I bought the Moon... and all I got was an Eclipse.

WM, BM wouldn't be impressed I don't think. As a (part time) writer for Stereophile Markus is clearly part of the global conspiracy between manufacturers and the hifi press to deny us all decent hifi

Michael.

 

It's not global conspiracy, it's global ignorance...

 

oh dear.

 

What point are you trying to make or is this just a points scoring excercise.

 

Not that he needs me to defend him, but...
Markus is a very un-ignorant person, and someone who chooses his words and makes his arguments *very* carefully and logically.

 

My point is simple:

In Tube Dude's null test the amp output is equal to its input when Vout = (1/A*Vin)*A. The A being the constant amp gain, which is always much higher than 1, and 1/A being the attenuation factor from the pot.

When we increase the input voltage we must change the volume pot position in order to mantain the same attenuation factor for the null. It's basic electronics.

It's obvious when we null test a power amp we must use a pot as we always use some kind of volume control in our systems.

And my doubt doesn't make sense either, so forget it:

[(*) I have one doubt though... if we use an input voltage with any wanted amplitude don't we face the risk of saturating the input stage of the amp?]

If it's not conspirancy, it only can be ignorance... and I am an ignorat; but at least I know it. That's the difference...

 

Thanks for the kind words, Joel.

I went to an all-day lecture in my profession today. The real world soemtimes makes demands on my time.

WM, that I occasionally write for Stereophile has absolutely no bearing on any discussion like this. I visit these fora to learn, and if Tube Dude really has come up with a meaningful test, why should I object to this? I've done a bit of reading on null testing, though, and it seems to be fraught with a few problems of its own.

BD, sorry, I'm moving this week-end. No more from me on this subject until Tuesday at the earliest, and even then I'll probably have to catch up with a pile of mail on my desk.

 

Don't be sorry...

What I really would like to know is what manufacturers have to say to the fact that I, as a music lover, can't buy a nice beautifully designed and constructed amplifier which could ally convenience and extreme ACCURACY, like a Porche 911 TURBO does for the passionate driver.

Why do I have to build my own amplifier in order to get ACCURACY? Sacrifying design and construction quality. Why I can't just buy it?

Why I must end up having a Lotus Elise 111R when I want a Porche?

 

Porche 911 turbo' 4's arn't accurate, but boy are they fun, keep the elise please, I used to work on them, like TVR's I'll pass

 

Wm,

The only way to know is by "null testing" the latest Porsche 911 turbo side by side with your fav production car in the Nurburgring circuit, providing both have the same power to weight ratio (~236.8 bhp/ton.).

You may choose the pilot...

 

No, you misunderstand the null test set up! The amps are working with the normal gain (otherwise you have to open it and change the defining gain feedback resistors ) is the pot that limit the signal at the input.
The signal in the null test must be the some at the input of the pot and the output of the amp..


[[ Your test may make sense for integrated amps which have in-built attenuation, but it's not for power amps.]]

Of course for a power , we must temporary hard wire a pot at the input .

DISCLAIMER!!!
The null test is to be done , by people with a basic understanding of electronics and in a workshop .
BD gave the wrong impression that the test is easily done by anyone...