125B · 3 knobs

Murdock Plus

Category: Distortion
Controls: Drive · Eq · Output
Price: $10.00in stock

Buy the PCB at God City Instruments Build document1.0

From the vendor

Overdrive/distortion with HM-2 EQ

GCI Murdock Plus is a similar circuit to Murdock but with the addition of hard clipping diodes, gain, and volume controls. It's a simple, somewhat transparent overdrive circuit with a maxed out HM-2 style EQ circuit as a parallel blend.

Build documentation can be found here below. Please read before purchasing.

Murdock Plus Build Guide

Sale is for PCB only. You must source the components and build the pedal yourself. To make foot switch wiring easier, we also suggest you buy the 3pdt utility switch.

Share your work, get tips, ask questions and help troubleshoot at our Facebook Group. Don't forget to agree to the group rules if you wish to join. GCI DIY PCB builders group

NOT FOR COMMERCIAL USE

Schematic

The schematic is in the vendor's build document. Open the build document. No KiCad fragment has been drawn for this circuit yet.

Parts list 53 rows

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Ref	Value	Normalized	Type	Notes
Resistors 19
CLR	4.7k	4.7k	1/4 watt resistor 1k-10k Current limit	ing resistor for LED
R1	2.7k	2.7k	1/4 watt resistor
R2	1M	1M	1/4 watt resistor 2.2M Pull down res	istor
R3	10k	10k	1/4 watt resistor 1k-33k Forms input L	PF with C3
R4	10k	10k	1/4 watt resistor
R5	10k	10k	1/4 watt resistor
R6	82k	82k	1/4 watt resistor
R7	100k	100k	1/4 watt resistor
R8	120k	120k	1/4 watt resistor 100k Stock HM-2
R9	1k	1k	1/4 watt resistor 1k-22k Affects amoun	t of hard clipping, less is more
R10	1M	1M	1/4 watt resistor 470k-2.2M Bias resistor
R11	47k	47k	1/4 watt resistor 10k-100k Affects gain	of output stage. More is more
R12	330R	330	1/4 watt resistor
R13	330R	330	1/4 watt resistor
R14	1k	1k	1/4 watt resistor
R15	10k	10k	1/4 watt resistor 1k-47k Forms voltage	divider with R16. Affects headroom
R16	47k	47k	1/4 watt resistor 47k-100k Forms voltage	divider with R15. Affects headroom
R17	10k	10k	1/4 watt resistor 4.7k-47k Affects gain	of output stage. Less is more
R18	390R	390	1/4 watt resistor 330R Stock HM-2
Capacitors 18
C1	0.1u	100n	Film cap 0.22u Affects overd	rive low end
C2	47n	47n	Film cap 22n-100n Input cap
C3	2.2n	2.2n	Film cap 1n-4.7n Input LPF
C4	270p	270p	MLCC 100p-470p System LPF. B	igger = darker
C5	1.5u	1.5u	Film cap do not substitute critical for	EQ bass frequency
C6	0.15u	150n	Film cap do not substitute critical for	EQ mid frequency
C7	6.8n	6.8n	Film cap
C8	68n	68n	Film cap
C9	1u	1u	Film cap
C10	4.7n	4.7n	Film cap
C11	0.1u	100n	Film cap
C12	270p	270p	MLCC 0-560p LPF for clipp	ing diodes. Bigger = darker
C13	0.1u	100n	Film cap
C14	560p	560p	MLCC 330p-1n LPF for EQ st	age. Bigger = darker
C15	0.15u	150n	Film cap 0.1u Stock HM-2
C16	100u	100u	Electrolytic cap 47u-220u Power filteri	ng
C17	100u	100u	Electrolytic cap 47u-220u Power filteri	ng
C18	0.1u	100n	MLCC
Diodes 4
D1	1n4148	1N4148	small signal diode 1n34a, 1n914, 1n456a, 1n5818 Any diode goo	d for hard clipping
D2	1n4149	1N4149	small signal diode 1n34a, 1n914, 1n456a, 1n5819 Any diode goo	d for hard clipping
D3	1n4150	1N4150	small signal diode 1n34a, 1n914, 1n456a, 1n5820 Any diode goo	d for hard clipping
D4	1N5818	1N5818	Schottky diode 1n4001, bat41 Any suitable	protection diode for 9v
ICs 2
IC1	TL072P	TL072P	Dual Op Amp LM833, RC4558, MC1458 Any pin compa	tible dual op amp
IC2	TLE2074	TLE2074	Quad Op Amp TL074, TLC2274 Any pin compa	tible quad op amp
Potentiometers 3
DRIVE	A250K	A250k	16mm potentiometer A100k-500k Affects gain	range of first stage. More is more.
EQ	A5K	A5k	16mm potentiometer B5k EQ blend pot.
OUTPUT	A100K	A100k	16mm potentiometer A50k Output volume
Switches 1
S	PAD	PAD	Send to PCB
LEDs 3
LED	LED3MM	LED3MM	status LED
L+	PAD	PAD	LED+
L-	PAD	PAD	LED-
Other 3
R	PAD	PAD	Return from PCB
V	PAD	PAD	9v input
G	PAD	PAD	Ground