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Old 20th January 2007, 10:51 PM   #1
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Question new sollution for output stage from JBroskie?

Reading Broskie’s blog I found a solution of an output stage that should lower distortion factor ~20dB than classic.
I tried to simulate it with the devices like 2N2955/3055, BD135/136, Zener 15V and regulated ccs made of BF245C.
It works, however idle current is above 5 amperes.
Did you try similar solution in your design which was working well?
What modification should be made to get practical circuit?
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regards, Pawel
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Old 21st January 2007, 06:39 AM   #2
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seems to me i've seen something similar before, but idle current was less than 100mA.....

it's local negative feedback to the driver emitters.......
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Old 21st January 2007, 07:43 AM   #3
CBS240 is offline CBS240  United States
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Yes and a Vbe multiplier that senses the driver temperature not the outputs for this type of arrangement.
All the trouble I've ever been in started out as fun......
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Old 21st January 2007, 08:09 AM   #4
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Please note, that John made a small mistake in schematic, the transistor marked as "in" should be npn
regards, Pawel
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Old 21st January 2007, 09:14 AM   #5
AndrewT is offline AndrewT  Scotland
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the 1k0 in the collector of the "driver" devices restricts collector current to a very low value (about 0.6 to 0.8ma).
try a lower value maybe in the range 100r to 220r.

The 100r at the output are resistor ladders that sense output voltage and feed these to the emitters of the drivers. But only sense output voltage when the current in the 0r1s are equal, i.e. no output current.

The Zener bias only needs to feed 2*Vbe+Vre into the bases of the drivers. Adjust bias voltage down to about 1300mV to 1400mV.

What happens to distortion when the output is delivering current and the sense voltages are no longer referring to output voltage?
regards Andrew T.
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