What are the advantages/disadvantages of different amp topologies?

[Cellcbern]

Let's see between all of us in the Switzerland/Liechtenstein area if we can get a bunch of amps together from all different topologies and then on a suitable speaker for all of them, see which have the best subjective sound and then hopefully we find measurements for many of them and see if there is some correlation once we calculate the prediction from one of the metrics? Maybe we can get funding from the Swiss science foundation ?

I think we have several SET (KR, Ayon, Horning, Silvercore, Amplifon, Line Magnetic, Ukranian amp etc.), a new TriodeFET hybrid (Essentia), a more traditional hybrid(Lamm M1.1), a Class A SS amp or two (Accuphase and Plinius), PP tube both pentode (Not sure) and Class A triode (Nagra 845) etc. Maybe some Class D (anyone?) in there as well. Maybe a Class AB SS amp (Spectral, Plinius in AB mode) or two... about the only thing missing would be likely an OTL...unless you know someone with one?

Missing from your list is Pathos' unique single ended, zero feedback, Class A, OTL, "Inpol" hybrid topology, the best sounding implementation of which to my ears is still the 20+ year old "TT" integrated amp design.

 

[Republicoftexas69]

Missing from your list is Pathos' unique single ended, Class A, OTL, "Inpol" hybrid topology, the best sounding implementation of which to my ears is still the 20+ year old "TT" integrated amp design.

The Inpol design is still one of my favorites, wonderful sound. Had one some time back, wish I never sold it, oh well.

 

[Cellcbern]

The Inpol design is still one of my favorites, wonderful sound. Had one some time back, wish I never sold it, oh well.

So imagine an Inpol amp upgraded by the late Bill Thalman in consultation with the Pathos factory, using "worlds best" parts. That's what I have the pleasure of listening to every day.

 

[Republicoftexas69]

So imagine an Inpol amp upgraded by the late Bill Thalman in consultation with the Pathos factory, using "worlds best" parts. That's what I have the pleasure of listening to every day.

Nice, you are very fortunate. Enjoy.

 

[Atmasphere]

Thanks, Ralph - I really appreciate you sharing your experience and knowledge. Nelson Pass talks about distortion at about 11 minutes into in the interview link below - would you agree about a more pleasing sound with greater 2nd than 3rd order distortion, and also with his finding about differences in a positive vs negative phase for the 2nd order distortion?

Ye; I've noticed something similar- it seems that if there is a 2nd or 3rd harmonic of enough amplitude, it seems to bring out some detail. I think more research needs to be done in this area but I'm not holding my breath.

 

[morricab]

Missing from your list is Pathos' unique single ended, Class A, OTL, "Inpol" hybrid topology, the best sounding implementation of which to my ears is still the 20+ year old "TT" integrated amp design.

Yes, because it’s not a SET but a hybrid. We can add other unusual amps to the mix. I wish someone had made measurements of the NAT Symbiosis SE that I used to own. It was also single ended hybrid but a whopping 70+kg! It had a pretty radical sound as well…in someways better than SET and in some key ways not.

 

[Hear Here]

Glad you like it. I have had some Class D on my horns and...well, no that sound doesn't work for me.

There is no such thing as "that sound" from Class D, any more than there is from any other Class or Tube amp.

If you dismiss Class D out of hand, that's your loss. If you keep an open mind and positively look for a Class D amp that provides the sound you like, you'll find one.

 

[Republicoftexas69]

There is no such thing as "that sound" from Class D, any more than there is from any other Class or Tube amp.

If you dismiss Class D out of hand, that's your loss. If you keep an open mind and positively look for a Class D amp that provides the sound you like, you'll find one.

Some simply have their prejudice.

 

[Atmasphere]

There is no such thing as "that sound" from Class D, any more than there is from any other Class or Tube amp.

If you dismiss Class D out of hand, that's your loss. If you keep an open mind and positively look for a Class D amp that provides the sound you like, you'll find one.

Right. (Sorry to repeat what you wrote) class D does not define a 'sound' any more than class A. The reason class A was a thing was in single-ended amps you had no choice; in PP amps it was done to prevent distortion at the zero crossing point (crossover and notch distortion) of the audio signal and to minimize distortion thru harmonic cancellation.

Once that issue is dealt with in the design, the topology dominates the sound regardless the class of operation. This is true for class D as well. As a result, anyone engaging in the 'class D sound' is promoting a made up story- literally there's no such thing.

Class D is immune to the zero crossing point problem so that's not an issue. How feedback is applied (if it has feedback- you can have zero feedback class D amps that can sound quite musical) and how much has something to do with how they sound; if they are self-oscillating or not, the encoding scheme, which might be Pulse Width Modulation (PWM) or Pulse Density Modulation, Delta Sigma and so on. From what I've heard, the variation in sound of class D amplifiers is wider than you hear from tube amps from worst to best. That's a pretty wide range! So if you hear someone talk about the 'sound of class D' you know right away its someone with very limited exposure and their comments should be viewed in that light only.

 

[morricab]

There is no such thing as "that sound" from Class D, any more than there is from any other Class or Tube amp.

If you dismiss Class D out of hand, that's your loss. If you keep an open mind and positively look for a Class D amp that provides the sound you like, you'll find one.

I have owned 3 different ones and heard a dozen or more others. There is indeed a "sound". I don't dismiss any topology out of hand (indeed, virtually the only type of amp I haven't owned is a singled ended OTL) but experience has steered me away from them. You like them, that's fine. My experience with some of the best ones was "meh" at best and "ouch" at worst. IMO, they definitely don't work on horns...at least all passive ones like I have, where the bass is horn as well.

 

[morricab]

Apologies - I should have read more closely.

No worries, I would like to try a Pathos TT one day.

 

[morricab]

Some simply have their prejudice.

Others simply have their experience...

 

[Republicoftexas69]

Others simply have their experience...

Interesting, you have auditioned every class D and or GaN amplifier to prove this out?

 

[morricab]

Interesting, you have auditioned every class D and or GaN amplifier to prove this out?

No, but after a dozen or more a pattern emerges...

 

[Republicoftexas69]

No, but after a dozen or more a pattern emerges...

Yes indeed. You need to broaden your horizons. So do tell us of this dozen or more…..

 

[Hear Here]

Others simply have their experience...

Yes and my experience with Class D has been varied, but always with horn speakers.

I had an early Tripath evaluation board-based 12V DIY amp that was dire. This was an experiment while still using tube amps, mostly SETs but also an OTL and a PP. Some years later I bought a Red Wine Signature 30 amp that was then receiving good reviews. It was battery operated, so another advantage in that it was free from any power supply problems. It wasn't particularly good and was sent back to their Europe distributor for checks and later back to Red Wine for changes to the power supply and to reduce its gain. Still not good with my horns. Inside I found a bog-standard Tripath board - to my surprise and disappointment!

It was just 3 years ago that I made a conscious decision to search for a solid state amp to replace my SETs but only if it provided as satisfying a listen as the tube amps. After a series of tests with 12 bought or borrowed amps, I chose a Class D one, not only because it sounded as good as any of the others, but also because it offered far more features and its price was highly attractive. Only a couple of others near-matched the Class D and they were simple power amps and cost 2 to 3 times the price of the far more feature rich M33.

If you insist on wanting to mimic the sound of a tube amp, you may not find a Class D that does this as accurately as you may like, but if you want an amp that offers an equally exciting listen (as you'd expect with horn speakers), you certainly can with Class D if you sniff around and choose carefully. It's a bit like saying you love film-based photos and insist on keeping your old roll-film camera when everyone else has now accepted the obvious advantages of a digital camera! They took decades to reach maturity - as Class D has and, like digital cameras, they continue to improve generation by generation.

 

[Atmasphere]

Interesting, you have auditioned every class D and or GaN amplifier to prove this out?

I see this sort of thing all the time. People hear one or five amps and they think they've heard them all. So ridiculous. It doesn't even seem to matter what kind of amp it is!

We've been making OTLs for 45 years and I still have people tell me that 'OTLs sound thin' and other such nonsense. OTLs vary quite a lot in sound qualities from one to the next since their sound qualities are topology dependent like any other amp. Some OTLs are quite complex and others (like ours) have a simpler signal path then even an SET, with only one stage of gain.

These days the class of operation is likely a red herring and has nothing to do with the sound, if the designer is at all competent.

 

[Ron Resnick]

These days the class of operation is likely a red herring and has nothing to do with the sound, if the designer is at all competent.

Does this suggest that you believe the SET's benefit of avoiding the crossover distortion of push-pull doesn't matter sonically much anymore? Or would that take your point too far?

 

[morricab]

Yes and my experience with Class D has been varied, but always with horn speakers.

I had an early Tripath evaluation board-based 12V DIY amp that was dire. This was an experiment while still using tube amps, mostly SETs but also an OTL and a PP. Some years later I bought a Red Wine Signature 30 amp that was then receiving good reviews. It was battery operated, so another advantage in that it was free from any power supply problems. It wasn't particularly good and was sent back to their Europe distributor for checks and later back to Red Wine for changes to the power supply and to reduce its gain. Still not good with my horns. Inside I found a bog-standard Tripath board - to my surprise and disappointment!

It was just 3 years ago that I made a conscious decision to search for a solid state amp to replace my SETs but only if it provided as satisfying a listen as the tube amps. After a series of tests with 12 bought or borrowed amps, I chose a Class D one, not only because it sounded as good as any of the others, but also because it offered far more features and its price was highly attractive. Only a couple of others near-matched the Class D and they were simple power amps and cost 2 to 3 times the price of the far more feature rich M33.

If you insist on wanting to mimic the sound of a tube amp, you may not find a Class D that does this as accurately as you may like, but if you want an amp that offers an equally exciting listen (as you'd expect with horn speakers), you certainly can with Class D if you sniff around and choose carefully. It's a bit like saying you love film-based photos and insist on keeping your old roll-film camera when everyone else has now accepted the obvious advantages of a digital camera! They took decades to reach maturity - as Class D has and, like digital cameras, they continue to improve generation by generation.

I want an amp that sounds more like what I hear live...

All amps have artifacts (or distortions if you will) but some amps have artifacts that signal "synthetic" to me. It's like the difference between feeling real silk and some polyester synthetic. No matter how hard you work at getting the polyester to feel soft, smooth, sleek etc. it still doesn't feel like real silk. The one who knows real silk intimately immediately can tell the difference even if others with less sense for the feel cannot tell.
BTW, it is not just "tube amps" ...I find most of those unacceptable as well. Only very good SET amps seem to hide their artifacts better and as a result sound less synthetic than other amp types. The only other technology that I have heard that is at that level (or perhaps higher) is the new generation of "neo" hybrids, Like what Aries Cerat is producing (the TriodeFET... it has only a single stage!) or the ones from Silbatone in Korea. NAT also now makes an amp they call the Nu-fet that combines a Nuvistor and a FET. The one mentioned above from Pathos is an interesting concept as was the NAT Symbiosis SE that I had in the past. The only OTL that I would perhaps consider today would be a single ended one.

It's the reduction of what tells my brain it's not silk but polyester that I look for in all my electronics...not just the amps.

 

[morricab]

I see this sort of thing all the time. People hear one or five amps and they think they've heard them all. So ridiculous. It doesn't even seem to matter what kind of amp it is!

We've been making OTLs for 45 years and I still have people tell me that 'OTLs sound thin' and other such nonsense. OTLs vary quite a lot in sound qualities from one to the next since their sound qualities are topology dependent like any other amp. Some OTLs are quite complex and others (like ours) have a simpler signal path then even an SET, with only one stage of gain.

These days the class of operation is likely a red herring and has nothing to do with the sound, if the designer is at all competent.

You should apply your logic the other way around...you haven't heard all SETs and yet you want to classify them.

Honestly, this is nonsense because different topologies do have characteristics that are common. For example, no matter how hard some people have tried, no one has made a Class A PP SS amp sound like a Class A PP triode amp...let alone sound like a SET. There have been some that on a casual listen might sound somewhat similar but a bit of critical listening quickly dispels that notion.

Even a Class A PP DHT triode amp (like with 300B or 2A3) with no feedback will not sound like a SET of similar quality. It is probably the closest I have heard besides these new "hybrids" but careful listening demonstrates the difference.