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Old 24th February 2014, 03:48 PM   #1
Vostro is offline Vostro  South Africa
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Default bad clipping

Just wanted to know if anyone experienced such bad clipping behavior,
The circuit is a blameless with enhanced vas.
The really bas waveform is without diode D8.

Does anyone have a suggestion as to any changes to improve clipping.
The circuit was just built so many changes to make.

Thanks
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Old 24th February 2014, 03:51 PM   #2
Vostro is offline Vostro  South Africa
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The circuit
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Old 24th February 2014, 03:56 PM   #3
Vostro is offline Vostro  South Africa
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This is with diode clamp D8 soldered in.
Still not great, but much much better
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Old 24th February 2014, 06:13 PM   #4
djoffe is offline djoffe  United States
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the shape of the behavior looks about as good as it gets. Is there a 10X factor missing on the scope display for amplitude? the legend implies 2V/box, but the amp's rails look like it should deliver much more swing before clipping.
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Old 25th February 2014, 07:18 AM   #5
Vostro is offline Vostro  South Africa
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The digital display on top showing ch1 P11.24V is peak to peak using a x10 Probe.
Giving a 56V peak output.
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Old 25th February 2014, 07:26 AM   #6
peufeu is offline peufeu  France
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Quote:
Originally Posted by Vostro View Post
Just wanted to know if anyone experienced such bad clipping behavior,
What you see on the scope is the VAS transistors getting saturated on negative clipping. When coming out of clipping it takes a long time to un-saturate them, which is why the output stays stuck on the negative rail. The diode prevents saturation of VAS transistors, making recovery quicker.
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Old 25th February 2014, 07:40 AM   #7
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2 things ...

Why run the CCS at high current ? As well as it also saturating during clip ,
it makes the active half of the VAS "misbehave" more so.
You have a triple EF , 3-5ma VAS I is plenty enough and will run cooler-
less heat and distortion.

10R (R20) as the active VAS Re does not allow Q19 to clamp saturation. With
CM/beta enhancement .. you don't need that low of a Re , try 100-150R instead.
Loop gain of this amp is already high , if you need more .... lower Re on the
LTP or CM instead.

OS
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Old 25th February 2014, 07:50 AM   #8
dadod is online now dadod  Croatia
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Beware, diode connected as this dramatically increases THD.
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Old 25th February 2014, 08:01 AM   #9
mcd99uk is offline mcd99uk  United Kingdom
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A superior VAS clamp and VAS current limit for the Blameless.
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Old 25th February 2014, 08:19 AM   #10
PMA is offline PMA  Europe
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Complementary-differential design with symmetrical VAS (no CCS) is the best cure
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