Low TIM, How to verify it!!! thanks a lot!!

[mclarenpingu]

Low TIM, How to verify it!!!

Hello every DiyAudio member
I have a question of TIM (Transient Intermodulation Distortion)

I have know some TIM information, but how could I simulate or measure my Amplifier TIM
and have found some tread in here

TIM generator

http://www.diyaudio.com/forums/showt...134#post355134

but there didn't refer TIM simulation and test method clear
could you teach me how to simulate it??
I want to verify my AMP, thanks you very much
this is a great help for me

thanks!!!

have a nice day!!!

[mclarenpingu]

Hello All
I have an idea of TIM test, sine we know TIM occur in high frequency and large, fast transient.
so could I use a fast and high frequency sine wave, large amplitude, but the amplitude won't make output clipping
and use spice and scope to measure output waveform, use FFT to see the spectrurm, find if there have any unwanted tone.
because the input is sine wave, ideal condition is one tone, and others is noise.
so if there have more than one tone, that mean this amplifier have a TIM.
please help me to check this method is right or not
I have found many information in google, but there have a few information,
There have a paper in AES, but I am not a member, after I read many document, I think this idea
but don't know this way is right or not???
please help me, thanks!!!
I will appreciate any feedback from you!!!


Best Regard!!!

[darkfenriz]

TIM has good correlation with slew rate ang THD at 20kHz close to clipping or rather THD vs. frequency slope.
An amplifier with THD constant in frequency and relatively low as well as >50V/us slew rate is often considered TIM-free.

Also, as a mix of THD and slew rate you can measure TIM as proposed in:
Leinonen Eero, Otala Matti, Curl John, Metod for Measuring Transient Intermodulation Distortion, AES reprint no 1185, presented at 55th convention, november 1976

Hope this helps
Adam

[mclarenpingu]

Thanks darkfenriz
I have use google to find this AES paper, but I am not a member, so I can't access it
In my condition, I just need to find does there have any simple method to verify my amplifier have TIM or not
I don't need a deep theorem, formula
so does there have someone can provide me some P-Spice simulation instrument method??
if I have the P-Spice simulation method, I think I can come out a instrument test method.

I have a idea of the TIM test, but don't know right or not.
as darkfenriz say TIM occur in frequency 20KHz,
could I give a 20KHz sine ware, large amplitude, don't make AMP clipping. and see the FFT of output wave
or just test slew rate to verify this AMP have TIM or not???

thank you very much, I think any informatoin will have help for me

have a nice day!!!!

[Pan]

19kHz + 20kHz IMD measurement at high level should tell the story.

If the amp has decent bandwith.. say 100kHz or thereabouts and low IM dist with the signal above.. then it will be fast enough and linear enough.

There's alot of controversy about that TIM thing.

/Peter

[john curl]

There is also controversy if man has actually gotten to the Moon, as well.

[Pan]

Has man gotten to the moon? :-O




Seriously though.. is there a way John that you can measure TIM and make it visible?

What is IYO necessary to avoid audible TIM distortion?

My thoughts about this subject is that since an amp that has the performance I listed above can pass a listeningtest* without detection everything is cool.

*Doesn't color the signal audibly when set up in a rig driving a speaker dummy load and signal is routed thru DUT and compared to bypass.


/Peter

[jacco vermeulen]

Mr Curl has been there.
(effect of too much Sinatra)

[fotios]

First of all, the term TIM, when reported especially in signal amplitude amplification arrangements in conjuction with the boosting of their output to sustain in large ammounts of current throwing in low value loads (this is exactly what called power amplifier), means Transient Intermodulation Distortion or (for a more detailed definition) Intermodulation Distortion in their output, caused by steep signals or scale functions injected in their input (these are the named Transients). Any other explanation of the abbreviation TIM it is outside from the subject as i think at least me. As for the appropriate signal for measuring the TIM the only that i know (from my books this and not from internet) it is a traditional method to produce it: We need two function generators, the one to produce an absolute symmetrical square wave of 500Hz, and the second to produce a sinus wave of 6KHz. After this we must adjust the amplitude of these two signals in a ratio of 5:1 (i.e. if the square has an amplitude of 1Vpp the sinus must has an amplitude of 0,2Vpp) and we mix down these two signals to get the final complex signal. All these as for the signal, for the measurement method i am not sure wich is the better (i don't think so that those PC "toys" called SPICE can isolate a such complex by its nature phenomenon as it is the TIM at the moment that we are unable to observe its presentation with real instruments such DSO) and if it is indispensable to estimate something in practice. Mainly the TIM has relation with the accurate calculation of whole the feedback loop and the many hidden nested feedback loops (we are unable also to calculate all of them in practice) in the amplification arrangement. In an amplifier with a level of gain A and with a level of feedback â the stable state distortion is reduced by: 1 / 1 - â.A. This relation says that, as much bigger the level of feedback (â) so much lower the stable state distortion but so much bigger the transient distortion of the amplifier in steep signals applied in its input. It is obvious that there is an antagonism between the stable state distortion and the transient distortion dependent from the feedback level (â). Concretelly the TIM it is the result of the time delay factor of whole the feedback loop when it is closed, which cause clipping in the output under steep variations of the input.
Now in the practice, i haven't seen yet a such distortion in any amplifier has passed from my workbench by applying the signal which i explained above and by observing the output (loaded with a clear resistive dummy load) via the scope. There is a uniformity always between input and output (yet by pressing the X10 mag. button of my 50MHz DSO i haven't seen any difference).
As for me, instead the sibylline (cryptic) answeer of the respected J. Curl (me, i understand very well his talking; the man he is tired to search for so many years the truth of each one theory and if it is applicable in the practice; so me also) i will give you an opportunity to see the TIM in your oscilloscope. Simply, remove the compensation capacitor of the Miller dominant pole (in high frequencies) from the b-e junction of the voltage amplifier stage transistor from any amplifier, and you can see enough TIM distortion on the screen of your oscilloscope connected in the output of the amplifier (there is no need for load).

Fotios

[Pan]

Well if the delay across the feedback loop creates TIM then it would be visible with a square on the scope and since this is not the case with any competently designed amp I don't see it happen.

Removing components inside the amp that totally change its behaviour (removing miller cap) and say "look, distortion"... what good is that? Then we create a problem that wasn't there from get go.

Or?

Also, how would you differentiate between IMD and TIM products with that 500hz square/6kHz sine test?

A full scale (or close to) 19kHz+20kHz is a harder signal for the amp than it will likely see with music. If it can reproduce that with reasonable low distortion then I can't see where TIM would enter the picture. Oh, throw a 10kHz squarewave at the input also at different levels and if it pass these tests shure TIM would be a non issue..?

Should add though that there is much I don't know or understand.


/Peter