That peak at 100K is a resonance, probably associated with the capacitance in the windings. That sort of thing can contribute to brightness if not tamed. A network to do that might be a good idea IMO.
Mastersound PF100 PSET Amplifier
- Thread starter Ron Resnick
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Yeah, a zobel might help. But going back to the phase question, do you have any thoughts how much phase rotation is audible at 10k+ ?
At 10KHz probably not a lot. That's still too high for much imaging information to be affected. I consider that the lower limit for that- the lower you have phase issues- the more audible it will become via tonal and imaging effects.
A high-powered SET or PSET is my alternative universe "fantasy amp," much like MikeL flirted with the ML3s for the same reasons.
Thank you, Ralph. I understand much of this.
In my idiosyncratic application little to nothing will be demanded from these amplifiers below 100 Hz. (A full range signal is high-passed to the ribbon towers at 200 Hz.) I would not use SET amplifiers full-range at anything remotely as insensitive as 88dB.
30 Watt is not high power.
200 Hz is an high crossover frequency to bi-amp with different amplifiers - I doubt that you can match a SS amplifier for the bass towers with a SET for ribbons. Remember that typical SETs have an output impedance of 3-5 ohm - an extremely low damping factor. The VTL Siegfried's seem a wiser match!
3-5 ohms? Some yes but many are closer to 1-2 ohms. Anyway the big BG driver in the Gryphon is a nice flat 4 ohms and given there is no bass what does damping factor have to do with anything?
+1
For this reason, for the ribbons, I have the Siegfried IIs on the lowest damping factor setting.
SETs and 4 ohms doesn’t seem like a match made in Heaven. High powered SET is an oxymoron to me. And those Wavac measurements sorta tell the tale.
Seriously, trying to get that 'SET magic' from an amp of this size, and actually needing the power is IMO a Bad Idea. What you might not be keeping in mind is that any SET sans feedback (which is almost all of them) really only has about 20-25% (the latter on a good day) usable power. Above that you get higher ordered harmonics appearing on transients (where the power usually is), causing the amp to sound 'dynamic'. This is because our ears use those higher ordered harmonics to sense sound pressure- they are interpreted in part as 'loudness'. The other part is they contribute to brightness so the amp gets 'shouty'; it sounds loud. This is why so many SET owners say that 80-85 dB is plenty loud for them.
Its the mark of the best systems that they don't sound loud even when they are.
IOW in a good system the higher ordered harmonics are not generated such that they are interpreted as loudness cues.
So if you really want to hear what any SET really brings to the table, your speakers have to be efficient enough that the amp is never asked to make more than -6dB of full power (about 20% of full power). So a 100 Watt SET is really good for about 20 to 25 Watts.
OTOH, push-pull amps can have 90-95% usable power, even when they are zero feedback. They usually have dramatically less distortion at any volume level. For example our MA-1 amplifiers (which are triode class A2 OTLs with zero feedback) make 140 Watts into 8 Ohms, making about 0.5 to 1% THD at full power. The distortion spectra is really similar to that of an SET in that the lower ordered harmonics easily mask the higher orders, but the distortion product falls off at a faster rate as the order of the harmonic is increased (which means they are smoother and more detailed than any SET). Like an SET, since they are zero feedback, the distortion falls off fairly linearly to zero as the output power is decreased.
At full power before clipping most SETs make about 10% distortion. So you can see right away that there is an order of magnitude less distortion- at any volume level. Actually its better than that- at 10 Watts with the MA-1 the distortion is closer to 2 orders of magnitude lower. In simple terms, distortion obscures detail so this simply means the system is more transparent- especially at normal listening levels.
The idea that we can hear things we can't measure is actually a myth. It was once true, probably back sometime in the 1980s or so but measurement technology has advanced like technology has a way of doing in any field. But many audiophiles hold on to this myth living their lives according to a something that ended 40 years ago. Building a high end stereo around a myth like this is very likely going to result in flushing tens of thousands of dollars down the loo.
A flat 4 ohms is no problem whatsoever. The WAVAC measurements only tell a story for that amp…nothing more.
So distortion measurements matters ..? How high is too high ..?
BTW ,, SET magic begins in the Bass , eliminating an SET amp from playing the bass means you might as well go PP with power!
Regards
What is an unacceptable distortion level? There is not a simple answer to this question as it depends heavily on the amp topology and also the SPL at which one is listening. So, I don’t see how you can make the statements you make regarding usable power.
For example, if an amp has a high order distortion without significant low order masking (orders above 5th probably aren’t masked at all) at low power, one could argue from a psychoacoustic perspective it has 0% usable power.
My amp generates 35 SET watts at 1% THD…most of which is 2nd and 3rd harmonic…it is rated at 42 watts. I would argue that is a lot more than 25% of the rated power as usable. Part of the usable power thing is semantics. Most 8 watt 300B amps are really 4-6 watt amps and should be regarded accordingly.
If an amp is predominantly low order distortion up to close to clipping, what % THD is considered unacceptable? 1%? 5%?
Many amps with low measured distortion still don’t sound good…then what? Geddes demonstrated that there is NO correlation between THD or IMD and sound quality. The pattern matters much more.
Actually this is pretty easy to answer and IMO you got most of it right in your post above.
Unacceptable distortion is where it becomes obvious. When you hear the brightness of solid state- that's not acceptable. It might be '0.01%' (which might be the THD of the amp but the actual distortion is likely much higher since most amps with feedback have rising distortion with frequency; if the distortion was measured at a frequency too low, it will sweep this problem under the carpet insofar as the spec sheet is concerned; we'll hear it but it won't show on the spec sheet).
In the case of SETs, unacceptable distortion is heard if the amp sounds 'dynamic'. That occurs at about -6db of full power in most designs and conforms with the values you stated. This is why I've stated so often that if you really want to hear what any SET is about, your speakers should be efficient enough that this power level is not exceeded.
If the distortion is benign to the human ear (which means its innocuous) then it can be quite high and not be a problem.
We are moving away of Ron objective - high power SET amplifiers of more than 100W. Do you have complete measurements - Stereophile suite or similar - of your incognito SET amplifier you can share with us?
Can you Define low distortion ..? The only low distortion amps which sounds odd to me are class D amps ..!
What is odd sounding? I have had the pleasure of hearing Ralphs Class D GaN amplifiers and the AGD GaN and they sound great. I also have the Gold Note PA-10's in my system for the summer and they are Class A GaN amplifiers and I just love them. Sorry for the diversion from the original discussion.
How are the Class D GaN amps vs the Class A . I find most class D detailed sounding but with odd Timbre
Regards
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