Calvin Buffer for Paradise phono stage
Many thanks to „Calvin“ a.k.a. Christoph for letting us use his clever buffer design.
This is the assembly instructions for the Calvin Buffer, a add-on for the Paradise phono
stage. But it can also be used as a standalone buffer. The schematic is shown below:
The JFET Q1 is cascaded with Q2, and its current flows through the base of Q3. R5 and
R6 are used to adjust the idle current. R1 and R2 serve as the load resistance for Q1, and
will provide a scaled-down version of the input voltage. The lower half of the buffer is
identical to the upper half, except the trimpot that is used to adjust the idle current in the
lower half, to allow setting the voltage offset to zero. And, the capacitor C3 will connect the
scaled-down input voltage to the lower buffer circuit, to help with distortion cancellation.
Not shown in the schematic is an inductor of approx. 10
μ
H that is connected in parallel
with R14.
The supply voltage is +/-18V, and the supply current is 30mA. The bandwidth is about
10MHz -3dB, and C1 and C2 can be used to adjust the square wave response for no
overshoot.
The following picture shows the stuffing of the PCB. It is 120mm wide and fits exactly on
top of the Paradise phono stage PCB. To the left and the right, the heatsinks with Q3 and
Q6 are located. In the middle of the PCB, the output resistor R14 and inductor are located.
The left half contains the upper buffer circuit, the right half contains the lower buffer circuit.
Below are the „IN“ and „GND“ terminals, that can be connected with small wires to the
„RIAA EXT“ connector on the Paradise PCB. Above are the „+18“ and „-18“ connectors as
