KdB Raptor

2 years ago 2226
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Description

License/Usage


This work is licensed under the CopyLeft and CC-BY-NC-SA 3.0 license agreements. By forking,sharing or downloading the contents of this project(herein referred to as the KdB Raptor(c) Bass Preamp) you acknowledge,accept and agree to abide by the terms & conditions of Copyleft and CC-BY-NC-SA 3.0 license agreements.

Project Description


The Raptor is a Bass preamp designed around the tone stack of the legendary Trace Elliot Valve amps made in the UK in late 90s. In order to achieve a tube-like sound, the KdB Raptor employs an Field Effect Transistor (FET) configuration known as the Fetzer Valve.

The preamp section of a Trace Elliot V8 head was created and simulated in LTspice based upon the schematic at El34 World. Once the LTspice simulation was complete, the frequency response of the V8 was duplicated in a FET version. While not 100% reproduction, the kdB Raptor reproduces the V8's frequency response fairly close at say 93%.

SW1 enables/disables a notch filter at 406.45 Hz based upon the Trace Elliot V8 schematic.

SW2 replaces the functionality of the V8's push-pull selector knob that provides a +/- 9dB increase/decrease at 200Hz of the Midrange band.

The Fetzer Valve


The Fetzer valve is based upon a 2002 Audio Engineering Society paper written by Dimitri Danyuk on triode emulation using a FET. In his paper, Danyuk demonstrates how by linearizing the current feedback of the FET source, the solid-state device drain current will emulate the operation of a vacuum tube and the 3/2 power law. The problem with the Fetzer valve is the quiescent point is not typically within 1/2 Vdd the way the most have tried to implement a Fetzer valve. The Raptor uses a +12 volt supply which allows more headroom and establishment of a Qpoint close to 1/2 Vdd. The Raptor contains 4 Fetzer valves which is equivalent of 2 12AX7's.

Test Configuration


The kdB Raptor (breadboard prototype) has been tested with the following rig:

Kramer Forum IV Bass --> Kdb Raptor --> BBE Harmonic Enhancer --> ISP Stealth Power(180W) Amp --> 2x12 Cab/w Celestion V30's

Ibanez SR505-5 Bass --> Kdb Raptor --> BBE Harmonic Enhancer --> ISP Stealth Power(180W) Amp --> 2x12 Cab/w Celestion V30's

Specifications:


Input impedance: 1 Meg

Output impedance: 1K

Current draw: 26.55 mA

Power dissipation: 318 mW

Power Supply: +12 vdc (center negative)

Noise(normal channel): 303.87 nV/Hz @14.289 Hz

Noise(bright channel): 476.28 nV/Hz @ 259.87 Hz

Build Notes:


1) Only the following FET's need to meet the specified Vpinch and Idss:

Q3 J113 Idss = 27.5:29.63mA Vpinch = -2.47: -2.60V

Q4 2N3819 Idss = 5.14:5.72 mA Vpinch = -1.99: -2.259V

Q7 2N5484 Idss = 2.1 mA Vpinch = -1.34

Q9 2N3819 Idss = 5.14:5.72 mA Vpinch = -1.99: -2.259V

2) All capacitors unless otherwise noted are box polyester.

3) 3.3uF & .68uF can be substituted for C11 & C12 respectively. Okay to use Tantalum or electrolytics

4) The circuit is quiet but use metal film for R8,R32 to reduce 1/f noise.

5) C14 Original value = 200pF

6) R38 on schematic is connected via rat lines on the PCB to RGB LED anode.

7) If using short pin PCB potentiometers with dust seals, recommend using long pin instead.

8) Voodoo Lab ISO-5 power supply and Hosa ACD-77 wall wart were used in the testing.

9) Optional if operating with 12 volt supply - D1,D2,R2,R51 limit output to roughly 2Vdc peak/1.414 RMS/ 0dBV

10) Operating at 9v will not provide enough headroom and output will be muddy, fuzzy and just plain nasty! Not tested with 18V supply, however would definitely recommend installing Zener didoes D1,D2 and resistors R2,R51

Audio Samples

The samples were recorded with an AKG P170 (-20db padding on) mic, Scarlett 2i2 and iPad with MultiTrack DAW from Harmonic Dog.

References:


AMT "Warmstone"

Trace Elliot V8 Manual & Schematic

Designing Valve Preamps for Guitar and Bass, Second Edition

Audio Engineering Society-Triode Emulation

Documents

KdB Raptor Preamp rev_1_0_0

Raptor PCB rev_1_0_0

Raptor PCB rev_1_0_1

BOM

ID Name Designator Footprint Quantity Mounted
1 1M R13,R14,R9,R16,R22,R27,R28,R17,R32,R35,R42 AXIAL-0.3 11 Yes
2 MPF102 Q2,Q8,Q10 TO-92-3 3 Yes
3 470K R15,R12 AXIAL-0.3 2 Yes
4 100nF C8,C14,C6,C9,C15,C21,C22,C1,C13,C24,C29 BOX CAPACITOR - 5MM POST SPAN (E.D.) 11 Yes
5 360 R8 AXIAL-0.3 1 Yes
6 470 R4 AXIAL-0.3 1 Yes
7 470nF C4 CERAMIC CAPACITOR (5MM) 1 Yes
8 1.5k R5,R1 AXIAL-0.3 2 Yes
9 330 R18,R11 AXIAL-0.3 2 Yes
10 470pF C10 CERAMIC CAPACITOR (5MM) 1 Yes
11 100K R19,R24 AXIAL-0.3 2 Yes
12 2K R7 AXIAL-0.3 1 Yes
13 560 R21 AXIAL-0.3 1 Yes
14 10K R23,R36,R39 AXIAL-0.3 3 Yes
15 300pF *C14 CERAMIC CAPACITOR (5MM) 1 Yes
16 10M R33,R30,R29 AXIAL-0.3 3 Yes
17 SWITCH-SPDT S2 SWITCH-SPDT_KIT 1 Yes
18 Notch Filter SW1 SWITCH SPST PADS 1 Yes
19 510 R31 AXIAL-0.3 1 Yes
20 *Treble/100K PR1 ALPHA POT - HOLES ONLY1 1 Yes
21 Bass PR2 ALPHA POT - HOLES ONLY1 1 Yes
22 Midrange PR3 ALPHA POT - HOLES ONLY1 1 Yes
23 Gain PR4 ALPHA POT - HOLES ONLY1 1 Yes
24 Volume Out PR6 ALPHA POT - HOLES ONLY1 1 Yes
25 220 R10 AXIAL-0.3 1 Yes
26 51 R2,R37 AXIAL-0.3 2 Yes
27 1N4614 D1,D2 SOD-123 2 Yes
28 680K R6,R34 AXIAL-0.3 2 Yes
29 330nF C18 BOX CAPACITOR - 5MM POST SPAN (E.D.) 1 Yes
30 2N5484 Q7 TO-92-3 1 Yes
31 3.9K R26,R3 AXIAL-0.3 2 Yes
32 75 R25 AXIAL-0.3 1 Yes
33 5.6K R20,R41 AXIAL-0.3 2 Yes
34 J113 Q3 TO-92-3 1 Yes
35 2.2uF C11,C12 CAP-D3.0XF1.5 2 Yes
36 2N3819 Q9,Q4,Q5 TO-92-3 3 Yes
37 27nF C3 BOX CAPACITOR - 5MM POST SPAN (E.D.) 1 Yes
38 22nF C7,C5 BOX CAPACITOR - 5MM POST SPAN (E.D.) 2 Yes
39 47nF C2,C17,C20 BOX CAPACITOR - 5MM POST SPAN (E.D.) 3 Yes
40 4.7nF C19,C23 BOX CAPACITOR - 5MM POST SPAN (E.D.) 2 Yes
41 500pF C25 BOX CAPACITOR - 5MM POST SPAN (E.D.) 1 Yes
42 2N3904 Q6,Q1 TO-92(TO-92-3) 2 Yes
43 330nF C26 CNP_7X4.5MM 1 Yes
44 1u C27 CNP_7X4.5MM 1 Yes
45 3K R40 AXIAL-0.3 1 Yes
46 1u C16 RAD-0.1 1 Yes
47 12K R38 AXIAL-0.3 1 Yes
48 SWITCH-DPDT S4 STOMP-SWITCH-DPDT 1 Yes

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Comments (2)

decibel_jr Reply

Update 03.18.2018  Received first version of PCB 1.0.0. Once all the soldering is done and placed in a case, i will
record some audio samples and post.

fapuchete Reply

Hi!, nice project, I want improve it, can we work together? Grettings

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