Dual Buffer PC Board CUSTOMIZED AMP STYLE INPUT BASIC PC BOARD This pcb has been designed to be only a buffer board, and it can be constructed using a jfet transistor or a dual opamp as the active device. What makes the board special is that the input has been designed to duplicate the input circuitry of the typical tube amp, and it thereby preserves the interaction between the guitar's pickups and the buffer circuit. This makes the sound of the guitar more natural, with a similar resonant peak, while still providing a low impedance output drive for your cables and pedalboard. Only one buffer can be constructed on the pcb so you must chose whether to use the transistor or opamp version. Both versions have the amp-like input but the opamp version is capable of giving lower output impedance (Z) and unity gain (gain=1), whereas the jfet's output will be higher impedance and slightly less than unity. The jfet has the advantage of using less current. Neither version uses all of the parts that are shown on the pcb, so any components that are not in the parts list will not be used, and their place on the pcb is left empty. A jumper is always required on the J1 pads so remember to check the instructions for the type buffer you have chosen to build. A single pc board is $10.00 US plus shipping. ALTERNATE JFET TRANSISTOR BUFFER This version of the buffer has the gate resistor connected to a reference voltage instead of to ground. This provides a better bias if you are unsure of the characteristics of the jfet that you have available. For example, it should be used if you only have access to the J201 transistor. R1 is a pulldown resistor. It is only used if you are going to use a footswitch to turn the buffer on/off. If you intend to leave the buffer on at all times, then R1 is not required and it should be left out. A small jumper wire is soldered on the top two pads of the J1 jumper. The bottom pad has no connection with the transistor buffer. Parts List R1 - 2.2M R2 - 1M R3 - 33k R4 - 10k R5 - 100 ohms R6 - 22k R7 - 22k R8 - 100k R9 - 100 ohms J1 - jumper C1 - 0.22uF C2 - 150pF C3 - 10uF C4 - 10uF C5 - 100uF Q1 - J-Fet transistor (2N5486, 2N5457 or similar) All resistors are 1/4w and capacitors are in uF, except for C2. NORMAL OPAMP BUFFER (without amp-like input) This buffer is the equivalent of one of the opamp buffers shown on the buffer page from the AMZ Lab Notebook. This one is a flat resposne buffer that does not have the amp-like input circuitry. R1 is a pulldown resistor. It is only used if you are going to use a footswitch to turn the buffer on/off. If you intend to leave the buffer on at all times, then R1 is not required and it should be left out. A small jumper wire is soldered on the top two pads of the J1 jumper. The bottom pad has no connection with the opamp buffer. Parts List R1 - 2.2M R2 - 1M R3 - Jumper R5 - 68 ohms R6 - 22k R7 - 22k R8 - 100k R9 - 47 ohms J1 - jumper C1 - 0.22uF C3 - 10uF C4 - 10uF C5 - 220uF IC1 - TL072 or similar dual opamp All resistors are 1/4w and capacitors are in uF, except for C2. MODIFICATIONS NOTES: Every buffer built on this pcb requires a jumper to be set on the J1 pads. The pads to use are noted in the instructions above for each type of buffer so make sure to solder the jumper in place on the board. The jumper in the picture to the left is on the bottom 2 pads of J1. The Ground pad (marked with a G) should have a wire connecting it with a common ground point inside the pedal, usually the ground lug on either the input or output jack. The +9v pad can be wired to the battery positive (usually the red wire) or to the voltage lug on the dc power jack, if you are using an external power supply. Be sure to read the Notes on the first buffer page before constructing any of these circuits. INPUT RESPONSE The value of R3 can be changed to 68k to imitate the response of certain tube amps. This has the effect of reducing the high frequency range and may give a warmer sound. I would not go any higher than 68k without also reducing the value of C2. The values of R3 and C2 can be altered to imitate other inputs than the common triode configuration, but I have not worked with that yet.