Hi Roger and all, > Around 2000 or so when I built my simple EME receiver to use with Linrad, > it looked like the AD797s had the best noise specs and so this is what I > used. > > Now it seems that some of the cognoscenti tout the LT1128A and don't even > mention the AD797. > > The typical noise at 1 kHz for the AD797 is 0.9 nV/sqrt[Hz] and that for > the LT1128 is 0.85, and max figures are 1.2 for the AD797 and 1.1 for the > LT1128, so the LT1128 is ever so slightly better in this respect. > > The gain bandwidth of the AD797 is 110 MHz and that of the LT1128 is 20 I > think; I guess that doesn't matter for our baseband amps. It all depends on where the performance limiting factors are.
The low end is noise, but there is a high end also and second order distortion is usually the interference that limits dynamic range. I think the AD797 has much lower harmonic distortion than the LT1128. The LT1028 is better, probably because it is faster. > The slew rate of the AD797 is 20 V/usec and of the LT1128 is 5V/usec. > > So my question is: > > For use as the 'last stage' of amplification before the soundcard for a > system sampling at up to 192 kHz, are these two chips pretty much > equivalent given the [to me] tiny differences in noise, or is the LT1128 > clearly superior, and if so, why. If the LT1128 would have advantanges > under some conditions, for some projects, what would those conditions or > projects be? > > If there is not a big difference in performance for this purpose, why is > the LT1128 currently the 'ultra low noise op amp of choice'? I don't > think it is cost, as from Digikey they both cost 8-9 USD in single > quantities. In case the signal source has a low output impedance, the noise voltage becomes more important. On the other hand, if you need a large output swing, linearity is more important. Those who like the LT1128 might use it on a 3 ohm source (vinyl player) Maybe a LT1128 followed by an AD797 that has only a small gain (and takes care of the differential amplifier task that references the output to the soundcard reference point) > PS I got a really pleasant surprise yesterday when I tried to compile and > run Linrad 02.14 on an old P3 with a pre-Fedora version of Redhat Linux > installed and everything compiled and ran perfectly, including XLinrad!! Linrad should be backwards compatible all the way to the 2.2 kernels and RedHat 6.1;-) 73 Leif / SM5BSZ ############################################################# This message is sent to you because you are subscribed to the mailing list <linrad@antennspecialisten.se>. To unsubscribe, E-mail to: <[EMAIL PROTECTED]> To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]> To switch to the INDEX mode, E-mail to <[EMAIL PROTECTED]> Send administrative queries to <[EMAIL PROTECTED]>
