JR wrote :- --snip--
>> Even a pair of 10 cent 2N4401's in front of a NE5532/4 will stomp about any of the expensive 'designer' low noise op amps ... Just ask the engineers at Soundcraft, Mackie, Yamaha, or Beringer who all use a pair of transistors ahead of the opamps in their professional balanced microphone preamps ... Do you have any more details of circuits for this PNP buffer? Common base? Common emitter? The Janus board in the HPSDR project uses LT1128s, which are single-eneded low noise op-amps. I was thinking of using AD4841s or the even lower noise LT1115s for the same function in the uWSDR project, both of which are somewhat cheaper than the LT1128. It may be the case that the noise of the op-amps is not too important, system noise figure being dominated by the noise of the RF front-end devices - I haven't done a system analysis yet. >> Problem is I'm at a standstill because my DDS's are too noisy to take advantage, hopefully the 995x based DDS Controller (David Brainerd's design) will be quiet and spur free enough to explore further The new AD9910 and especially the AD9912 are the current 'best in class' - by a big margin. I've done some spur measurements of the AD9910 and it looks very good indeed - no spurs above approx -70dBc or so, phase noise measurements are a little more involved but I hope to have those done before Christmas. For now, I think it's safe to rely on the 9910/9912 data sheets, which show exceptionally low levels of phase noise. >> JR regards Grant
