PI2Media 502HTA
Hardware Reference Manual – P3 - 8/31/2017
PAGE 16
8.4
W2 – 3-PIN BIAS ADJUST HEADER
W2 is a 3-pin .1” single row header. It allows access to the Left and Right Channel Bias
points. The pins are marked R-G-L for Right, Ground and Left respectively.
8.5
P2 – 40-PIN GPIO HEADER
This is a standard 40-Pin .1” Dual Row Female Header. It is designed to plug into the
40-pin GPIO Header on a Raspberry Pi single board and conforms to the standard
Raspberry Pi pinout. It is located on the bottom side of the 502HTA. P2 is not populated
on the 502HTA-SA.
8.6
P2 – DC JACK
This jack is designed to accept a 5.5mm x 2.1mm center positive plug for external
power in. Voltage must be 24V +/- 5%, 2 Amp minimum.
8.7
P3 – 3-PIN HEATER VOLTAGE SELECT
P3 is a 3-pin .1” single row header. It is used to select between 6V or 12V (in series
mode) tube heaters.
8.8
RP1 AND RP3 TRIMPOTS
RP1 and RP3 are the bias adjustment potentiometers for the Left and Right Channels
respectively.
8.9
RP5 –VOLUME POT WITH ON/OFF SWITCH
RP5 is an Alps RK09 Low Noise, Conductive Plastic Volume Control with built-in On/Off
Switch.
8.10
SW1 – ATTENUATION SWITCH
SW1 – a Single Pole, Double Throw (SPDT) toggle switch that controls the attenuation
relay.
8.11
SW2 – OUTPUT RESISTANCE SLIDE SWITCH
SW2 is a Double Pole, Three Position (DP3T) Slide Switch. It adds 0, 47 and 100 ohm
headphone output resistance when in the Left, Middle and Right positions respectively.
8.12
W2 – BIAS ADJUST HEADER
W2 is a 3-pin right angle header. It carries the Left (L) and Right (R) Bias signals along
with Ground (G). This allows the bias voltage to be measured while adjusting for the
current tube.
