[Laser] discrete vs op amp sensitivity

[Art]

Hi all,

I followed the recent discussion about the relative performance of 
the discrete type of front end (vs op amp based) very closely. I'm 
not sure we ever resolved whether front ends like the PGP front ends 
provide better performance than the conventional op amp front end.

But, I did want to let the group know that I ran across so me 
additional information on this topic in another mailing list and that 
I'm following that discussion as well. It seems the BAD thing about a 
conventional op amp front end is that the resistor that determines 
the bandwidth/gain also contributes noise because this resistor is 
large and because it is in the gain determining path of the circuit. 
This is a problem that the PGP front end doesn't have, whether it 
tips the scale in favor of a PGP type discrete FET front end or not 
is still a big question.

The same group has also been evaluating sound card performance and 
the discussion has been very enlightening. It seems not all sound 
cards are created equal or even remotely equal. Many have high noise 
levels that might render them incapable of receiving a very weak 
signal. The group has also measures the MDS of many types of sound 
cards and found that some high end 24 bit (vs 16 bit) sound cards 
allow much weaker signals to be received.

I don't know how many are actually using a computer sound card for a 
laser receiver....but for those that do, be aware that a bargain 
basement sound card can definitely degrade the ability to decode weak 
signals. Cost is not an absolute measure of performance, the very 
expensive Sound Blaster Audigy 24 bit sound card performs no better 
than many bargain basement 16 bit sound cards. For all out 
performance, nothing equals the performance of the Delta 44 and Delta 
66 (both 24 bit) sound cards.

I am following the ongoing discussion of both of these topics and 
will report to the group as more information becomes available.

Regards,

Art