square wave in = square wave out - Page 2 - 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 14th April 2003, 09:40 AM   #11
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default square waves

I don't think square waves are good to judge the sound reproduction quality of an amp. But there are quite usefull to test the stability margin (which has an influence on the sound quality of course).
The amp should pass a square wave like the 2nd curve of phase-accurate's previous post.
The rise time of the edges determines the 3dB freq response point (3dB = about 1/pie the equivalent freq of the rise/fall time).
There should be not more than 10-15% overshoot (that's my target, YMMV). Then what I normally do is load the amp capacitively (from 10.000pF to 1uF) and keep an eye on the square wave response. For poweramps I use some cable between the amp and the cap load to introduce some inductive impedance, because it really isn't fair to ask the amp to cope with a cap directly at its output jacks.

The same with preamps, I use up to 1000pF to simulate (too) long high-cap interconnects.

If in any of these cases the amp oscillates or is marginally stable the square wave response will show very high overshoot and/or oscillatory bursts.


Jan Didden
  Reply With Quote
Old 14th April 2003, 11:03 AM   #12
Account Disabled
 
Join Date: Aug 2002
Location: Near to the Pacific Ocean
Quote:
Originally posted by phase_accurate

a squarewave of 200 Hz

It seems to show

- LF gain: good
- LF delay: insufficient
- HF gain: good
- HF delay: excessive
- Damping: high.

Am I correct?

JH
Attached Images
File Type: jpg op_yax2_measure_20k_test.jpg (7.6 KB, 346 views)
  Reply With Quote
Old 14th April 2003, 11:31 AM   #13
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
This has not much to do with gain or delay. Since the topic was mentioned within a speaker thread of Richard as well, I posted the response of a phase accurate two-way speaker system.
The waveshapes are those of a wide fourth-order bandpass. The tilt is caused by the lacking ability to reproduce DC. All waveshapes are damped quite well and the tilt is not to be mistaken as overshoot, though one is led to believe this. The flattened slopes of the rising and falling edges are simply caused by the finite rising and falling speed.

Many amps would be better than this example in terms of HOW MUCH, at least at the lower end (where a very low first order rolloff is easily achieved with SS amps, even DC reproduction, but more difficult with tube amps). But the general SHAPE would be the same, as long as there is no ringing.
But keep in mind most speakers will be worse.....

As Peranders stated, rectangular tests are quite good for determining stability. It is not by accident one of the vavourite test signals for almost any feedback control system !


Regards

Charles
  Reply With Quote
Old 14th April 2003, 11:40 AM   #14
Account Disabled
 
Join Date: Aug 2002
Location: Near to the Pacific Ocean
Quote:
Originally posted by phase_accurate

the topic was mentioned within a speaker thread

Understood. I was thinking about the amp...

JH
  Reply With Quote
Old 14th April 2003, 11:55 AM   #15
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Quote:
Understood. I was thinking about the amp...
And I am afraid that I wasn't clear enough before......

Regards

Charles
  Reply With Quote
Old 14th April 2003, 07:58 PM   #16
Pedja is offline Pedja  Serbia
diyAudio Member
 
Join Date: Jun 2002
Location: Belgrade
Default squarewave and...

With speakers, it is a bit different than with amps or digital.

With speakers there is a problem of aligning two or more sections in parts which in sum give that what was the starting point. It is not a hard task in the term of the amplitude response, but the things become worst when phase come in story. As sad in another thread, assuming linear amplitude response, impulse (transient) response is directly related to the phase response.

Charles, can you give us some more info about the system whose graphs you posted? Thanks in advance.

Pedja
  Reply With Quote
Old 14th April 2003, 08:16 PM   #17
diyAudio Member
 
Pjotr's Avatar
 
Join Date: Nov 2002
Location: Netherlands
Square waves are a good test signal. But….

You need to band-limit the input signal between 50 kHz and 100 kHz with at least a 1st order filter. Otherwise if the slew rate of the input signal is too high you will drive the amp partly into limiting (saturation) somewhere. Most time the input stage.

Also a good test signal is a 80% 50 Hz sine with a 20% 1 kHz square wave added. It shows dynamic instability if apparent.

  Reply With Quote
Old 14th April 2003, 10:26 PM   #18
PMA is offline PMA  Europe
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
Square wave is a very useful signal to test the amplifier. You can calculate both amplitude and phase characteristics from step response or impulse response by means of Fourier transform, I do not want to get into more details.
High frequency limit (-3dB) can be calculated from rise time tr (10%-90%) as fh = 0.35/tr. It imeans that for tr = 1us fh = 350 kHz. From long time duration of square wave (low repetition frequency) one can see low frequency limit of the amp, it corresponds to exponential decay of square wave top line. Square wave is excellent for testing of stability of the amp together with diffrent kinds of load (capacitive etc.). But you have to use several different repetition frequencies of square wave, say 100Hz, 1kHz and 10kHz.
  Reply With Quote
Old 15th April 2003, 07:08 AM   #19
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Pedja

The examples shown are from a simulation of a two-way active system using an MSW (Manger Schallwandler).
It was done with a subtractive crossover and equalisation. The equalisation is necessary because the MSW is not that well behaved at it's lower end. More details and discussions can be found within the Manger thread.
I will try another principle for the MSW in the future and the Veroboard prototype of this crossover will find it's final destination in a phase_accurate box with a cheap fullrange (Monacor SPH68X).


Regards

Charles
  Reply With Quote
Old 15th April 2003, 11:45 AM   #20
diyAudio Member
 
Join Date: Jan 2003
Location: Sweden
Quote:
You need to band-limit the input signal between 50 kHz and 100 kHz with at least a 1st order filter. Otherwise if the slew rate of the input signal is too high you will drive the amp partly into limiting (saturation) somewhere. Most time the input stage.
I dont understand this one, any competently modern designed amplifier has either a low pass filter included on the input in order to avoid this phenomena or is otherwise designed so that no saturation can occur.

BTW there is a misunderstanding that tube amps can not be good when reproducing squarewaves, even many transformer coupled amplifiers can be give quite respectful results and OTL amps can compete easily with any transistor amp. My own OTL amp have a rise time of ~ 1 us and no overshoot or ringing with capacitive loads up to 3.3uF.

Using square waves is usually a good method of testing amplifiers for stability and frequency response and is easy to use.

Regards Hans
  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
Sine wave - Square & Triangle wave generator using Transistors / OP-Amps lineup Solid State 20 9th October 2006 12:15 AM
Square wave Prune Everything Else 11 28th June 2004 06:17 AM
Microphone turns triangle wave into square wave? Circlotron Analogue Source 18 25th January 2003 06:44 AM


New To Site? Need Help?

All times are GMT. The time now is 08:08 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