Hi,  looking at the simple op amp inverting mixer ckt;
I don't think it will work.  Never, ever, ever set your feedback resistor values for less than unity gain, or you will produce an oscillator!  If you want to attenuate the signal do that with an attenuation network, such as; the pot at the beginning of the ckt.  Which, by the way, is also part of your input resistance.

Thanks,

Mike