Q&A
■ WITH RUSSELL KINCAID
In this column, I answer questions about all
aspects of electronics, including computer hardware,
software, circuits, electronic theory, troubleshooting,
and anything else of interest to the hobbyist. Feel
free to participate with your questions, comments,
or suggestions.Send all questions and comments to:
Q&A@nutsvolts.com
WHAT’S UP:
Join us as we delve into the
basics of electronics as applied
to every day problems, like:
Lightning Protection Circuit ✓
● Fan Control
Op-Amp Tester
✓
✓
PREAMP MODIFICATION
QA lot of us still have big (size) sound systems at home. However, most of the turntables for vinyl
records may have become obsolete
but the integrated amplifiers still
have an input (PHONO) which I
think might be converted for other
inputs. Other than changing the RCA
jacks to 6. 5 mm microphone jacks,
can you kindly suggest any
modifications in the electronic circuit
that are deemed necessary? I am
thinking of using 600 ohms
unbalanced dynamic (coil)
microphones so that I can utilize the
set as a sort of PA system.
— Francis Wan
AThe preamp has RIAA compensation which attenuates the high frequencies. I don’t think
that will be a problem for voice; I would
make the jack change as you suggest
and see how it sounds. Otherwise, you
will need to remove the compensation
network from the preamp which is
not an easy job without a schematic
and parts placement guide. Your
amplifier no doubt has tone controls;
just turn down the bass and turn up
the treble. It should sound fine.
Checker by Charles Hansen.
I built the unit as shown, but I
was unable to wire a socket to test
an LM3900 (Norton current feedback
op-amp).
— Russ Proesel
OP-AMP TESTER
FOR LM3900
AI believe that all you need to do to make the LM3900 work in that tester is to connect a 1 meg resistor
from the positive input to VCC and
use the negative input for the signal.
Your question brought to mind
an application for a microprocessor
to do the job with one socket. I
haven’t worked out the details, but
any op-amp that works on +5V and
GND could be tested. An op-amp
that requires a negative supply would
need a separate socket.
■ FIGURE 1
QI need an op-amp checker similar to
the one in
Poptronics, Nov.
2001, P43, Op-Amp
and Comparator
VOLTAGE REGULATOR
LAYOUT
■ FIGURE 2
QDo you know of anyone that has or will make a printed circuit board circuit
for the voltage regulator you
designed in the June issue,
page 22 of Nuts & Volts I
have not contacted Far
Circuits because I don’t
know if they will do this
since it is not a big circuit. I
tried to make my own
circuit, but the only resist
pens have too fine a point to
be of any use. Thanks for
24
December 2010
