Gainclone and clipping (may also be appliable to other high feedback amps) - diyAudio
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Old 25th November 2003, 08:46 PM   #1
Bricolo is offline Bricolo  France
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Default Gainclone and clipping (may also be appliable to other high feedback amps)

I was playing on my workbench this evening, with my inverting gainclone, a scope and a function generator.

This is well know, gainclones have a very bad behaviour when clipping. I can't post illustrations because I don't have the digital camera right now, and I don't know how to connect my Tek 2232 scope to my computer to acquire data (if you know, tell me!), but the curve is really ugly!

But I saw another phenomen, that I haven't read about here: the input signal is deteriorated when the gainclone clips!


At first, I thought that my source was clipping, and that I was seeing the amplified clipping input signal at the amp's output. But when I disconnected the signal generator from the amp, and looked at the signal, it was perfect!


Any other feedback (this is the more appropriate word I found ) about this phenomen?
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Old 25th November 2003, 09:16 PM   #2
OliverD is offline OliverD  Germany
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That's an intrinsic problem of feedback amplifiers: Coupling stuff back to the input. If that's a clipped waveform, it'll show up as such at the input.
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Old 25th November 2003, 09:54 PM   #3
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And the back coubling can be real bad!!!

I managed to do something stupid (not uncommon ) and this caused the magic smoke to leave the output cap's on my sound card (I was using it as source).

It was a lm3886 and I messed up by putting a 94uf cap in || with the resistor from - to mute, instead of from the mute leg and to ground.

I guess a non inverting opamp doesn't have this issue?
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Old 26th November 2003, 01:00 AM   #4
ronc is offline ronc  United States
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My quesion is why all of a sudden it started clipping when i didnt before?I had my home amp IGC (LM3875 300k/10 K loop, battery P/S +/- 24V) start clipping about 2 weeks ago and it is clipping at a lower power level than it did for about 6 months.Right now i am getting approx 4 watts before clipping.I really cant point out the actual point as my trusty old heathkit scope died.
ron
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Old 26th November 2003, 05:00 AM   #5
Bricolo is offline Bricolo  France
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Discharged batteries?
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Old 26th November 2003, 06:54 AM   #6
ronc is offline ronc  United States
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Nope!
ron
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Old 26th November 2003, 10:16 AM   #7
Bricolo is offline Bricolo  France
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How did you see it's clipping? Did you look at the output with a scope? If yes, what was the peak voltage?
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Old 26th November 2003, 01:02 PM   #8
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maybe some bad cells in your batteries....I would try another power supply to verify this
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Old 26th November 2003, 01:46 PM   #9
ronc is offline ronc  United States
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Yes,i used my old Heathkit scope i built about 20 yrs ago.It died shortly thereafter.I believe its the CRT as i am gettig voltage to the crt.Happened last week.I Noticed the amp distorting so i hooked up the scope to the speaker leads and turned up the amp till i saw the signal start to flatten out slightly.Then i hooked up my heath signal generator to conferm.
I tested the voltage on each battery and all 4 measured within 12.4 to 12.72.
Sorry i am having a hard time typing as i had a cycle accident yesterday and my hand and sholder are messed up.
ron
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