223 lines
8.5 KiB
Markdown
223 lines
8.5 KiB
Markdown
# ambium
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Analog brown-noise generator. Single **+12 V** supply, breadboard-friendly.
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Deep filtered rumble to a **4 Ω speaker** via a TIP120 driver.
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Reference designators and model numbers are consistent across every diagram, the
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BOM, and the connection list — the connection list is the authoritative netlist.
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## Parts
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- **U1** = LM358 (dual op-amp, DIP-8). U1B = amp + brown shaping. U1A unused (parked).
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- **Q1** = 2N3904 (NPN). Avalanche noise source.
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- **Q3** = TIP120 (NPN Darlington, TO-220). Class-A speaker driver.
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## Nets
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`+12V` · `GND` · `VREF` (6 V mid-supply) · `NOISE` · `AMP` · `SPKR`
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## Signal chain
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```
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[noise] [amp + brown] [driver]
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Q1 2N3904 → U1B LM358 −6dB/oct → Q3 TIP120 → 4Ω speaker
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NOISE AMP (class A)
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```
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Legend:
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```
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[Rxx val] resistor ──┤├── film / non-polar cap ● junction
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──+┤├── polarised cap (+ = + terminal)
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│\ × no-connect
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────┤−\ op-amp: IN− top, IN+ bottom, OUT right. ► net continues
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│ >── Powered from +12V / GND (LM358 pins 8 / 4).
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────┤+ /
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│/
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E transistor: E / B / C labels outside the box.
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│
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┌──┴──┐
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B ───┤ Qx │ NPN
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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
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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, midpoint = 6 V. VREF = AC ground (single supply).
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---
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## Stage 1 — White noise (R1, Q1, C1)
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Reverse-biased B–E junction of Q1 into avalanche = broadband white noise. R1 limits
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current; C1 couples it 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 (+ → 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 × no connect
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```
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NOISE = the AC-coupled output after C1. The ● node is raw noise on a DC pedestal —
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internal, don't label it.
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> Avalanche varies part-to-part. If quiet, swap the 2N3904. Needs full +12 V.
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---
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## Stage 2 — Amplifier + brown shaping (U1B, Rin1, Rf1, Cf1)
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Single inverting amp, low-frequency gain −Rf1/Rin1 = ×1000, centred on VREF. A feedback
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cap Cf1 across Rf1 makes it a leaky integrator: flat gain below the corner, then −6 dB/oct
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above it. That −6 dB/oct slope turns white noise into **brown**. One stage does gain and
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browning together — no separate integrator needed.
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- corner fc = 1/(2π·Rf1·Cf1) ≈ **19 Hz** with Rf1 1M, Cf1 8.2nF.
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- below fc: flat ×1000. above fc: −6 dB/oct, reaching unity (×1) at ~20 kHz.
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- so the whole audible band (20 Hz–20 kHz) rides the brown slope; peak gain ×1000 at the
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bottom, rolling off inaudible ultrasonics at the top for free.
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**Why not a flat ×1000 stage?** LM358 GBW = 1 MHz → a flat ×1000 stage has only 1 MHz/1000
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≈ **1 kHz** bandwidth, collapsing the band (measured ~27 mV pp at AMP). Here Cf1 makes the
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demanded gain *fall* with frequency, so the op-amp GBW is never the limit — the RC feedback
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does the shaping, not the op-amp rolloff.
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LM358 DIP-8, notch at top, pin 1 top-left. Amp = **unit B** (pins 5/6/7).
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```
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┌─────∪────┐
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OUT A 1 ─┤● ├ 8 V+ ──── +12V
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IN− A 2 ─┤ ├ 7 OUT B ──●──────────────► AMP
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VREF ─ IN+ A 3 ─┤ LM358 ├ 6 IN− B ──●
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GND ─ V− 4 ─┤ ├ 5 IN+ B ──── VREF
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└──────────┘
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feedback (pin 7 ↔ pin 6): pin 7 ●──[Rf1 1M]────● pin 6 Rf1 ∥ Cf1
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pin 7 ●──[Cf1 8.2nF]──● pin 6 brown slope, corner ~19 Hz
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input: NOISE ─[Rin1 1k]──● pin 6
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```
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DC handling: C1 blocks DC into Rin1, so the op-amp's own offset sees unity gain — output
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sits at VREF (6 V), no railing.
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Unit A unused → park as a follower so it can't oscillate: pin 3 → VREF, pin 2 → pin 1.
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Power/decoupling (whole chip, once): pin 8 → +12V, pin 4 → GND. 47µF bulk + 0.1µF at
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pin 8.
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---
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## Output driver — TIP120 class-A follower (Q3), 4Ω speaker
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AMP is line level; the LM358 can't drive a speaker. Q3 emitter follower supplies the
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current. Class A — needs a heatsink.
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```
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+12V +12V
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│ │
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[Rb1 10k] C (collector)
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│ ┌──┴──┐
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●───────●───────────────────B──┤ Q3 │ TIP120
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│ │ └──┬──┘
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[Rb2 10k] │ │
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│ │ E
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GND │ │
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│ ●──+┤├──► SPKR ─ GND
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AMP ─+┤├───┘ │ Cout2 470µF (+ → emitter)
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Cc 10µF [Re 22Ω 3W] 4Ω
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│
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(base node ● = Rb1/Rb2/Cc) GND
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```
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The base node ● sits at ~6 V (Rb1/Rb2). Cc lands there and adds the AC — it never
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connects to +12V.
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- Rb1/Rb2 = 10k/10k → base ~6 V. Cc AC-couples AMP onto the base.
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- Emitter ~4.5 V (base − ~1.5 V Darlington drop). Iq = 4.5V/Re ≈ 200 mA.
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- Cout2 blocks DC; speaker sees AC only.
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- **Heatsink Q3** (~1.5 W idle). Re ≥3 W.
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- Cooler/quieter: Re = 47 Ω → Iq ~100 mA.
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- Bias sag (hum/distortion): stiffen divider to 4.7k/4.7k.
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TIP120 pinout (TO-220, face up, pins down): **1 Base · 2 Collector · 3 Emitter**.
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---
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## Bill of materials
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| Ref | Value | Part | Function |
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|-----|-------|------|----------|
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| U1 | — | LM358 (DIP-8) | U1B amp (U1A unused) |
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| Q1 | — | 2N3904 | avalanche noise source |
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| Q3 | — | TIP120 | class-A speaker driver |
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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 (low-freq gain ×1000) |
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| Rb1, Rb2 | 10k | resistor | Q3 base bias (~6 V) |
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| Re | 22Ω 3W | resistor | Q3 idle-current set |
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| C1 | 10µF | electrolytic | noise coupling |
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| Cref | 10µF | electrolytic | VREF bypass |
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| Cf1 | 8.2nF | film / ceramic | feedback / brown shaping (−6dB/oct, corner ~19 Hz) |
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| Cc | 10µF | electrolytic | AMP → base coupling |
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| Cout2 | 470µF ≥16V | electrolytic | speaker coupling (big, for lows) |
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| — | 0.1µF | ceramic | LM358 decoupling |
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| — | 47µF | electrolytic | +12V bulk |
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Chip count: 1× LM358 + 1× 2N3904 + 1× TIP120. Q3 needs a heatsink.
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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, Rb1.1, Q3.collector, 47µF+
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GND : R3.2, Q1.base, Cref.−, U1.4, Rb2.2, Re.2, 47µF−, 0.1µF
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VREF : R2.2, R3.1, Cref.+, U1B.IN+(5), U1A.IN+(3)
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U1A.OUT(1) = U1A.IN−(2) (spare amp parked as follower)
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(src) : R1.2, Q1.emitter, C1.+ (internal raw-noise node)
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NOISE : C1.−, Rin1.1 (after C1)
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AMP : U1B.OUT(7), Rf1, Cf1, Cc.1 (Rin1.2, Rf1, Cf1, U1B.IN−(6) = summing)
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base : Cc.2, Rb1.2, Rb2.1, Q3.base (~6 V bias)
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SPKR : Q3.emitter, Re.1, Cout2.+ ; Cout2.− → speaker → 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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1. **VREF** — confirm ~6.0 V.
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2. **Noise (R1, Q1)** — scope Q1 node → hiss (~mV). None? swap 2N3904 or raise supply to 12–15 V.
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3. **Amp (U1B)** — scope AMP → deep rumble (~volts), darker than the raw Q1 hiss (that's the brown slope).
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4. **Driver (Q3)** — feed AMP through Cc. Speaker hisses. Q3 warm, not hot; too hot → raise Re.
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## Tuning
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| Want | Change |
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|------|--------|
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| Louder | ↑ Rf1 (raises low-freq gain; watch clipping) |
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| Darker / deeper | ↑ Cf1 (lowers corner, more brown) |
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| Brighter (toward white) | ↓ Cf1 (raises corner) |
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| Cooler driver | ↑ Re |
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| More headroom | ↓ Re (hotter — bigger heatsink) |
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