PSET vs SET vs Push Pull for Similarly Powered Amps. Which are Most Musical? More Resolving? What are the Trade-offs?

[caesar]

Assuming proper speakers, of course

How does SET compare to PSET?

Does Push Pull always lose?

What have you heard?

 

[ddk]

Assuming proper speakers, of course

How does SET compare to PSET?

Does Push Pull always lose?

What have you heard?

https://forum.audiogon.com/discussions/set-vs-pset

 

[caesar]

https://forum.audiogon.com/discussions/set-vs-pset

Hi DDK,

Thank you. Will read through that.

I also wonder if push - pull always give up musicality in favor of detail

 

[ddk]

Hi DDK,

Thank you. Will read through that.

I also wonder if push - pull always give up musicality in favor of detail

More detailed than a SET? Of course everything is based on the design and designer's competence but all things being equal and great, sonically you'll have get the most natural sound with most resolution and detail from a pure SET design given the right speaker. You can get almost similar resolution from a competent PP amplifier but not the same degree of naturalness.

david

 

[microstrip]

IMHO we can't debate categories in general. Implementation can surpass the existing dogmas. The Marantz Project T1 did not sound like other tube pushpull amplifiers I have owned.

Some SETs have terrible distortion and measurements, others not. Which of those is a "typical" SET?

 

[Atmasphere]

More detailed than a SET? Of course everything is based on the design and designer's competence but all things being equal and great, sonically you'll have get the most natural sound with most resolution and detail from a pure SET design given the right speaker. You can get almost similar resolution from a competent PP amplifier but not the same degree of naturalness.

david

This is simply false; not picking on David as this is a very commonly held opinion with SET owners. Let's 'unpack' this a bit. The first thing that comes up (which should be obvious but somehow is overlooked with such comments) is that the SET in question usually runs a directly-heated triode and no feedback, while the push pull amp is often a pentode based amp operating class AB with more power and often with feedback.

Obviously this isn't a fair comparison, its apples and oranges. If you really want to know what the difference is about, you need to do the comparison in one of two ways: since the SET uses a DHT output tube, perhaps so should its push-pull competition. The type 45 is a venerable power tube for an SET; perhaps if we compared this to a push-pull type 45 amp? What?- there isn't one?? Actually I built one for fun and compared it to a type 45 SET; the former had more bandwidth, more usable power and you could make out vocals and the like with greater ease... this on a full range speaker of 101dB and 16 ohms.

But anecdotes aside, the other variables are the driver and voltage amplifier tubes, which should be the same in both amps, as well as things like coupling caps and rectification. But the other way to approach this is if you have an 7-watt SET, maybe the push-pull amp should only make that power too- so maybe you would use something like a 45 for that (it will make 6-7 watts).

To really hear what an SET does, you need a loudspeaker that is efficient enough that the amp is never driven above about 20-25% of full power. This is because at about that level, the higher ordered harmonics start to show up as a distortion product, initially only on transients. The ear uses the higher ordered harmonics to sense sound pressure, so if they are showing up on transients, this will make the amp sound 'dynamic'. But its really distortion masquerading as 'dynamics' (hence the quotes). This is where SETs get that reputation for being so dynamic- what is happening is that a speaker of too low efficiency is being used with the amp. As you decrease the power, the distortion falls off to the point of unmeasurable. This is the source of that 'magical inner detail' so many associate with these amps.

Most push-pull amps start to make more distortion below a certain minimum power level, often about 5-7% of full power. But not all; if the amplifier is fully differential from input to output and employs no feedback then it too will share this property of 'linearly decreasing distortion as power is decreased' with SETs.

I suspect that if one did such a comparison on this basis, it would be found right away that the advantage of SETs is pretty much nil. I agree; its obvious that it would be difficult, but if you really want to be able to say something like the quote above then what I've laid out here would have to be the convention. Otherwise there's simply no basis for it.

 

[Kingrex]

To ask this question you have to drag speakers into the equation. Amps don't make sound, speakers do.

 

[Atmasphere]

To ask this question you have to drag speakers into the equation. Amps don't make sound, speakers do.

That is true. Since nearly all SETs operate without feedback, it can be a pretty good assumption that the speaker needed to do any sort of valid comparison be one that is designed for amplifiers with a higher output impedance. For more on this see
http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html

SETs tend to operate as 'power sources' rather than 'voltage sources' for which most speakers are designed. In fact almost any tube amp not running feedback will act as a power source (albeit an imperfect one, but most solid state amps that can behave as voltage sources aren't perfect either...).

In a way the holy grail of SETs is one that makes a bit of power. But this is also anathema to the SET experience as the output transformer imposes severe limitations on bandwidth as more output power is designed into them. For this reason alone I would expect an SET to outperform (and sound better than) a PSET although the former would not make as much power.

 

[Kingrex]

Ralph always knows so much more about how and why amps and speakers behave the way they do. I'm just a dumb user.

FWIW. I bought a used set of Audio Black Shadow that were in my system driving my PAP Trio 15 horn speaker for about 2 weeks . They were the most "Real" and "life like " amp I have had in my setup. But it had major ground fault issues and was incredibly noisy. It was close to unusable due to noise. But I liked what I heard enought to send it off for repairs. I was told someone wired the circuit wrong, there were two snappd in half wires and missrouted wires all injecting and creating noise. Repairing those issues should dramatically improve the way the amps perform. As in less noise and ground issues.

I have played a PPKT88/El34 amp and a PP 811A amp on these speakers. And a Class D amp. The 845 SET is quite a bit more natural and musically beautiful. I actually opted to have the BS totally recapped with high end caps in the signal, new high quality tube sockets and proprietary tube isolators to keep noise down. I also swapped out the crappy 19 year old alps pot for a stepped ladder attenuator. The builder says the amps will be a significant upgrade from what I heard.

But my system is one system with one set of speakers. Others results may vary.