This is only a preview of the December 2013 issue of Silicon Chip. You can view 23 of the 104 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 Electronic Bellbird":
Items relevant to "PortaPAL-D: A Powerful, Portable PA System, Pt.1":
Items relevant to ""Tiny Tim" 10W/Channel Stereo Amplifier, Pt.2":
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100W Digital Amplifier, Li-Po Battery . . .
PortaPAL-D
Powerful, Portable
Public Address
Loudspeaker System
by John Clarke
With battery operation, high efficiency loudspeakers and a class-D
amplifier, the PortaPAL-D PA system has enough power to blow your
socks off! It’s ideal for busking, sports events, meetings or anywhere
you need a powerful, portable PA system.
W
hile we have published
a portable public address
loudspeaker system previously (also called the PortaPAL), that
was more than 10 years ago, in February 2003.
The main semiconductors used in
that design have become unavailable
and technology has marched ahead
with efficient class-D amplifiers, along
with the advent of lithium batteries
which are much more energy dense.
Our new PortaPAL-D uses the
CLASSiC-D Amplifier published in
November and December 2012, along
with its matching speaker protector
from the same months and the DC-DC
Converter published in May 2013.
With that combination we have a
high-power amplifier that can be run
from a 12V battery. One year later, we
have added the preamplifiers, mixer,
tone controls and power supervision
necessary for the PortaPAL-D to function.
We are using two 8 200mm loudspeakers (with concentric tweeters)
34 Silicon Chip
in parallel to hand the full 100 watts
available from the amplifier. Buying
the commercial equivalent could
easily set you back by more than a
thousand dollars!
The PortaPAL-D is in a timber cabinet measuring 620 x 350 x 330mm and
weighing about 20kg. It is covered in
speaker carpet with corner protectors,
to guard against damage from bumps
and roadie use.
The two loudspeakers are mounted
behind protective steel grilles that
are themselves protected by being
recessed into the box.
On the rear is the main control
panel, again recessed into the box for
protection against damage.
A top hat socket, for use with a
speaker stand and a carry handle are
included.
The cabinet and chassis for the electronics can be made using standard
tools. And you need not be worried
by small imperfections while building
the cabinet since these will be covered
by the carpet anyway. The result will
be a PA box that looks professionally
finished.
Sealed enclosure
The cabinet includes an open section to mount the PortaPAL-D electronics but the rest of the box is an infinite
baffle design. This has advantages
over an open-back design in that the
sealed cabinet provides damping of
the speaker cone at low frequencies,
preventing the cone from being overdriven with high power bass signals
(or when accidentally dropping a
microphone onto the floor!).
Another advantage is that the microphone just needs to be positioned
behind the front edge of the speaker
cabinet to minimise acoustic feedback.
Two XLR sockets are provided
for balanced microphones with one
channel providing phantom power, if
required. Both inputs can be used with
dynamic microphones. Guitar input
is via a standard 6.35mm jack socket
while RCA stereo sockets mix left and
right line inputs into a mono signal.
siliconchip.com.au
PortaPAL-D Features
• Class D low-distortion power
amplifier delivering up to 100W
to the loudspeakers
• Portable 12V Li-Po batterypowered amplifier with charger
• Twin 200mm loudspeakers with
integral tweeters
• Two microphone inputs (4.5mV)
• Guitar input (50mV)
• Line input (1V) and output
• Individual level controls
• Bass and treble controls
• Standby power-down to
conserve battery power
• Low battery shutdown
• Standby indication
• Charger indication
• Thermostat-operated air
circulation fan
• Rugged cabinet with carpet, corner
protectors and speaker grilles
• Top hat included for use with
speaker stands
Each input has its own level control
and bass and treble tone controls are
provided.
A line output is also provided to
feed an additional amplifier, recorder,
etc.
Power source & management
The PortaPAL-D is powered via a
12V Lithium Polymer (Li-Po) battery
rather than the sealed lead acid (SLA)
type of the original PortaPAL.
This makes it much lighter. While a
typical 7.2Ah SLA battery will weigh
2.55kg, the much smaller 8Ah Li-Po is
less than a third of this. Plus, the Li-Po
battery can be discharged much more
deeply before recharging.
In effect, you get more than double
the SLA’s capacity for a fraction of the
weight and size.
As well as a main power switch,
a two-stage standby circuitry automatically powers down sections of the
circuit to reduce power drain if the
PortaPAL-D is not making noise. Two
LED indicators show the standby status.
siliconchip.com.au
Power
is restored
quickly
when an
input signal
is detected.
A low-battery shutdown is also
included which protects the battery
from over-discharge. We estimate
that the PortaPAL-D should run for
at least eight hours with normal use
and longer with periods of shutdown.
A commercially-made charger (intended for Li-Po cells) is set into the
front panel, so that its controls can be
accessed and its status LED visible.
This can be powered from a nominal
12V (11-15V) supply, with a current up
to 4.5A if the supply can deliver that.
The battery can be charged at any
time, regardless of whether the PortaPAL-D is in use or even switched off.
Typically a 12V plugpack would
be used to charge the PortaPAL-D,
although a larger battery could also
be used, either free-standing or in a
vehicle.
Circuit overview
Fig.1 shows the general arrangement of the PortaPAL-D. As already
mentioned, we use the CLASSiC-D
amplifier module, the loudspeaker
protector and the DC-DC Converter
published previously. Full details
for these projects can be found in the
November and December 2012 issues
for the amplifier and protector and
the May 2013 issue for the DC-DC
Converter. They can also be accessed
on-line via www.siliconchip.com.au.
The CLASSiC-D amplifier is used
mainly due to its efficiency (and
therefore power saving). It can run
at high power without generating too
much heat. This is a distinct advantage
December 2013 35
PROTECT
LK4
SIGNAL
CLASSIC-D
AMPLIFIER
IN
MIXER AND
PREAMPLIFIER
SPEAKER
OUT
OUT
(NOV/DEC 2012)
LK3
IN
8
COAXIAL
SPEAKERS
LOUDSPEAKER
PROTECTOR OUT
(NOV/DEC 2012)
+35V,
0V
SHUTDOWN
–35V
+12V
0V
CELL
MONITOR
CELL
EQUALISATION
– +
Li-PO 3-CELL
BATTERY
8Ah
Fig.1: the PortaPAL-D brings together several
recent and quite innovative projects into one
handy unit. The mixer and preamplifier sections
are new and based on proven designs but the
main amplifier, the CLASSiC-D 100W digital
amplifier, the DC-DC converter which powers it
and the loudspeaker protector which prevents
catastrophic failure are state-of-the-art designs
from the past twelve months. Also of note is the
use of the 12V Lithium Polymer battery, saving
significant weight and size, and the commercial
Li-Po battery charger with added battery
protection circuitry.
DC-DC
CONVERTER
(MAY 2013)
50°C
SWITCH
+
OUT
Li-PO
CHARGER
FAN
IN
–
CHARGER
SUPPLY
over conventional class AB amplifiers
which are nowhere near as efficient
and generate significant heat.
Another reason is that the amplifier
has proven reliable and has low levels
of distortion and noise with extra features such as temperature cut out and
over-current protection.
The CLASSiC-D amplifier is powered by a DC-DC converter, delivering
plus and minus 35V DC supply from
a 12V supply. With this, it can deliver
up to 100W into 4 for short periods
and 50W on a continuous basis.
CON3
MIC 2 IN
GAIN
IC1b
Battery-saving auto shutdown
To conserve battery when not actually being driven, the PortaPAL-D has
a two-stage shutdown.
First, after a short period of no
signal, the amplifier module is shut
down. This is controlled in part by
the power supervision section. In the
second stage, after a longer period of no
signal, the power supervision circuitry
VR1
BASS &
TREBLE
IC5b
IC3a
VR2
LEVEL + GAIN
GAIN
IC2
CON9
VR6
MIXER
IC5a
IC4a
CON10
CON8
VR3
LINE INPUTS
SIGNAL DETECTOR
(CON12)
TO CLASS D
AMPLIFIER
‘SHUTDOWN’
LED1
DELAY
VR4
Q3, IC7, Q4
G
S
POWER
LED3
POWER
SUPERVISION
(RELAYS 1-3)
+12V TO
PREAMPLIFIERS
& MIXER
36 Silicon Chip
RELAY4
IC6a, D1, D2, IC6b
10-WAY IDC
CONNECTORS
S1
SIGNAL
OUT
STANDBY1
LEVEL
L
R
LINE
OUTPUTS
LEVEL + GAIN
IC3b
GUITAR
INPUT
switches off the DC-DC Converter and
so powers down the system.
The power supervision circuitry also
controls the charging of the battery.
While power is applied, the charger
continually measures the voltage of
each cell, ensuring each is not over- or
under-charged.
Typically, the lithium-polymer cell
balancing leads would connect directly
to the charger. However, this could
mean the cells would discharge via the
charger over time and possibly flatten
the battery. To avoid this, we connect
VR5
LEVEL + GAIN
(CON10)
GAIN
IC1a
6-WAY SIL
HEADER
& SOCKET
CON11
MIC 1 IN
A small fan is switched by a thermostat when the amplifier heatsink
reaches 50°C, circulating cooling air.
(CON8)
BATTERY
LEADS
+35V
+12V SWITCHED
POWER
SUPERVISION
STANDBY2
LED2
Q5
D
DC-DC
CONVERTER
+12V SWITCHER
Fig.2: the circuit elements
in more detail. These are
explained in the text – and you
can compare these elements
with the circuit diagrams on
following pages.
siliconchip.com.au
the cell monitor leads via the power
supervision circuitry.
Detail of the preamplifier, mixer and
standby circuitry is shown in Fig.2.
Microphone inputs (Mic1 and Mic2)
and their gain stages (IC1a and IC1b)
are on their own PCB and connect
to the main PCB via a 6-way single
in line (SIL) header and socket. The
guitar input and line input plus the
line outputs are also on a separate PCB
and similarly connect via 10-way IDC
socket and plug.
The level potentiometers control
the gain, with additional gain provided after the level controls for the
microphone and guitar inputs. A mixer
combines the four signals (Mic1, Mic2,
Guitar and Line) and its output is fed to
the bass and treble tone controls. From
there the signal goes to the input for
the CLASSiC-D amplifier, to the line
outputs and also to a signal detector
which forms part of the shutdown
circuitry.
In “Standby 1” state, if the signal is
off for longer than 15s, relay 4 is triggered, shutting down the CLASSiC-D
amplifier. The amplifier is still powered but in shutdown. LED1 lights to
show this state. Any input signal will
instantly restore full operation to the
amplifier.
If there is still no input signal af-
PortaPAL-D Specifications
Output Power:
100W into 4 short term
50W into 4 continuous
Output sound level:
Typically 96dB (SPL) at 1W
Input sensitivity and
Microphone: 4.5mV; <20Hz-20kHz
Frequency Response (-3dB): Guitar: 50mV; 25Hz-25kHz
Line: 1V; <20Hz-50kHz
Tone Controls:
Bass +11dB and -14dB at 100Hz
Treble +9.5dB and -12.6dB at 10kHz
Signal-to-Noise Ratio:
-80dB with respect to 50W into 4 (inputs at
minimum gain; 20Hz-20kHz bandwidth);
Muting:
Threshold at <150mW output power
Standby modes (no input):
15s typical for Standby1
100s typical for Standby2
<1s return to normal operation
Battery consumption:
“Low battery” state activated – 8.5A
Standby2 – 45mA (DC-DC converter turned off)
Standby1 – 320mA (amplifier only turned off)
Powered, before either standby state – 730mA
“Low Battery” thresholds:
Typically 10.5V switches PortaPAL-D off
11.2V switches PortaPAL-D on
Battery Charger:
Input 11-15VDC, 4.5A charging current maximum
Dimensions:
620 x 350 x 330mm inclusive of corner protectors
Mass:
17.5kg
Here’s a view of
the electronics
module in its
metalwork,
removed from
the PortaPAL-D
speaker box.
A commercial
charger is
incorporated
because it is
perfectly suited
to the Li-Po
battery pack we
used and will
result in longest
battery life.
siliconchip.com.au
December 2013 37
+12V
4
4
+12V
10k*
10F* 10k*
10k*
* THESE COMPONENTS
FOR PHANTOM POWER
MIC1
INPUT
1
3
2
CON1
1k
FB°
1k
1
IC1a
3
47F FB°
2
470pF
CON2
10k
FB°
MIC1
OUT
SIGNAL
GND
3
+Vref
150pF
3
1
IC1: LM833
22k
°FERRITE BEADS
1
150
6
150pF
Vref
22k
1k
6
7
IC1b
150
5
CON8
6
+12V
POWER
GND
SIGNAL
GND
6
2 x 47F
1k
3
10pF
2
CON4
7
6
IC2
LINE
INPUTS
R
CON6
R
LINE
OUTPUTS
SC
2013
10k
PORTAPAL-D
GND
LINE
IN
MIC2
LEVEL
1F
#
VR2
10k
LOG
+12V
8
9
1
9
+Vref
10F
4
#
LINE
IN
2
LINE
OUT
5
2.2F
MICROPHONE, GUITAR & LINE INPUTS & OUTPUTS
lights to show power is on.
Main power is controlled via switch
S1. If on, the battery voltage is monitored by the low voltage shutdown
section (IC8 and Q1).
Should the battery supply drop
below about 10.5V, the power to the
330nF
LINE
OUT
1F
VR3
10k
LOG
NP
5
GUITAR
LEVEL
7
Vref
Fig.3: the input circuitry for the two
microphones, guitar (which of course could
be used for other sources) and the line inputs
(suitable for audio players such as MP3s
or tablets) are quite conventional. Only
Mic1 input has provision for microphones
requiring phantom power but you can use
ordinary (dynamic) mics on this input too.
ter about 100s, “Standby2” state is
entered. Power is switched off to the
DC-DC Converter and this in turn
switches off the CLASSiC-D amplifier,
while LED2 lights showing Standby 2.
When there is audio, power is restored
to the amplifier within 1 second. LED3
38 Silicon Chip
GND
(10-WAY IDC
CONNECTOR)
L
6
3
+Vref
10F
CON7
4
8
2.2k
10F
CON10
+12V
GUITAR
IN
680pF
2.2k
1F
# POT BODIES
WIRED TOGETHER
WITH 330nF TO
EARTH
(6-PIN SIL
HEADER
SOCKET)
+Vref
1
7
2.2F
MIC1
LEVEL
VR1
10k
LOG
CON11
GUITAR
IN
1M
L
150
4
4.7k
+Vref
10F
3
TP3
4.7k
CON5
+12V
5
MIC2
10F
100nF
IC2: TL071
7
4
#
2
150pF
GUITAR INPUT
1
MIC1
(6-PIN SIL
HEADER)
22k
10k
MIC2
OUT
CON3
4
47F
3
+Vref
TP2
5
1k
100F
6
8
IC4b
TP1
8
2
10k
MIC2
INPUT
5
10k
47F
10k
10k
POWER
GND
22k
47F FB°
470pF
2
10F
100nF
150pF
+12V
#
LINE IN
LEVEL 10F
VR4
10k
LOG
2
(10-WAY IDC
CONNECTOR)
SC
2013
PORTAPAL-D
preamplifiers and mixer is removed
and the whole system shuts down.
Current draw is only that of the low
voltage shutdown circuitry at 8.5A.
Circuit detail
Balanced microphone inputs for
Mic1 and Mic2 are via XLR sockets,
with the signals fed to the inputs of
low noise op amps IC1a & IC1b. Assuming 600 microphones, these preamplifiers have a gain of 22. Both are
identical, except that the Mic1 input
provides phantom power for electret
microphones (if used).
Phantom power is limited to 0.5mA
or so, sufficient for the typical electret microphones used in PA systems
siliconchip.com.au
+12V
10F
100nF
150
100nF
1000F
CHASSIS
+Vref
IC5: TL072
10nF
15nF
100pF
8
IC3a
2
10F
18k
NP
2
3
TP4
10k
100k
IC5a
4
NP
TP7
CUT
VR5 100k LIN
1k
10k
TREBLE
+Vref
8
IC5b
7
10F
10k
CUT
VR6 100k LIN
x11 AMPLIFIER
47pF
6
5
1.5nF
BOOST
330pF
10F
BOOST
1F
1
30k
1k
+Vref
1
15k
18k
BASS
30k
3
100F
100nF
OUTPUT TO
AMPLIFIER
CON9
10
LK1
10k
47k
IC3: LM833
MIXER
5
100k
7
IC3b
6
4
15k
TP5
10k
1k
100k
IC4a
1
10k
15k
TP6
330pF
x11 AMPLIFIER
10k
MIXER & TONE CONTROL SECTION (MAIN PCB)
but not condenser microphones. If
more current is required, reduce the
10kresistors, possibly to 2.2k or
less.
High frequencies above 48kHz are
rolled off by the 150pF capacitors
across the 22kfeedback resistors. The
470pF capacitor shunting the balanced
input lines, in conjunction with the
microphone impedance, also roll off
the high frequencies.
Ferrite beads in the 1k input resistors help to reduce RF pickup, while
the use of 1% resistors in the balanced
microphone circuits ensures good rejection of common mode signals such
as mains hum.
The unbalanced outputs are each
siliconchip.com.au
TO POINT A
IN POWER
SUPERVISION
SECTION
(SIGNAL
DETECTION)
To whet your appetite
ready for the assembly
details next month,
this shot shows the
internal make-up of the
PortaPAL-D.
At left (vertical) is the
main CLASSiC-D amplifier
board, while at top right is
the mixer and tone control
PCB. Below that is the
mic, guitar and line input/
output board while the
long blue object is the Li-Po
battery. Its charger is the
“black box” almost hidden
at rear, along with the
DC-DC converter in its own
diecast case.
IC4: LM833
2
+Vref
Fig.4: from the audio input boards, signal is fed to level control
pots, more amplification and thence to the mixer and tone
control stages. The ouput from this goes to the CLASSiC-D digital amplifier.
x11 AMPLIFIER
3
10F
150
330pF
10F
1k
TONE CONTROLS
fed to level potentiometers VR1 & VR2
via a 150 stopper resistor and 10F
AC coupling capacitor. The signals are
then applied to op amps IC3a and IC3b,
both of which have a gain of 11. This
means that maximum gain for microphone signals before the mixer is 242.
Guitar input
The guitar input stage comprises IC2,
a TL071 Fet input op amp connected as
a non-inverting amplifier with a gain
of 2 for mid-band frequencies.
The guitar signal is coupled via two
47µF capacitors in series. These are
equivalent to a non-polarised capacitor and are included to cater for inputs
with a positive or negative bias voltage,
that goes beyond the voltage bias set
by the Vref (at half supply).
We have specified the high load
resistance of 1M to ensure optimum
high frequency response with the
relatively high inductance of typical
guitar pickups. With such a high load
resistance, you might wonder why we
have used such a large input coupling
capacitance. After all, to maintain a flat
response to below 20Hz, all you need
is an 8.2nF input capacitor. The reason
is to minimise noise, which occurs
when op amp IC2 sees as low a source
impedance as possible.
Output from IC2 is coupled to the
“guitar” level control, VR3, via a
150resistor and 10F capacitor. The
December 2013 39
+12V
FROM IC5b
PIN 7 IN
TONE
CONTROL
SECTION
100nF
10F
LED1
K
3
8
1
IC6a
2
1k
1F
A
CHARGER
OUTPUT
CHARGER
SUPPLY
OUT
CHARGER
SUPPLY
IN
220F
10F
1k
4
3
IC7
7555
6
2
10k
1M
C
B
10k
B
100k
SIGNAL
DETECTOR
8
7
A
10F
BATTERY
470k
470k
K
22pF
1k
A
7
IC6b
5
D1
1N4148
100F
CON12
6
K
4
470k
K
D3
4.7k
D2
1N4148
CLASS-D
AMPLIFIER
SHUTDOWN
RLY4
470k
TP9
DC-DC
CONV
MAIN
SUPPLY
A
STANDBY1
IC6: LM358
A
+12V’
10
SCHMITT
TRIGGER
C
1
Q3
BC337
K
E
Q2
BC337
A
E
10k
D4
1N4148
DELAY
CON13
+
–
+
–
+
–
+
–
+
–
4
5
7
L1 16H
1
2
10A
8
9
10
S1
CHASSIS
RLY1
o
11
K
POWER
D6
1N5404
12
13
RLY2
K
50
THERMAL
CUT-IN
(NO)
–
3
2
3
2
CELL SENSING
RLY3
A
4
D1– D4: 1N4148
A
1
CON14
270k
Li-PO
3-CELL
BATTERY
CON15
4
2.2M
12V
FAN
+
1
D5
1N4004
270k
+
A
–
CHARGE
SENSE
INPUTS
(CON13)
F1
6
SC
2013
PORTAPAL-D
K
1N4004
POWER SUPERVISION SECTION (MAIN PCB)
A
K
Fig.5: here’s where the PortaPAL-D excels over earlier mixers – it uses a Li-Po battery and a commercial charger to give
much more “bang for buck” when it comes to portable use. For a full explanation, see the accompanying text.
signal is then fed to op amp lC4a, which
is identical to IC3a & IC3b.
Line signal
Stereo line inputs (eg, from a CD
player or MP3 player) are mixed to a
mono signal with 2.2k resistors and
fed to potentiometer VR4 via a 2.2F
coupling capacitor.
Signals from all four input sources
are mixed via 15k resistors for the
mic and guitar signals and a 10k
resistor for the line signal in inverting
amplifier IC5a. This has a gain of minus
two for the first mic and guitar signals,
with slightly higher gain for the line
input signals (due to the 10kresistor
40 Silicon Chip
to compensate for a slight gain loss in
the resistive mixing of the stereo line
inputs).
IC5a drives the tone control stage
comprising IC5b, VR5 and VR6 and
associated resistors and capacitors.
IC5b’s output signal is fed to three
separate places; the line output via
RCA and 6.35mm jack sockets, the
signal detection stages involving IC6a
and the input to the CLASSiC-D power
amplifier.
All of the op amps in the circuit used
as signal amplifiers are biased via the
Vref line, which is at half supply (about
+6V). This is derived from the +12V
line by a voltage divider consisting
of two 10k resistors with the centre
point bypassed by a 100F capacitor.
The bypassed supply is then buffered
by op amp IC4b to provide the Vref
line. All these biased op amp outputs
will sit at about half the battery voltage,
with the audio signal rising and falling
about this DC voltage
Shutdown
As noted above, we have incorporated signal detection into the circuit
to shut down the power amplifier in
order to reduce current consumption
when no signal is present. Op amp
IC6a is a non-inverting amplifier with
a gain of 471, set by the 470k and
siliconchip.com.au
5
+12V’
A
+12V
STANDBY2
LED2
K
10k
Q5
IRF9540
4.7k
S
G
10k
D
10k
B
A
POWER
C
Q4
BC337
E
LED3
3
(CON13)
K
TO DC-DC
CONVERTER
SWITCHED
INPUT
4.7k
+12V
2200F
25V
1F
MMC
LOW
ESR
2
3
S
+12V’
Q1
IRF9540
G
8
V+
HYST
D
100k
100k
4
IC8
OUT
MAX8212
THRESH
GND
5
LOW VOLTAGE SHUTDOWN
BC337
B
LEDS
E
K
A
C
IRF9540
1N5404
G
A
K
D
D
S
1kfeedback resistors. The 22pF capacitor rolls the gain off above 15kHz,
while the 10F capacitor in series
with the 1k resistor rolls off signals
below 15Hz.
The amplified signal from IC6a is
then fed to a diode pump circuit consisting of diodes D1 & D2 and the 1F
& 10F capacitors connected to them.
Peak level of the signal from IC6a will
be stored in the 10F capacitor which
is continuously being (slowly) discharged via the 1M resistor across it.
IC6b, connected as a Schmitt trigger inverter, monitors this voltage.
A 470k resistor between pin 5
and pin 7 applies positive feedback
siliconchip.com.au
to give hysteresis. This makes the
comparator output switch cleanly
between high and low, and to prevent
oscillation at the switching threshold.
The inverting input of IC6b is set
at +2.1V (ignoring the effect of the
470kfeedback resistor) using the
470kand 100kresistors across the
12V supply.
When power is first applied to the
circuit, the 10F capacitor between
the 12V supply and the inverting input to IC6b is initially discharged and
therefore pulls pin 6 low, causing the
output (pin 7) to be high. This turns
on transistor Q2, so relay 4’s contacts
close and the CLASSiC-D amplifier is
shut down.
At the same time, transistor Q3 is
turned off so IC7’s inputs (pins 2 and
6) are high due to the 220F capacitor
connecting to the 12V supply being
initially discharged. The output (pin
3) is low so Standby 2 LED (LED2) is
lit. The low output holds both Q4 off
and Mosfet Q5 off. This removes power
from the DC-DC converter switch and
as a result the CLASSiC-D amplifier
is off.
When audio signal is detected by
IC6b, the input (pin 6) will go above
the 2.1V at pin 5 so the output (pin
7) goes low, switching off Q2 and the
relay. Diode D3 quenches the backEMF of the collapsing relay coil field .
There is still a low current flow
through the relay coil and Q3 – not
enough to pull the relay in but enough
to turn Q3 on. This provides a path to
ground (via the 1k resistor) which
charges the 220F capacitor.
The now-low input to the 7555
cause its output (pin 3) to go high,
switching on power LED (LED3)
and transistor Q4 and switching off
the Standby 2 LED. Mosfet Q5 also
switches on and the DC-DC Converter
is powered, in turn powering the
CLASSiC-D amplifier.
Low battery
Regardless of the battery type, it
is important that it not be over-discharged and permanently damaged.
While the Lithium-Polymers used in
the PortaPAL-D are better than SLAs in
this regard, care still needs to be taken.
Low battery voltage is detected using IC8, a micropower voltage monitor
that compares the voltage at pin 3 to
an internal 1.15V reference. With a
12V supply, the voltage divider across
IC8s input will ensure that pin 3 is
always above 1.15V. However, as the
battery discharges, this voltage will
drop. Below 10.5V, IC8s output (pin
4) will go high, turning off Mosfet Q1.
This removes power from the rest of
the circuit thus preventing the battery
being discharged any further.
Pin 2 provides hysteresis, stopping
the circuit oscillating back and forth
around the 1.15V threshold. While
ever the voltage at pin 3 stays above
1.15V, pin 2 is effectively connected
to the supply rail, thus shorting out
the 270k resistor to 12V.
However, if the pin 3 voltage drops
below 1.15V pin 2 is effectively open
circuit. So that extra 270k resistance is added to the voltage divider,
which drops the voltage at pin 3 even
lower (just over 1V with a 10.5V supply). Therefore the battery needs to
be charged to more than 11.6V before
the output (pin 4) goes low, allowing
the Mosfet to power the circuit again.
Power
Power from the battery passes
through the 10A fuse, F1 and power
switch S1. Inductor L1 and the 2200F
capacitor filter the supply, helping
prevent DC-DC converter switching
noise from entering the supply for the
audio op amps. Additional filtering is
provided with the 10 resistor and
the supply decoupling capacitors on
the 12V rail.
Note that the high current supply
required by the DC-DC Converter is
tapped off before the switch. Only
the low power switching current to
control the DC-DC Converter is at the
output to Q5.
Reverse polarity protection is via
diode D6: this will blow the fuse if
the supply polarity is inadvertently
connected back to front.
Charging
Three relays are used to switch in
the charger connections. The supply to the charger is tapped at pins
10-13 of CON13 so that when power
is available, relays (Relay1, Relay2
and Relay3) will be switched on. The
charger output is switched to the battery positive via relay 1 contacts while
the cell balancing outputs from the
battery are connected to the charger
via relay 2 and relay 3 contacts.
When there is no power applied to
the charger input, the relay contacts
open and completely disconnect the
charger from the battery.
December 2013 41
PortaPAL-D – Parts List
Main PCB (Mixer and power supervision)
1 PCB coded 01111131, 212 x 100mm
1 10-way IDC PCB mount socket (CON10)
2 10-way IDC line plugs
1 100mm length of 10-way IDC cable
1 6-way SIL socket (CON11)
1 2-pin header, 2.54mm spacing (LK1)
1 2-pin polarised header, 2.54mm spacing (CON12)
2 2-way pin header sockets
1 jumper shunt
6 DIL8 IC sockets (optional)
2 M205 PCB fuse clips
1 M205 10A fast blow fuse (F1)
1 iron powdered toroid 28 x 14 x 11mm [Jaycar LO1244] L1
5 2-way PCB mount screw connectors (5.08mm pin spacing)
(CON13)
1 3-way PCB mount screw connectors (5.08mm pin spacing)
(CON13)
1 vertical PCB mount RCA socket (CON9)
2 RCA line plugs
1 12V 10 or 16A SPDT relay [Altronics S4197, S4170A, Jaycar
SY-4050] (RELAY1)
2 12V 1A DPDT relays] Altronics S4150, Jaycar SY-4059]
(RELAY2,RELAY3)
1 12V SPST DIL reed relay [Altronics S4101A, Jaycar SY-4032]
(RELAY4)
4 16mm single PCB mount 10klog potentiometers and nuts
(VR1-VR4)
2 16mm single PCB mount 100klinear potentiometers and
nuts (VR5,VR6)
6 knobs to suit above potentiometers (4 blue, 2 grey)
3 M3 tapped spacers 15mm long
1 solder lug
4 M3 x 10mm machine screws
2 M3 x 15mm machine screws
6 pot nuts (providing for an extra nut under potentiometer)
1 3S 250mm 2xJST-XH parallel balance lead
[http://hobbyking.com.au/hobbyking/store/__32036__JST_
XH_Parallel_Balance_Lead_3S_250mm_2xJST_XH_.html]
1 1.5m length of 1mm diam. enamelled copper wire for L1
1 150mm length of 7.5A rated green hookup wire
1 150mm length of single core screened cable
1 270mm twin figure-8 light gauge wire
1 190mm length of 0.7mm diam. tinned copper wire
1 100mm cable tie
2 PC stakes
Semiconductors
2 LM833 dual low noise op amps (IC3,IC4)
1 TL072 dual op amp (IC5)
1 LM358 dual op amp (IC6)
1 7555 CMOS 555 timer (IC7)
1 MAX8212 voltage monitor (IC8)
2 IRF9540 P-channel Mosfets (Q1,Q5)
3 BC337 NPN transistors (Q2-Q4)
4 1N4148 diodes (D1-D4)
1 1N4004 1A diode (D5)
1 1N5404 3A diode (D6)
3 3mm high brightness LEDs (LED1&2 [red]; LED3 [green])
42 Silicon Chip
Capacitors
Electrolytic (PC type)
1 2200F 25V low ESR
1 1000F 16V 1 220F 16V
3 100F 16V 12 10F 16V
1 10F NP 50V 1 2.2F NP 50V 4 1F 16V
1 1F 50V NP
MKT polyester
1 330nF
4 100nF 1 15nF
1 10nF
1 1.5nF
Ceramic
1 1F monolithic multilayer (MMC)
3 330pF 1 100pF 1 47pF
1 22pF
Resistors (0.25W, 1%)
1 2.2M 1 1M
4 470k 2 270k 6 100k
1 47k
2 30k 2 18k 3 15k 15 10k
3 4.7k
7 1k
2 150 2 10
Guitar input, line input and output PCB
1 PCB coded 01111133, 109 x 35mm
2 PCB mount 6.35mm switched jack sockets (CON4,CON7)
2 stereo RCA vertical stacked PCB mount (CON5,CON6)
1 10-way IDC PCB mount socket (CON8)
1 DIL8 IC socket (optional)
Semiconductors
1 TL071 single op amp (IC2)
Capacitors
Electrolytic (PC type)
2 47F 16V
2 10F 16V
1 100nF MKT polyester
1 2.2F 16V PC
1 680pF ceramic
Resistors (0.25W, 1%)
1 1M 1 10k 2 4.7k
2 2.2k
1 10pF ceramic
1 1k
1 150
Microphone input PCB
1 PCB coded 01111132, 64 x 73mm
2 PCB mount XLR female connectors [Altronics P 0883]
(CON1,CON2)
1 right angle 6-way pin header with backing plate removed (CON3)
1 chassis mount 6.4mm spade terminal
1 female spade 6.4mm quick connector
4 ferrite beads 4mm ID x 5mm long [Jaycar LF-1250 or
equivalent]
1 DIL8 IC socket (optional)
4 4g x 6mm self tapping screws or M3 x 6mm screws
1 M3 x 10mm machine screw
1 M3 nut
2 3mm star washers
Semiconductors
1 LM833 low noise dual op amp (IC1)
Capacitors
4 47F 16V PC electrolytic
1 100nF MKT polyester
4 150pF ceramic
2 10F 16V PC electrolytic
2 470pF ceramic
Resistors (0.25W, 1%)
4 22k
7 10k
4 1k
2 150
siliconchip.com.au
Extras
1 CLASSiC-D amplifier set for a ±35V output
(see SILICON CHIP November & December 2012)
1 speaker protector for the CLASSiC-D set for a 35V supply
(see SILICON CHIP, November/December 2012)
1 50°C NO thermostat (Jaycar ST-3831)
1 10F 16V PC electrolytic capacitor (used in speaker protector)
1 DC-DC Converter for the CLASSiC-D (see SILICON CHIP, May ’13)
1 10k0.25W 1% resistor (used in DC-DC converter)
1 Li-Po 11.1V battery (ZIPPY Flightmax 8000mAh 3S1P 30C)
(http://hobbyking.com.au/hobbyking/store/__19530__ZIPPY_
Flightmax_8000mAh_3S1P_30C_AUS_Warehouse_.html)
1 HobbyKing E4 Li-Po balance charger
(http://hobbyking.com.au/hobbyking/store/__14633__
HobbyKing_E4_Balance_Charger.html)
1 Polymax 5.5mm Gold Connector plug and socket set [Jaycar
KG55001 set of 10 but only one plug and one socket required]
(http://hobbyking.com.au/hobbyking/store/uh_viewitem.
asp?idproduct=18659)
1 strap handle [Jaycar HS-8022, Altronics C 3660]
1 1.8m x 3m speaker box carpet [Jaycar CF-2755]
8 corner protectors [Jaycar HM-3843 (or HM-3829 – pack 8),
Altronics C 3620 or C 3623]
1 speaker box “top hat” mount [Jaycar HS-8035, Altronics C 3602]
2 200mm speaker grilles [Jaycar AX-3594, Altronics C 3708]
2 8 200mm coaxial speakers [Altronics C 2005]
1 40mm 12V fan [Jaycar YX-2502, Altronics F 0010]
1 SPST mini rocker switch (S1)
2 9mm M3 tapped standoffs (for fan)
2 M3 x 10mm countersunk screws (for fan mounting standoffs to
chassis)
2 M3 x 15mm machine screws (for fan mounting to standoffs)
1 solder lug
1 “P” cord clamp with M3 x 10mm screw, nut and washer
2 6.4mm crimp female spade connectors
1 200mm length of 10mm diameter heatshrink tubing (for
covering charger and battery bracket)
1 red right angle banana plug [Jaycar PP-0394]
1 black right angle banana plug [Jaycar PP-0395]
1 2.5mm DC panel connector
1 2.5mm DC line plug
2 aluminium sheets 295 x 295mmm, 1mm gauge
[Jaycar HM-9500]
1 350mm length of 12mm x 3mm aluminium
6 M3.5 tapped right angle (RA) bracket standoffs
[Jaycar HP-0872]
16 M3 x 10mm machine screws (for mounting PCBs to chassis
RA brackets to chassis – see note in construction article)
7 M3 x 15mm machine screws (3mm aluminium brackets to
RA brackets, through 12mm standoffs on brackets 3mm
aluminium to standoffs)
1 M3 x 20mm machine screw
10 M3 x 6mm countersunk screws (DC-DC Converter mounting,
battery and charger brackets, RA brackets to chassis)
12 M3 nuts (RA brackets)
2 small cabinet handles (45mm long x 15mm high x 6mm wide
or similar) (optional)
1 2-way 15A terminal strip (optional for extension speaker)
1 1m length of 7.5A figure-8 wire for speaker connections
3 1m lengths of 7.5A hookup wire (1 each red, black, green)
2 25mm length of 6mm heatshrink tubing (1 each red & black)
2 25mm length of 10mm heatshrink tubing (1 each red & black)
2 100mm cable ties
Box Hardware
8 8g 12mm panhead wood screws (for speaker mounting)
24 6g 16mm countersunk wood screws (bronze) (for attaching
corner protectors)
5 4g x 16mm panhead screws (for mounting the chassis to the
cabinet)
1 500ml tin of contact adhesive
2 strips of putty adhesive (eg, Blu-Tack)
2 cushion bags of polyester wadding (eg, Innerbond)
1 3m length 18mm x 18mm DAR (dressed all round) pine
1 6m length 12mm x 12mm DAR pine
2 900mm x 600mm x 16mm sheets of MDF (or single 1800 x
600mm x 16mm sheet )
Resistor Colour Codes
Total No. Value
o
1
2.2MΩ
o
2
1MΩ
o
4
470kΩ
o
2
270kΩ
o
6
100kΩ
o
1
47kΩ
o
2
30kΩ
o
1
27kΩ
o
4
22kΩ
o
2
18kΩ
o
3
15kΩ
o 22
10kΩ
o
4
4.7kΩ
o
2
2.2kΩ
o 12
1kΩ
o
3
150Ω
o
2
10Ω
siliconchip.com.au
4-Band Code (1%)
red red green brown
brown black green brown
yellow violet yellow brown
red violet yellow brown
brown black yellow brown
yellow violet orange brown
orange black orange brown
red violet orange brown
red red orange brown
brown grey orange brown
brown green orange brown
brown black orange brown
yellow violet red brown
red red red brown
brown black red brown
brown green brown brown
brown black black brown
5-Band Code (1%)
red red black yellow brown
brown black black yellow brown
yellow violet black orange brown
red violet black orange brown
brown black black orange brown
yellow violet black red brown
orange black black red brown
red violet black red brown
red red black red brown
brown grey black red brown
brown green black red brown
brown black black red brown
yellow violet black brown brown
red red black brown brown
brown black black brown brown
brown green black black brown
brown black black gold brown
Capacitor Codes
Value F Value IEC Code EIA Code
330nF 0.33F 330n 334
100nF 0.1F 100n 104
15nF 0.015F
15n 153
10nF 0.01F
10n 103
1.5nF 0.0015F 1.5n 152
680pF
NA
680p
680
470pF
NA
470p
470
330pF
NA
330p
330
150pF
NA
150p
150
100pF
NA
100p
100
47pF
NA
47p
47
22pF
NA
22p
22
10pF
NA
10p
10
NEXT MONTH:
We’ll present Part 2 with all the
construction details, including
making & wiring the electronics.
SC
December 2013 43
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