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Old 17th December 2003, 05:19 PM   #1
sam9 is offline sam9  United States
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Default Soft Clipping Schematic

Anyone havew or know where to find a schematic of a "soft clip" circuit. I'm curious to know how these work. NAD comes to mind but I imagine that's proprietasry and can't be posted. All I can find on a web search related to guitar amps.

On LT-spice I stuck an oposed pair of diodes in the NFB loop. It does indeed round off the top a bit when clipping but generated heinous harmonics even when well below clipping. So obviously it's not as simple as that. (I also noticed that the diodes need to be snubbed or be Schottky's lest a visible crossover appears in the wave form.
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Old 17th December 2003, 05:34 PM   #2
Geoff is offline Geoff  United Kingdom
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NAD3020

http://www.tcaas.btinternet.co.uk/nad3020pwr.gif

SW7 is the 'Soft Clipping' switch.
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Old 17th December 2003, 05:57 PM   #3
sreten is offline sreten  United Kingdom
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A pair of diodes across the LTP inputs can work for higher gain
power amplifiers, for 'normal gain ' power amplifiers you probably
need 4 in series/parallel but they'll probably act a bit too late.

The other alternative is a pair of zener diodes in series,
connected across the large feedback resistor of the feedback
loop, varying the effect by the voltage rating and regulation of
the zeners (or adding a resistor). Here you need to be mindful
of the compensation of the amplifier as you are reducing gain.

With a line level circuit, before the power amplifier, here there's
an awful lot you can do, you can include capacitors for frequency
dependence for example.

A good soft clipping circuit will have no effect at low volume,
But hideous distortion specifications at medium to high outputs.
It should not add any crossover non-linearity.
I haven't really thought about diode turn off spikes.

Another alternative is a compressor - different kettle of
fish all together - much less distortion involved here.

sreten.

update : just seen Geoffs post - it is in effect a line level circuit.
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Old 17th December 2003, 07:54 PM   #4
sam9 is offline sam9  United States
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Thans for the schematics. I'll stick in with an existing amp simulation and see what happens. I presume it has to be tuned somehow to the rail voltage of different amps. How it works isn't immeadiatel clear but jooking at it simulation will help.

Diodes in the feed back loop, in any configuration seem problematic at best.

BTW, my practical philosophy hore actual home listening just to be sure I have enough power so that clipping isn't an issue. I understand, though, that there could be considerable appeal in a commercial product.
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Old 17th December 2003, 08:04 PM   #5
sreten is offline sreten  United Kingdom
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Quote:
I understand, though, that there could be considerable appeal in a commercial product.
None at all, well outside guitar and bass amplifiers.

the most apposite application could have been subwoofers,
if it wasn't for the compressor approach being far better.

sreten.
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Old 17th December 2003, 08:05 PM   #6
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cannot you make the normal V-I limiter into a soft clipping device? sounds doable if you can slow-down the turn-on / turn-off of the transistor in the limiter.
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Old 17th December 2003, 09:57 PM   #7
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Default Soft clipping idea

made by NAD is little bit swindle for human ear. It works like voltage limiter, but cause increase of distortion in " middle " of power. Much more better are antisaturation circuity, which cause stopping of " avalanche " saturation of all stage in amplifier. Example of this circuits you can find for example in amp Ampzila.
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Old 17th December 2003, 10:01 PM   #8
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with a digital amp, you would be able to program your soft clipping to your liking,
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