From: - René -
Subject: Re: Amplifying stage with *negative* Voltage gain??
Date: Fri, 06 Dec 2002 14:36:08 +0100
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On Fri, 06 Dec 2002 07:56:21 -0500, Mike Monett wrote:
>Paul Burridge wrote:
>> On Thu, 05 Dec 2002 09:10:32 -0500, Mike Monett opined
>> >Thanks for the reply. Tony raised a good point - what's the attenuation
>> >of your scope probe?
>> It's rated up to 60MHz, Mike. And switchable for X1/X10.
>Do you get the same indicated voltage in either mode?
>> >As far as a lower impedance driver, has you considered a complimentary
>> >NPN/PNP pair with the bases and emitters tied together? You can use John
>> >Larkin's trick of connecting a resistor between the bases and emitters to
>> >reduce the crossover distortion. I tried this - it really works well.
>> I don't doubt it, but right now I'm more concerned with trying to
>> establish why this circuit as built doesn't conform to expectations.
>> I'm determined to get to the bottom of it and with the assistance I've
>> had from your good self and others here I'm optimistic that I may
>> eventually prevail.
>> "I was going to help him up, but then I thumped him."
>> Michael Head's plea in mitigation to Weybridge Magistrates, Sept. 1975
>Well, Paul, I've tried simulating your circuit with the emitter and collector
>swapped, and with the collector open. In both cases, I get a lot more than 2V
>So aside from a bad transistor, miswire, parasitic oscillation, bad probe,
>scope out of calibration, probe out of calibration, poor bypassing, bad probe
>ground, poor circuit ground, excessive wire length, mismarked component,
>defective component, or a bad solder joint, I haven't got the foggiest clue
>what could be causing the problem:)
Apart from all the above / earlier, I am still curious what the
results are for a smaller Re. Hfe usually varies with average Ice,
and for a HF amp I would hesitate to use such a large value resistor.