Wich Pass do you recommand to a SET lover?

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PASS

Hi,

I love the sound of this one and I'm a SET lover.
I now use the (modified) F4 and am really happy with it on my ESL's.

Best regards,


Audiofanatic ;)
 

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The one and only
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I think there is a problem with assuming too much based on whether the
amp or preamp is tube or solid state. Reputations aside, I've heard lots
of good and bad examples of both.

To add to that, the assumption that a tube circuit, more specifically a single-
ended triode, has a second harmonic character is unreliable. There are
quite a few that suppress the 2nd harmonic through working the load-line.

So the result is that while many people do sweeten up their SS sound with a
tube preamp, it's best to take a listen to them before you commit.

:cool:
 
Load-line cancellation of 2nd harmonic

To add to that, the assumption that a tube circuit, more specifically a single-
ended triode, has a second harmonic character is unreliable. There are
quite a few that suppress the 2nd harmonic through working the load-line.
Would you mention few good examples of those?

Also some scientific papers about that technique would be good to know.
 
Load-line cancellation

Is this the thing?
Ordinarily in a tube amplifying an AC signal, a positive change in Grid voltage causes an increase in Plate current and is accompanied by a decrease in Plate voltage. The gain due to Plate current increases, and the gain due to Plate voltage decreases. The opposite happens when the Grid voltage goes negative.

These two gain variations tend to cancel each other, resulting in more constant gain and lower distortion. If you choose your conditions so that the simultaneous gain increases and decreases are equal, you can lower the distortion a lot.

This technique is often referred to as load-line cancellation. It is called that because the range of the device's operation sits on a line in the transfer curve, and the particular shape and position of that line results in minimum distortion.

By some criteria, this would be the sweet spot. At this point you will probably find that your second harmonic has largely disappeared and you are left with some third harmonic. This is because you can't completely cancel two square law distortions without leaving a cubic trace – the third harmonic.
Is there a mathematical way to predict where the sweet spot should be? Or is it just "match impedances and then listen and tweak, listen and tweak, iterate that until you are there, in the sweet spot" ?
 
You want the article titled "The Sweet Spot"

http://www.passlabs.com/pdfs/articles/sweet_spot.pdf

:cool:

I have read this before, but having a slightly better understanding now, i see, from both the comments and the graphs, that there is some real meat here. I also just happened upon some of your comments on the last couple of pages of the Bob Cordell Book thread. The illustration of the different amps and the corresponding waveforms and distortion were mind tickling. I really should just go study and play around for a couple of months and come back, but it is difficult and i am not yet fully equipped. THank you for the pointers anyway. BTW any opinions on PC based ARTA as distortion analyzer? Sorry for thread jack, although i believe in the end it is realted.:D
 
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