**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"][1] [Trace Elliot V8 Manual & Schematic][2] [Designing Valve Preamps for Guitar and Bass, Second Edition ][3] [Audio Engineering Society-Triode Emulation][4] [1]: http://www.diale.org/pdf/SOLID-STATE-TRIODE-AMT.pdf [2]: http://el34world.com/charts/Schematics/files/trace_elliot/Trace%20Elliot%20V8%20400W%20bass%20amp%20Service%20Manual.pdf [3]: http://www.valvewizard.co.uk/Common_Gain_Stage.pdf [4]: https://www.scribd.com/doc/65330169/Triode-Emulator-by-Dimitri-Danyuk