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Revision Date: 250331 Information contained on these web pages copyright
W8KHK / N1BCG. Amateur or individual use is encouraged. |
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The "MAX" Audio
Processor - Pricing and Availability The Max Audio Processor, Series 500, has been available in several
different models. Each model is
provided as a kit of parts, with printed circuit boards and documentation, everything
needed except an enclosure and power
transformer. These two items must be
selected separately, or obtained locally by the builder. Available kit models
are 500, 510, 520, 530, 540 and 540L (Lite); the various features are
described below: All 500-series kits include all the features of the previous model 500,
but each adds some incremental feature updates. Version 500 was the first to eliminate hand
wiring of the front panel controls, introducing a new “front panel interface”
printed circuit board that completed all the panel interconnections, using
pin connectors and prefabricated ribbon cables between the front panel board
and the main processor board. Model 510 also employed the ribbon cable interface, and all other
features of model 500, except the output attenuator pot for microphone input
compatibility on the newer transceivers.
Unveiled with revision 510 is an enhanced peak limiter design, with
the asymmetric “greater than 100%” positive peak limiter being adjustable
from 100% to approximately 135%. There
is also an adjustable second-stage negative peak limiter, to be employed when
absolutely no zero-crossings are permitted in the negative direction. The high-impedance utility output was
replaced by a second discrete balanced differential output driver, allowing
multiple transmitters to be connected and adjusted, thus enabling much more
convenient QSY to different bands or transmitting equipment. Model 520 provides a feature set identical to model 510, but offers a
much-improved method of interconnecting the front panel controls. Instead of several flat ribbon cables, a
row of pins on the main processor board connects to a female header at the
bottom of the front panel interface PC board, directly completing all the
required connections; no cabling needed. Model 530 also provides an identical feature set to the previous
models. In addition, it includes a
pair of jumper interfaces to enable the insertion of either an internal or
external EQ component. In order to
interface an external balanced differential EQ, the second differential
output might be dedicated to route the “send” signal, while the line input circuit
may provide a path for the return signal from the EQ. This configuration allows the external EQ
to function without the need for a separate microphone preamplifier or mix
board, instead using the internal low noise SSM2019 microphone preamplifier
circuit. (It has been determined by
extensive field testing that the 540 series “Audio Sculpting” provides
superior performance and better level control than earlier attempts to use
external EQ products with the Max Audio Processor. The latest model 540 builds further on the EQ platform, replacing the
three panel switches of earlier versions (low cut, low boost, and
pre-emphasis) with an internal adjustable EQ tailored specifically for
amateur voice communications on the HF band with amplitude modulation. The three new controls are continuously
variable: a cut and boost low frequency gain control, a variable depth sharp
notch filter at about 300 Hz, and a pre-emphasis control from flat response
to optimal, then on to excessive pre-emphasis levels. In addition to the standard pair of inputs
for microphone and line level, and the two discrete balanced differential
output circuits, the 540 includes an optional expansion area (not populated)
which the creative experimenter might employ to add another dedicated
balanced differential (high or low gain) custom input circuit, and possibly
another low impedance balanced differential output to connect another
transmitter or other device. Finally, a subset of the 540 is the new 540L, or “Lite” version, which
is identical to the 540 in features, with the exceptions that it provides
only one input, one output, and no unpopulated expansion area. The single input still employs the SSM-2019, therefore the gain may be set to either low-level
microphone or high-level line mode via a single jumper. This feature retains the high CMR
performance when using line level inputs, as opposed to the typical noise
prevalent “attenuate-then-over-amplify” method typically used to feed line
level program material into a microphone level stage. (Note that the selection of mic or line
level must be set via an on-board jumper, and because there is only one input
preamplifier, the front panel “Mic/Line” switch must remain in the Mic
position. The 540L printed circuit
board is sized to fit within the much smaller desktop enclosure, only 10”
wide, 7” deep, and 2” high. If this
combination is selected, an external wall transformer must be used for power,
as there is insufficient space for an internal transformer. Note: While many of the above
versions are no longer available, the details are listed to reflect the
additional features and incremental improvements provided with each
update. (Assembly instructions and
other resources will remain on the web for some time to support users of
these earlier versions of the Max Audio Processor). The cost of current versions 540 and
540L (lite) has been reduced due to savings resulting from volume discounts realized
on recent component purchases. The Max
Audio Processor has always been provided “at cost”, with minimal overhead,
but never at a profit. The full kit, with the exception of the enclosure and power transformer,
is priced as follows:
You may select a power option to include with your order as follows:
Sample configurations and ordering information may be found on the
CONTACT page. If one wishes to purchase the PC boards and acquire the components
separately:
Note that the above photos represent current versions 540 and 540L. While the previous versions used three
switches for the EQ functions, the 540 and 540L provide continuously variable
adjustment via a potentiometer with front panel accessible knobs, or a
one-turn trim pot accessible through the front panel with a small
screwdriver, at the builder’s option. (If
trim pots are desired, in lieu of pots with knobs, please specify this
feature when ordering. If you have no resources or capability to complete the necessary assembly
tasks, several folks have indicated an interest in building kits for other
amateurs, and this resource may be found in a related “kit builders’ thread
on QRZ.com. Interested parties are
encouraged to evaluate this resource on their own. Note: While Circuit Specialties has enclosures available direct, the
shipping cost for unit quantities is rather expensive. The Bud Industries
enclosure is occasionally available from Amazon, not offered with prime free
shipping. Overall shipping costs will
likely be lower when ordering the entire bundle from a single source,
assuming they are in stock when your order is received. Power transformer options range from around $20 to $30, depending upon
fluctuating vendor prices. A couple examples are listed elsewhere on the
website, additional references provided upon request. Contact Rick at wb4gnr@gmail.com |
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