Comparing FFT of Two Amplifiers - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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
Reply
 
Thread Tools Search this Thread
Old 30th November 2014, 06:36 PM   #1
Jay is offline Jay  Indonesia
diyAudio Member
 
Join Date: Feb 2003
Location: Jakarta
Default Comparing FFT of Two Amplifiers

First, we cannot judge an amp from FFT alone (in fact, I don't want to tell detailed differences from other criteria). But still, I want to hear what you can see in an FFT alone (i.e. which one do you prefer: A or B).

So no more information other than the image showing FFT of two amplifiers. Each with 1W, 5W and 40W FFT.

I haven't built the two amplifiers, but is in the soldering process for amp B and drawing and transistor matching process for amp A.
Attached Images
File Type: png CompareNewAmps.png (40.2 KB, 242 views)
  Reply With Quote
Old 30th November 2014, 09:06 PM   #2
fonon is offline fonon  Poland
diyAudio Member
 
Join Date: Mar 2007
FFT spectrum should be presented with linear frequency scale due to linear sampling in frequency domain. Regardless, the harmonics are better visible in linear scale. When you show FFT spectrum, the parameters of analysis must be specified (number of samples in record, window function, etc.). The data outside dynamic range of analysis aren't valid.
Regards,
f.
  Reply With Quote
Old 30th November 2014, 09:29 PM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
You do understand that "FFT" is a mathematical operation, not a measurement technique? I think what you mean here is "single frequency distortion spectrum."

You have vastly too little information to make any sort of intelligent judgment. Frequency response, distortion, noise, source impedance, stability. That's your basic measurement set, and yes, you can use FT techniques to measure all of them, once you actually have some real amps to compare.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 30th November 2014, 09:57 PM   #4
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
I agree with SY - build your amps and measure them equally, then present the FFT for viewing. Until then, it's just pretty pictures.

Also, if you haven't built the amps, where did you get the FFT that you posted?
  Reply With Quote
Old 30th November 2014, 10:46 PM   #5
fonon is offline fonon  Poland
diyAudio Member
 
Join Date: Mar 2007
Quote:
Originally Posted by SY View Post
You do understand that "FFT" is a mathematical operation, not a measurement technique?
Not exactly. FFT is mathematical operation used as measurement technique. It's a kind of transformational methods of spectral analysis (in technical classification).
Type 7770 - FFT Analysis - Type 7770 - Brel & Kjr
f.
  Reply With Quote
Old 30th November 2014, 10:47 PM   #6
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
A fast Fourier transform (FFT) is an algorithm to compute the discrete Fourier transform (DFT) and its inverse. Fourier analysis converts time (or space) to frequency and vice versa; an FFT rapidly computes such transformations by factorizing the DFT matrix into a product of sparse (mostly zero) factors.[1] As a result, fast Fourier transforms are widely used for many applications in engineering, science, and mathematics. The basic ideas were popularized in 1965, but some FFTs had been previously known as early as 1805. Fast Fourier transforms have been described as "the most important numerical algorithm [s] of our lifetime".[2]
  Reply With Quote
Old 30th November 2014, 11:31 PM   #7
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Originally Posted by fonon View Post
Not exactly.
Yes, exactly. You are conflating different concepts- an FT is a mathematical transformation of data gathered in a measurement- no matter what the measurement. FFT is a particular algorithm used for the calculation.

@Jay: Build two amps, generate frequency response, distortion spectra at various frequencies and power levels, source impedance versus frequency (at different levels if you're dealing with a poor design), noise, and stability. Use FT techniques on the data if you like. Try all this with a few different loads, including speakers.

Then you can start talking about making valid comparisons.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 30th November 2014, 11:34 PM   #8
Jay is offline Jay  Indonesia
diyAudio Member
 
Join Date: Feb 2003
Location: Jakarta
Quote:
Originally Posted by SY View Post
You have vastly too little information to make any sort of intelligent judgment. Frequency response, distortion, noise, source impedance, stability. That's your basic measurement set, and yes, you can use FT techniques to measure all of them, once you actually have some real amps to compare.
I guess the more information doesn't mean the more informed decision? For example if there were 10 criteria, amp-A excels in 4 criteria and amp-B excels in 6 criteria, doesn't mean that amp-B is better.

Of course, I know you are right that technically the information is insufficient and that there's a necessity to build both amps (which I will). It's like I'm sure both will work (which it might not ) and I'm guessing their quality from FFT alone to choose which one to build (I regard other criteria, even tho different for both amps, are equally acceptable).

Quote:
Originally Posted by 6L6 View Post
I agree with SY - build your amps and measure them equally, then present the FFT for viewing.
If I have built the amps, I will have no questions as I know how they both sound.

Quote:
Originally Posted by 6L6 View Post
Also, if you haven't built the amps, where did you get the FFT that you posted?
Simulation of course?

Quote:
Originally Posted by fonon View Post
FFT spectrum should be presented with linear frequency scale due to linear sampling in frequency domain. Regardless, the harmonics are better visible in linear scale. When you show FFT spectrum, the parameters of analysis must be specified (number of samples in record, window function, etc.). The data outside dynamic range of analysis aren't valid.
Is it not visible (the harmonics) in this windowing? The "exact numbers" are not valid, I know, but subjective comparison is I believe valid.

Assuming that parts and power supply will be cost no object (the amps were simulated without the PS), I believe amp-B will have more details. But look at second order harmonic domination (and absence of higher order harmonics) in amp-A for example. In my experience, such simulated performance is always telling the truth.
  Reply With Quote
Old 30th November 2014, 11:42 PM   #9
6L6 is offline 6L6  United States
diyAudio Member
 
6L6's Avatar
 
Join Date: Oct 2010
Location: Denver, Colorado
Quote:
Originally Posted by Jay View Post
Simulation of course?

... In my experience, such simulated performance is always telling the truth.
I am a Professional Learjet Captian by trade. I can tell you all about simulation. (And the fact that the sims cost usually 3X the price of the airplane...)

Simulation, although useful, ain't the real thing.
  Reply With Quote
Old 30th November 2014, 11:53 PM   #10
diyAudio Member
 
vzaichenko's Avatar
 
Join Date: Jan 2010
Location: Moscow, Russia
Send a message via Skype™ to vzaichenko
Hi Jay, the "A" spectrum looks more like the one for VFA, the "B" spectrum looks like CFA one. In general, the less harmonic components are visible - the better. Also, having 3-rd harmonic significantly lower than the 2-nd one, and then just a little bit of 4-th and that's it - a very good profile. The "B" spectrum looks much more "nervous", but it doesn't automatically mean the amp "B" is bad. It may have other benefits - better slew rate, square wave and phase responses...

Cheers,
Valery
__________________
If you can't explain it simply, you don't understand it well enough (c) Albert Einstein
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
comparing various Alpair's Bob Brines Markaudio 19 22nd October 2014 10:32 PM
Comparing drivers ziocalepino Full Range 13 17th March 2011 09:17 AM
Comparing Bose(o) Chip Amps 5 29th July 2005 10:19 PM
Comparing sensitivities Grahamt Multi-Way 2 20th September 2004 07:42 PM
Comparing GC's yuval Chip Amps 20 10th June 2004 06:26 PM


New To Site? Need Help?

All times are GMT. The time now is 01:37 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2