Gainclone and clipping (may also be appliable to other high feedback amps)

Bricolo · 25th November 2003, 08:46 PM

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?

OliverD · 25th November 2003, 09:16 PM

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.

Flemming J P · 25th November 2003, 09:54 PM

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?

ronc · 26th November 2003, 01:00 AM

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

Bricolo · 26th November 2003, 05:00 AM

Discharged batteries?

ronc · 26th November 2003, 06:54 AM

Nope!
ron

Bricolo · 26th November 2003, 10:16 AM

How did you see it's clipping? Did you look at the output with a scope? If yes, what was the peak voltage?

JOE DIRT® · 26th November 2003, 01:02 PM

maybe some bad cells in your batteries....I would try another power supply to verify this

ronc · 26th November 2003, 01:46 PM

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

25th November 2003, 08:46 PM	#1
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	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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25th November 2003, 09:16 PM	#2
OliverD diyAudio Member Join Date: Nov 2002 Location: Germany	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.

25th November 2003, 09:54 PM	#3
Flemming J P diyAudio Member Join Date: Oct 2001 Location: Sweden	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?

26th November 2003, 01:00 AM	#4
ronc diyAudio Member Join Date: Mar 2003	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

26th November 2003, 05:00 AM	#5
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	Discharged batteries?

26th November 2003, 06:54 AM	#6
ronc diyAudio Member Join Date: Mar 2003	Nope! ron

26th November 2003, 10:16 AM	#7
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	How did you see it's clipping? Did you look at the output with a scope? If yes, what was the peak voltage?

26th November 2003, 01:02 PM	#8
JOE DIRT® diyAudio Member Join Date: Apr 2003 Location: Brantford, ON	maybe some bad cells in your batteries....I would try another power supply to verify this

26th November 2003, 01:46 PM	#9
ronc diyAudio Member Join Date: Mar 2003	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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