VAMISOUND LDC84 User manual

LDC84
BUILDING
INSTRUCTIONS

Dear DIY friend,
first of all thank you for your support and choice of the VAMISOUND product.
We wish you a happy DIY and the joy of a new microphone in your arsenal!!
Jan and Milan
LDC84 BUILDING INSTRUCTIONS

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Document info
Document name
LDC84 building instructions
Document revision
1.0
PCB revision
1.0
Date
November 2023
Project difficulty
Complexity of soldering
Risk of electrick shock
Changes and notes
Before you start building your new microphone please carefully read this
building instructions.
Attention: VAMISOUND LDC84 is a medium-heavy project. The circuit is made
up of only a few components. However, it should be borne in mind that certain
manual skills will be required or the successful completion of the mic
construction. Good soldering experience and soldering stations with fine
soldering tip are recommended. If you do not have this, please delegate the
construction to a more experienced technician with proper equipment. We
are not responsible for malfunctioning construction or injuries associated
with improper assembly of our kits.
LDC84 BUILDING INSTRUCTIONS

The VAMISOUND LDC84 circuit board allows you to build a microphone that is based on the circuitry from the
legendary KM84 small diaphragm microphone. However, thanks to a small modification of the input section of
circuit, it can use a large diaphragm capsule. The circuit is frequency flat, with no internal equalizer, so capsules
like the C12, M7 or K47 fit perfectly with it.
So let's start fitting the board with resistors.
Proceed by installing the two teflon pins on the top of the board.

Now solder resistors R1 and R2 with value 1G. Note that one leg of the resistors is always resting on the teflon
pin and is as if in the air.
Continue by soldering two inductors L1 and L2 and a zener diode D1.

The capacitors are next. Start with ceramic C1 and film ones. One leg of the C11 capacitor is connected to a
teflon pin in the air.
Note that the teflon pins have been shortened at the bottom.

Connect the Q1 FET transistor (or rather its GATE let) to the teflon pin. On the 2N3819 transistor, the GATE leg
is the middle one. Always check the pin out of the transistor you are using against the datasheet.

Continue by installing the trimmer resistor. This trimmer will serve you later for the bias procedure.
And now it's the turn of the three electrolytic capacitors. Do not install C3 if you will later use a PIO hi-end
capacitor at the output capacitor position.

Clean the underside of the board thoroughly with iso propyl alcohol. Remove any residual flux and other
contaminants. Also focus on cleaning the HiZ section around the two teflon pins.
Now comes the fun! Installing the transformer. Use the remaining resistor legs to attach the transformer to the
pcb. Make sure the transformer is not glitching.

Connect the wires of the transformer primary to the pads on the board which are labeled P1 (primaries start)
and P2 (primaries end). Transformer secondary wires to pad S1 (secondaries start) and S2 (secondaries end).
Do not shorten the wires too much, so that you will be able to swap them if necessary. Always check the phase
of a finished microphone against a commercial microphone that you know has the phase right. If your DIY
microphone has the opposite phase, just swap the two cables S1 and S2 with each other.
Solder the 1uF PIO output capacitor as the last component on the board.