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Old 17th November 2012, 07:18 AM   #311
crt is offline crt  Indonesia
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Halo Juma

just test my amp with scope (4 Ohm / 80 Watt Resistor as LOAD)
here the result

any suggestion about it ?
Attached Images
File Type: png f5 10k.png (5.9 KB, 459 views)
File Type: png f5 100k.png (6.0 KB, 454 views)
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Old 17th November 2012, 09:52 AM   #312
juma is offline juma  Serbia
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Hi crt,
it's a fast amp and your pics show slight but well controlled overshoot - nothing to worry about. If you want to eliminate that overshoot some answers are needed so we can get the whole picture:
1. The scope picture of the input signal at 10kHz and 100kHz recorded under same conditions as output signal pics which you attached
2. what's the value of gate resistors at output MOSFETs' gates ?
3. what's the value of resistors in the feedback loop ?
4. do you have bypass caps on amp PCBs ?
5. details about amp's power supply ?
6. pictures of your amp's insides - wiring etc.
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Old 17th November 2012, 11:34 AM   #313
crt is offline crt  Indonesia
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Quote:
Originally Posted by juma View Post
Hi crt,
it's a fast amp and your pics show slight but well controlled overshoot - nothing to worry about.
Well, if you say that

Quote:
Originally Posted by juma View Post
If you want to eliminate that overshoot some answers are needed so we can get the whole picture:
1. The scope picture of the input signal at 10kHz and 100kHz recorded under same conditions as output signal pics which you attached
2. what's the value of gate resistors at output MOSFETs' gates ?
3. what's the value of resistors in the feedback loop ?
4. do you have bypass caps on amp PCBs ?
5. details about amp's power supply ?
6. pictures of your amp's insides - wiring etc.
1. Yes. 1V square wave
2. Bit bigger than schema. i use 243R
3. 150R / 3 in parallel with 10R
4. None
5 & 6 Already in my posting at page 20
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Old 17th November 2012, 11:52 AM   #314
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5&6 - you need to write exact # of post

pages are browser dependent
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Old 17th November 2012, 12:47 PM   #315
juma is offline juma  Serbia
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Crt
I found pics in posts #192 & 193. It looks OK. You used a lot of small caps in PSU - it gets you rid of one sort of problem but it puts you in another sort of predicament. Never mind, it would not be practical to deal with it now.

I asked you for a picture of input signal. I don't know if your input signal has some overshoot. Check it, and if it does, it's OK. If it doesn't, there are three easy things to do (pick what's easier for you):
1. Disconnect one of three 150R power resistors in every feedback loop so that in your stereo amp instead of 4 x (3 x 150R) you get 4 x (2 x 150R). That will raise the gain and slightly change the frequency and phase response of the amp. If you choose to do this you'll have to check the bias/DC offset again.
2. Connect one 220pF cap in parallel to every 150R triplet (you'll need four 220pF caps). Those caps can be bigger (330 or even 470 pf) since the feedback loop has very small impedance. They can also be smaller - you'll have to experiment to find the lowest value that will eliminate the overshoot. This change affects the frequency and phase response of the amp, too.
3. Increase the value of gate resistors on the output MOSFETs but that's the less effective method.

Now you have something to play with, you can try all three methods and decide what you like the best - all of them will influence the sound, some for the better, some for the worse - it depends on your build's characteristics.

Have fun
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Old 17th November 2012, 01:08 PM   #316
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It's helpful to remember that a pulse generator likes to have the correct termination -- the input impedance of an F5 is not 50 ohms.
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Old 17th November 2012, 01:59 PM   #317
juma is offline juma  Serbia
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Quote:
Originally Posted by jackinnj View Post
It's helpful to remember that a pulse generator likes to have the correct termination -- the input impedance of an F5 is not 50 ohms.
Of course, but we don't even know what's crt's square wave source - that's why I asked for input waveform pics...
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Old 17th November 2012, 02:49 PM   #318
crt is offline crt  Indonesia
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Quote:
Originally Posted by Zen Mod View Post
5&6 - you need to write exact # of post

pages are browser dependent



Quote:
Originally Posted by juma View Post
Crt
I found pics in posts #192 & 193. It looks OK. You used a lot of small caps in PSU - it gets you rid of one sort of problem but it puts you in another sort of predicament. Never mind, it would not be practical to deal with it now.

I asked you for a picture of input signal. I don't know if your input signal has some overshoot. Check it, and if it does, it's OK. If it doesn't, there are three easy things to do (pick what's easier for you):
1. Disconnect one of three 150R power resistors in every feedback loop so that in your stereo amp instead of 4 x (3 x 150R) you get 4 x (2 x 150R). That will raise the gain and slightly change the frequency and phase response of the amp. If you choose to do this you'll have to check the bias/DC offset again.
2. Connect one 220pF cap in parallel to every 150R triplet (you'll need four 220pF caps). Those caps can be bigger (330 or even 470 pf) since the feedback loop has very small impedance. They can also be smaller - you'll have to experiment to find the lowest value that will eliminate the overshoot. This change affects the frequency and phase response of the amp, too.
3. Increase the value of gate resistors on the output MOSFETs but that's the less effective method.

Now you have something to play with, you can try all three methods and decide what you like the best - all of them will influence the sound, some for the better, some for the worse - it depends on your build's characteristics.

Have fun
Ok will do experiment tomorrow
Which one you prefer to do first ? number 1 or 2

here output from signal generator connect directly to scope
Attached Images
File Type: png scope 10k.png (5.7 KB, 291 views)
File Type: png scope 100k.png (5.9 KB, 282 views)

Last edited by crt; 17th November 2012 at 02:56 PM.
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Old 17th November 2012, 04:47 PM   #319
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Quote:
Originally Posted by crt View Post
Ok will do experiment tomorrow
Which one you prefer to do first ?
I think you want some capacitance across the 100 ohm feedback resistor.
Start with 1 nF.

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Old 17th November 2012, 05:00 PM   #320
juma is offline juma  Serbia
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Input looks fairly OK if the picture is taken under same conditions - func. gen. loaded by amp's input.

Try first the nr. 3 (add 330R in series with 240R at the gates of MOSFETs) - just to eliminate the last thing first...
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