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Revision Date: 250329 Information contained on these web pages copyright
W8KHK / N1BCG. Amateur or individual use is encouraged. |
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Max Audio Processor -
Calibration & Performance Checks Users can make changes to suit personal taste, but the following are how
the MAX Audio Processor is supposed to be set for optimal results. An audio
generator or other source of creating a tone between 20Hz and 10kHz is needed
for the following procedure as is a VU reading meter or A.C. meter with a dB
scale. Note: All audio level measurements
referenced in this document assume 0 dBm is equal to 1 milliwatt (0.001
watts) into a 600 ohm non-reactive load.
Some generators and meters reference 0 dBm to 50 ohms, 75 ohms, or
possibly a different load resistance; generators and meters other than those
calibrated for a 600 ohm load will yield different voltages, but for all
practical purposes, the “relative” dB levels in these cases will be close
enough for successful calibration. The 0 dBm voltage level at 600 ohms is 0.7745966692 volts RMS, rounded
to 0.775. Calculation: 0 dBm at 600 ohms equals sqrt (0.001 watts
* 600 ohms). For oscilloscope measurements, peak voltage = RMS voltage *
1.414 = 1.09585, rounded to 1.1 volts, while peak-to-peak voltage is twice
the value of peak, 2.1917 volts, rounded to 2.2 volts. Peak voltage calculation is RMS voltage *
2.828.
Jumper settings may vary, depending upon the assembly
options selected by the builder Microphone Gain Setting Jumper: Location GN, (either a 3-pin jumper or 100
to 500 ohm trim pot) Jumper 1 to 2 for Line Level input – or – Jumper 2 to 3
for Mic Level input (default) Line Input Level Jumper: Location R10, (either a 3-pin jumper or a
10 Kohm trim pot) NOTE: If a trim pot is not used, Jumper must be set
from 2 to 3 or signal will not pass beyond this stage! Microphone Input Level Jumper: Location R12, (either a 3-pin jumper or a
10 Kohm trim pot) NOTE: If a trim pot is not used, Jumper must be set
from 2 to 3 or signal will not pass beyond this stage! EQ Jumper: Location
EQ: Bypass or Enable the Audio
Sculpting EQ section: A three pin jumper; Disable: jumper 1 to 2, Enable: jumper
2 to 3 Compressor Jumper:
Location CMP, Bypass or Enable the Compressor Module: A three pin jumper; Disable: jumper 1 to 2, Enable:
jumper 2 to 3 SCAF Jumper:
Location SCAF, Bypass or Enable the Switched Capacitor Audio Bandwidth
Filter Module: A three pin jumper; Disable: jumper 1 to 2, Enable:
jumper 2 to 3 Limiter Diode Jumper:
Location LDR, Selection of either half or full wave rectification of
gain reduction signal A three pin jumper; Half-Wave (negative peaks) for AM
and SSB: jumper 1 to 2, Full Wave for FM: jumper 2 to 3 Gain Reduction Drive Jumper: Location R108, Not a jumper, but an option
for fixed or variable drive resistor Default configuration is a 4.7 Kohm resistor from pin 1
to 4 Alternate Configuration is a 10K trim pot from pin 1 to
3, (setting screw positioned over pin 1) initially set to mid-range, approximately
5 Kohm
MIC/LINE: Line (or internal jumper INSW to
"Line") PHASE ROTATOR: Off MAX models through 530: LOW FREQUENCY: Flat, Flat (Cut
& Boost Off), PRE EMPHASIS: Off MAX models 540 and up: LOW GAIN: 12 o'clock, NOTCH:
Fully clockwise, PRE-EMPH: Fully counter-clockwise DYNAMIC PROCESS: Off DENSITY: Dense BANDWIDTH: Wide +PEAK: 100% Power: On
1) With no signal input, turn on DYNAMIC PROCESSING. 2) The blue LIMIT ONLY LED should illuminate. 3) Turn off DYNAMIC PROCESSING.
1) Connect a VU meter or A.C. voltmeter with VU scale
between test point "TP L" and chassis ground. 2) Connect an audio signal generator to the line input.
If unbalanced, connect hot to the + input and shield to both - and ground.
1) Set the audio signal generator output to 400Hz at
0dBM 2) Verify that the input switch or INSW jumper is set
to LINE 3) Adjust LINE INPUT level for "0 dBm" (0 VU)
on the meter. The yellow NORM LED should be on. 4) Reduce the audio signal generator output until the
NORM LED extinguishes. This should occur around -8dBM. 5) Increase the audio signal generator output until the
PEAK LED illuminates. This should occur around 6dBM.
1) Set the audio signal generator output to 400Hz at
0dBM. 2) Adjust LINE INPUT level for "0 dBm" (0 VU)
on the meter. The yellow NORM LED should be on. 3) Turn PHASE ROTATOR on. The VU meter should read
between -1 and 1dBm. Turn PHASE ROTATOR off. 4) Set the audio signal generator output to 100Hz at
0dBM. MAX models through 530: 5) Turn LOW CUT on. The VU meter should read between -4
and -5dBm. Turn LOW CUT off. 6) Turn PRE EMPHASIS on to enable LOW BOOST. 7) Turn LOW BOOST on. The VU meter should read between
2 and 3dBm. Turn LOW BOOST off. 8) Reduce the audio signal generator output to -10dBm
at 5kHz. The VU meter should read between -1 and 1dBm. MAX models 540 and up: 5) Turn LOW GAIN fully counter-clockwise. The VU meter
should decrease between 5 and 7dB. Return control to 12 o'clock 6) Turn LOW GAIN fully clockwise. The VU meter should
increase between 5 and 7dB. Return control to 12 o'clock 7) Set the audio signal generator output 300Hz. 8) Turn NOTCH fully counter-clockwise. The VU meter
should read between -11 and -13dB. Return control to full clockwise. 9) Set the audio signal generator output to -13dBm at
5kHz. 10) Turn PRE-EMPH fully clockwise. The VU meter should
read between -1 and 1dBm. Return control to full counter-clockwise.
1) Set the audio signal generator output to 400Hz at
-60dBM. 2) Connect the audio signal generator to pins 2 (+) and
3 (-) on the microphone input. If unbalanced, connect hot to pin 2 (+) and
shield to pin 3 (-). 3) Verify that the input switch or INSW jumper is set
to MIC and the Mic Input Gain Set jumper is closest to the board edge. Note: If a gain trim pot is used at R16 instead of a
fixed-gain jumper, skip to step 6. 4) Adjust MIC INPUT level for "0 dBm" (0 VU)
on the meter. The yellow NORM LED should be on. 5) This is a good level starting point for most dynamic
microphones. Ignore the following steps, needed only for the variable gain
trim option. 6) Set the MIC INPUT level control to 60 or 70 percent
(about 2 o'clock). 7) Adjust the gain trim pot R16 for "0 dBm"
(0 VU) on the meter. The yellow NORM LED should be on. 8) This is a good level starting point for most dynamic
microphones.
1) Connect an audio signal generator to the line input.
If unbalanced, connect hot to the + input and shield to both - and ground. 2) Set the audio signal generator output to 400Hz at
0dBM. 3) Verify that the input switch or INSW jumper is set
to LINE. 4) Connect a VU meter or A.C. voltmeter with VU scale
between terminals 2 (+) and 3 (-) on main output. 5) Adjust output level (trimpot
R181) for a reading of "0 dBm" (0 VU) on the meter. 6) Increase the audio signal generator output to 10dBm.
The VU meter should read between 0 and 1dBm.
1) Set the SCAF jumper to bypass the SCAF (not on pins
marked with __ ) 2) Set the audio signal generator output to 400Hz at
0dBM. 3) Adjust LINE INPUT level for "0 dBm" (0 VU)
on the meter. The yellow NORM LED should be on. 4) Sweep the audio signal generator from its lowest
frequency setting up to 5kHz. The output should remain within +0dB and -3dB. 5) Increase the audio signal generator frequency to
10kHz. The meter should show a loss of 7dB.
This procedure sets the maximum frequency response of
the transmitted signal. The bandwidth will be the same as the frequency
response for SSB transmissions and 2x the frequency response for AM
transmissions. For example, if you want a maximum AM bandwidth of 10kHz then
use a frequency response of 5kHz. 1) Set the SCAF jumper to activate the SCAF (on pins
marked with __ ) 2) Set the audio signal generator output to 400Hz at
0dBM. 3) Adjust LINE INPUT level for "0 dBm" (0 VU)
on the meter. The yellow NORM LED should be on. 4) Set the BANDWIDTH switch to NARROW. 5) Increase the frequency of the audio signal generator
and note when the output level drops to -12dB. This is the current narrow
bandwidth setting. Use trimpot R123 to adjust the
cutoff frequency either lower (counterclockwise) or higher (clockwise).
Verify the -12dB cutoff by sweeping the audio signal generator frequency
around this setting. Note that the level will continue to drop off steeply
as the frequency is increased. 6) Set the audio signal generator output to 2kHz at
0dBM. 7) Set the BANDWIDTH switch to MED (medium). 8) Increase the frequency of the audio signal generator
and note when the output level drops to -12dB. This is the current medium
bandwidth setting. Use trimpot R124 to adjust the
cutoff frequency either lower (counterclockwise) or higher (clockwise).
Verify the -12dB cutoff by sweeping the audio signal generator frequency
around this setting. 9) Set the BANDWIDTH switch to WIDE. 10) Increase the frequency of the audio signal
generator and note when the output level drops to -12dB. This is the current
wide bandwidth setting. Use trimpot R125 to adjust
the cutoff frequency either lower (counterclockwise) or higher (clockwise).
Verify the -12dB cutoff by sweeping the audio signal generator frequency
around this setting.
The R130 trimpot has been
added to set the positive peak limit from +100% (fully counterclockwise) to
around +130% (clockwise) which is the default. The PEAK switch on the front
panel selects between +100% (symmetric) and the R130 setting (asymmetric). An
accurate peak indicating modulation monitor is needed for accurate
adjustment. NOTE: While it is possible to completely defeat
positive peak limiting, we do not recommend this as it removes protection
against transmitter and/or modulator damage due to voltage spikes. Also,
there is no loudness advantage of having unrestricted positive peaks since
there is no increase in waveform density.
While the positive and negative limiters should provide
sufficient peak control, there may be an extreme case where even tighter
limiting of the negative peaks is required. Trimpot
R140 provides a means to add a second stage of negative peak limiting if
desired. An accurate peak indicating modulation monitor is needed for this
adjustment. 1) A source of "busy audio" such as music or
white noise is needed as an input source. 2) Note the negative peak indications on the monitor. 3) Beginning with R140 set fully clockwise (default)
watch your modulation monitor while slowly turning the trimpot
counterclockwise until the peaks are limited to your needs. |
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