I like to present an overdrive / low gain fuzz—a lockdown project:
Starting from a fuzz face with lower beta germanium transistors, a fuzz circuit was tweaked to lower gain, softer clipping and the ability to handle (fat sounding) humbuckers:
- Low cut / mid boost including low cut control was inserted before input—to allow using guitars with “fat” pickups.
- Low cut condenser value / low cut frequencies could be set in useful steps using jumper
- T1's collector resistor (R4) was changed (from 33k to 10k) to adapt the circuit to the higher beta of a standard silicon transistor.
- Second fuzz stage was tweaked to most possibly soft clip using DMOS (LND150) transistor.
- Source Diodes care for a proper operation point for DMOS and stretch the DMOS's cut off.
- DMOS (LND150) in second stage could be replaced by harder distorting MOSFET 2N7000) or by an npn-transistor—the source diodes should be shortened then.
- Upper collector resistor of second transistor (R3; often 1k in standard fuzz, 2k2 here) was enlarged due to the fact, that “TONE” control “eats” volume—causes a loss of volume.
- On output there is a two stage hi cut filter (a 5 kHz low cut filter with R3||C3 and as helving filter TONE control).
- Strip layout was used (verified) and
- Second (slightly tuned, not verified) layout for different transistors in second stage.
Layout Version I—three pins socket for M2
- L: Low Cut
- A: Attack
- T: Tone
- V: Volume
- 0: Begin
- T: Taper
- 1: End/Max.
- LowCut_1 = LowCut_T = FX Input (foot switch)
- Tone_T = Vol_1
- Vol_T = FX Output (foot switch)
- Input / Low cut capacitors value could be set with Jumper (O2-O5):
- Jumper O2-O3: 6nF
- Jumper O1-O2: 10nF
- Jumper O3-O4: 15nF
- Jumper O1-O2 & O3-O4: 25nF
- No Jumper O2-O5, no low cut -- Low cut pot becomes something like “smooth” control.
- Jumper (A7A8) shortens the source / emitter diodes of second transistor (open with M1 default LND150).
- Blue bridges are ground bridges.
- Dashed bridges are on solder side.
- Red Bridge A13-B13—there a test pin for U_Drain resp. U_Collector should be set.
- Harder clipping second transistor: Instead of second transistor an MOSFET M1 (default: LND150) is used (in Layout: F11 [Source], F12 [Gate] and F13 [Drain]).
M1 could be replaced by 2N7000 or an NPN transistor (F11 [Emitter], F12 [Base] and F13 [Collector]).
For 2N7000 or NPN transistor as second transistor, set jumper 5|6 (on A6A7).
- A 100pF input filter capacitor was set parallel to R7 (on holes N1 to N5, not in layout sheets).
- Fat green bridge between holes D3-D6 could be replaced by R11, e.g. 22 Ohms, to reduce maximum gain.
- R8 (10k, no mid boost on Tone Pot) could be squeezed between output (second transistors Drain/Collector) and tone control; e.g. R8 on F15-H15 with a cut on G15. Without R8, Tone control on maximum a little mid boost (~1-2dB from 1kHz to 2kHz) appears.
- Four-pin-socket for second transistor allows other pin schemes (e.g. JFET scheme GSD).
- Additionally, some problems were solved (place for R8, distance between bridges on E17 and D17/E18).
- Layout not verified.
http://www.gitarrebasteln.de/primitiv_5 ... ufbau.html and http://www.gitarrebasteln.de/primitiv_4 ... osfet.html
(Additionally, it was a long journey from a low gain fuzz gimmick using low gain germanium transistor to these schematic—journey is described in first three chapters: http://www.gitarrebasteln.de/primitiv_0_abstract.html ff.; in german language too)
NegationOfNegation | Graue_Theorie
Spring 2020 (device finished during first lockdown) / 2022-04-11