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Leco modules bridged on 8 and 4 ohm dummy load
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DjLeco View Drop Down
Young Croc
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    Posted: 10 March 2012 at 11:32pm

I have conected 2  modules in bridge, one master, second slave (oficial amp will have 180 degrees phase inverter for minimum distortion possible.

Intro:

http://www.youtube.com/watch?v=AnGkY01DQR8&feature=youtu.be

Bridge 8 ohm dummy load:

http://www.youtube.com/watch?v=0KCCtZOnqH8&feature=youtu.be

Bridge 4 ohm dummy load:

http://www.youtube.com/watch?v=5oCNWHKCmYI&feature=youtu.be

 Sin 100Hz/8 ohm

Square 10000Hz/8 ohm:
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Points: 2962 		Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 11 March 2012 at 12:03am
have been looking at your lower image of square wave output.
Tthere seems to be some symmetrical frequency domain effects occurring - is this intentional or do you have an explanation as to why this is happening?
Am aware this is a 10kHz signal but things don't seem quite correct.....
Mik
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At that amount of power, alot of amplifiers FAIL, on squarewave, or enter in limmiting, of final stage...
 
It was just a test of  brute power...


Edited by DjLeco - 11 March 2012 at 12:43am
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Yes, generally agree with that!

However it seems a little strange that there appears to be a '2f' component appearing where limiting should give the more common 'flat' top to the square wave.
It also doesn't really appear as overshoot which would tend to be closer in time to the leading/trailing edges of the square wave given your good 'mid power' slew rate.

Interesting to find out what it is?
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Claudiu

you really should get over here for a visit and then we can, perhaps with others who have also offered invitations to you, have a bit of a 'tech-fest' on Amplifiers!

Thinking somehow it could be a very interesting meeting!
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Nice ideea, I will think about that!
 
But I want to come with a finished amp, for make some tests too!
 
So, opinions, comments about power obtained(continuous power not burst) and stability, anyone?
 
Forget to tell, in 2 oscilogrames above (on first post), modules was without any compensation, even at input filter (missing capacitor) and negative feedback (missed capacitor too), to see if amp oscilates or have any problem or spikes on output sinusoidal waveform, to check stability, limmitings,  or any problem that could occur.
 
Oficially alot of amps FAIL or enter in limit or protect mode at suc a test like I do, especially, on 10Khz squarewave test at max power.
 
The next oscilogrames, is with all compensations and capacitors planted on PCB.
 
Like this is correct, amp is compensated!
 
 
 


Edited by DjLeco - 11 March 2012 at 12:56pm
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Young Croc
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And the last oscilogrames.
 
First two represents one channel, last two represents both channels in bridge mode.
 
In both cases, output load is 8 ohms dummy load resistors (2x4 ohms seried).
 
 
 
 
 
 
 
 
 
 
 
 
 
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I'm not really familiar enough with real life torture tests to know what a good response looks like, but I would be interested to know the open and closed loop response of the amplifier (gain and phase), along with the impulse response. Have you measured these out of interest?
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I don't have necessary instruments to made that kind of measurements.

 
What I show, it  was pure power electrically delivered by modules.
 
I want some comments about power obtained, please!


Edited by DjLeco - 11 March 2012 at 10:56pm
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Claudiu
Re: "I don't have necessary instruments to made that kind of measurements."
think we'll have to try to find you some!
In the meantime you should be able to do reasonable Phase measurements with your 'scope using the cursor readout?

Your Power results look good, however you need to add some reactive elements to your loads to see what is happening when the voltage/current phase of your output signal rises to about 50ยบ or so..... as with 'real 'speaker loads'.

Usual tests include capacitance in parallel with your resistive load to look for overshoot and ringing on a squarewave and inductance in series to look at reflected power handling within your design load line with a sinewave.
These are certainly stress type tests; so watch out for temperature rises especially with the inductive component added!
this thread might be of interest to you:
http://forum.speakerplans.com/amplifier-damping-factor-dynamic-testing_topic41777_page1.html

Mik


Edited by audiomik - 12 March 2012 at 1:06am
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Points: 950 		Post Options Post Options   Thanks (0) Thanks(0)   Quote VentureSound Quote  Post ReplyReply Direct Link To This Post Posted: 12 March 2012 at 1:15pm
I seem to remember reading here that the Crown service manuals for the MA series, ask you to do a torture test with caps and inductance at the load. As Claudiu is very familiar with the Crown amps, he could start with those tests?
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Some info on the Crown tests at the bottom of page 2 in the thread linked above.
They seem a bit 'short term'; but then I guess they are for production testing rather than development testing which needs to be more 'severe'.
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