This is only a preview of the August 2015 issue of Silicon Chip. You can view 43 of the 112 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 "Ultra-LD Mk.4 200W RMS Power Amplifier, Pt.1":
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Notes & Errata
Driveway Monitor (July 2015): IC1
is incorrectly listed as an AD723AN
in the parts list. It should be an
AD623AN as shown on the circuit.
This error has been corrected in
the on-line edition of the magazine.
Next Issue
The September 2015 issue of SILICON CHIP is due on sale in newsagents by Thursday 27th August. Expect postal delivery of subscription
copies in Australia between August
24th and September 4th.
Ultra-LD Mk.4 Amplifier Module,
Pt.1 – continued from p39
the exception of C0G/NP0 types, have
very high voltage coefficients. As the
voltage across the capacitor increases,
its capacitance drops. While electrolytics have a reputation for non-linearity,
they are nowhere near as bad as these
multi-layer ceramics in this respect.
It’s so bad that with just 10mV RMS
across the coupling capacitor, we were
measuring distortion levels as high as
0.1% at 10kHz.
Luckily, the same attribute that gives
C0G/NP0 a near-zero temperature coefficient means they also have a very
low voltage coefficient and so are free
of this problem.
The output filter capacitor can either
be a high-voltage SMD NP0 ceramic
or through-hole polypropylene. Its
linearity is absolutely critical to performance. Both types are acceptable.
However, the NP0 ceramic may be a
better bet as we’ve found several different 250VAC polypropylene capacitors
with less-than-ideal linearity.
We tested several suitably-rated
polypropylene capacitors, some of
which were X2 types, intended for
mains applications. Of these, two introduced measurable distortion of around
0.001% in a simple RC filter (with a
6.8Ω resistor) at just 12V RMS. One X2
capacitor, and the a 400V DC/250VAC
type from Epcos/TDK, measured much
lower at around 0.0004%.
So if you are going to use a polypropylene capacitor we highly recommend sticking to the type we have
specified in the parts list. Others may
have similarly low distortion but
without a high-performance distortion
analyser, there’s no way of telling. We
do not recommend you use an X2-rated
polypropylene as a consequence.
Semiconductors
In the preview last month, we explained the rational behind changing
the small-signal transistors and the
advantages of the new parts. Besides
replacing the obsolete parts, one of the
biggest benefits is that with the input
pair in a single package, there will be
very little drift in the output offset
voltage with temperature as they will
track closely.
The output transistors, driver transistors and VBE multiplier are identical
to those used in the Mk.3 amplifier as
these all need to be mounted on the
heatsink. The driver and output transistors are among the best available so
we didn’t see any point in changing
those. By the way, the heatsink mounting arrangement is identical, so it’s easy
to replace a Mk.2 or Mk.3 module with
the Mk.4 version, by simply replacing
the PCB assembly.
Next month
That’s all we have space for now.
Advertising Index
Altronics.................................. 80-83
Aust. Exhibitions & Events.............. 5
Av-Comm Pty Ltd........................... 7
Emona Instruments...................... 63
Gooligum Electronics................... 12
Hare & Forbes.......................... OBC
High Profile Communications..... 111
HK Wentworth Pty Ltd.................. 64
Icom Australia.............................. 13
Jaycar .............................. IFC,53-60
KCS Trade Pty Ltd........................ 75
Keith Rippon .............................. 111
Keysight Technologies.................. 65
LD Electronics............................ 111
LEDsales.................................... 111
Master Instruments........................ 3
Microchip Technology................... 11
Mikroelektronika......................... IBC
Ocean Controls.............................. 8
Premier Batteries Pty Ltd............... 9
Qualieco Circuits Pty Ltd.............. 63
Questronix.................................. 111
Radio, TV & Hobbies DVD............ 25
Sesame Electronics................... 111
Silicon Chip Online Shop.... 104-105
Silicon Chip Subscriptions......... 103
Silvertone Electronics.................. 15
Trend Lighting............................. 111
Tronixlabs................................... 111
Worldwide Elect. Components... 111
Next month we will present the power
supply, PCB overlay and photos of
the final prototype, along with construction details. We’ll also describe
a slightly cheaper, cut-down version
of the amplifier for lower power applications, without compromising its
SC
excellent performance.
WARNING!
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projects should be considered dangerous or even lethal if not used safely.
Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or
high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you
are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone
be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine.
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112 Silicon Chip
siliconchip.com.au
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