Hi Glenn-
on Feb.12, Glenn Swanson <gswanson@arrl.org> wrote:
>> Like the 38 Special(?), my NN1G SW-40 uses a NE5532 op amp.
With that in mind, here's another gem from KB6FPW and AE6C
as quoted from the book "QRP Power:"
>> <snip>
>>KB6FPW: "5 to 8 mA of the 22 [the SW-40 draws in receive] are wasted away
>>warming the NE5532 (a JRC device was supplied as a substitution in the
>>kit)."
>>"AE6C: You don't have to use the current-hungry op amp in the kit. The dual
>>pinout is an industry standard and many newer products will give you
>>equivalent or better performance for far less current. I chose an LMC662.
When I designed the SW-40, the NE5532 was a good choice from a
cost/performance standpoint. Before I used it, Zack Lau had specified it in
his 'QRP 3-bander'. Its internal limiting delivers considerably more
current than the other garden- variety op-amps. In practice, it yielded
about 10 dB more audio (into low-impedance phones) - before limiting onset-
than the other devices I tried. I found this trade to be worth the added 5
mA or so of supply current, and I'd suspect Ori reached the same conclusion
with the 38 Special. In the case of the 38S, the decision to spend- or
not- an extra buck-and-a-half on parts for a $25 kit was likely a very simple
one.
Thanks to Glenn for mentioning this change- a worthwhile improvement for
battery/portable operation. :-)
73, Dave Benson- NN1G
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