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

Strange, it works for me. Others?

 

When I click the link, I get a diagram Tube Dude posted on diyAudio. Maybe one needs to be logged in there to see it?

 

Forget the link... The diagram Tube Dude posted on diyAudio is all that matters.

 

may i mumble banana to the dog patch?

 

So who won the argument then?

 

Markus,

Let me rephrase what I said... what I wanted to say is as follows:

For the time being your only pertinent question remaining unanswered regarding the arrengement I first mentioned is related to the fact of the null test effectively measuring the amp performance at only one gain point.

You can always use an attenuator in the amp's output going into the amp used to measure the difference, but now you are introducing another factor (extra amp) of distortion. I don't know if a voltage divider made with fixed resistances that you can swap for different attenuation values and therefore different gain points is a viable solution.

 

BM,

You might lose some bits on some digi volume controls (anyway who said I was using the one that came with the cdp?), but there one or 2 about that defy logic, or has your mentor forgotten to mention this possible?

 

Wm,

I'm the only responsible for my own affirmations. As for digital control volume defying logic... well, when we look to the sky at different hours of day we do think the sun has moved when in fact it was Earth that did it... go figure!

Get a pot for those powers... do trust your ears! By the way, is Tom Evans your mentor?

 

Not in a million years BD Did he have any orginal idea's, that wern't his maybe , I have many a parnter in crime, as for the Digi vol control, prehaps I saw an oppotunity to add a few bits

 

Beryllium Dust,

I am now beginning to understand your audio philosophy.

You look at the test results - for example comparing an active pre-amp with a passive pre-amp and you deduce that the product with the best test measurements are the best sounding.

If thats the case, Id reccomend Musical Fidelity and changing your Yamaha's for studio monitors with a flat response.

Chris

 

BD, the link doesn't make the physical layout of the test set-up at all clear to me. There are conncetions labeled A, B, C and D, but what those connections are is not specified.

Anyway, the basic problem of the proposed null test remains: you test the amp with an output voltage of 2 V max. It would be easy to optimize an amp for those conditions; in fact, I think all one would need is a basic power supply and a good op amp chip; it would probably give an excellent null result. Come to think of it, almost any pre-amp would be sufficient for driving the speakers under those conditions, no power amp needed at all.

However, driving speakers under real world conditions and at real world spl makes entirely different demands on an amp.

Also, I'd be very interested to know which speakers were used in the test set-up, and whether the null result would be the same with different, possibly more demanding speakers.

Don't get the thrust of my argument wrong: null-testing is interesting, and is probably valid within the test's limits, However, I remain to be convinced it allows definitive judgements about power amp quality.

 

For any person that can read a schematic they are intuitive :
-A - input live
-B - input ground
-C - output live
-D - output ground


[[ Anyway, the basic problem of the proposed null test remains: you test the amp with an output voltage of 2 V max. It would be easy to optimize an amp for those conditions; ]]

But why , do you must do the test only with 2 volts...you can use a signal with the voltage you want ( driving the the amp under test by another amp for ex. ) and of course , in this case ,the test become even more stringent ...



[[ I think all one would need is a basic power supply and a good op amp chip; it would probably give an excellent null result ]]

Try it...and you will be surprised (for the bad!!! )...



[[ Come to think of it, almost any pre-amp would be sufficient for driving the speakers under those conditions, no power amp needed at all. ]]

Another mistake , you forgot the output impedance...and if the amp under test don't have a output impedance near zero , the null test (with speakers attached ) will tell it clearly .And any pre -amp , has the output impedance , that can permit , to have a good null with a speaker load (laws of physic ).



[[ However, driving speakers under real world conditions and at real world spl makes entirely different demands on an amp.]]

Of course ...for the null to be meaningfull , it must be done with the speakers connected .
The beauty of the test , is that you can measure what amp do the better null test with your own speaker!!!




[[ Also, I'd be very interested to know which speakers were used in the test set-up, and whether the null result would be the same with different, possibly more demanding speakers ]]

You can use the speakers you want....but a more demanding speaker , will turn the test even more difficult to the amp under test and if two amps , can have a similar null in a easy load , the difficult load will help in separating the men from the boys.

Regards

Jorge

PS: The null test tell everything!!...Sorry!! :MILD:

 

You forgot to add Imho

 

IMHO?...NO way...IMO of course!

I'm to old to try to change the world...but still young , to pursuit accuracy in audio amplification!

Anyway I don't sell anything...amps, cables,even my own ideas....

I do it just for the fun of IT ! :MILD:

 

No, you misunderstand me. The basic purpose of a power amp is to amplify the input signal, i.e. give a gain (usually 26 dB) to the input signal. If you test the amp under conditions where its output is the same as the input (i.e. unity gain), you do not test it under real world conditions.

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

And of course, I didn't make out to say that driving speakers from a pre-amp makes sense, I just wanted to illustrate the fact that in your test set-up the power amp basically doesn't do anything. In fact, it can be thought of as a buffer stage for the pre-amp output.

And I still don't understand the test set-up.

BD said

So you connect the +ve output from the amp under test to the ground of the spare amp and the speaker. Providing the impedance of the ground of the spare amp is reasonably low, doesn't that mean that the current flows not through the speaker but to the spare amp ground?

 

Markus,

Give it a second thought:

1) If the power amp section is doing nothing why in hell the speakers are playing louder when you test it with an higher input voltage? (*)

2) It's unuseful to think about an amp without some kind of volume control.

3) All an amplifier do is amplifying the voltage between live(+) and ground(-). Additionally, the input impedance of a voltage amplifier is always very high when compared to its output impedance.

Tube Dude,

(*) 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?

 

Markus,

Are you still there? Do you already understand the test set-up?

 

I wonder if you know what Markus actually does for a Living BM?

 

But I know you are always there... defying logic.