Pro Audio Design Forum

I think Hfe un balance should be considered as well as Vbe un balance. Assuming ZTX851 Hfe=150 5% accuracy, with R4=R5=499 and Ic=5.5mA: Delta Vb=499x( 5.5/150)x0.05 mV. That is about 1mV Delta Vb, to compare to a lower than 1mV Delta Vbe achieved by matching. Who knows ZTX851 Hfe tempco ? About sma...

Thanks for your welcome and fast answer. I forgot to mention the preamps I worked on use two LM394 cross parallelled. I am impressed by the ZTX851 and the most excellent work you made from it. The noise figure is great. I see matching can be better than the 500uV I figured from reading earlier posts...

I am very interested in this thread. I built a mic preamplifier using 4 modules based on the Grahem Cohen double balanced design. I am so found of this design, I wish to build more, but the major trouble is the availability of low noise matched bjts. I found this: AS194 AS394 Matched NPN transistor ...