The look of distortion.

Joel · 26th June 2003, 05:45 PM

Steve Bench has a nice article with that same title, and it's useful in using the o-scope more as a tool to diagnose distortion. He lays out what the different levels and shape of 2nd, 3rd, 4th, etc look like - but he does not go into evaluating essentially clean signals.
In other words, can someone out there with a good distortion analyzer dial up what appears to be a clean waveform from their amp's output - and then measure what the distortion is at that point?
What I'm concerned with is, how far back do I have to roll the gain below clip to get into the region of 1% or less. Is the statement, "if it looks clean, it'll sound clean", fully accurate?

I like the old style desciptive power figures, ie. "undistorted power output is..." It seems to me that this is a more useful number than "1.7% THD". And I would assume that the 1930's engineers simply clipped the amp, then dialed it down until the sinewave looked clean, no?
Thoughts?

Joel

dhaen · 26th June 2003, 06:24 PM

Joel,

It really depends how the distortion is happening.
With clipping, 1% is easily visible on a scope displayed sinewave.
However, you can have 5% discrepency between the upper and lower sinewave amplitudes, and hardly notice.

So the answer in my opinion is that you can "see" distortion on your scope when it is between 1% and 5% depending on the case.

Hope this helps.

Cheers,

Joel · 26th June 2003, 06:39 PM

It helps some, John, thanks. But what type of evaluation do you personally do on your amps? Do you even consider distortion?

The brain so easily compensates, doesn't it?

dhaen · 26th June 2003, 10:51 PM

Joel,

At home I have 2 distortion analysers, both quite simple, that will check at 1KHz only. It's up to me to look at the nulled output (the distortion products) on the scope to determine the proportion of odd and even. However that is usually predictable from the circuit topology since I only use triodes.

Better equipmnt is available elsewhere, but a valve amp doesn't fit in the briefcase!

Cheers,

26th June 2003, 05:45 PM	#1
Joel diyAudio Member Join Date: Oct 2002 Location: Brooklyn, NY	The look of distortion. Steve Bench has a nice article with that same title, and it's useful in using the o-scope more as a tool to diagnose distortion. He lays out what the different levels and shape of 2nd, 3rd, 4th, etc look like - but he does not go into evaluating essentially clean signals. In other words, can someone out there with a good distortion analyzer dial up what appears to be a clean waveform from their amp's output - and then measure what the distortion is at that point? What I'm concerned with is, how far back do I have to roll the gain below clip to get into the region of 1% or less. Is the statement, "if it looks clean, it'll sound clean", fully accurate? I like the old style desciptive power figures, ie. "undistorted power output is..." It seems to me that this is a more useful number than "1.7% THD". And I would assume that the 1930's engineers simply clipped the amp, then dialed it down until the sinewave looked clean, no? Thoughts? Joel

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to get the less distortion with BJT?	dododio	Solid State	24	6th September 2008 09:55 AM
Neo 8 distortion?	studiotech	Multi-Way	4	17th April 2005 05:22 PM
Non Linear Distortion testing - Harmonic Distortion	JMB	Multi-Way	0	20th July 2004 02:54 PM
op amp distortion	zahlm	Parts	3	15th May 2004 07:45 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

26th June 2003, 06:24 PM	#2
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	Joel, It really depends how the distortion is happening. With clipping, 1% is easily visible on a scope displayed sinewave. However, you can have 5% discrepency between the upper and lower sinewave amplitudes, and hardly notice. So the answer in my opinion is that you can "see" distortion on your scope when it is between 1% and 5% depending on the case. Hope this helps. Cheers,

26th June 2003, 06:39 PM	#3
Joel diyAudio Member Join Date: Oct 2002 Location: Brooklyn, NY	It helps some, John, thanks. But what type of evaluation do you personally do on your amps? Do you even consider distortion? The brain so easily compensates, doesn't it?

26th June 2003, 10:51 PM	#4
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	Joel, At home I have 2 distortion analysers, both quite simple, that will check at 1KHz only. It's up to me to look at the nulled output (the distortion products) on the scope to determine the proportion of odd and even. However that is usually predictable from the circuit topology since I only use triodes. Better equipmnt is available elsewhere, but a valve amp doesn't fit in the briefcase! Cheers,