Mad Bean Pedals TRXPN User manual

TRXPN
Total Recall Expansion Board
© 2015 madbeanpedals
1.8" H x 1.25" W
The TRXPN is an expansion board for the Total Recall project. It allows one to use four MN3008 BBDs in place of two
MN3005 (both totaling about 550ms of delay). The TRXPN has its own bias trimmers for the two added BBD stages and
when wired to the TR main board, they are inserted as stages 2 and 3 of the delay. This makes the exact sequence of
BBD stages as follows (referring to both the TR and TRXPN schematics):
IC6
BBD
TR
IC10
BBD
TRXPN
IC11
BBD
TRXPN
IC4B
Gain
Recovery
TR
IC7
BBD
TR
D_IN XS XR D_OUT
IC4A
Gain
Recovery
TR

2
V
alue QTY Type Rating
R62 6k8 2k4 4 Metal / Carbon Film 1/4W
R63 82k 6k8 2 Metal / Carbon Film 1/4W
R64 2k4 82k 2 Metal / Carbon Film 1/4W
R65 2k4 100k 2 Metal / Carbon Film 1/4W
R66 100k 1uF 2 Film 25v min.
R67 6k8 BBD 2 MN3008
R68 82k 100k 2 Bourns 3362P
R69 2k4
R70 2k4
R71 100k
C47 1uF
C48 1uF
IC10 BBD
IC11 BBD
BIAS3 100k
BIAS4 100k
IC
Trimmers
B.O.M. Shopping List
Resistors
Caps

3
Wiring
You should use wires to connect the boards rather than straight-pin connectors. This will allow access to the trimmers
underneath the TRXPN board when it is attached to the main board. To keep everything locked down, use a small blob of
Blue Tac or double-sided foam tape under the TRPXN when you have it all boxed up.

4
Biasing and Calibration
The calibration procedure for the TRXPN is the same as the one used for the Total Recall. I just requires a few added
steps. This is the procedure in its entirety for both the TR and TRXPN boards. If you are using a scope for calibrating the
Total Recall, refer the to link included the Total Recall document. This method is "ear calibration" only, which is what most
builders will likely use.
Procedure
Tools required: audio source, audio probe.
To begin, make sure you have wired the TRXPN board to the Total Recall board. Install all ICs except IC7, IC10 and
IC11. We will bias one BBD at a time. Set your controls as follows:
DELAY - full up
FDBK - a little less than halfway up
MOD - all the way down
LEVEL - about 1/3rd up
BLEND - doesn't matter (you should leave the circuit output disconnected since we will be audio probing)
CH/VB switch - doesn't matter
Leave all the trimmers in their halfway position to start.
 Connect the TR PCB to your power supply. Use an audio source at the input of the circuit (J1). While you can just
strum your guitar it might be difficult to make trimmer adjustments at the same time. If you have a looper, record a
few single notes a few seconds apart and feed that into the circuit. Or, improvise with something else.
 Connect your audio probe to either pin3 or pin4 of IC6. Now adjust BIAS1 until you hear delay output. Adjust
BIAS1 further until you find the min and max settings where you have clean delay output. Set BIAS1 to
approximately the middle point of this range. Now make very small adjustments left and right until you find the
spot where the delay output is cleanest and strongest.
 Disconnect the power and install IC10 to the TRXPN board. Reconnect power and repeat the same biasing
procedure done above using the BIAS3 trimmer on the TRXPN board and pins 3/4 of IC10.
 Disconnect the power again and install IC11. Repeat the same procedure with BIAS4 and pins 3/4 of IC11.
 Now connect your audio probe to pin7 of IC4_B. Adjust GAIN1 until the volume output is approximately the same
as the volume input on pin7 of IC6 (this balances the signal volumes between the two BBDs).
 Disconnect the power supply from the circuit and install IC7. Reconnect the power supply.
 Connect your audio probe to pin3 or 4 of IC7. Do the same type of adjustment to BIAS2 to get clean delay output.
 Re-connect your audio probe to pin7 of IC4_B. Make any adjustments needed to GAIN1 to reach the same
volume output you had before. This part is a bit of fine tuning between GAIN1 and BIAS2 to get the optimal result.
 Leave the BAL trimmer in the middle position. Connect your audio probe to pin1 of IC4_A. Adjust the GAIN2
trimmer until the output is the same or slightly above the volume input of pin7 on IC6.
 You are done!
For voltages, refer to the list in the Total Recall build document. You should have about the same readings on IC10 and
IC11 as you have for IC6/7.