Mastersound PF100 PSET Amplifier

[Atmasphere]

Yeah, and this is why (IMO) "voicing" is important. If you've ever listened to something like a Benchmark amplifier - really any amplifier designed primarily for absolute minimal distortion - you'll generally hear the opposite effect: dead, compressed sound. So the trick is to strike the right balance in order to.soumd natural. Of course, there are many other factors that effect the final sound but design point and resulting distortion is certainly one.

In our 45 years of operations we've never 'voiced' anything we've made. I'm not even sure what that might mean. We've always designed for lowest distortion. Reviews and awards (and the fact we're still around...) seem to indicate that our amps don't sound 'dead' or compressed (and I know what you mean by that, having heard a few amps recently that sounded exactly that).

So I think its something else; if the response to our class D amp is any indication, it appears that the distortion signature of the amp is what is going on. If by 'voicing' this is what you mean, then we're on the same page. IMO/IME since distortion can't actually be eliminated, what distortion the circuit does have should be as innocuous as possible, since the ear interprets all forms of distortion as some kind of tonality (just in the same way that harmonics create the tone colors of musical instruments).

 

[Ron Resnick]

Yeah, and this is why (IMO) "voicing" is important. If you've ever listened to something like a Benchmark amplifier - really any amplifier designed primarily for absolute minimal distortion - you'll generally hear the opposite effect: dead, compressed sound.

I stipulate it's not my field, but I have never understood the concept of voicing an amplifier. (I can understand the concept of voicing a loudspeaker, where crossover frequency and slope affect the resulting sound and frequency response of the loudspeaker.)

 

[Atmasphere]

I stipulate it's not my field, but I have never understood the concept of voicing an amplifier.

Neither have I!

 

[mtemur]

Yeah, and this is why (IMO) "voicing" is important. If you've ever listened to something like a Benchmark amplifier - really any amplifier designed primarily for absolute minimal distortion - you'll generally hear the opposite effect: dead, compressed sound. So the trick is to strike the right balance in order to.soumd natural. Of course, there are many other factors that effect the final sound but design point and resulting distortion is certainly one.

Another example for distortion free but dead, lifeless sounding amplifier is Halcro. I still remember DM58 or 68 from early 2000s. It was so lifeless that I even started to love my Mark Levinson 333.

 

[PYP]

In our 45 years of operations we've never 'voiced' anything we've made. I'm not even sure what that might mean. We've always designed for lowest distortion. Reviews and awards (and the fact we're still around...) seem to indicate that our amps don't sound 'dead' or compressed (and I know what you mean by that, having heard a few amps recently that sounded exactly that).

So I think its something else; if the response to our class D amp is any indication, it appears that the distortion signature of the amp is what is going on. If by 'voicing' this is what you mean, then we're on the same page. IMO/IME since distortion can't actually be eliminated, what distortion the circuit does have should be as innocuous as possible, since the ear interprets all forms of distortion as some kind of tonality (just in the same way that harmonics create the tone colors of musical instruments).

@Atmasphere Have you ever chosen one component over another (capacitors, for example) when they both measure the same (or very similar)? Or do you go entirely by measuring lowest distortion? And consistent build and availability.

When I read about folks who have heard dead amplifiers (and I don't doubt their ears), I wonder if sometimes the amplifier is transparent and what is heard it an impedance mismatch or noise generated by upstream components. My personal experience with very low distortion class D amps led me to identifying upstream noise and eliminating it where I could (sometimes that meant new gear).

 

[bazelio]

I stipulate it's not my field, but I have never understood the concept of voicing an amplifier. (I can understand the concept of voicing a loudspeaker, where crossover frequency and slope affect the resulting sound and frequency response of the loudspeaker.)

Design choices and component selection effect the final sound of an amplifier. It's that simple. As an example, if you've ever avoided negative feedback despite its positive effect on measurable parameters, then I'd say you've voiced your amplifier. I'm suggesting that making design decisions in both objective and subjective manners is preferable.

 

[Atmasphere]

@Atmasphere Have you ever chosen one component over another (capacitors, for example) when they both measure the same (or very similar)? Or do you go entirely by measuring lowest distortion? And consistent build and availability.

We've definitely chosen resistors and capacitors over their brethren. If you know what to look for in the component specs you can also predict which will sound better. However, the more feedback you are able to use, the less the components will influence the sound, as feedback gives the circuit the ability to reject such influences. For this to work, the feedback must be properly applied! Its control theory and IMO, control theory isn't that well understood in the audio world... so feedback has gained a bad rap amoungst audiophiles and rightly so, because if poorly applied it adds distortion... /rant.

 

[bazelio]

We've definitely chosen resistors and capacitors over their brethren. If you know what to look for in the component specs you can also predict which will sound better. However, the more feedback you are able to use, the less the components will influence the sound, as feedback gives the circuit the ability to reject such influences. For this to work, the feedback must be properly applied! Its control theory and IMO, control theory isn't that well understood in the audio world... so feedback has gained a bad rap amoungst audiophiles and rightly so, because if poorly applied it adds distortion... /rant.

As another example of subjective "voicing", I have found that aiming for absolute lowest ripple on B+ doesn't sound best to me, at least for DHT SET designs. That is to say, I don't find that a design goal of near zero hum with your ear up to the speaker and the volume cranked is the right approach because trying to achieve this also seems to suck the life out of the music. A better approach to my ears is hum being inaudible from the listening position at nominal listening volume, i.e. no more filtering than absolutely necessary. This of course may only be feasible when you're designing for yourself as opposed to designing a general.purpose product for the masses.

 

[morricab]

We've definitely chosen resistors and capacitors over their brethren. If you know what to look for in the component specs you can also predict which will sound better. However, the more feedback you are able to use, the less the components will influence the sound, as feedback gives the circuit the ability to reject such influences. For this to work, the feedback must be properly applied! Its control theory and IMO, control theory isn't that well understood in the audio world... so feedback has gained a bad rap amoungst audiophiles and rightly so, because if poorly applied it adds distortion... /rant.

But always creates a noise modulated "noise" floor...and is susceptible to back EMF from the loudspeaker...that comes from Otala.

 

[Salectric]

As another example of subjective "voicing", I have found that aiming for absolute lowest ripple on B+ doesn't sound best to me, at least for DHT SET designs. That is to say, I don't find that a design goal of near zero hum with your ear up to the speaker and the volume cranked is the right approach because trying to achieve this also seems to suck the life out of the music. A better approach to my ears is hum being inaudible from the listening position at nominal listening volume, i.e. no more filtering than absolutely necessary. This of course may only be feasible when you're designing for yourself as opposed to designing a general.purpose product for the masses.

That’s been my experience too.

 

[Atmasphere]

But always creates a noise modulated "noise" floor...and is susceptible to back EMF from the loudspeaker...that comes from Otala.

Crowhurst wrote about the noise floor created in the 1950s.

That is true if the feedback node is non-linear.

The EMF thing is a non-issue if the output impedance of the amplifier is low.

I'll add another problem: feedback can be problematic if the circuit does not have the Gain Bandwidth Product to support the feedback across the bandpass desired in the circuit. If the feedback is not supported, distortion will rise with frequency above a turnover point (which can be calculated easily enough if the GBP is known and the loop gain of the circuit is known). At the turnover frequency, the distortion will rise on a 6dB/octave slope but may increase at a high rate at high frequencies. So you can imagine that if the turnover frequency is at 1KHz, at 7KHz there could be quite a lot more distortion than the THD figure would suggest! 7KHz is right at the upper end of the ear's most sensitive region (Fletcher Munson).

Most amplifiers made with feedback have this problem. Its why feedback got a bad rap. Its not feedback's fault; its the fault of designers not understanding how to use it.

I'm of the opinion that rising distortion with frequency is a Bad Thing. FWIW, zero feedback amplifiers do not have this problem. But if you can generate sufficient Gain Bandwidth Product, then an amp with feedback can have a nice flat distortion vs frequency graph too. Its also possible to have a linear feedback node. That is why I talk about feedback being 'properly applied'.

 

[bazelio]

Crowhurst wrote about the noise floor created in the 1950s.

That is true if the feedback node is non-linear.

The EMF thing is a non-issue if the output impedance of the amplifier is low.

I'll add another problem: feedback can be problematic if the circuit does not have the Gain Bandwidth Product to support the feedback across the bandpass desired in the circuit. If the feedback is not supported, distortion will rise with frequency above a turnover point (which can be calculated easily enough if the GBP is known and the loop gain of the circuit is known). At the turnover frequency, the distortion will rise on a 6dB/octave slope but may increase at a high rate at high frequencies. So you can imagine that if the turnover frequency is at 1KHz, at 7KHz there could be quite a lot more distortion than the THD figure would suggest! 7KHz is right at the upper end of the ear's most sensitive region (Fletcher Munson).

Most amplifiers made with feedback have this problem. Its why feedback got a bad rap. Its not feedback's fault; its the fault of designers not understanding how to use it.

I'm of the opinion that rising distortion with frequency is a Bad Thing. FWIW, zero feedback amplifiers do not have this problem. But if you can generate sufficient Gain Bandwidth Product, then an amp with feedback can have a nice flat distortion vs frequency graph too. Its also possible to have a linear feedback node. That is why I talk about feedback being 'properly applied'.

GBP is an important factor, but it's not the only one. Other considerations like the open-loop gain, phase margin, stability, and the specific circuit design also play roles in determining the overall performance of the feedback system.

 

[Atmasphere]

GBP is an important factor, but it's not the only one. Other considerations like the open-loop gain, phase margin, stability, and the specific circuit design also play roles in determining the overall performance of the feedback system.

Of course! IMO phase margin and stability are the same thing if the feedback loop is properly designed.

 

[KeithR]

Observations, not attacks. Are you really surprised that folks might describe your demeanor and behavior as fanatical, biased, and defensive? In any event, I just read "The Perception Of Distortion" and it does not explicitly suggest a specific threshold where an audible difference between distortion levels becomes apparent. Instead it introduces a Gm metric as a better predictor of subjective perception of distortion versus THD and IMD. But my point has been that there is an audible difference between THD levels such as 1% and 2%. And the study doesn't address this one way or the other. It does suggest higher order distortion in low signal levels may be more perceptible. But my experimentation has been with DHTs recently and it's plenty audible in that context already. It's not too difficult to set up. A multi-tapped OPT allows you to effectively change the load the tube sees on the fly. Headphones allow you to really drive up that load value in order to affect THD. So adjust the load, listen, measure THD, repeat. There's also the inline THD generator boards that were given away as door prizes at a Burning Amp a few years ago. That's an educational gizmo to play with as well. I just prefer any hands-on approach to reading theories.

BTW that study is of very limited scope and specific test conditions - e.g. one song. And with no mention of who the 42 participants are other than randos having normal hearing sensitivity, I'd be very cautious about hanging my hat on the results. Did those randos have any musical background, are they even audiophiles or in any way calibrated to audio playback nuances (which the majority of the general public are not), etc. Major grain of salt. I think you're over-selling it.

Just wait till you read Cheevers thesis lol.

 

[morricab]

Just wait till you read Cheevers thesis lol.

Have you read it?

 

[KeithR]

Have you read it?

I did, surprised you think it’s anything noteworthy as a scientist. N=5 iirc

 

[morricab]

I did, surprised you think it’s anything noteworthy as a scientist. N=5 iirc

It’s the methodology and the hypothesis…just because the number of trials is insufficient for a firm conclusion is not necessarily relevant. You might have heard of the falsifiability principle that was put forward by philosopher Karl Popper? Basically, you can’t prove a hypothesis…you can only falsify it. I think Cheever’s trials demonstrated his hypothesis has merit…his limited trial did not falsify his hypothesis.

I think Cheever’s logic is sound, the hypothesis looks well rooted in what’s known about hearing and psychoacoustics, the history of the testing interesting and his metric potentially very useful. I think Geddes corroborated a lot of points that Cheever made and an overall picture of preference on general can be made.

You seem to think you can hear 2nd order distortion made by SETs and this is why you discount them. The data suggests otherwise. You are most likely hearing higher order effects from poor design like undersized output transformers or inadequate driver circuits.

 

[Atmasphere]

You seem to think you can hear 2nd order distortion made by SETs and this is why you discount them.

The 2nd ordered harmonic manifests as 'warmth' or 'bloom' (audiophile terms used in the US...). Given that SETs are the 'warmest' and have the most 'bloom' it follows that they should have more 2nd ordered harmonic than other amps, and when you measure them you find this is true.

This may be a false assumption on my part, but in the last 30 years I've not seen a contradiction.

 

[PYP]

Nelson Pass (https://6moons.com/industryfeatures/distortion/distortion_3.html):

"Many audiophiles believe that 2nd harmonic is to be preferred over 3rd harmonic. Certainly it is simpler in character and it is well agreed that orders higher than third are more audible and less musical. However, when given a choice between the sound of an amplifier whose characteristic is dominantly 2nd harmonic versus 3rd harmonic, a good percentage of listeners choose the 3rd.

I have built many examples of simple 2nd and 3rd harmonic 'types' of amplifiers over the last 35 years. When I say types, I mean that they used simple Class A circuits described as 'single-ended' versus 'push-pull' and so tended to have a 2nd harmonic versus 3rd harmonic in the character of their distortion but were not made to deliberately distort.

Anecdotally, it appears that preferences break out roughly into a third of customers liking 2nd harmonic types, a third liking 3rd harmonic and the remainder liking neither or both. Customers have also been known to change their mind over a period of time."

 

[morricab]

The 2nd ordered harmonic manifests as 'warmth' or 'bloom' (audiophile terms used in the US...). Given that SETs are the 'warmest' and have the most 'bloom' it follows that they should have more 2nd ordered harmonic than other amps, and when you measure them you find this is true.

This may be a false assumption on my part, but in the last 30 years I've not seen a contradiction.

Only above a certain level…below that level it is inaudible.