SET Shootout China VS The USA

Shugang has liscened out its facilities to Psvane and Lin Lai to make their tubes INSIDE Shugaung’s manufacturing tool shop.

FWIW the Shugang plant that made their 6SN7s burned to the ground about 2 1/2 years ago (so that tube has gotten hard to get). I've heard they are rebuilding. But somehow the Psvane and LinLai 6SN7s are readily available so I don't think the statement above is entirely correct .

@mozartfan That Phillips amplifier is Push-pull.

my fav pre tubes are AX, AU, but honestly thats not based on exp, as i’ve not heard a 6SN7 series type pre tubes. I have no idea how they perform.

Once you hear what they do there’s no going back. If your SETs don't use 6SN7s there's a whole better world out there...

I take it you have a 12AT7 LTP @ +-300V with something like a cascode 10M45S CCS below?

@pesky_wabbit Yes, something very similar to that although the CCS is our own design. There's a 'steering diode' so the cathode voltage can't fall below -0.7 Volts; this protects the tube from developing cathode/filament shorts during warmup.

They just have come to learn that you have to listen to an audio product to really know if it’s for you. People realize there is no better way to select these products.

Yes- heaven forbid that audio companies actually publish spec sheets that told you how the gear sounds! As a result the only way to know if something works for you is to play it at home.

@alexberger

He used classic schematics. He runs his amplifiers without feedback and with feedback. The question is why you and my friend got so different results? What is the difference of your schematics to classical EL84 PP schematics?

Do you use balance input "+" for input and input "-" for feedback? Did you publish your schematic?

I think the problem comes in when you combine single-ended and PP circuitry at the same time! Thru algebraic summing you wind up with a more prominent 5th harmonic. Seems to me Norman Crowhurst wrote about this in some of his tomes back in the late 1950s- so this shouldn’t be a revelation (although I’ve come to suspect many designers are ignorant of his work). Back then the solution was to add feedback, which causes the circuit to be brighter due to added higher ordered harmonics (so to me does not seem like a solution). Crowhurst also wrote about this too, so none of this is new.

What strikes me as odd is, when these things have been known for so long, why do people persist in making what to me seems the same mistakes, over and over?

I am suggesting that your friend possibly made this mistake also. IME if you really want to hear what PP can do, you can’t combine it with single ended circuits or you’ll shoot the project down before it gets off the ground.

You do one or the other, but not both!

I didn’t publish my circuit, (which is very simple; two stages of gain including the output section which is a simpler signal path than most SETs), but I did publish an in-depth description over on audioasylum.com in the DIYtube section- search on ’EL95 amp’. The description allows anyone to build the circuit if they have the know how to build amps from scratch. The only tricky bit is I used some very effective constant current sources for the differential voltage amp which is something you don’t usually see in tube circuits (and so leaves performance on the table). To this end the Voltage amp also ran on + and - Voltages of the same value.

You are correct- the audio input is the + input and the feedback is on the - input. In that way there would be no intermodulations introduced at the feedback node. I got such good linearity out of the circuit I didn’t need the feedback at all; it was only used to reduce gain. IMO/IME if you are applying smaller amounts of feedback (like 15dB) that is really the only way to do it.

Upon introduction to a good DHT SET some listeners find a purity, aliveness, transparency and most importantly a genuine deep emotional connection with their music listening experience. These traits were found lacking to some degree with their previous non SET amplifiers. Some do return at some point to other amplifier types, but many do not. So perhaps other manufacturers should heed your guide lines for improving their push pull amplifiers.

@charles1dad 

They're not actually my guidelines- just good engineering practice. I think there's too much 'by gosh and by golly' going on in this sport where real engineering just isn't being done- instead you see an awful lot of rehashed circuits from yesteryear. I know a lot of audiophiles look askance at measurements but the simple fact is that if you have the right measurements you can tell how an amp will sound if you also have an understanding of how we perceive sound.

Why did you use EL95 in ultralinear mode? Why you didn’t use 2a3 or 45 tubes for your push-pull amp?

@alexberger

I’d already built the PP 45 amps and they were rather large. One problem of DHTs is you have to run DC if you want the output section to not make hum. So that means a DC supply which takes up room. The EL95 amp is silent on ’phones with AC filaments- its also a stereo integrated amp (2 inputs with volume control) and has a footprint smaller than a sheet of notebook paper. I did actually want this amp to fit easily into the space I have for it in my bedroom...

Its far more practical than any SET of the same power. For now anyway, the tubes are cheap and you can leave it on all night without it getting into trouble or worrying about the life of the tubes (they’ve held up just fine over the last year). Despite being class A it really doesn’t make much heat.

When people compare PP amps to SETs, one variable is that they are often using different tubes with far greater power (apples and oranges)! So this exercise sought to eliminate those variables, first by using the same DHTs in PP with the same components and tubes as used in the SET version, and the second by comparing an SET to a PP amp that made the same power at clipping.

If I had to describe the little EL95 amp, its very nimble compared to SETs of anywhere near the same power. Its not subtle. One problem with it was that when I was done it had too much gain. Since it used a differential amp for the input and since the inputs were all single ended, that allowed me to use the unused input of the differential amp for feedback, which was used solely to reduce the gain. IMO/IME this is the only legitimate use of feedback unless you can run over 35dB at all frequencies.

BTW there’s nothing special about this amp unless you think that attention to the kind of distortion it was going to make might be considered special. There is a reason SETs went the way- despite improvements in things like coupling caps and power supplies, they are simply an antiquated technology that can be easily surpassed IF the designer is paying attention to the distortion issue and understands how that interacts with the human ear. IMO its a tell of the sorry state of affairs in high end audio that there are SETs that actually do sound better than their PP brethren- it really shouldn’t be that way!

The new OP Q is

KT series tubes PP

I've been exploring SETs for nearly 30 years. I started with 300bs, then it was the 2A3, finally the type 45. Then I decided to see how a PP 45-based amp would sound and it ran circles around the SET version- smoother, more delicate, greater resolution, more grunt, better bass- no downside whatsoever.

Of course I was measuring these things too. What I found was the distortion signature defines any amplifier. Its what we call the 'sonic signature' since distortion is very audible as tonality.

Since SETs express a certain type of distortion (quadratic nonlinearity) and a fully differential amp expresses a different type (cubic nonlinearity) and since PP amps with single-ended circuits express both, I set out to see if I could build a PP amp using small power pentodes that could outperform SETs of the same power.

This little amp makes 5 watts and is class A. It uses EL95s which are a little brother to the 6AQ5. The tube is meant to be very easy to drive. I set up the output section in ultralinear, using cathode bias so it would have a substantial differential effect on the output section, giving it greater linearity. I then built a 12AT7 differential amplifier to be both the input voltage amplifier and driver. So the amp is fully differential and thus has a cubic nonlinearity.

A cubic nonlinearity expresses the odd ordered harmonics since the even orders are cancelled. A quadratic nonlinearity expressed both even and odd.

The ear treats the 2nd and 3rd harmonics the same- they are relatively innocuous. But they are also useful as they serve to mask the presence of the higher orders. That is why an SET sounds so smooth, despite making more of the higher orders than any other kind of amplifier!

Because the 2nd is suppressed, this little amp makes a fraction of the distortion that an SET of the same power makes- its about 0.5% at full power and vastly lower at any other power level, and because the 3rd harmonic is able to mask the higher orders, its very smooth. Its actually smoother than any SET I've heard, while also being more detailed and transparent. It also has wider bandwidth, being full power to 100KHz and good down to 5Hz.

Having heard it, there is no going back to an SET. I wanted an amp small enough that it would be good in a desktop or bedroom system, also good for headphones or a main system if you have speakers of sufficient efficiency.

Put another way, this isn't about KT vs 2A3; IME its about design. You can make a bad sounding PP amp and you can make a good sounding SET. But you can also make great PP amps that go places no SET can at any price: smoother, more detailed, more musically involving, IF you know what you are doing with the design.

KT type tube offers wonderful colors, imagery, low distortion, no coloration, no fatigue.

I know this fora fact hearing the DEfy7.

Jadis Is not the only one to make amps based on the KT88. You might want to hear a Harmon Kardon Citation 2 prior to saying you know how a KT88 sounds. Keep in mind this comes from a manufacturer that has only made triode power amps (and now also a class D amp...).

Regarding your speakers, what you are experiencing is that there is some destructive cancellation that is happening in your system because of the spacing of the drivers. This is actually helping prevent some of the more painful comb filtering that can otherwise occur when two such drivers are placed side by side. I’ve heard speakers set up this way. They are not bad, but seriously are not the last word in resolution by any means. They are attractive IME because all you have to do is get them in a box, wire them up and sound comes out. But if you want to hear proper imaging out of them, your head needs to be in a vise so as to be held always in the right position...

The box in the image above this post looks as if its ported. Did you do anything to prevent slap echos inside the box?

**the 2A3 PP  is just 1 of many options, 1 circuit is not superior to any other..**

BALONEY. Just a simple one  size fits all platitude.

The 2A3 PP is superior to any and all KT circuits.

@mozartfan 

If you run a KT88 UltraLinear, using an output transformer with the UL taps set up properly, you can get the same or better linearity out of that circuit that you get from a 2A3. If the taps aren't right neither will be the linearity so I am stressing that point. If the driver and voltage amplifier are then fully differential, the distortion without feedback will be dramatically lower than the 2A3 amp at nearly any power level.

You'll wind up with a more transparent, more musical distortion signature and therefore a more transparent, more musical amp with a lot more power.

Although I don't know of such an amp there may well be one out there (most I know of use textbook circuits from the 1950s); having been a manufacturer for over 47 years I'm really hesitant to make a blanket statement such as yours in the quote above- in a nutshell, its blatantly false.

@mozartfan Just so you know, that 5% figure is for the tube alone; it does not include the rest of the circuit of an SET. The distortion of that at full power is more like 10%. If you really want to hear what almost any SET does, you need a speaker that makes no demands of the amp over about 20% of full power, so as to avoid higher ordered harmonic generation. Of that means a speaker that is more efficient than any 'full range' speaker can be- for a 2A3 no if ands or buts you need horns.

At least if you want to produce realistic sound pressure.