I built a fet input amp to amplify a 11mvpp signal. the source resitance is 0.02 ohms.
It is a 2 stage amp, both stages are identical, each is designed for a gain of 12.5.
I tested it on my bench with a 50 ohm signal generator, the gain of the first stage is 3,
the gain of the second stage is10.
I found that if I put a 6k resistor in series with my 50 ohms signal generator,
the gain of the first stage increase to 8.8.
I don't understand that, but know it will get worse when I use a 0.02 ohm source resistance.
Here is the schematic I used, 2nd amp schematic on the page.
http://www2.eng.cam.ac.uk/~dmh/ptialcd/trf/trf.htm#detector

Thanks for your help.Mikek

 

Is your C1 100pF or 100nF?
What frequency did you use?
Is the circuit on breadboard or pcb?

 

Is your C1 100pF or 100nF?
What frequency did you use?
Is the circuit on breadboard or pcb?

I dropped them down in value for the AM BC band.
It's on a pcb.
I just found my problem, my frequency is 500kHz. I was using a X1 scope probe,
this was loading the circuit, when I went to a X10 probe all my gains came up.
Now my circuit has 11mvpp input and almost 1 volt output.
Thanks much for responding.
Mikek