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# 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.
Analog white-noise generator. Single **+12 V** supply, breadboard-friendly.
Broadband hiss to a **4 Ω speaker** via a TIP120 driver.
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.
Reference designators and model numbers are consistent across every diagram, the
BOM, and the connection list — the connection list is the authoritative netlist.
## Parts used (model numbers)
## Parts
- **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.
- **U1** = LM358 (dual op-amp, DIP-8). U1B = amp. U1A unused (inputs tied to VREF).
- **Q1** = 2N3904 (NPN). Avalanche noise source.
- **Q3** = TIP120 (NPN Darlington, TO-220). Class-A speaker driver.
## Nets
`+12V` · `GND` · `VREF` (6 V mid-supply) · `NOISE` · `AMP` · `BROWN` · `LFO` ·
`LFO_CV` · `VCA` · `AUDIO_OUT`
`+12V` · `GND` · `VREF` (6 V mid-supply) · `NOISE` · `AMP` · `SPKR`
## 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)
[noise] [amplify] [driver]
Q1 2N3904 → U1B LM358 ×1000 → Q3 TIP120 → 4Ω speaker
NOISE AMP (class A)
```
Legend for the diagrams:
Legend:
```
[Rxx val] resistor ──┤├── film / non-polar cap ● junction (connected)
──+┤├── polarised cap × no-connect
│\ (the + marks the + terminal) ► net continues (label)
────┤−\ op-amp: IN− top, IN+ bottom, OUT right.
│ >── Powered from +12V / GND via LM358 pins 8 / 4 (see Power).
[Rxx val] resistor ──┤├── film / non-polar cap ● junction
──+┤├── polarised cap (+ = + terminal)
│\ × no-connect
────┤−\ op-amp: IN− top, IN+ bottom, OUT right. ► net continues
│ >── Powered from +12V / GND (LM358 pins 8 / 4).
────┤+ /
│/
E transistor box — E / B / C labels sit OUTSIDE the box:
E transistor: E / B / C labels outside the box.
│
┌──┴──┐
B ───┤ Qx │ NPN 2N3904
B ───┤ Qx │ NPN
└──┬──┘
│
C
@@ -50,7 +44,7 @@ Legend for the diagrams:
---
## Power · VREF divider (R2, R3, Cref)
## Power · VREF divider (R2, R3, Cref)
```
+12V
@@ -58,258 +52,139 @@ Legend for the diagrams:
[R2 10k]
│
●───────────────┬────────► VREF (6 V)
│ + Cref 10µF (+ terminal → VREF)
│ + Cref 10µF
[R3 10k] ──┤├──
│ −
│ │
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).
R2/R3 = 20 kΩ across 12 V, midpoint = 6 V. VREF = AC ground (single supply).
---
## Stage 1 — White noise (R1, Q1, C1)
## 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.
Reverse-biased B–E junction of Q1 into avalanche = broadband white noise. R1 limits
current; C1 couples it out.
```
+12V
│
[R1 100k]
│
●──+┤├──────────► NOISE (stage-1 output → Stage 2)
│ C1 10µF
│ (+ terminal → emitter side; − → NOISE)
●──+┤├──────────► NOISE
│ C1 10µF (+ → emitter side; − → NOISE)
E
┌──┴──┐
GND─B─┤ Q1 │ 2N3904
└──┬──┘
│
C
× collector: no connect
The ● node (R1 / Q1 emitter) is the raw noise on a DC pedestal — internal, don't
label it NOISE. `C1` strips the DC; **NOISE = the AC-coupled output after C1.**
C × no connect
```
> 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).
NOISE = the AC-coupled output after C1. The ● node is raw noise on a DC pedestal —
internal, don't label it.
> Avalanche varies part-to-part. If quiet, swap the 2N3904. Needs full +12 V.
---
## Stage 2 — Amplifier ×1000 (U1 unit B, Rin1, Rf1)
## Stage 2 — Amplifier ×1000 (U1B, Rin1, Rf1)
Inverting amp, gain ≈ −Rf1/Rin1 = **×1000**. Output centred on VREF.
Inverting amp, gain ≈ −Rf1/Rin1 = ×1000, centred on VREF. Clips into the rails at
this gain — that's the loud hiss fed to the driver. Too harsh? Drop Rf1 (e.g. 470k).
LM358 DIP-8, notch at top, pin 1 top-left. Amp = **unit B** (pins 5/6/7).
```
┌───[Rf1 1M]────┐
├───[Cf1 22pF]──┤ Cf1 ∥ Rf1 — kills oscillation, limits BW
│ │
NOISE ─[Rin1 1k]───● │
pin 6 │ │\ │
(IN−) ───────┴───┤−\ │
│ >──● pin 7 (OUT) ──► AMP
(IN+) ───────────┤+ /
pin 5 VREF │/ U1 = LM358 (unit B)
┌────∪────┐
┌───── OUT A 1┤● ├8 V+ ──── +12V
└───── IN− A 2┤ ├7 OUT B ──●──────────────► AMP
VREF ──── IN+ A 3┤ LM358 ├6 IN− B ──●
GND ──── V− 4┤ ├5 IN+ B ──── VREF
└─────────┘
Power + decoupling (whole LM358 U1 — wired ONCE, not per unit):
feedback (pin 7 ↔ pin 6): pin 7 ●──[Rf1 1M]──● pin 6 Rf1 ∥ Cf1
pin 7 ●──[Cf1 22pF]─● pin 6 anti-osc, limits BW
pin 8 (V+) ── +12V pin 4 (V−) ── GND
+12V ──+┤├── GND 47µF +12V ──┤├── GND 10nF (or 0.1µF)
(bulk electro, (HF ceramic,
+ to +12V, near U1) right at pin 8)
input: NOISE ─[Rin1 1k]──● pin 6
```
> This stage uses **unit B** (pins 5/6/7) — as built. The integrator (Stage 3) uses
> the **other half, unit A** (pins 1/2/3). Power (8/4) + decoupling are shared by both
> halves — wire them once. To use unit A here instead: IN− = **2**, IN+ = **3**, OUT = **1**.
Unit A unused → park as a follower so it can't oscillate: pin 3 → VREF, pin 2 → pin 1.
Power/decoupling (whole chip, once): pin 8 → +12V, pin 4 → GND. 47µF bulk + 0.1µF at
pin 8.
---
## Stage 3 — Integrator → brown (U1 unit A, Rin2, Cint, Rf2)
## Output driver — TIP120 class-A follower (Q3), 4Ω speaker
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.
AMP is line level; the LM358 can't drive a speaker. Q3 emitter follower supplies the
current. Class A — needs a heatsink.
```
┌──────[Rf2 1M]──────┐
│ │
├───────┤├───────────┤ Cint 100nF (Rf2 ∥ Cint)
│ │
AMP ─[Rin2 10k]───● │
pin 2 │ │\ │
(IN−) ───────┴───┤−\ │
│ >──● pin 1 (OUT) ──► BROWN
(IN+) ───────────┤+ /
pin 3 VREF │/ U1 = LM358 (unit A)
+12V +12V
│ │
[Rb1 10k] C (collector)
│ ┌──┴──┐
●───────●───────────────────B──┤ Q3 │ TIP120
│ │ └──┬──┘
[Rb2 10k] │ │
│ │ E
GND │ │
│ ●──+┤├──► SPKR ─ GND
AMP ─+┤├───┘ │ Cout2 470µF (+ → emitter)
Cc 10µF [Re 22Ω 3W] 4Ω
│
(base node ● = Rb1/Rb2/Cc) GND
```
Darker/deeper: ↑ Cint or Rf2. Lighter (toward pink): ↓ Cint.
The base node ● sits at ~6 V (Rb1/Rb2). Cc lands there and adds the AC — it never
connects to +12V.
- Rb1/Rb2 = 10k/10k → base ~6 V. Cc AC-couples AMP onto the base.
- Emitter ~4.5 V (base − ~1.5 V Darlington drop). Iq = 4.5V/Re ≈ 200 mA.
- Cout2 blocks DC; speaker sees AC only.
- **Heatsink Q3** (~1.5 W idle). Re ≥3 W.
- Cooler/quieter: Re = 47 Ω → Iq ~100 mA.
- Bias sag (hum/distortion): stiffen divider to 4.7k/4.7k.
---
## 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.
```
VCA
│
C
┌──┴──┐
LFO_CV ─[Rb2 100k]─B─┤ Q2 │ 2N3904
└──┬──┘
│
E
│
VREF
BROWN ──[Rs 47k]────────► VCA (Rs feeds VCA; Q2 shunts VCA to VREF)
VCA ───┤+\
│ >──●──+┤├──●──[Rvol 10k]──► AUDIO_OUT
┌─────┤−/ │ Cout │ (wiper)
│ │/ U2B 10µF GND
│ LM358
│ unit B
└─────────● (OUT → IN− = unity buffer; Cout + → buffer out)
```
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.
---
## Output driver — LM386 (U3), for the 4Ω speaker
`AUDIO_OUT` is **line level** — the LM358 **cannot** drive a speaker. Add an **LM386**
power amp for a 4 Ω / 8 Ω speaker. (For bring-up you can feed it from `AMP` or `BROWN`
instead of `AUDIO_OUT`.)
```
+12V
│
●──────┤ pin 6 (V+)
──+┤├── ──┤├──
47µF 0.1µF (→ GND, at the chip)
│ │
GND GND
AUDIO_OUT ─+┤├─[VOL 10k]────► pin 3 (+IN) pin 5 (OUT) ─+┤├──► SPKR ─ GND
Cc 1µF (wiper) 470µF 4Ω
pin 5 ─[10Ω]─┤├─ GND (Zobel)
pin 2 (−IN) ── GND 10nF
pin 4 ── GND
pin 7 (BYPASS) ─+┤├─ GND (10µF)
pins 1 & 8 ── OPEN (gain ×20)
```
LM386 pinout: `1` gain · `2` IN− · `3` IN+ · `4` GND · `5` OUT · `6` V+ · `7` bypass · `8` gain.
**Notes**
- **Output cap must be big (~470µF, ≥16V).** Into 4 Ω, 47µF high-passes at ~850 Hz →
kills the bass (brown noise is all lows). Fat electrolytic, **+ → pin 5**.
- **Gain ×20** (pins 1 & 8 open). Back off with VOL to avoid clipping. A 10µF between
pins 1 & 8 gives ×200 — usually not needed.
- **On +12 V the LM386 runs warm into 4 Ω** (LM386N-1 max = 12 V). OK for testing;
for cooler running feed it from ~9 V.
---
## 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−).
TIP120 pinout (TO-220, face up, pins down): **1 Base · 2 Collector · 3 Emitter**.
---
## 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 |
| Ref | Value | Part | Function |
|-----|-------|------|----------|
| U1 | — | LM358 (DIP-8) | U1B amp (U1A unused) |
| Q1 | — | 2N3904 | avalanche noise source |
| Q3 | — | TIP120 | class-A speaker driver |
| 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 |
| Rb1, Rb2 | 10k | resistor | Q3 base bias (~6 V) |
| Re | 22Ω 3W | resistor | Q3 idle-current set |
| C1 | 10µF | electrolytic | noise coupling |
| Cref | 10µF | electrolytic | VREF bypass |
| Cf1 | 22–100pF | ceramic | amp feedback — **stops oscillation**, limits BW |
| Cint | 100nF | film | integrator (brown shaping) |
| Cout | 10µF | electrolytic | output coupling |
| Ct | 10µF | **non-polar** | LFO timing (bipolar swing) |
| U3 | — | **LM386** | speaker power amp (drives 4Ω/8Ω) |
| Cc | 1µF | film/electro | LM386 input coupling |
| Cout2 | **470µF** ≥16V | electrolytic | speaker output coupling — **big, for bass** |
| — | 10Ω + 10nF | — | LM386 Zobel network (stability) |
| — | 10µF | electro | LM386 pin 7 bypass |
| — | 0.1µF ×3 | ceramic | chip decoupling (one per LM358 + one at LM386 pin 6) |
| — | 47µF ×2 | electrolytic | +12V bulk (main rail + at LM386) |
| Cf1 | 22–100pF | ceramic | amp feedback / anti-oscillation |
| Cc | 10µF | electrolytic | AMP → base coupling |
| Cout2 | 470µF ≥16V | electrolytic | speaker coupling (big, for lows) |
| — | 0.1µF | ceramic | LM358 decoupling |
| — | 47µF | electrolytic | +12V bulk |
**Chip count: 2× LM358 + 1× LM386 + 2× 2N3904.** Single +12 V supply
(feed the LM386 from ~9 V if it runs hot into 4 Ω).
Chip count: 1× LM358 + 1× 2N3904 + 1× TIP120. Q3 needs a heatsink.
---
## 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
(src) : R1.2, Q1.emitter, C1.+ (internal raw-noise node, DC pedestal)
NOISE : C1.−, Rin1.1 (stage-1 output, AC-coupled — after C1)
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)
+12V : R1.1, R2.1, U1.8, Rb1.1, Q3.collector, 47µF+
GND : R3.2, Q1.base, Cref.−, U1.4, Rb2.2, Re.2, 47µF−, 0.1µF
VREF : R2.2, R3.1, Cref.+, U1B.IN+(5), U1A.IN+(3)
U1A.OUT(1) = U1A.IN−(2) (spare amp parked as follower)
(src) : R1.2, Q1.emitter, C1.+ (internal raw-noise node)
NOISE : C1.−, Rin1.1 (after C1)
AMP : U1B.OUT(7), Rf1, Cc.1 (Rin1.2, Rf1, U1B.IN−(6) = summing)
base : Cc.2, Rb1.2, Rb2.1, Q3.base (~6 V bias)
SPKR : Q3.emitter, Re.1, Cout2.+ ; Cout2.− → speaker → GND
Q1 : collector = no-connect
```
@@ -317,22 +192,16 @@ 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.
1. **VREF** — confirm ~6.0 V.
2. **Noise (R1, Q1)** — scope Q1 node → hiss (~mV). None? swap 2N3904 or raise supply to 12–15 V.
3. **Amp (U1B)** — scope AMP → loud hiss (~volts).
4. **Driver (Q3)** — feed AMP through Cc. Speaker hisses. Q3 warm, not hot; too hot → raise Re.
## 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) |
| Less harsh | ↓ Rf1 |
| Cooler driver | ↑ Re |
| More headroom | ↓ Re (hotter — bigger heatsink) |