Moderators: Dave Moll, Andrew Davie, Steve Anderson
AncientBrit wrote:Keep up the good work Harry.
It's looking good,
Cheers,
Graham
Steve Anderson wrote:Hi Harry,
Just as an exercise I simulated the circuit above and really there wasn't that much change from 7, 8 or 9V. (See below) A slight increase in gain at 9V, a slight decrease at 7V - as you'd expect.
Frequency response shows a boost at 2kHz and over as expected, the LF bump can be ignored.
Red=8V, Green=7V & Blue=9V.
Instead of expensive BC109Cs use BC548Cs or BC549Cs, better (maginally) than the originals...drop-in replacements.
Gain and frequency response will be dependant on the characteristics of the solar cell to some extent...
Why R6 (original diagram) needs to be such a strange value is beyond me...there is even less change than the variation of supply volts between 2k2 or 2K7...even varying the temperature between 0, 27 and 70 Celcius made little difference. Also a Monte-Carlo run with 10% resistors was no issue...
erm...what I don't see in your photograph is any supply decoupling/bypass capacitors - unless you've hidden them on the underside (I often do)...this is a hi-gain stage and given the chance it will burst into oscillation...at many MHz, often beyond the ability of oscilloscopes to catch it...the Ft of BC10x transistors is over 100MHz...i.e. they (just) have gain at these frequencies...and that's all they need to become a headache...
To be honest I would suggest a simple lo-noise op-amp, a LM833 or a NE5532, simpler and stable.
Steve A.
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