Sunday, 13 May 2018

NuTube Overdrive - Assembly, Test, source files

Disclaimer

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.

Assembly

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:

Videos

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

Tuesday, 1 May 2018

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

Disclaimer

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.

Schematics

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
PJ-202A CUI CONN POWER JACK 2.1MM PCB 1 J2 DCJ0202
SSL-LX5093GD Lumex LED GRN DIFF 5MM ROUND T/H 1 LED1 GREEN
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
MHS122K APEM Inc. SWITCH SLIDE SPDT 300MA 30V 1 S1 clip

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

NuTube Overdrive - Spice simulations

Disclaimer

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.

NuTube Overdrive Schematics

NuTube Overdrive is basically a Tube Screamer TS808 classic circuit (with a couple of mods I will explain later) where two NuTube triodes amplifier stages have been added between the preamp and the tone circuit, the original Tube Screamer output of the preamp is mixed with the output of the two triode amp sections by means of a 100K linear potentiometer, the buffered output of the mix is connected to the original tone circuit.

The following figure shows the LTSpice schematics of the NuTube Screamer pedal:
NuTube Screamer LTSpice schematics

NuTube Screamer Mods

The following mods have been made to the original schematics:
  1. Bass boost mod: 220nF capacitor added in parallel to 47nF on the high pass filter connected to the preamp section inverting input. This mod can be remove by just removing a series 0R resistor
  2. Tone mod: 20K tone potentiometer has been replaced by 5K linear potentiometer providing a more gradual response of the tone potentiometer.
  3. Asymmetric clipping: The original pedal had symmetric clipping, here an additional diode has been added in series to the positive output cycle.
  4. Output buffer: Resistor biasing has been slightly changed using 1000K resistor bridge from +9VDC instead of a 510K single resistor to +4.5VDC. It is basically the same.
Some components have been changed due to availability, performance or space gain:
  1. Original diodes were silicon MA150, they have been changed by dual BAV199 silicon diodes for space gain, and easier asymmetrical circuit construction.
  2. Original opamp JRC4558 has been replaced by LME49723 which has better performance in terms of harmonic distortion, noise, bandwidth, offset voltage and slew rate. See comparison here
  3. Original transistors 2SC1815 used for buffers  have been replaced by MMBT5089 in a small SOT23 package

Frequency response

The following figure shows the gain response from 0 to 10 with tone at 5 and mix at 10, maximum gain is 56 dB and minimum gain is 36 dB:
NuTube Screamer Gain = 0 to 10, Tone = 5, Mix = 10
The following figure shows tone response from 0 to 10 with gain at 10 and mix at 10:
NuTube Screamer Tone = 0 to 10, Gain = 10, Mix = 10
 The following figure shows Mix response from 0 to 10 with gain at 10 and tone at 5, maximum gain is 56 dB and minimum gain is 38 dB:
NuTube Screamer Mix = 0 to 10, Gain 10, Tone = 5
The total gain of NuTube triode amps section is 17.7dB, 8.2 dB for the first section, almost flat from 10 Hz to 20KHz (82mdB loss at 20 kHz) and 9.5dB for the second section (with 141dB loss at 20kHz)

Time response

Time response shows the pedal output signal with different settings with a 60 mVp-p 30s-1 decaying 440Hz sinewave input signal. Clipping is always on.

The following figure shows Gain response from 0 to 10 with Tone at 5 and Mix at 5:
NuTube Screamer time response with Gain = 0 to 10, Mix = 10, Tone = 5
The following figure shows Tone response from 0 to 10 with Gain at 10 and Mix at 5:
NuTube Screamer time response with Tone = 0 to 10, Mix = 5, Gain = 10
The following figure shows Mix response from 0 to 10 with Gain at 10 and Tone at 5:
NuTube Screamer time response with Mix = 0 to 10, Tone = 5, Gain = 10



Sunday, 17 September 2017

Wednesday, 9 August 2017

Korg Nutube 6P1 vs 12AX7 tube: Hybrid Amplifier (6)

Distortion analysis

A 1kHz 600mVpp sinewave is injected into the amp input, the waveform and spectrum at the output is analyzed for several gain values (0, 0.5, 1) to check the level of 2nd and 3rd order harmonics.

The volume level at 1kHz is set at 0dB for the maximum gain values (G1 = G2 = 1) and the relative attenuation is shown for different gain values combinations. The level in dB at 1kHz, 2kHz and 3KHz is measured. The relative attenuation of the second and third harmonic respect to 1kHz is also measured.

NuTube 6P1 results

With BOOST off:
G1 generates an attenuation of 1 and 4dB at G1= 0.5 and 0 respectively
G2 generates an attenuation of 4 and 19dB at G2= 0.5 and 0 respectively
Second harmonic has an attenuation of 20 dB (G2=1), 20 dB (at G2=0.5) and 21 dB (at G2=0)
Third harmonic has an attenuation of  35dB (G2=1), 36 dB (at G2=0.5) and 39 dB (at G2=0)
As we can see there is almost the same harmonic distortion at all gain levels.

With BOOST on:
G1 generates an attenuation of 0 and 1dB at G1= 0.5 and 0 respectively
G2 generates an attenuation of 4 and 19dB at G2= 0.5 and 0 respectively
Second harmonic has an attenuation of 10 dB (G2=1), 12 dB (at G2=0.5) and 16 dB (at G2=0)
Third harmonic has an attenuation of 21 dB (G2=1), 21 dB (at G2=0.5) and 23 dB (at G2=0)
As we can see there is a bit more harmonic distortion at higher gain levels.

Harmonic distortion is higher with BOOST on, this means that some distortion happens in the last JFET amplifier stage and some at the triode amplifier stages.

G1 G2 Boost Vpp (mV) Att (dB) 1kHz (dB) 2kHz (dB 3kHz (dB) 2nd /1st (dB) 3rd/1st (dB)
0.0 0.0 0 31 -23 -24 -44 -63 -20 -39
0.0 0.5 0 162 -8 -9 -29 -48 -21 -39
0.0 1.0 0 275 -4 -4 -25 -43 -21 -39
0.5 0.0 0 40 -20 -21 -41 -58 -20 -36
0.5 0.5 0 211 -6 -6 -26 -43 -20 -37
0.5 1.0 0 358 -1 -2 -22 -38 -20 -36
1.0 0.0 0 46 -19 -20 -40 -55 -20 -35
1.0 0.5 0 249 -4 -5 -24 -40 -19 -35
1.0 1.0 0 415 0 0 -20 -35 -20 -35
0.0 0.0 1 306 -20 -20 -37 -44 -16 -24
0.0 0.5 1 1747 -5 -5 -21 -29 -16 -23
0.0 1.0 1 2800 -1 -1 -17 -23 -16 -22
0.5 0.0 1 334 -19 -20 -32 -41 -12 -21
0.5 0.5 1 1937 -4 -5 -17 -26 -12 -21
0.5 1.0 1 3000 0 -1 -13 -21 -12 -21
1.0 0.0 1 350 -19 -20 -30 -41 -11 -21
1.0 0.5 1 1958 -4 -4 -15 -25 -10 -21
1.0 1.0 1 3080 0 0 -11 -21 -11 -21

12AX7 results

With BOOST off:
G1 generates an attenuation of 1 and 5dB at G1= 0.5 and 0 respectively
G2 generates an attenuation of 4 and 17dB at G2= 0.5 and 0 respectively
Second harmonic has an attenuation of 3 dB (G2=1), 8 dB (at G2=0.5) and 17 dB (at G2=0)
Third harmonic has an attenuation of 8 dB (G2=1), 12 dB (at G2=0.5) and 21 dB (at G2=0)
As we can see there is more harmonic distortion at higher gain levels, as expected.

With BOOST on:
G1 generates an attenuation of 0 and 3dB at G1= 0.5 and 0 respectively
G2 generates an attenuation of 4 and 18dB at G2= 0.5 and 0 respectively
Second harmonic has an attenuation of 4 dB (G2=1), 8 dB (at G2=0.5) and 19 dB (at G2=0)
Third harmonic has an attenuation of 11 dB (G2=1), 15 dB (at G2=0.5) and 21 dB (at G2=0)
As we can see there is more harmonic distortion at higher gain levels, which means that distortion and saturation depends a lot on tube grid input level.

Harmonic distortion is similar with BOOST off or on, since the BOOST happens in the last JFET amplifier stage this means that most of the distortion happens in the tube amplifier stages.

G1 G2 Boost Vpp (mV) Att (dB) 1kHz (dB) 2kHz (dB 3kHz (dB) 2nd /1st (dB) 3rd/1st (dB)
0.0 0.0 0 55 -26 -22 -39 -43 -17 -21
0.0 0.5 0 265 -12 -8 -26 -29 -17 -21
0.0 1.0 0 380 -9 -5 -22 -25 -17 -20
0.5 0.0 0 103 -20 -19 -26 -30 -8 -12
0.5 0.5 0 480 -7 -5 -13 -16 -8 -12
0.5 1.0 0 732 -3 -1 -9 -12 -8 -11
1.0 0.0 0 147 -17 -18 -21 -26 -3 -8
1.0 0.5 0 670 -4 -4 -7 -13 -3 -8
1.0 1.0 0 1060 0 0 -3 -8 -3 -8
0.0 0.0 1 248 -24 -21 -40 -42 -19 -21
0.0 0.5 1 1300 -10 -7 -26 -28 -19 -21
0.0 1.0 1 2025 -6 -3 -19 -22 -16 -19
0.5 0.0 1 442 -19 -18 -26 -32 -8 -15
0.5 0.5 1 2272 -5 -3 -12 -18 -8 -15
0.5 1.0 1 3280 -2 0 -9 -12 -9 -12
1.0 0.0 1 530 -18 -18 -21 -31 -4 -13
1.0 0.5 1 2705 -4 -4 -7 -17 -4 -13
1.0 1.0 1 4060 0 0 -4 -11 -4 -11

Conclusion

More harmonic distortion is observed in the 12AX7 tube than in the NuTube.
It is easier to obtain grid clipping and saturation in the 12AX7 tube than in the NuTube.