--- In [email protected], "jr_dakota" <[EMAIL PROTECTED]> wrote: >
A link might help here huh? http://www.nitehawk.com/sm5bsz/linuxdsp/hware/optiq.htm Figure 2 > > Here's a neat little "Compound" opamp circuit with uses a transistor > on the input AND in the feedback path and takes an otherwise mediocre > opamp and makes it nearly as good as the most expensive ones ... The > 4136 is one of the orginal low noise audio opamps but it's only good > up to 2v p-p before distortion becomes a problem ... Think what this > circuit could do with a NE5532/4 and adapted to a balance > configuration ... Somewhere in one of my hundred or so noebooks I have > several circuits like this but I still haven't found them > > When I finalize a design don't worry I'll share it > > JR > > JR > > JR > > > --- In [email protected], Grant Hodgson <grant@> wrote: > > > > 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 > > >
