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| The MAX Audio Processor For Amateur Radio, LPAM, And Podcasting | |
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Information contained on these web pages copyright W8KHK / N1BCG. Amateur or individual use is encouraged. Commercial use of any kind is prohibited without the express written permission of the author, Richard A. Maxwell The "MAX" Audio Processor Assembly Information - General Guidelines
(Read this section before progressing to the actual component insertion and soldering section. It is also STRONGLY RECOMMENDED that the builder also review the entire customization documentation before starting to install components. The choice to install headers or trim-pots, and other components, is dependent upon the builder’s choices for controls and other options!)
Three versions of the parts lists are provided:
1) Organized by Component Value for parts acquisition and inventory
The bill of materials with component value and counts will also be helpful to organize the inventory.
While most component number legends are visible on the silkscreen after parts are soldered, the multitude of resistors obscure their R### designation. Therefore, having a printout of the board silkscreen legends might prove very helpful while populating the fixed resistor components.
Determine which functions are to be installed, and mask un-needed functions in parts list.
Also note that there are customization variations in the input microphone preamplifier circuits to allow the use of many types of microphones with no external adaptors, transformers, or modifications. Please review these options and record the planned installation procedure before proceeding with mass component installation and soldering. |
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Special note for the experienced custom builders
If no other customizations are desired, proceed with assembly instructions below. However, if any specialized customizations are desired, such as balanced line in/out inserts (Send and Return) are planned for other audio chain components, please study the customization section to enable correct component selection and header access to enable these functions, because the enabling of this customization flexibility was planned in the initial product design phase.
Following the suggested “Board Assembly Sequence” ensures ease of mounting components flush with the printed circuit board.
By mounting the lowest, smallest components first, the board may be inverted and the work surface will retain the components flush against the board.
Solder one or two lands of the multiple-connection components, and verify the component is flush with the board surface and in proper alignment before soldering the remaining connections. |
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Component insertion and soldering instructions
IMPORTANT! The SSM2166 can be damaged by static discharge. Be sure to discharge any static buildup on yourself before handling the board!
Special Note: Trim-pots, selected fixed resistors, and header installation requirements may be altered by customization section, which MUST be reviewed first to avoid the need for changes if components are installed unnecessarily. Depending upon choice of options, some components MUST NOT be installed!
Install components in the following order:
1 [__] Solder the surface-mount Compressor/Limiter chip (SSM-2166) - Optionally you may use an SMD carrier, with male header pins, then install female headers to plug the carrier into the main board when the other headers are installed.
2 [__]All signal and power diodes - Observe polarity band.
3 [__]All fixed resistors - To reduce the chance of placement errors, start with large groups of same value resistors, ie, 10 K ohm. In order to easily identify resistor values after assembly, it is customary to orient resistors so that color codes all read from left to right, or from top to bottom.
4 [__] All Integrated Circuit Sockets - All IC sockets have the orientation notch (pin 1) toward the top of the board.
5 [__] All “Dupont” pin headers (male and female) – MUST REVIEW CUSTOMIZATION SECTION prior to installing headers or any trim-pots! See detailed information below to properly configure the required male and female headers.When installing multiple-pin headers, notice the silkscreen has a (box) painted around pin 1. This is obscured when installing either male or female header strips. Also note that the header identifier (matching the identifier in the schematic diagram) is always printed close to pin 1. Other silkscreen information near the header is either a pin-by-pin signal ID list, or a general function identification for that specific header.
6 [__] All .1 uF disk bypass capacitors U###n and U###P designation.
7 [__] All other non-polarized capacitors - Depending upon vendor, wires may need to be adjusted to fit with PCB hole spacing.
8 [__] All trim-pots - MUST REVIEW CUSTOMIZATION SECTION prior to installing headers or any trim-pots! Note the position of the adjustment screw on the silkscreen and align accordingly. If this requirement is not met, then the adjustment screw will need to be turned opposite to the normal direction for level decrease or increase. See detailed information below to properly configure the required male and female headers.
9 [__] All electrolytic capacitors - Observe correct polarity using the white negative marking, or the long lead to + legend.
10 [__] All transistors - Solder transistors with ¼ to ½ inch lead exposed. Do not mount transistors flush with PC board surface.
11 [__] All power status LEDs - Adjacent to their respective regulator ICs.
12 [__] All 78xx/79xx linear regulators - The metal tab is oriented close to the edge of the board as in the silkscreen legend. No heat sinks are required.
Note: the regulators are normally mounted vertically above the PCB, and soldered on the bottom. However, it is possible to heat-sink the regulators by mounting them on the bottom of the enclosure, to the left of the PCB. Bend the last ¼” to 3/8” of the leads up at a 90 degree angle, insert the pins into the PCB from the bottom, and solder the center pin of each regulator at the top side of the PCB. Secure the PCB to the enclosure with 3/8” standoff hardware. Then drill the bottom of the enclosure and mount the regulators, Finally, solder the remaining regulator leads to the top of the PCB. If the regulators are heat-sinked in this manner, the negative regulators must be insulated from the metal enclosure. It is actually preferable to insulate all four regulators, in the interest of eliminating any ground loops. (There should only be one ground point to the chassis, and that should be at the lowest-level input connector. Considering the input power connector passes AC to the on-board rectifiers, the common power input lead should also be isolated, and not grounded to the enclosure.) Note: Male and Female Dupont Headers are cut to length (by builder) from 40 pin raw stock. |
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It is STRONGLY RECOMMENDED that the builder review the entire customization section before installing any headers or trim-pots. Make notes in your parts list to avoid incorrect placement of headers or trim-pots before soldering!
Male and Female Header selection and installation:
Female headers should be installed at:
13 [__] Power Bus, 6 pins (for measuring regulator outputs or connecting other options)
14 [__] LEDs, 8 pins (for connecting NEG, POS, NORMAL, and PEAK panel-mounted LEDs)
15 [__] P102, 7 pins (test points for compressor chip signals)
16 [__] P103, 7 pins (test points for compressor chip signals)
Three Pin Male Headers should be installed at:
17 [__] H01: Microphone input one
18 [__] H02: Microphone input two
19 [__] H03: Line Input one
20 [__] H04: Line input two
21 [__] H05: Line output one
22 [__] H06: Line output two
23 [__] H07: Utility output
24 [__] H51: Line output one negative signal pad (optional, may use wire jumper)
25 [__] H52: Line output one positive signal pad (optional, may use wire jumper)
26 [__] H61: Line output one negative signal pad (optional, may use wire jumper)
27 [__] H61: Line output one positive signal pad (optional, may use wire jumper)
28 [__] ACIN: AC transformer connection, pin 1: common = center-tap, pins 2 and 3: start and end of secondary
29 [__] J01: Input configuration from summing network
30 [__] J02: Custom gain stage
31 [__] Pre-Emp: pre-emphasis configuration
The following may have either three-pin male headers to interconnect front-panel pots, or on-board trim-pots may be used to permanently set the nput and output levels. (Normally the inputs are front-panel controls and the outputs are on-board trim-pots.)
32 [__] R17: Microphone one gain control
33 [__] R29: Microphone two gain control
34 [__] R38: Line one input gain control
35 [__] R48: line two input gain control
36 [__] R251: Utility output level
37 [__] R261: Line one output level
38 [__] R281: Line two output level
Four Pin Male Headers should be installed at:
39 [__] MIC2PH: Set phase of microphone two pre-amplifier
40 [__] HPF: High-pass filter (low-cut) enable/disable
41 [__] APF: All-pass filter (phase rotator) enable/disable
42 [__] SCAF: Switched-capacitor audio filter enable/disable
43 [__] BW: Bandwidth control (frequency selection for SCAF clock)
44 [__] COMPRESSOR: Compressor / limiter enable/disable
45 [__] CLIPPER: Configure clipper behavior
Builder Note: Even if you have decided upon a permanent configuration for any or all of the above options, using headers and jumpers (instead of hard-wired jumpers) greatly improves the ability to perform calibration and troubleshooting tasks, conveniently enabling you to isolate each individual stage for any required measurements or signal insertion.
A seven pin male header should be installed at:
46 [__] RESP_LIM_COMP_GATE: Configure compressor options
Errata issues with revision 3.0 Printed Circuit Boards
The legend on the PCB is reversed, and should read (left to right) GATE_COMP_LIM_RESP. More detail regarding this is covered in the Customization (jumper configuration) section.
For version 3.0 of The MAX processor, one schematic error and one design enhancement is mecessary. Several trace cuts will be performed prior to board or kit shipment. Several wires and resistors must be soldered to the bottom of the PCB. Two wires must be added for the level indicator balance trim-pot. An additional wire, and two 4.7 Kohm resistors (R207 and R208) must be added to complete the clipper circuit. Refer to photo in the Gallery section for locations and orientation. Text details are provided in the Customization section.
Board Assembly Completed!
The component portion of the PCB is assembly is now completed. It may be desirable to test the modular functionality, or, if you wish, you may proceed with the enclosure preparation and component mounting prior to performing electrical verification. |
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Perform enclosure layout plan; mark locations and drill for all components with these considerations
A suggested front-panel layout might include a row of option switches low on the panel, and input gain potentiometers and other controls above the row of switches. Left would be the two microphone input gain controls, and to their right the line input gain controls. Far right might be the bandwidth and compressor controls.
The four LED indicators may be grouped in a vertical or horizontal arrangement. The blue LED indicates predominant negative peaks in the mix, while the green indicates predominant positive peaks, which of course are preferred in AM transmission. The yellow LED indicates normal input level to the compressor, and should be illuminated almost continuously while talking, and the red Peak LED indicates the compressor is in operation and it should be illuminated occasionally. Note: Vertical orientation appears similar to the familiar traffic stop-light configuration, and thus is easily interpreted.
Plan to install connectors near to their respective headers on the printed circuit board. For example, when viewing the enclosure from the rear, place the output connectors on the left, the line inputs in the center, and the microphone inputs on the right. The power connector should be near the far left, as distant from low-level microphone inputs as possible.
Be sure to allow for clearance between board and components entering from the front and rear panels. This can be accomplished by allowing sufficient vertical clearance between bottom of panel component, and the devices which rise above the surface of the PC board.
Review locations of connection headers on board to allow easy access for wiring after the connectors and controls are installed. If an over-sized enclosure is chosen, for example, a 1U rack enclosure, then front and rear panel components may be far removed from the circuit board, and clearance conflicts are virtually eliminated. For smaller enclosures, clearance requirements should appear rather obvious. Connection cables may be groups of wires, as needed, with the exception of the high-impedance microphone input for ceramic, crystal, i.e. D-104 microphone input connections. This low-level, high impedance connection requires shielded cable to minimize hum and noise. |
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Prepare a careful, symmetrical and aesthetically pleasing layout, then punch and drill for
1) Connectors
Note: Connectors may be any combination of XLR, TRS, RCA, or terminal strips, as desired. XLR and TRS connectors may be connected in parallel add flexibility and eliminate the need for adaptors.
Mount all components
Cut wire and/or use “Dupont wires” to solder or plug each component wire to respective headers on the board. |