This is only a preview of the November 1996 issue of Silicon Chip. You can view 23 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "Build An 8-Channel Stereo Mixer; Pt.1":
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Items relevant to "Build A Multimedia Sound System; Pt.2":
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Items relevant to "600W DC-DC Converter For Car Hifi Systems; Pt.2":
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Getting more
bass boost
I have recently completed the
50W Stereo Amplifier and preamp,
and it works very well. Having
stated it works very well, I would
like greater or more bass boost.
What components should I change
to increase bass response? Also, if
I wished to tape record, say, “phono”, it would seem that “phone” to
“tape out” bypass the preamp and
amplifier. Can you help please? (M.
D., Beechboro, WA).
• You can increase the available
bass boost and cut at very low
frequencies by reducing the 22kΩ
resistors at each end of the bass
pot (VR2) to 10kΩ. However, doing
this is also likely to increase the
possibility of amplifier overload on
problem but this could then make the
warranty void.
Even when the washing machine
is switched off at the machine, there
is still interference but not so severe,
so the machine has to be switched off
also at the power point. I have contacted other people via my CB radio
that have the same problem so it is
generalised and I was disappointed
with the reply from Fisher & Paykel
who made it sound as if mine was an
isolated case.
I thought that because it was a problem affecting the public in general you
might be able to suggest some form
of suppression that could be added
externally to stop or at least reduce
the interference. The suggestion by the
SMA that none of the affected items
be used when the washing machine is
being used is unacceptable in 1996. (J.
C., Waroona, WA).
• We agree that the interference does
seem rather severe. At this stage we
can only suggest that you invest in a
good line filter; it will need to have a
rating of at least 10 amps and should
be capable of coping with any surge
current from the motor.
Single channel operation
for VHF receiver
I am a fanatical reader of your magazine which I am getting from a relative
of mine in Australia. As a student of
94 Silicon Chip
bass-heavy program material.
A better approach, which will
increase the apparent bass boost
and cut, is to reduce the .01µF
capacitor shunting VR2. This will
raise the turnover frequency of
the bass control so that it has a
more audible effect at higher bass
frequencies. Try a capacitor value
of .0068µF.
We should point out that raising
the bass turnover frequency in this
way will increase the interaction
between the bass and treble controls.
In virtually all amplifiers, when
the tape monitor function is used,
the amplifier circuitry is effectively
out of the picture. The only exception is if you are taping a record
and then the RIAA preamplifier is
in circuit.
electronics, I am very interested in RF
communications devices and I found
an article from your magazine, the
VHF Monitor Receiver from the March
1989 issue. I would be very obliged to
you if you can send me any schematics
to modify it in order to operate it as a
single channel receiver. (L. P., Athens,
Greece).
• There is no need to make any
modification to the circuit to operate
it as a single channel. Just use a multi-turn trimpot to tune it to the wanted
channel.
Message recorder
variations
I bought the 16-Second Solid State
Message Recorder at the time it was
published in October 1993. Then, in
October 1994, the Talking Headlight
Reminder circuit was published. I
kept the two magazines inside each
other, with the idea of using the message recorder for the headlights at a
later date.
Now that I have examined the two,
I notice that the updated ISD1416 has
a record pin (27) and a playback pin
(23). In the Message Recorder circuit,
pin 27 gets connected to the positive
rail to play back and to the negative
rail to record.
Could I still use the 555 of the later
circuit to turn on a PNP transistor
between pin 27 and the positive rail
to make the older chip work for the
headlights? Do you have any ideas
about this please? (D. S., Caloundra,
Qld).
• The Solid State Message Recorder
was published in July 1993, while a
version from Dick Smith Electronics
was published in the October 1993
issue. We are not sure which you are
referring to. However, for the October
1993 version we recommend connecting the pin 27 input of the recorder
to play back as selected by S1. The
cathode (K) of LED1 should go to
ground and the Vccd pin (pin 28) to a
switched positive supply. This could
be obtained directly from the pin 3
output of 555 timer IC1 for the Talking
Headlight Reminder.
If you are using the July 1993 recorder, the pin 3 output of the 555 can
connect directly to the S1 play switch.
TV pattern generator
output is distorted
I have a problem with the Colour
TV Pattern Generator which I have
put together in the correct format. The
seven separate patterns, except the dot
pattern, appear on the television but
there is a lot of distortion on the screen
and, therefore, the patterns don’t show
up as being clear. I get a lot of vertical
distorted lines with zig zags and it’s
off frequency. Could you please advise
me as to where the problem might be?
(M. S., Chiswick, NSW).
• From your description of the symptoms it appears likely that the circuit
is affected by hum breakthrough from
the power supply. The most common
cause of this is the failure to use a plugpack transformer of adequate rating. It
needs to be rated at 500mA or more.
A 300mA unit is inadequate.
Notes & Errata
175W Power Amplifier, April 1996:
to further increase the safety margin
in the event of amplifier failure, we
suggest that the fuses be changed to 3A
instead of 5A when 8Ω loudspeakers
are used.
Photographic Timer, April 1995: the
bridge rectifier specified as “WO4”
does not have the same pinout as
the DIP rectifier depicted on the PC
overlay on page 27. If a WO4 type is
used, two of the leads will have to
be swapped and sleeved so it can be
SC
installed in the PC board.
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