Kittenqueen

Full schematic — Kittenqueen V1.0 (circuit by Catalinbread, layout © TH Custom Effects 04/2016).

Architecture

The signal path is three NPN gain stages in cascade (Q1, Q2, Q3) feeding a diode-clipping + tone-shaping junction (D2 / D3 / FILTER / C10), then a fourth high-gain recovery stage (Q4) and the VOLUME pot. SENSITIVITY at the input acts as a variable input attenuator — useful for matching different pickup outputs.

Stage 1 — Q1 input gain stage

Signal enters via the SENSITIVITY pot (250 k linear), through C12 (68 n) into a network of R3 (100 k series) and R4 (1 M to GND) at Q1's base. C4 (1 n) shunts high-frequency noise to ground at the base. Q1 (BC549) is in common-emitter configuration: collector load R1 (10 k) to +9 V, emitter R5 (1 k) bypassed by C6 (22 µF). At Q1's collector, R2 (470 k) sets the output node impedance to ground, with C3 (47 p) providing a high-frequency rolloff that softens the top end of the first stage.

Stage 2 — Q2 second gain stage

Q1's collector is AC-coupled by C5 (150 n) to Q2's base via R6 (22 k). Q2 is again common-emitter — collector load tied to the +9 V rail. The emitter circuit is more interesting: R8 (1 k) feeds the GAIN pot wiper, and C8 (10 µF) bypasses to ground. The combination of GAIN pot resistance plus the bypass cap creates a variable emitter degeneration network — turning the GAIN pot up reduces the AC emitter resistance, increasing stage gain. This is the same gain-control trick used in classic Big-Muff-style fuzz circuits.

Stage 3 — Q3 third gain stage

Q2's output drives Q3's base. R13 (2 k2) is Q3's collector load to +9 V. The emitter has R9 (1 k) and a small R14 (150 Ω) to ground, with C9 (22 µF) bypassing — same emitter-degeneration tricks as Q2 for further gain control. R7 (3 k9) and C7 (4.7 µF) provide power-supply decoupling for the Q3 stage, isolating it from supply noise that would otherwise be amplified along with the signal.

Diode clipping + FILTER section

This is the heart of the Katzenkönig sound. Q3's collector drives a junction node through R8 (1 k). Two 1N4148 silicon diodes (D2 / D3) are connected antiparallel from this node to ground — they hard-clip the signal whenever it tries to swing more than about ±0.6 V. The FILTER pot (100 k log) and C10 (3 n3) form a variable low-pass filter after the clipping, letting you sweep the harshness of the clipped harmonics from dark/woolly to bright/aggressive. R17 (1 M) provides a DC bias return path.

Stage 4 — Q4 output recovery

Q4 (BC549) is a common-emitter stage with an unusually high collector load resistor R16 (1 M) — this gives it very high voltage gain and makes up for the signal loss through the clipping/filter network. Its base is biased through R17 (1 M); the emitter has R18 (3 k3) without a bypass cap (deliberately, to keep the gain manageable and add a touch of negative feedback). Output is taken at Q4's collector through C11 (1 µF MLCC) into the VOLUME pot (100 k log).

Power supply

9 V DC enters through D1 (1N4001) for reverse-polarity protection — wrong polarity blocks at the diode and nothing else gets damaged. C1 (47 µF) is the main rail filter, and C2 (10 n) provides RFI bypass. There's no charge pump or virtual-ground splitter — the whole circuit runs from a single +9 V / GND rail in classic transistor-fuzz fashion.

The Kittenqueen has one user-controllable filter (FILTER pot) and several fixed RC corners that shape its overall response. Calculating them gives a clear picture of where the pedal is dark, where it's bright, and what the FILTER pot actually does.

FILTER pot — the main tone control

Practical sweep: 500 Hz at full CW → ultrasonic at full CCW. The audio log taper (A) on the FILTER pot puts most of the perceptual action in the upper part of the rotation, where you're sweeping across the upper midrange (1–5 kHz) — where guitar tone "lives".

Other filter corners (fixed)

The cascaded RC networks elsewhere in the circuit determine the overall low-end and high-end rolloff. None of them are user-adjustable, but knowing where they sit explains why the pedal sounds the way it does:

• Input HP (C12 / R4): 1 / (2π · 1 M · 68 n) ≈ 2.3 Hz — bass passes through completely flat.
• Q1→Q2 inter-stage HP (C5 / R6): 1 / (2π · 22 k · 150 n) ≈ 48 Hz — slight roll-off below the low E (~82 Hz). Tightens the bottom end before the heavy clipping.
• Q1 collector HP corner (R2 / C3): 1 / (2π · 470 k · 47 p) ≈ 7.2 kHz — gentle high-frequency softening at the first stage's output, smooths the input transient.
• Output HP (C11 / VOLUME): 1 / (2π · 100 k · 1 µF) ≈ 1.6 Hz — flat all the way down.

The clipping diodes

D2 / D3 (1N4148 antiparallel) hard-clip at approximately ±0.6 V — one silicon diode forward drop. Whatever signal arrives from Q3's collector via R8 gets brutally squared off at the FILTER pot input. This is the classic "harsh fuzz" sound: lots of odd and even harmonics generated by the abrupt waveform truncation, filtered (or not) by the FILTER pot afterwards. The clipping is the same family of distortion as a Big Muff or a Distortion+ — silicon hard-clipping to ground, just deployed in a different topological context.

The BOM has been cross-checked against the V1.0 schematic. Substitution alternatives are tagged in the Notes column.

Standard low-to-high component order. The pots mount on the back side of the PCB — same procedure as on the other 9 mm Alpha-based TH boards.

Component placement reference — top view. The four 9 mm pots mount on the back side of the board.

Resistors and diodes

All metal film, ¼ W. Match each reference designator on the silkscreen to the BOM value — the colour-band column makes verification quick. Then fit the diodes: D1 (1N4001) is the larger black plastic protection diode, D2 / D3 (1N4148) are the small glass clipping diodes — orientation matters on all three. Note that D2 and D3 are antiparallel, so their bands point in opposite directions to each other — match the silkscreen.

Transistor sockets (recommended)

If you want to experiment with different transistors (which is a fun thing to do with this circuit — different hFE values change the character substantially), fit DIP-style 3-pin sockets for Q1–Q4 now. Otherwise solder the BC549s directly. BC549 pinout (flat side facing you, leads down): C – B – E. If you substitute 2N5088s, those have reverse pinout (E – B – C) and need to be inserted rotated 180°; BC550 is pin-compatible with BC549.

Ceramic and MLCC capacitors

Non-polarised, no orientation. C3 (47 p ceramic) first (smallest), then C11 (1 µF MLCC) — note that the MLCC is the one with the larger body and may be radial-leaded; it goes where the silk shows C11.

Box film capacitors

Populate ascending: 1 n (C4), 3 n3 (C10), 10 n (C2), 68 n (C12), 150 n (C5). Push them flat against the board.

Electrolytic capacitors

All electrolytics here are 5–8 mm Ø, 8 mm height — small radial cans. Polarised, so long lead is positive (+) and the can has a stripe marking the negative side. Match the (+) on the silkscreen for each: C6 (22 µF), C7 (4.7 µF), C8 (10 µF), C9 (22 µF), and the larger C1 (47 µF). Reversing any electrolytic risks a small explosion when powered.

Off-board pads

Solder the off-board wire pads or pin headers for IN, OUT, +9V, GND, and any LED connections.

Pots — back-side mounting

The four 9 mm Alpha pots mount on the opposite side of the board from all other components. See the photo below — that's the fully-mounted view from the pot side. Solder the centre pin of each pot first, pull the pot back about 1 mm so it sits flat against the board, let the solder set, then solder the remaining pins. With 9 mm Alpha pots there are no anti-rotation brackets to clip — they have small lugs that locate them on the PCB.

Insert the transistors (if socketed)

Match the flat side of each transistor to the silkscreen flat. Don't force anything.

Standard external-bypass wiring. Four pads off the board: IN, OUT, +9V, GND.

Enclosure

This PCB does fit a 1590B enclosure easily. Drill templates for TH Custom Effects PCBs are available at diy.thcustom.com/drill-templates/.

Controls

SENSITIVITY — input level / pickup match. Linear taper. Higher values feed more signal into Q1 — appropriate for low-output single-coils. Lower values attenuate hot humbuckers so they don't overdrive the first stage on impact.

GAIN — drive amount. Audio log taper. Sweeps the emitter degeneration on Q2 and Q3 — at low settings the pedal is closer to a gritty distortion, at high settings it's a thick fuzz.

FILTER — post-clipping tone. Audio log taper. Fully CCW = bright/full (filter corner above audio); fully CW = dark/woolly (corner ~480 Hz).

VOLUME — output level. Audio log taper. Plenty of swing — at full settings the Kittenqueen is loud.

The SENSITIVITY pot is optional

If you don't want a SENSITIVITY control on the enclosure, you can replace the pot with a fixed 150 k resistor (between the wiper position and one outer leg, simulating mid-rotation). Other values may sound a little better depending on your pickup type — experiment with values from 100 k to 220 k to find the right input attenuation for your guitar. This frees up enclosure real-estate for an enclosed-LED indicator or a 3PDT toggle if you want one.

Suggested starting points

Crunchy mid-gain distortion — SENSITIVITY at noon, GAIN at 9–10 o'clock, FILTER at 1 o'clock, VOLUME to taste. Audible saturation but still articulate.

Classic Katzenkönig fuzz — SENSITIVITY at noon, GAIN at 1–2 o'clock, FILTER at noon, VOLUME to taste. Heavy but musical — the natural sweet spot.

Wall of fuzz — SENSITIVITY high (2–3 o'clock with humbuckers will be too much; back off), GAIN max, FILTER 1–2 o'clock. Big thick gated-sounding fuzz.

Dark fuzz — Any GAIN setting, FILTER fully CW. Useful for getting under a busy mix, or for processed-via-amp fuzz tones where you want the amp's voice to dominate.

Bright bite — GAIN 11–12 o'clock, FILTER fully CCW. Aggressive top-end, lots of harmonic detail through the clipping. Try with neck pickups for an unexpected articulation.

Transistor swapping

If you socketed the transistors, this is the most worthwhile experimentation point. BC549 with hFE ≈ 290 is the prototype's reference. Try a matched set of BC549Cs (the highest-hFE bin, typically 420–800) for a thicker, more saturated character; BC549Bs (200–450) sit closer to the prototype; lower-hFE devices like BC547 push the pedal toward distortion. Mixing different transistors at different positions also works — Q4 in particular has a lot of influence on the overall character because it's the high-gain output stage.

Have fun

The Kittenqueen is a nice-sounding circuit from distortion into fuzz territory — depending on the transistors being used. Useful in a lot of its settings. Have a lot of fun with it.