339 lines
13 KiB
Markdown
339 lines
13 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 ──┤├── film / non-polar cap ● junction (connected)
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──+┤├── polarised cap × no-connect
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│\ (the + marks the + terminal) ► net continues (label)
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────┤−\ op-amp: IN− top, IN+ bottom, OUT right.
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│ >── Powered from +12V / GND via LM358 pins 8 / 4 (see Power).
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────┤+ /
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│/
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E transistor box — E / B / C labels sit OUTSIDE the box:
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│
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┌──┴──┐
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B ───┤ Qx │ NPN 2N3904
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└──┬──┘
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│
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C
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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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│ + Cref 10µF (+ terminal → VREF)
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[R3 10k] ──┤├──
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│ −
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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 (stage-1 output → Stage 2)
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│ C1 10µF
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│ (+ terminal → emitter side; − → NOISE)
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E
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┌──┴──┐
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GND─B─┤ Q1 │ 2N3904
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└──┬──┘
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│
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C
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× collector: no connect
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The ● node (R1 / Q1 emitter) is the raw noise on a DC pedestal — internal, don't
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label it NOISE. `C1` strips the DC; **NOISE = the AC-coupled output after C1.**
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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 (U1 unit B, 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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├───[Cf1 22pF]──┤ Cf1 ∥ Rf1 — kills oscillation, limits BW
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│ │
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NOISE ─[Rin1 1k]───● │
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pin 6 │ │\ │
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(IN−) ───────┴───┤−\ │
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│ >──● pin 7 (OUT) ──► AMP
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(IN+) ───────────┤+ /
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pin 5 VREF │/ U1 = LM358 (unit B)
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Power + decoupling (whole LM358 U1 — wired ONCE, not per unit):
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pin 8 (V+) ── +12V pin 4 (V−) ── GND
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+12V ──+┤├── GND 47µF +12V ──┤├── GND 10nF (or 0.1µF)
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(bulk electro, (HF ceramic,
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+ to +12V, near U1) right at pin 8)
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```
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> This stage uses **unit B** (pins 5/6/7) — as built. The integrator (Stage 3) uses
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> the **other half, unit A** (pins 1/2/3). Power (8/4) + decoupling are shared by both
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> halves — wire them once. To use unit A here instead: IN− = **2**, IN+ = **3**, OUT = **1**.
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---
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## Stage 3 — Integrator → brown (U1 unit A, 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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pin 2 │ │\ │
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(IN−) ───────┴───┤−\ │
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│ >──● pin 1 (OUT) ──► BROWN
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(IN+) ───────────┤+ /
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pin 3 VREF │/ U1 = LM358 (unit A)
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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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VCA
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│
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C
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┌──┴──┐
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LFO_CV ─[Rb2 100k]─B─┤ Q2 │ 2N3904
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└──┬──┘
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│
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E
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│
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VREF
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BROWN ──[Rs 47k]────────► VCA (Rs feeds VCA; Q2 shunts VCA to VREF)
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VCA ───┤+\
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│ >──●──+┤├──●──[Rvol 10k]──► AUDIO_OUT
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┌─────┤−/ │ Cout │ (wiper)
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│ │/ U2B 10µF GND
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│ LM358
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│ unit B
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└─────────● (OUT → IN− = unity buffer; Cout + → buffer out)
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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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## Output driver — LM386 (U3), for the 4Ω speaker
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`AUDIO_OUT` is **line level** — the LM358 **cannot** drive a speaker. Add an **LM386**
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power amp for a 4 Ω / 8 Ω speaker. (For bring-up you can feed it from `AMP` or `BROWN`
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instead of `AUDIO_OUT`.)
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```
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+12V
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│
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●──────┤ pin 6 (V+)
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──+┤├── ──┤├──
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47µF 0.1µF (→ GND, at the chip)
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│ │
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GND GND
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AUDIO_OUT ─+┤├─[VOL 10k]────► pin 3 (+IN) pin 5 (OUT) ─+┤├──► SPKR ─ GND
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Cc 1µF (wiper) 470µF 4Ω
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pin 5 ─[10Ω]─┤├─ GND (Zobel)
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pin 2 (−IN) ── GND 10nF
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pin 4 ── GND
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pin 7 (BYPASS) ─+┤├─ GND (10µF)
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pins 1 & 8 ── OPEN (gain ×20)
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```
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LM386 pinout: `1` gain · `2` IN− · `3` IN+ · `4` GND · `5` OUT · `6` V+ · `7` bypass · `8` gain.
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**Notes**
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- **Output cap must be big (~470µF, ≥16V).** Into 4 Ω, 47µF high-passes at ~850 Hz →
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kills the bass (brown noise is all lows). Fat electrolytic, **+ → pin 5**.
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- **Gain ×20** (pins 1 & 8 open). Back off with VOL to avoid clipping. A 10µF between
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pins 1 & 8 gives ×200 — usually not needed.
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- **On +12 V the LM386 runs warm into 4 Ω** (LM386N-1 max = 12 V). OK for testing;
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for cooler running feed it from ~9 V.
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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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| Cf1 | 22–100pF | ceramic | amp feedback — **stops oscillation**, limits BW |
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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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| U3 | — | **LM386** | speaker power amp (drives 4Ω/8Ω) |
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| Cc | 1µF | film/electro | LM386 input coupling |
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| Cout2 | **470µF** ≥16V | electrolytic | speaker output coupling — **big, for bass** |
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| — | 10Ω + 10nF | — | LM386 Zobel network (stability) |
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| — | 10µF | electro | LM386 pin 7 bypass |
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| — | 0.1µF ×3 | ceramic | chip decoupling (one per LM358 + one at LM386 pin 6) |
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| — | 47µF ×2 | electrolytic | +12V bulk (main rail + at LM386) |
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**Chip count: 2× LM358 + 1× LM386 + 2× 2N3904.** Single +12 V supply
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(feed the LM386 from ~9 V if it runs hot into 4 Ω).
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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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(src) : R1.2, Q1.emitter, C1.+ (internal raw-noise node, DC pedestal)
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NOISE : C1.−, Rin1.1 (stage-1 output, AC-coupled — after C1)
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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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