Building the LM4500 Board

Parts

I’ve decided to buy parts from Mouser from now on, as Digi-key has discontinued many of the parts needed to construct this project. The updated Mouser parts list is available as either an Excel spreadsheet, Word Document, or PDF file. As of December 2011, all parts were checked for ability to buy quantity “one”, and were “in stock” at Mouser in large quantities. Resistors have been upgraded to all brown Dale RN55, and de-emphasis caps are Wima film and foil polypropylene construction. The input and output coupling caps are green Nichicon ES Bipolar, and the power supply caps are Panasonic FM type, with dark blue and gold colors

The links to the parts files are here -

LM4500 Parts Excel spreadsheet

LM4500 Parts Word Document

LM4500 Parts PDF File

Tools required - Soldering iron, solder, needle nose pliers, small wire cutters

In general, you want to load all the passive components first. I usually start with the resistors, pots, small capacitors, and then large capacitors. I load about 5 components, bend the leads, flip the board, then solder in place. Then clip the excess component leads with wire cutters, and repeat. Next load the active devices, using caution for static protection of the active parts. For assembly I prefer to use 2% silver solder from Radio Shack. It is designated “High Tech Rosin Core Silver Bearing Solder, 62/36/2, .022 dia., 1.5oz., part no. 64-013E.

The board is double sided, and holes are plated through to both sides. Please be careful and double check on placement of parts (especially when working late at night). Disassembly of soldered parts is more difficult on this type of board, versus single sided boards.

Many parts, including most caps, will fit right into the holes with no lead bending required. Some caps, especially C2 (.0062uF or .0068uF) will require the leads to be bent. Use needle nose pliers to bend the leads, and then use tape to hold the cap in place before flipping the board to solder in place.

Input and Output Connections

 You may notice there are a many labeled pads brought out on the board. Here is an overview of those pads, starting at left top, to right bottom.

GND, IN +18 - These are the connections for DC power. If you use the standard parts in the regulator, you’ll need to connect this point to a small regulated or unregulated power supply that can furnish +18V DC, 100ma. I usually use 18-20 gauge twisted wire for this connection.

Unmarked Pads next to D1 - These are taps for regulated 14.4V to power optional input and output buffer boards. The input buffer uses one, and the output buffer uses two, being a dual mono type layout. Again, use twisted leads for these. There are no extra ground  pads to correspond with these, instead use the close by (-) ground stub from caps CS1 and CS2 for the power ground connections to optional boards.

V1 19kHz TP - This pad a has a dual use. First, it is used to adjust the 5K VCO pot, P1, when using an external frequency counter. There should be no other connection (other than the counter probe) to the pad when that adjustment is done. Second, the voltage on this pad can be adjusted to vary the stereo blend, reducing background hiss, yet still maintaining some stereo separation. This is explained in the data LM4500 data sheet. The easiest way to control the voltage is a connect a front panel controlled pot, value about 100K (or larger) between this test point, and ground.

GND for MONO - Connect this pad to a front panel mounted switch, with the other switch contact going to ground. This is used to engage mono operation for weak signal conditions.

C IN, C GD - These pads are the connections for the composite input. C IN is plus(+), C GD is minus or ground(-). These connection are for the MPX or detector output of the tuner.

LED + - This is for the LED, which can be mounted directly on the board for testing, or externally on the front panel. The extra pads are used to connect the two wires needed to mount the LED remotely on the front panel. There is a double pad here, used to distinguish the + connection to the diode, the single pad is for the - connection.

GDL, L O - Single ended, left channel output. L O is plus(+), GDL is ground or minus(-) 

GDR, R O - Single ended, right channel output. R O is plus(+), GDR is ground or minus(-)