different makes of tubes behave, or different tubes in a particular batch. Usually the practical effect of these differences is different harmonic distortion characteristics. In the end though, these changes can be very subtle to the ear from tube to tube.
Myself, I don't do tube rolling, instead I buy high quality tubes (no Chinese in other words) and let it go at that since my system uses so many tubes that small differences between them tend to average out through the signal chain. I can see however where changing one tube in a headphone amplifier which has only two tubes would make a more substantial difference since in that case you're changing 50% of the tubes.
Myself, I don't do tube rolling, instead I buy high quality tubes (no Chinese in other words) and let it go at that since my system uses so many tubes that small differences between them tend to average out through the signal chain. I can see however where changing one tube in a headphone amplifier which has only two tubes would make a more substantial difference since in that case you're changing 50% of the tubes.