JLH69 MOSFET Class AB 80W

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Has anyone tried to classAB the JLH69 ? This quick simulation gives excellent results. Biased 170ma. The distortion at 82 watts is 0.2% but mainly 2nd order which can be balanced out. What do you think?
 

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I used basically this circuit 1989 in car stereo. 125w into 4 ohms ( 33v rails) IRF530 , 9530. 5.6v zener as bias. Gain of 3, op amp front end distortion falls to .01 % or less.
pros: excellent bandwidth , flat response
cons: poor input impedance, bad DC offset.
circuit was used in Sanyo portable radio with Ge output transistors and resistors for current sources.
 
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Stocktrader, your amp uses complimentary outputs , this JLH69 version uses a pair of identical N channel. May be yours is JLH1970 classAB . My purpose of this amplifier is not to have near zero distortion, but on the contrary to have at least 0.5% 3rd harmonic at 5watt , but, of opposite phase if you please . My speaker full range driver (home made) has 0.5% 3rd order measured at 100hz, 5W . I want experimentally see if I can reduce it by the amplifier . The problem , the speaker distortion is variable with power but the amplifier produces a constant distortion . The shown bellow has from 0.1W to 50W about 0.4% above it decreases.
 

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Hello anti . Thank you for showing the JLH character of ne5534 . Indeed it works as well except 4.5v drop out on positive max . I started first to MOSFET the LM3886 which is also JLH type , and ended with the original JLH .
 

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This is a variation of an early amplifier circuit that never became popular because it is sensitive to slight variations in load and variations in supply voltages. It has been used with some success as a class-A circuit because that avoids the poor AB cross-over predictability. Distortion results from the fact that positive output has local feedback but negative output does not. The bias structure is similar to that used in TTL logic chips.
 
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This is a variation of an early amplifier circuit that never became popular because it is sensitive to slight variations in load and variations in supply voltages. It has been used with some success as a class-A circuit because that avoids the poor AB cross-over predictability. Distortion results from the fact that positive output has local feedback but negative output does not.

Which circuit do you refer to . The JLH69 circuit cannot function in class AB at all with BJT transistors. Indeed it is sensitive to voltage variations , but I will run it with single floating power supply of switching type . The output impedance is adjusted 0.5 ohms to have the minimum NFB in order not to decrease the valuable opposite phase odd harmonics. Why it can be sensitive to load variations ? Due to bootstrap , the positive output doesn't have local feedback , or else it will produce even order harmonics .
 
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The gate charge needed to drive the mosfets depends, generally, on di/dt of the output current and may be greater than the CCS for short, large magnitude transients.. It is best to drive mosfets with as low of output impedance as possible. The internal reactive components of the mosfet is more likely to ring with a higher drive Z. CCS is by definition high Z output. Bootstrap provides a lower Z drive to the gate. Also, bootstrap provides the extra gate drive voltage to saturate the mosfet. I use bootstraps in my mosfet output stage and it is [complementary, but it eliminates the need for higher driver voltage supplies.:)
 
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NE5534 output in classB

The CCS supplies both the driver and R3 . If the driver pulls more current to feed the R5 , less current of same magnitude flows in R3 . By this the two outputs are driven perfect complimentary. But the R3 current flows to the drain of the lower output, hence in ac the driver and the lower output function in push pull , how about cutting the bias of the upper output ? I adjusted it just at threshold 40ua ,and applied triangular wave of 20khz for 1.5VP output . You can see on scope there is not slightest trace of crossover, miracle.
 

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Imho with mosfets you will have to delete the ccs and revert to use a bootstrap to get closer to the positive rail.

You can bootstrap a CCS. In fact you can boostrap the whole VAS, best just partially/attenuated, just enough to add a bit more than the FET vto.

Similar to bootstrapping but without the feedback, you can drive the middle or top of the VBE multiplier so that the gate voltage is offset towards the rail. ie you need a small pull down as well as up. LV did this in his EZMOS posted in DIYA.
 
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