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Old 24th March 2003, 10:35 PM   #251
jam is offline jam  United States
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Default Peter Rules!

If it were not for Peter's posts, which I attribute to raising the standards of the quality of our projects, most us would be happy with the amplifiers we built in cake pans.

We all owe him a lot for sharing his time and experience and more power to him if he wants to sell some of his work.

Regards,
Jam

P.S. ... besides he is one the few decent moderators left.
 
Old 24th March 2003, 10:38 PM   #252
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Quote:
Originally posted by SY
Tube Dude, let it go. Peter hasn't done anything beyond responding to direct questions about his work.
Yeah, right.

Then why am I bombarded with unsolicited EMails with topics like "WILD HORNY XXXXXX COLLEGE GIRLS DO IT ALL!!!" only to open it up and find out it's just Peter using a spoofed account saying "Psssst! Wanna buy a GainKlone?"

se
 
Old 24th March 2003, 10:38 PM   #253
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Default To Peter...

This post is not sarcastic...i'm talking sincearly...
I wish you the best in the world of business...if sometimes i made some remarks is because i think that your target is the Hi-Fi consumer...so the brands of capacitors the sound of wires are much important in a magazine hi-fi revue...but you can't espect that in a world wide forum like this there are no others people with diferents opinions...
So let's respect anyone opinion...and make this forum a democracy!!!

For me no reason to delet your post!
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Old 24th March 2003, 10:42 PM   #254
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Thanks SY... my thoughts below...

Quote:
Originally posted by SY
1. "Quality" is a matter of how well an amp achieves its design goals. Not all amps are intended to have an output that replicates the input times a scalar. If you want an amp with large amounts of 2nd HD and a high source impedance, it won't pass a null test, no matter how much the designer and his customers like the sound.
Yes I agree. If we're back to wanting amplifiers that intentionally alter the sound (amplifiers as "art") the null test could still be useful but you wouldn't want to minimize the difference signal if you're designing for errors.

Quote:
Originally posted by SY
2. It is possible, actually probable, that two amps which perform differently in a null test will sound indistinguishable in a controlled test.
Agreed, but what about the converse? If they measure similarly on the test, won't they sound the same? So in my capacitor example above, wouldn't the null test save you the trouble of doing the blind test if both caps produced extremely similar difference signals?

Quote:
Originally posted by SY
3. Objectively sonically-neutral phenomena can result in very poor (misleadingly so) performance on a null test. This might be considered a subset of point 2.
I also agree, but that still doesn't invalidate the test as an indicator of all amplifier distortions. In other words, if you work to minimize ALL forms of distortions while playing real music and driving real speakers, you're certainly not hurting anything are you?

Where this gets a bit tricky is when you ask "Ok, so how good of a null is good enough?" In other words, what level and type of difference signal can be strongly argued as inaudible. In my experience it's around -50db within the audio band.

If you bandwidth limit the equipment you're using to monitor the difference signal to 20k (something that's very easy to do with my setup) I find if the difference signal is at last 50db down from the output of the amplifier nobody can pick it out from ANY other amplifier with at least as low of difference signal. And that's regardless of the frequency spectrum of the difference signal. To be safe, however, I usually say -60db in case there are some really golden eared types and systems out there that can pick stuff out that mere mortals can't. The best amp I've tested managed -70db.

But you're right, a more accurate way to handle this would be to somehow "weight" the difference signal components according to how audible they're likely to be (and/or compensate the test so that it won't detect inaudible differences in the first place). That's opening a much bigger can of worms however, and I would argue unnecessary.
 
Old 24th March 2003, 10:43 PM   #255
jam is offline jam  United States
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Steve,

Did you get off work early today?

Regards,
Jam
 
Old 24th March 2003, 10:52 PM   #256
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Default The transconductance amplifier...

Quote:
If you want an amp with large amounts of 2nd HD and a high source impedance, it won't pass a null test,
Yes 2nd HD is distortion so the test will tell!!!

But in the case of a high output impedance...it can pass a null test if is driving a 8 Ohm resistif load!
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Old 24th March 2003, 10:55 PM   #257
SY is offline SY  United States
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Quote:
In other words, if you work to minimize ALL forms of distortions while playing real music and driving real speakers, you're certainly not hurting anything are you?
nw, there are deviations that aren't worth bothering with. Consider two amps with identical and vanishingly low distortion. They null nearly perfectly. Now, put a perfect 1 ms delay at the input of one of the amps. Now the nulling at midband and high frequencies is horrible, yet you have a "distortion" that is meaningless. HD and IM aren't the only things out there.

And another question in the case of HD and IM is what to do (if anything) to minimize them even after they're below the threshold of audibility. If I have a transparent amp (transparent in that input and output cannot be distinguished by a skilled listener) with 0.5% THD and a 0.1 ohm source Z and want to make that null better, am I "hurting anything" if I increase the parts count, making the amp more expensive and less reliable? Am I "hurting anything" if I increase the O/P stage idle current, thus increasing heat, lowering reliability, and increasing the customers' electricity bills?

In the limited case where lowering distortion or source Z past an already-insignificant amount carries no cost or reliability penalty, sure, why not? But that's only one case, and I'd argue that it's exceptional.
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Old 24th March 2003, 11:02 PM   #258
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Quote:
Originally posted by jam
Steve,

Did you get off work early today?
You kidding? Soon as my feet hit the floor in the morning I'm "at work."

se
 
Old 24th March 2003, 11:04 PM   #259
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Default The delay...

Quote:
nw, there are deviations that aren't worth bothering with. Consider two amps with identical and vanishingly low distortion. They null nearly perfectly. Now, put a perfect 1 ms delay at the input of one of the amps. Now the nulling at midband and high frequencies is horrible, yet you have a "distortion" that is meaningless. HD and IM aren't the only things out there.
The beuty of this test is if you put a perfect 1ms delay and hear the null...the null is a perfect rendiction of the musical signal...
But in the case of distortion or frequency dependent delay what you will hear at the null point is a very distorted rendiction of the musical signal...

The null tell everything!!
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Old 24th March 2003, 11:08 PM   #260
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Quote:
Originally posted by Steve Eddy


You kidding? Soon as my feet hit the floor in the morning I'm "at work."

se
I'm not trying to be cranky, but can we please try for a little better signal-to-noise ratio in this thread? On the previous page, out of 15 posts, 5 have something to do with the thread topic. Some previous pages are even worse.
 

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