[sdiy] transistor op-amp problems

Phil Macphail phil.macphail at liivatera.com
Fri May 25 21:46:50 CEST 2012


If you have used the same bias circuit, then the amplifier can only source/sink around 100uA. Into 10k that is about 1 volt,
Either increase the bias current or increase the load impedance ( or both), add a buffer or other gain stage and it should start to work,

Good luck,

Phil

On 25 May 2012, at 16:00, Elain Klopke <functionofform at gmail.com> wrote:

> Hey all,
> 
> I built the simple op-amp in the non-inverting amplifier setup shown
> at the bottom of this page:
> http://www.allaboutcircuits.com/vol_6/chpt_5/17.html
> 
> I used 2N3906s for the PNP transistors and 2N3904s for the NPNs and
> put a 10Kohm reistor in the feedback loop and a 1Kohm resistor to
> ground from the inverting input. In theory that should have produced a
> gain of 11. However, when I adjust the pot so that one volt is going
> into the non-inverting input of the circuit, I get 1.04 volts at the
> output. I measured between the wiper of the pot and the ground
> connection and between the output and ground. I can't quite figure it
> out.
> 
> -Ian Smith
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