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