This is an update sheet for the "Making Mikes Better" project published in the January 2002 issue of Recording magazine. It is current for board revision 3B. LAYOUT TYPOS ------------ The layout has a small problem; there are two C6es listed on it. The C6 on the top of the layout in the center between the FET and the input pin really is C6, the 820 pF cap. The C6 on the bottom left which is across the zener is really C4, the 10 uF tantalum cap. The schematic has two caps marked C4, 10 uF tantalum. The one across the zener really is C4. The cap between the base of Q2 and the source of the FET is really C3, the 1 uF film cap. (Remember, C2 and C3 have to be the same type and value so the circuit can be symmetric). These changes were listed in the Feb 2002 issue, but I include them here for completeness since many folks are building this project from back issues and don't have that update. PARTS CHANGES ------------- In the past couple years, European RoHS (Reduction of Hazardous Substances) laws have meant that part numbers on a number of items have changed as those items have been replaced with lead-free versions. In addition, Panasonic has discontinued the FC line of tantalum capacitors and they do not have replacements available. So I am recommending equivalent capacitors from Kemet which are also excellent. Here, therefore is the current list of part numbers from Digi-Key: Z1 1X 12V zener diode 1N5242BDICT-ND C1, C4 2X 10 uF 16V tantalum cap 399-1403-ND C2, C3 2X 1uF 100V film caps EF1105-ND C5 1X 4.7 uF 50V tantalum cap 478-1908-ND C6 1X 820 pF COG ceramic capacitor P4860-ND or try alternately 1004PHCT-ND R1, R2 2X 2.21K resistors 2.21KXBK-ND R3 1X 332 ohm resistor 332XBK-ND R4, R5, R7, R8 4X 100K resistors 100KXBK-ND R6 1X 6.8K resistor 6.81KXBK-ND R9, R10 2X 1000M (1G) resistor MOX200J-1000ME-ND (optional) Chemtronics flux remover pen CW9100 I am now including two 2N5087 transistors in the kit so you don't have to order them from Digi-Key. It has been increasingly difficult to get consistent quality transistors in small orders. STANDOFFS --------- The boards I am now shipping are Revision IIIb or later, which have two 1/8" mounting holes added around the FET. These are sized to accept Concord type 1110-02 teflon-insulated standoffs. These standoffs are available for an extra five dollars when you purchase the board. If the standoffs are used, C6 should be soldered between the two standoffs, and R9 and R10 should be soldered with one lead on a standoff and one lead on the PC board. The gate of the FET should be soldered directly to the standoff as well. The wire from the capsule, then, is soldered to the standoff on the opposite side of C6 from the FET gate. The circuit is identical to the configuration with the parts soldered to the board, but all of the high impedance connections are made to standoffs raised above the board for better insulation. This makes flux removal much less critical and makes the microphone less likely to become noisy in very humid environments. You can use the standoffs or not as you prefer.