SET amp owners thread

[Atmasphere]

This is a new word in electrical engineering and radio engineering. After it, the debate can be stopped.

?? Nothing new here- this is how balanced lines have operated since their inception with telephones. take a look at the input to an Ampex 351 electronics circuit and you will see that the input transformer does not have a center tap. The microphone signal is received as I described. I don't like transformers, so we did it the way you do it when no transformer is used.

We also do it another way using 3 resistors. In this hookup, all three resistors are the same value. The ones from the signal pins 2 and 3 meet the third from pin 1. In this way the 3rd resistor forces common mode operation, and negates any idea that the signal is being generated with respect to ground.

In a balanced line system, the signal of pin 2 is generated with respect to pin 3 and vice versa. Neither require ground, in fact you can operate a balanced line without using ground at all. However in a low level situation you might exceed the CMRR range and noise doing that will be heard. The point here is that does not even have to be a shield- a ground wire will do the job so the whole thing does not need any shielding at all.

If it were as you describe, that connection would not work.

Here's a helpful link:
https://www.ranecommercial.com/kb_article.php?article=2107

 

[Atmasphere]

I can see that this will be news to you, but the mode of operation of the tube with a common grid has been used since the invention of the tube. This is the highest frequency mode and is used in radio signal receivers and transmitters.
This is not a differential mode.

I've known about grounded grid operation for 50 years. It appears you missed the point. Go back and read that post again.

 

[morricab]

I suspect there is a religion of sorts in the SET world where things like differential operation are verboten. Its based on myth and a misunderstanding of how tubes actually work.

They operate differentially. The cathode voltage, if it swings in tandem with the grid, will result in no amplification. There must be a difference between them (other than just the bias/operating point) in order to amplify. This can come from ground, or the cathode can be actively driven.

Cathode drive (grounded grid) preamps have been around for a while, so the idea that there is cathode drive should not be mysterious; it should also not be mysterious that when the cathode is driven, the output is in phase with the input, whereas when driven by the grid, the output is out of phase. This should tell you something, but in case its not obvious at this point, it means that the tube amplifies due to differential operation...

As a result all SETs have differential inputs, even if the designer is unaware of this fact. Normally they are set up so that the difference is between the ground and the signal applied to the grid. As I described earlier, this means you can drive them differentially by driving the cathode as well as the grid. Also as I described earlier, I've been doing this for about 20 years. The reason for doing this is that with a true balanced source, neither output is referenced to ground. So if you only connect one side of it (for example pin 2 of the XLR, leaving no connection to pin 3) you'll get a buzz due to an open circuit. By connecting pin 3 to the cathode, the tube can be driven differentially (as all tubes are) and there's no longer an open circuit.

So I do know of SETs with differential inputs, which is to say: All of them. This is different from saying they all have balanced inputs BTW. I know of only a few with that.

The most common circuit I have seen on the input of SET amps is the Grounded Cathode. THis does not have differential input...the signal goes only to the grid...the cathode is...grounded. The output is off the plate and inverted. This is not differential operation.

No one is doubting that the cathode can also be used as an input or output and yes a single tube can be used to make a differential amplifier. Most SET input stages do not use it that way though and are using a grounded cathode either to a follower circuit of some kind, a transformer or perhaps a push/pull stage like an SRPP.

 

[Atmasphere]

The most common circuit I have seen on the input of SET amps is the Grounded Cathode. THis does not have differential input...the signal goes only to the grid...the cathode is...grounded. The output is off the plate and inverted. This is not differential operation.

It is differential operation. But its not balanced, as previously stated.

What is different between the grid and the grounded cathode in your example? The signal of course.

You know we've been making differential amplifiers for decades on now, right? Our amps and preamps are often driven by single-ended signals. Since our circuits are also symmetrical, we are using two tubes to compose our differential amplifiers- so the cathode isn't available as an input (although the cathodes play a crucial role...).

So with a single-ended input we ground one grid. The circuit works because it amplifies what is different between the two inputs; ground and the single-ended signal. A single tube works the same way but you don't get the benefit of constant load on the power supply nor the benefit of equal input impedance to ground with the two inputs.

We're having this conversation because you are conflating differential operation and balanced operation as the same thing. They are two different things, and work best when together.

 

[awsmone]

It is differential operation. But its not balanced, as previously stated.

What is different between the grid and the grounded cathode in your example? The signal of course.

You know we've been making differential amplifiers for decades on now, right? Our amps and preamps are often driven by single-ended signals. Since our circuits are also symmetrical, we are using two tubes to compose our differential amplifiers- so the cathode isn't available as an input (although the cathodes play a crucial role...).

So with a single-ended input we ground one grid. The circuit works because it amplifies what is different between the two inputs; ground and the single-ended signal. A single tube works the same way but you don't get the benefit of constant load on the power supply nor the benefit of equal input impedance to ground with the two inputs.

We're having this conversation because you are conflating differential operation and balanced operation as the same thing. They are two different things, and work best when together.

Thanks Ralph I never knew set was differential, can you explain, I had heard Set tubes have inherent feedback is that true

 

[geetee1972]

Can someone also please explain what Class A2 (as opposed to A1) means in practise and how it impacts the presentation and sound. My amps are A2 but I've never really understood what that means.

 

[SVS]

Can someone also please explain what Class A2 (as opposed to A1) means in practise and how it impacts the presentation and sound. My amps are A2 but I've never really understood what that means.

Class A generally means that the amplification device (it is a tube or a transistor) amplifies the entire signal. All SE amplifiers work in class A, PP amplifiers can also work in class A. Unlike class AB, in which only PP amplifiers can work and this means that the upper half-wave of the signal is amplified by one tube, the lower half-wave is amplified by the second tube.

The tube is a low-current electronic device. Most tubes require a signal in the form of a voltage for control. This is class A1 mode. At high voltages, the grid of the tube begins to consume current. This tube "enters" the class A2 mode. Some tubes from the very beginning work in class A2 mode.
The presence of grid current greatly affects the driver, and if it is not designed for the operation of the output lamp in class A2, strong distortions appear.

If the amplifier is designed correctly, then mode A1 or A2 should not affect the sound. In class A2, the tube can give a much higher output power.

 

[acousticsguru]

Can someone also please explain what Class A2 (as opposed to A1) means in practise and how it impacts the presentation and sound. My amps are A2 but I've never really understood what that means.

You might enjoy reading this, both a technical explanation as well as the reason why the difference between A1 and A2 is often what makes or breaks the sound quality of so-called “Single-Ended Class A”:

https://www.tubecad.com/2018/01/blog0410.htm

Greetings from Switzerland, David.

 

[Atmasphere]

Thanks Ralph I never knew set was differential, can you explain, I had heard Set tubes have inherent feedback is that true

In tube amplifier designs where feedback is used, its often applied to the cathode as a second input to the tube. The significance is that its applied out of phase with the input signal on the grid. This implies differential operation within the tube itself.

There is an idea out there that triodes have built-in feedback, which is part of their lower gain and suggested by their inherently lower plate resistance and greater linearity. Personally I don't buy it; this idea seems to suggest a tetrode or pentode were the 'natural' device that is sans feedback.

 

[Kingrex]

OTOMON Laboratory(音門ラボ)

Anyone use one of these Otoman Labs amps. I am thinking of a better big bottle than what I have. These seem good for not a lot of $$$.

 

[Kingrex]

What I have a hard time getting my head around with SET is how much more real it sounds. Why is that. And why do I feel people think thats bad. I definitely hear frequency issues and lots of noise with SET. Hum and such. But there is no denying, a piano, violin, saxophone etc sound much more like the real instrument in the room than with other amp topology I have had in my system. Why is this a bad coloration? Why do I want less natural and real with better specifications? I thought the goal, ir at least for me, is the recreation of the actual event. SET has gotten me much closer than any other topology.

 

[bonzo75]

What I have a hard time getting my head around with SET is how much more real it sounds. Why is that. And why do I feel people think thats bad. I definitely hear frequency issues and lots of noise with SET. Hum and such. But there is no denying, a piano, violin, saxophone etc sound much more like the real instrument in the room than with other amp topology I have had in my system. Why is this a bad coloration? Why do I want less natural and real with better specifications? I thought the goal, ir at least for me, is the recreation of the actual event. SET has gotten me much closer than any other topology.

The problem people have is only matching it to wrong speakers when lack of drive and bass bloat become negatives

 

[Fishfood]

The problem people have is only matching it to wrong speakers when lack of drive and bass bloat become negatives

Agreed! I'm using a similar Japanese Sun Audio 300B with Tango transformers. No noise, no hum. I'm amazed at just how quiet it is but that's with really good tubes and the right speaker match (96db bass reflex Diatone studio monitors). Amazing bass for just 8W. I'm comparing it to EL34 push pull this week just for fun.

 

[Kingrex]

Do you think a Parallel Single Ended 45 with about 12 watts will drive the PAP Trio 15 coax? Its maybe 96db. My SET 845 does not seem to struggle any more than a 55 watt KT88 PP or the Dartzeel NHB108 with 100 watts. I never got a Whammerdyne as I felt 3 watts of 2A3 was not enough.

 

[Fishfood]

Do you think a Parallel Single Ended 45 with about 12 watts will drive the PAP Trio 15 coax? Its maybe 96db. My SET 845 does not seem to struggle any more than a 55 watt KT88 PP or the Dartzeel NHB108 with 100 watts. I never got a Whammerdyne as I felt 3 watts of 2A3 was not enough.

I don't see why not. Honestly, the way I found my amp was just by buying used stuff online, trying it all out with my speakers, one or two amps at a time, reselling the stuff that didn't work until I found the configuration that worked the best for me and then I had someone do a careful rebuild/restore for me so it was like buying a new amp! The other benefit of this was I know just how much it'll probably cost me improve on this amp.

 

[bonzo75]

Do you think a Parallel Single Ended 45 with about 12 watts will drive the PAP Trio 15 coax? Its maybe 96db. My SET 845 does not seem to struggle any more than a 55 watt KT88 PP or the Dartzeel NHB108 with 100 watts. I never got a Whammerdyne as I felt 3 watts of 2A3 was not enough.

it’s not just about sensitivity. some where efficiency is published high, have tough to move woofers. I don’t know the PAP enough. The horns universum which is a 96db speaker requires 30 to 40 watt type amps. But Devore orangutan who are also mid 90s require only 10 - 12. That’s because they are easier to drive. if universum gets biamped using a class D on woofer, then you can easily use a less than 10w amp above that. your 845 probably has sufficient drive. hum and noise issues can be poor build and you have to get that fixed

 

[Atmasphere]

What I have a hard time getting my head around with SET is how much more real it sounds. Why is that. And why do I feel people think thats bad. I definitely hear frequency issues and lots of noise with SET. Hum and such. But there is no denying, a piano, violin, saxophone etc sound much more like the real instrument in the room than with other amp topology I have had in my system. Why is this a bad coloration? Why do I want less natural and real with better specifications? I thought the goal, ir at least for me, is the recreation of the actual event. SET has gotten me much closer than any other topology.

What you are hearing is how the 2nd and 3rd harmonics interact with the fundamental tone.

The 3rd harmonic, if out of phase with the fundamental, can cause the amp to sound more dynamic. It can cause the amplifier to 'project' into the room a bit, giving a false sense of the musicians in the room, even more so than was in the original recording.

Its fun, but not true to the recording. To know that though, you really would need the original recording and know what things sounded like when it was made.

Because its a change to the sound that isn't true to the recording, that's why some people think its bad.

Here's a fun little applet that allows you to see how this works:
https://www.falstad.com/fourier/
Pick 'Sine' and then look at the little dots below the sine wave. They represent the harmonics. The 3rd harmonic is the third dot (the fundamental tone has its own dot). Pick and hold it with your mouse and move it up and down. When you go down (out of phase) watch as the waveform increases in height.

This happens with the 2nd harmonic too. If in phase, it can make the amp seem more vivacious. Look at how the leading edge is steeper when you increase the 2nd harmonic. The amplitude goes up too!

 

[Kingrex]

Owe god. I had my amp rebuilt 3 times. Its still a bucket of issues. I don't ever want to go down that road again. I have as much into it as a new amp, and still I have to use Ebtech HumX. Now a guy wants another $4k to $6k to rebuild the power supply. Rebuilding the Audion Black Shadow had been my single biggest waste and loss of money in audio so far. The only mistake I would say I have made.

 

[Kingrex]

What you are hearing is how the 2nd and 3rd harmonics interact with the fundamental tone.

The 3rd harmonic, if out of phase with the fundamental, can cause the amp to sound more dynamic. It can cause the amplifier to 'project' into the room a bit, giving a false sense of the musicians in the room, even more so than was in the original recording.

Its fun, but not true to the recording. To know that though, you really would need the original recording and know what things sounded like when it was made.

Because its a change to the sound that isn't true to the recording, that's why some people think its bad.

Here's a fun little applet that allows you to see how this works:
https://www.falstad.com/fourier/
Pick 'Sine' and then look at the little dots below the sine wave. They represent the harmonics. The 3rd harmonic is the third dot (the fundamental tone has its own dot). Pick and hold it with your mouse and move it up and down. When you go down (out of phase) watch as the waveform increases in height.

This happens with the 2nd harmonic too. If in phase, it can make the amp seem more vivacious. Look at how the leading edge is steeper when you increase the 2nd harmonic. The amplitude goes up too!

You had some comments above about staying true to the source recording. And you mention it again here. That's part of my head scratch. I too have played a lot of instruments. Listened to plenty live. I know what they sound like. So I have distortions that make it sound more natural and real. But they are distortions. So I am suppose to listen to something that has less distortion, but does not create playback I perceive as natural?

Are we talking about the argument of accurate vs musical?

 

[acousticsguru]

it’s not just about sensitivity. some where efficiency is published high, have tough to move woofers. I don’t know the PAP enough. The horns universum which is a 96db speaker requires 30 to 40 watt type amps. But Devore orangutan who are also mid 90s require only 10 - 12. That’s because they are easier to drive. if universum gets biamped using a class D on woofer, then you can easily use a less than 10w amp above that. your 845 probably has sufficient drive. hum and noise issues can be poor build and you have to get that fixed

As mentioned here or in the flea-watt thread, we tried the 2.3 Watt Decware 25th Anniversary Zen Triode (and I'm really just mentioning the lowest-powered amp I own as an example) with a variety of speakers whose "nominal sensitivity" (note e.g. @christoph believes all speaker manufacturers are lying when it comes to sensitivity, and I'm starting to think he's right) range from 85-96dB - it didn't perform in order according to the respective sensitivity rating at all. I build (or used to) loudspeakers, and have always been under the impression that there are other factors that make loudspeakers more or less benign as a load to tube amplification (e.g. acute electrical phase angles/shifts), partly information no loudspeaker manufacturer or reviewer publishes (anymore - people don't know how to correlate measurements to sound quality anyways, despite their deplorable belief in numbers), so that sadly, there is no way of determining synergy without trying first-hand. Perhaps the closest one can get to an educated guess is when speakers are "know factors" (e.g. Infinity Kappa 9, just kidding…), i.e. someone whose ears you trust is using the same type of speakers with a flea watt SET, and even there I'd say it's far from a safe bet. And I do not mean to be negative about this at all: I've heard some surprising combinations one would be tempted to dismiss out of hand, so caveat emptor…

Greetings from Switzerland, David.