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Revision Date: 240512 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, is 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 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
is dedicated to route the “send” signal, while the line input circuit provides
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. 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 also provides dedicated balanced differential output
and input circuits for send and return to an external EQ device, respectively,
when this functionality is required. 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 support for a balanced differential send
or return to an external EQ. 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. 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. The full kit, with the exception of an 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 versions prior to model 540, as
they use three switches for the EQ functions, while 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 you have no resources or capability to complete the necessary
enclosure metalwork (drilling) we may be able to offer assistance for a
nominal charge. We have inventory of the Circuit Specialties and Bud
Industries enclosures, either to-be-drilled or as supplied by the vendor. 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 $15 to $55, depending upon
vendor fluctuating prices. A couple examples are listed on the website,
additional references upon request. Contact Rick at wb4gnr@gmail.com |
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