Google statistics

Monday, 10 April 2023

All Overdrive/Distortion effects pedals in one... or most of them

Inception and Inspiration (Analog Morphing Core)

Recently I came up with a technology used on Kernom RIDGE overdrive pedal called Analog Morphing Core. This technology uses a single knob called MOOD, that can be seen in action in this link and the pciture below. It allows to change the shape of the signal going from a pure sinewave, to soft clipped asymmetric, then symmetric, then hard clipped asymmetric, then symmetric.

Additionally, this pedal includes PRE TONE and POST TONE knobs that allow to change and equalize the tone before and after the clipping stage.

I think that Analog Morphing Core technology must require some digital processing in order to use a single control knob to modify several resistance values in the clipping circuit. Digitially controlled potentiometers maybe? I don't know.

My goal was not to acquirately emulate the exact behaviour of this complex pedal, that probably required thousands of hours for its development, but I liked the idea of being able to generate hard / soft, symmetric / asymmetric clipping, and also the idea to be able to change the tone before and after the clipping.

So I decided to design and make a guitar pedal circuit that was able to include all these different functions: Pre-Equalizer (PreEq), Gain (G), Soft Clipping (SC), Hard Clipping (HC), Post-Equalizer (PostEq) and Volume.

Kernom RIDGE is a quite complex piece of equipment but I decided to go for simplicity using analog potentiometers... but is it really less complex? 

Actually controlling all these function requires using lots of potentiometers, 12 in total!!:

3x 100kB for PreEq

3x 100kB for PostEq

1x 500kB for Gain

2x 10kB for Soft Clipping

2x 100RB for Hard Clipping

1x 100kA for Volume

Circuit Design and Simulation

For circuit design and simulation I use LTSpice. I will need a minimum of 3 opamps: one for PreEQ, one for Gain / Soft Clipping, and one for PostEQ, if I use two dual opamps, there is one left to be used as input unty gain buffer.


Pre and Post Equalizer will be identical circuits based on an opamp with Bass, Mids and Treble circuits:

Equalizer simulation, PreEQ + PostEQ Bass response:

Equalizer simulation, PreEQ + PostEQ Mid response:

Equalizer simulation, PreEQ + PostEQ Treble response:

Clipping section

An opamp soft clipping section followed by a hard clipping section. Schottky diodes (BAT54 or similar) used as clipping diodes:


Gain frequency simulation with no PreEQ, no PostEQ. 20 dB gain:

Gain transient simulation with no clipping:

Asymmetric soft clipping transient simulation at max gain:

Asymmetric hard clipping transient simulation at max gain and max soft clipping:

Symmetric hard clipping transient simulation at max gain and max soft clipping


I used Eagle for schematics design:

Usually I design the PCB layout with Eagle and then I send the files to a PCB manufacturer, but this time I wanted to go "simple", at the end of the day the PCB is quite small and simple, but there will be many wires going from PCB to potentiometers. I decided to use bare board vith no copper, glue SMD components on the PCB and solder wires between components, and between components and potentiometers / connectors.

This is the bare PCB with components glued in, quite simple isn't it?

Well actually it was quite a nightmare to solder the wires, I had to be very quick and precise because if the component gets hot, the super glue will melt.
I used 30AWG wire wrap cable with one solid wire and thin insulation as this one 

I then used hot glue to fix the wires and avoid breaking the thin wires sue to tensions during installation.
Usually I use Hammond type die cast aluminum boxes 1590B or 1590N1, which I personally prefer because it provides a bit more space, but this time I needed a bigger box to fit 12 potentiometers, the footswitch and an LED. I found a black ABS plastic box MB8 150 x 80 x 50mm that was just the side needed.

With all these simplifications, wasn't I risking to have poor shielding and being susceptible to get external noise and hum? Ususally a 2 sided PCB allows to have a full ground plane on bottom layer, so that all signals have good grounding and reference, But using wires I risked to create current ground loops that could capture external noise. The metal box is grounded and provides good shielding, but a plastic box can be exposed to external noise and capture 50 Hz hum, specially on a high gain pedal.

I added copper tape on bottom side of bare PCB connected to ground to try to improve grounding and shielding, and I was not sure I would need to internally shield the plastic box with copper or aluminum tape. At the end this was not needed and the pedal is not noisy.

I do not include pictures of the wired pedal because is quite messy and not very elegant or aesthetic.

I was worried to break the thin wire wrap wires and was extremely careful when assemblying the pedal, but the hot glue provided enough robustness to support tensions and bendings. 

Below a picture of the assembled and powered pedal. The 8 potentiometers on the left are 16mm diameter and had to be misaligned to be able to fit the in the box. 

I haven't yet labelled the knobs, which it is probably recommended on a pedal with so many knobs.


PreEQ +PostEQ frequency response

PreEQ frequency response

PostEQ frequency response

No Gain time response

SC1 at max
SC1 and SC2 at max

SC2 at max:

Gain at max:
Gain and HC1 at max:

Gain, HC1 and HC2 at max:

Gain and HC2 at max:

Gain, HC1, HC2, SC1, and SC2 at max

Gain, HC1 and SC1 at max:


I am very satisfied with the sound and the possibilities of this pedal, maybe too many tweaking knobs but it has a wide range of sounds from boost to overdrive to quite hard distortion without entering into fuzz zone. The pre and post equalizer allow to shape the tone as desired, compressing or increasing mids, providing more brightness or top end or making it sound fatter.

Sunday, 13 May 2018

NuTube Overdrive - Assembly, Test, source files


This is just an amateur pedal with no intention for profit or to infringe any trademark.
Tube Screamer is a trademark of Hoshino Gakki Co.
Nutube is a trademark of KORG INC.
This pedal is not for sale. If you want to buy a similar pedal I recommend you Ibanez NTS Screamer.


Nude PCB before assembly, components side:

PCB with SMD components assembled:

PCB fully assembled connectors and potentiometers side. Tests without enclosure were quite noisy:

PCB fully assembled connectors and potentiometers side:

PCB fully assembled on SMD components side:

Guitar pedal fully assembled verified and ready for tests:

Source files

Source files for Eagle schematics, BoM and layout as well as FreeCAD 3D files can be found on github:

Sound files

Chords tests:
Solo test:


NuTube Overdrive Test playlist video with Stone Roses solo, bluesy solo and chords:

Tuesday, 1 May 2018

NuTube Overdrive - Schematics, BoM, PCB layout, 3D


This is just an amateur pedal with no intention for profit or to infringe any trademark.
Tube Screamer is a trademark of Hoshino Gakki Co.
Nutube is a trademark of KORG INC.
This pedal is not for sale. If you want to buy a similar pedal I recommend you Ibanez NTS Screamer.


Some ferrites are used to filter noise at the input and output. +9VDC power voltage is also filtered by means of an EMI filter Murata NFM3DPC223R.
Op-Amps +4.5V mid voltage is generated by a LM4041 voltage reference.
Grid DC bias voltage is generated from +5V DC-DC output via a 4K7 resistor in series with a 10K trimmer. The trimmer midpoint is filtered with 10µF capacitor and connected to the grid via 33K resistor as recommended by manufacturer.
An MMBT5089 NPN transistor buffer is used between the two triode sections.
NPN buffers are also connected at the input and the output of the pedal.
An Op-Amp buffer is used at the output of the second triode section, the buffer output is connected to the 100K Mix linear potentiometer.
NuTube triodes have 500K linear trimmers on anode loads connected to +9VDC.
+5VDC is connected via 240R series resistor and filtered with 1µF capacitors to provide the required filament voltage to triodes.
R8 and R38 pull-down resistors are required to avoid popping when engaging or disengaging the effect via true-bypass 3PDT footswitch.
S1 is the switch that allows disconnecting the clipping diodes. BAV199 are dual diodes in a single SOT23 package. R14 shorts one of the diodes to provide asymmetrical clipping.
R13 can be removed to disconnect C8 220nF capacitor and disable bass-boost mod.
The output of the mix potentiometer is connected to the tone section via an Op-Amp buffer.
Volume potentiometer is a 100K audio/log taper.

NuTube Screamer Schematics, page 1
NuTube triodes require a +5VDC filament voltage with 200mA current per triode . A TPS62175DQCR DC-DC converter generates +5VDC 500mA from +9VDC input. +5V is also used to generate grid DC bias between +2V and +3V.

NuTube Screamer Schematics, page 2. Grid bias voltage +5V DC-DC converter

Bill of Materials

Part Number Mfg Name Description Qty Reference Value
CRCW06030000ZSTB Vishay Thick Film Resistors - SMD 0603 1/10watt ZEROohm Jumper 2 R13, R14 0R
ERJ-3EKF1001V Panasonic Thick Film Resistors - SMD 0603 1Kohms 1% Tol 7 R5, R9, R16, R23, R25, R27, R33 1K
CR0603-FX-1004ELF Bourns Thick Film Resistors - SMD 0603 1M 1% 1/10W 7 R3, R7, R8, R11, R24, R26, R31 1M
C1608X7R1V105K080AE TDK CAP CER 1UF 35V 10% X7R 0603 8 C3, C4, C5, C6, C7, C18, C19, C23 1u
RC0603FR-073K3L Yageo Thick Film Resistors - SMD 0603 3.3kohms 1% Tol 1 R28 3.3k
ERJ-3EKF4701V Panasonic Thick Film Resistors - SMD 0603 4.7Kohms 1% Tol 1 R15 4.7k
C2012X5R1E475K125AB TDK CAP CER 4.7uF 25volts X5R 10% 0805 2 C21, C31 4.7u
ERJ-3EKF4701V Panasonic Thick Film Resistors - SMD 0603 4.7Kohms 1% Tol 1 R35 4k7
CR0603-FX-1002HLF Bourns Thick Film Resistors - SMD 0603 10KOHM 1/10WATT 1% 6 R1, R2, R10, R12, R22, R32 10k
GRM21BR6YA106KE43L Murata CAP CER 10UF 35V X5R 0805 15 C1, C2, C10, C12, C13, C14, C15, C16, C17, C20, C24, C25, C26, C30, C33 10u
SRN4018-100M Bourns FIXED IND 10UH 1.3A 180 MOHM SMD 1 L1 10u
C2012X5R1V226M125AC TDK CAP CER 22UF 35V X5R 0805 1 C32 22u
CR0603-FX-3302ELF Bourns Thick Film Resistors - SMD 0603 33K ohm 1% 2 R17, R18 33k
06035D473MAT2A AVX CAP CER 0.047UF 50V X5R 0603 2 C9, C29 47n
GCM1885C2A470JA16D Murata CAP CER 47PF 100V C0G/NP0 0603 1 C11 47p
ERJ-3EKF5102V Panasonic Thick Film Resistors - SMD 0603 51Kohms 1% Tol 1 R19 51k
RC0603FR-0768KL Yageo Thick Film Resistors - SMD 0603 68kohms 1% Tol 1 R34 68k
ERJ-3EKF8202V Panasonic RES SMD 82K OHM 1% 1/10W 0603 1 R41 82k
RC0603FR-07100RL Yageo RES SMD 100 OHM 1% 1/10W 0603 1 R29 100
ERJ-3EKF1003V Panasonic RES SMD 100K OHM 1% 1/10W 0603 2 R6, R40 100k
EEE-1VA101XP Panasonic CAP ALUM 100UF 20% 35V SMD 1 C22 100u
RC0603FR-07180KL Yageo Thick Film Resistors - SMD 0603 180K 1% 1/10W 1 R36 180k
ERJ-PA3F2200V Panasonic RES SMD 220 OHM 1% 1/4W 0603 2 R30, R37 220
GRM188R61H224KAC4D Murata CAP CER 0.22UF 50V X5R 0603 3 C8, C27, C28 220n
ERJ-3EKF2400V Panasonic RES SMD 240 OHM 1% 1/10W 0603 2 R20, R21 240
CR0603-FX-4303ELF Bourns Thick Film Resistors - SMD 0603 430K ohm 1% 1 R39 430k
CR0603-FX-5103ELF Bourns Thick Film Resistors - SMD 0603 510kohms 1% Tol 1 R4 510k
PTV09A-4020S-A104 Bourns Potentiometers 9mm 100Kohms Audio 1 VOL A100K
PTV09A-4020F-B502 Bourns Potentiometers 9mm 5Kohms Linear 1 TONE B5K
3314G-2-103E Bourns TRIMMER 10K OHM 0.25W SMD 1 RV1 B10k
PTV09A-4020S-B104 Bourns Potentiometers 9mm 100Kohms Linear 1 MIX B100K
PTV09A-4020S-B504 Bourns Potentiometers 9mm 500Kohms Linear 1 GAIN B500K
3314G-1-504E Bourns TRIMMER 500K OHM 0.25W SMD 2 VR1, VR2 B500k
BAV199235 NXP Rectifiers DIODE LOW LEAKAGE 2 D1, D2 BAV199
BLM31PG121SN1L Murata EMI Filter Beads Chips & Arrays 1206 120 OHM 2 FB1, FB2 BLM31PG121SN1L
NMJ4HCD2 REAN Phone Connectors 2C MONO 2-SPST NC 1 J1 INPUT
LM4041CIDBZR Texas Instruments Voltage References Adjustable Precision Mcrpwr Shunt .5% 1 U4 LM4041CIDBZ
LME49723MA/NOPB Texas Instruments Audio Amplifiers Dual Audio Op Amp 2 U1, U3 LME49723
MBR0520LT1G ON Semiconductor Schottky Diodes & Rectifiers 0.5A 20V 1 D3 MBR0520LT1G
MMBT5089 Fairchild Semiconductor Transistors Bipolar - BJT NPN Transistor General Purpose  3 T1, T2, T3 MMBT5089
NFM3DPC223R1H3L Murata EMI/RFI Suppressors & Ferrites 0.022uF 50V 2A' 1 CF1 NFM3DC
831-87-032-10-001101 APEM Inc. Conn SIP Socket Strip SKT 32 POS 2mm Solder ST Thru-Hole 1 U2 NUTUBE 6P1
NMJ4HCD2 REAN Phone Connectors 2C MONO 2-SPST NC 1 J3 OUTPUT
TPS62175DQCR Texas Instruments IC REG BUCK BST ADJ 0.5A 10WSON 1 U5 TPS62175DQCR

PCB Layout

Top side

This is where all SMD components are mounted

NuTube Screamer PCB layout Top side (components)

Bottom side

This is where all the connectors and through-hole components are mounted: DC jack, input/output jacks, switch, potentiometers, LED and battery clipping contact for GND contact with enclosure
NuTube Screamer PCB layout Bottom side (connectors)
The following figure shows NuTube Screamer PCB pedal dimensions 72 x 54 mm and 1590B enclosure internal dimensions 107 x 55.45 mm
NuTube Screamer PCB and 1590B enclosure dimensions

3D assembly

Eagle layout can be imported into FreeCAD 3D to create a 3D assembly image that allows placing the different holes in the assembly and checking proper mechanical assembly.
LED had to actually be moved because it interfered with tone pot.

NuTube Screamer 3D assembly drawing