125B · 3 knobs
424 Preamp
Based on the Tascam 424
- Category
- Distortion· Boost / Distortion
- Controls
- Input · Low · Output
- Difficulty
- Beginner
- Price
- $12.50in stock
From the vendor
A pedal conversion of the input preamp of the Tascam 424 four-track tape recorder, most notably used by Mk.gee for his main drive tone.
The 424 Tape Preamp replicates the dry audio path of one channel of the Tascam 424 Portastudio Mk. I, a 4-track tape recorder from the late 1980s to the early 1990s. While 4-track recorders have a long history of being misused to create interesting drive and distortion effects, the 424 in particular is one of the foundational pieces of Mk.gee’s unique guitar tone.
The 424 Preamp has four knobs, each corresponding to a control on the original Tascam unit. The Input control is the equivalent of “Trim” on the Tascam, a potentiometer that cuts the input signal. It’s intended to prevent clipping, but can be used to intentionally overload the op-amp stages as a drive control.
This is followed by a standard 2-band Baxandall EQ which boosts or cuts frequencies by +/-10dB, centered at 100 Hz and 10 kHz. The volume control is equivalent to the channel’s “Master” slider. These are the only four controls that affect the audio signal; the slide switches only control the routing of the signal to the tape recorder or outboard effects.
The Demo Tape Fuzz by Mid-Fi Electronics (available as our Torus project) is a similar circuit that was also designed to sound like an overdriven tape recorder, and no doubt the Tascam was one of the inspirations for that circuit. But, the DTF is not based directly on any specific model as far as we know—so while it does capture the spirit and functionality, the 424 Preamp is actually an exact copy of what Mk.gee uses.
Schematic
The schematic is in the vendor's build document, page 6. Open the build document. No KiCad fragment has been drawn for this circuit yet.
Parts list 49 rows
Report a wrong parse| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 17 | ||||
| R1 | 100k | 100k | Metal film resistor, 1/4W | |
| R2 | 470k | 470k | Metal film resistor, 1/4W | |
| R3 | 100R | 100 | Metal film resistor, 1/4W | |
| R4 | 10k | 10k | Metal film resistor, 1/4W | |
| R5 | 10k | 10k | Metal film resistor, 1/4W | |
| R6 | 22k | 22k | Metal film resistor, 1/4W | |
| R7 | 18k | 18k | Metal film resistor, 1/4W | |
| R8 | 5k6 | 5.6k | Metal film resistor, 1/4W | |
| R9 | 470k | 470k | Metal film resistor, 1/4W | |
| R10 | 47k | 47k | Metal film resistor, 1/4W | |
| R11 | 110k | 110k | Metal film resistor, 1/4W | |
| R12 | 100k | 100k | Metal film resistor, 1/4W | |
| R13 | 10k | 10k | Metal film resistor, 1/4W | |
| R14 | 10k | 10k | Metal film resistor, 1/4W | |
| R15 | 47R | 47 | Metal film resistor, 1/4W | Power supply filter resistor. |
| RPD | 2M2 | 2.2M | Metal film resistor, 1/4W | Input pull-down resistor. Can be as low as 1M. |
| LEDR | 10k | 10k | Metal film resistor, 1/4W | LED current-limiting resistor. Adjust value to change LED brightness. |
| Capacitors 16 | ||||
| C1 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C2 | 100pF | 100p | MLCC capacitor, NP0/C0G | |
| C3 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C4 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C5 | 1n8 | 1.8n | Film capacitor, 7.2 x 2.5mm | |
| C6 | 15n | 15n | Film capacitor, 7.2 x 2.5mm | |
| C7 | 15n | 15n | Film capacitor, 7.2 x 2.5mm | |
| C8 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C9 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C10 | 47pF | 47p | MLCC capacitor, NP0/C0G | |
| C11 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C12 | 10pF | 10p | MLCC capacitor, NP0/C0G | |
| C13 | 10uF | 10u | Electrolytic capacitor, 5mm | |
| C14 | 47uF | 47u | Electrolytic capacitor, 5mm | Reference voltage filter capacitor. |
| C15 | 100uF | 100u | Electrolytic capacitor, 6.3mm | Power supply filter capacitor. |
| C16 | 100n | 100n | MLCC capacitor, X7R | Power supply filter capacitor. |
| Diodes 1 | ||||
| D1 | 1N5817 | 1N5817 | Schottky diode, DO-41 | |
| ICs 2 | ||||
| IC1 | LM833 | LM833 | Operational amplifier, dual, DIP8 | |
| IC2 | NJM4565D | NJM4565D | Operational amplifier, dual, DIP8 | |
| Potentiometers 4 | ||||
| INPUT | 10kC | C10k | 16mm right-angle PCB mount pot | Reverse audio (antilog) taper. |
| OUTPUT | 10kA | A10k | 16mm right-angle PCB mount pot | Audio (log) taper. |
| HIGH | 100kB | B100k | 16mm right-angle PCB mount pot | Linear taper. |
| LOW | 100kB | B100k | 16mm right-angle PCB mount pot | Linear taper. |
| Switches 1 | ||||
| FSW | 3PDT | 3PDT | Stomp switch, 3PDT | Available from Aion FX. |
| LEDs 1 | ||||
| LED | 5mm | 5MM | LED, 5mm, red diffused | |
| Jacks & sockets 5 | ||||
| IC1-S | DIP-8 socket | DIP-8 SOCKET | IC socket, DIP-8 | |
| IC2-S | DIP-8 socket | DIP-8 SOCKET | IC socket, DIP-8 | |
| IN | 1/4" stereo | 1/4" STEREO | 1/4" phone jack, closed frame | Switchcraft 112BX or equivalent. |
| OUT | 1/4" mono | 1/4" MONO | 1/4" phone jack, closed frame | Switchcraft 111X or equivalent. |
| DC | 2.1mm | 2.1MM | DC jack, 2.1mm panel mount | Lumberg NEB/J 21 C or equivalent. |
| Hardware 2 | ||||
| BATT | Battery snap | BATTERY SNAP | 9V battery snap | Optional. Use the soft plastic type—the hard-shell type will not fit. |
| ENC | 125B | 125B | Enclosure, die-cast aluminum | Can also use a Hammond 1590N1. |