# ambium Analog **brown-noise generator** with a slow amplitude swell (LFO). All-analog, breadboard-friendly, single **+12 V** supply. Deep, drifting rumble that slowly breathes in and out over ~20 s. Each stage is drawn as ASCII below. **Reference designators and model numbers are consistent across every diagram, the BOM, and the connection list** — that list is the authoritative netlist. ## Parts used (model numbers) - **U1, U2** = **LM358** (dual op-amp, DIP-8). U1 = amp + integrator; U2 = LFO + buffer. (LM258P is the same part — fine.) - **Q1, Q2** = **2N3904** (NPN). Q1 = avalanche noise source; Q2 = shunt VCA. ## Nets `+12V` · `GND` · `VREF` (6 V mid-supply) · `NOISE` · `AMP` · `BROWN` · `LFO` · `LFO_CV` · `VCA` · `AUDIO_OUT` ## Signal chain ``` [noise] [amplify] [integrate] [VCA] [buffer] Q1 2N3904 → U1A LM358 ×1000 → U1B LM358 −6dB/oct → Q2 2N3904 → U2B LM358 → AUDIO_OUT NOISE AMP BROWN VCA (line out) ▲ swell U2A LM358 LFO (~0.05 Hz) ``` Legend for the diagrams: ``` [Rxx val] resistor ──┤├── capacitor ● junction (connected) │\ × no-connect ────┤−\ op-amp: IN− top, IN+ bottom, ► net continues (same label) │ >── OUT right. Powered from +12V/GND ────┤+ / via LM358 pins 8/4 (see Power). │/ (C) │ (B)┤< NPN 2N3904 (C=collector, B=base, E=emitter) │ (E) ``` --- ## Power · VREF divider (R2, R3, Cref) ``` +12V │ [R2 10k] │ ●───────────────┬────────► VREF (6 V) │ │ [R3 10k] ──┤├── Cref 10µF │ │ GND GND ``` `R2`/`R3` = 20 kΩ across 12 V → 0.6 mA, midpoint = **6 V**. `Cref` holds VREF steady. VREF is the AC ground every stage rides on (single supply, no negative rail). --- ## Stage 1 — White noise (R1, Q1, C1) Reverse-biased base–emitter junction of `Q1` driven into avalanche = broadband white noise. `R1` limits current; `C1` couples the noise out. ``` +12V │ [R1 100k] │ ●──────┤├──────► NOISE │ C1 10µF (C) × (collector: no connect) │ (B)─┤< Q1 2N3904 │ (E) │ GND ← base to GND; avalanche appears across B-E, out at the R1/collector node ``` > Avalanche quality varies part-to-part. Try one 2N3904; if quiet, swap for another. > Needs the full +12 V (9 V is often too low to avalanche). --- ## Stage 2 — Amplifier ×1000 (U1A, Rin1, Rf1) Inverting amp, gain ≈ −Rf1/Rin1 = **×1000**. Output centred on VREF. ``` ┌──────[Rf1 1M]──────┐ │ │ NOISE ──[Rin1 1k]──● │ │ │\ │ └───┤−\ │ │ >──●───────┴────► AMP VREF ───────┤+ / U1A │/ (LM358, unit A) ``` --- ## Stage 3 — Integrator → brown (U1B, Rin2, Cint, Rf2) Leaky integrator = **−6 dB/octave** → turns white into brown. `Rf2` bounds DC so the output can't rail. Corner ≈ 1/(2π·Rf2·Cint) ≈ 1.6 Hz. ``` ┌──────[Rf2 1M]──────┐ │ │ ├───────┤├───────────┤ Cint 100nF (Rf2 ∥ Cint) │ │ AMP ──[Rin2 10k]──● │ │ │\ │ └───┤−\ │ │ >──●───────┴────► BROWN VREF ───────┤+ / U1B │/ (LM358, unit B) ``` Darker/deeper: ↑ Cint or Rf2. Lighter (toward pink): ↓ Cint. --- ## Stage 4 — LFO (U2A, Rt, Ct, Ra, Rh) Single-op-amp relaxation oscillator. Period ≈ 2.2·Rt·Ct ≈ **~22 s**. The control voltage is the ramp on `Ct` (net `LFO_CV`) — it drives the VCA in Stage 5. ``` ┌──────────[Rt 1M]──────────┐ │ │ ●──────┤├──── VREF │ Ct 10µF (non-polar) │ Ct │ │ │\ │ LFO_CV ●──────┤−\ │ │ │ >──●──────────────┴──► LFO (and to Rh) ┌──────┤+ / │ U2A │ │/ │ (LM358, unit A) ●──[Ra 100k]──┤ │ └── VREF [Rh 100k] │ └───────────────────────────────────► LFO (hysteresis feedback) ``` `Ra`/`Rh` set the hysteresis (both 100k). `LFO_CV` ramps ~3.5–8.5 V. > `Ct` sees a bipolar swing about VREF — use a **non-polar** 10 µF (film or bipolar > electrolytic), not a standard polarised cap. --- ## Stage 5 — VCA + buffer + output (Rs, Q2, Rb2, U2B, Cout, Rvol) `Q2` shunts the brown-noise signal to VREF (AC ground) by an amount set by `LFO_CV` → amplitude swells and fades. `U2B` buffers; `Cout` blocks DC; `Rvol` sets level. ``` (C) │ BROWN ──[Rs 47k]──●───────┤< Q2 2N3904 │ │ VCA (E) │ │ │ VREF │ LFO_CV ──[Rb2 100k]──(B) ← control voltage into Q2 base │ │ │\ └───┤+\ │ >──●──────┤├──────●──[Rvol 10k]──► AUDIO_OUT ┌───┤−/ U2B Cout (wiper) │ │/ (LM358 10µF │ │ unit B) GND └──────────● (buffer: OUT tied back to IN−) ``` When `LFO_CV` is low → Q2 off → signal passes (loud). High → Q2 conducts → shunts to VREF (quiet). ~20 s swell. Soften the swell: 1 µF from `LFO_CV` to VREF. --- ## LM358 power + decoupling Each LM358 (U1, U2) is powered once via its package pins — **not** per op-amp unit: ``` +12V ──┬── U1 pin 8 (V+) GND ──┬── U1 pin 4 (V−) │ │ └── U2 pin 8 (V+) └── U2 pin 4 (V−) Decoupling: 0.1µF from +12V to GND at EACH chip, plus one 47µF bulk on the +12V rail. ``` LM358 unit A = pins 1(OUT) 2(IN−) 3(IN+); unit B = 7(OUT) 6(IN−) 5(IN+); power 8(V+) 4(V−). --- ## Bill of materials | Ref | Value | Part / model | Function | |-----|-------|--------------|----------| | U1 | — | **LM358** (DIP-8) | U1A amp, U1B integrator | | U2 | — | **LM358** (DIP-8) | U2A LFO, U2B buffer | | Q1 | — | **2N3904** | avalanche white-noise source | | Q2 | — | **2N3904** | shunt VCA | | R1 | 100k | resistor | avalanche current limit | | R2, R3 | 10k | resistor | VREF divider | | Rin1 | 1k | resistor | amp input | | Rf1 | 1M | resistor | amp feedback (×1000) | | Rin2 | 10k | resistor | integrator input | | Rf2 | 1M | resistor | integrator leak / brown corner | | Rs | 47k | resistor | VCA series | | Rb2 | 100k | resistor | LFO_CV → Q2 base | | Rt | 1M | resistor | LFO timing | | Ra, Rh | 100k | resistor | LFO hysteresis | | Rvol | 10k | potentiometer | output level | | C1 | 10µF | electrolytic | noise coupling | | Cref | 10µF | electrolytic | VREF bypass | | Cint | 100nF | film | integrator (brown shaping) | | Cout | 10µF | electrolytic | output coupling | | Ct | 10µF | **non-polar** | LFO timing (bipolar swing) | | — | 0.1µF ×2 | ceramic | chip decoupling | | — | 47µF | electrolytic | +12V bulk | **Chip count: 2× LM358 + 2× 2N3904.** Single +12 V supply. --- ## Connection list (authoritative netlist) ``` +12V : R1.1, R2.1, U1.8, U2.8, (47µF+) GND : R3.2, Q1.base, Cref.−, U1.4, U2.4, Rvol.3, (47µF−), (0.1µF ×2) VREF : R2.2, R3.1, Cref.+, U1A.IN+(3), U1B.IN+(5), Ct(VREF end), Ra.1, Q2.emitter NOISE : R1.2 / Q1.emitter-node, C1.+ (C1.− → Rin1.1) AMP : U1A.OUT(1), Rf1, Rin2.1 (Rin1.2, Rf1, U1A.IN−(2) = summing node) BROWN : U1B.OUT(7), Cint, Rf2, Rs.1 (Rin2.2, Cint, Rf2, U1B.IN−(6) = summing) LFO : U2A.OUT(1), Rt, Rh LFO_CV : Rt, Ct(CV end), U2A.IN−(2), Rb2 (ramp that swells the VCA) VCA : Rs.2, Q2.collector, U2B.IN+(5) (U2B.OUT(7) = U2B.IN−(6) = Cout.+ → buffer) AUDIO_OUT : Rvol.wiper(2) (Cout.− → Rvol.1; Rvol.3 → GND) Q1 : collector = no-connect ``` --- ## Build & test order Build one stage at a time — verify before adding the next. 1. **VREF** — R2/R3/Cref up. Confirm ~6.0 V. 2. **Noise (R1 + Q1)** — scope Q1 node → hiss (~mV). No noise? swap the 2N3904 or nudge supply to 12–15 V. 3. **Amp (U1A)** — scope AMP → loud hiss (~volts). 4. **Integrator (U1B)** — BROWN sounds darker/deeper than AMP. That's brown noise. 5. **LFO (U2A)** — scope LFO_CV → slow ramp, ~20 s. 6. **VCA + buffer (Q2, U2B)** — full chain: noise swells and fades on the LFO cycle. ## Tuning | Want | Change | |------|--------| | Deeper/darker | ↑ Cint or Rf2 | | Lighter (toward pink) | ↓ Cint | | Slower swell | ↑ Rt or Ct | | Faster swell | ↓ Rt or Ct | | Softer swell onset | 1µF from LFO_CV to VREF | | Louder | ↑ Rf1 (watch clipping) |