235 lines
9.2 KiB
Markdown
235 lines
9.2 KiB
Markdown
# ambium
|
||
|
||
Analog brown-noise generator. Single **+12 V** supply, breadboard-friendly.
|
||
Deep filtered rumble to a **4 Ω speaker** via a cool-running **Class-AB push-pull** output.
|
||
|
||
Reference designators and model numbers are consistent across every diagram, the
|
||
BOM, and the connection list — the connection list is the authoritative netlist.
|
||
|
||
## Parts
|
||
|
||
- **U1** = LM358 (dual op-amp, DIP-8). U1B = amp + brown shaping. U1A = output driver.
|
||
- **Q1** = 2N3904 (NPN). Avalanche noise source.
|
||
- **Q2** = PN2222 (NPN). Push-pull top half (sources +).
|
||
- **Q3** = PN2907 (PNP). Push-pull bottom half (sinks −).
|
||
|
||
## Nets
|
||
|
||
`+12V` · `GND` · `VREF` (6 V mid-supply) · `NOISE` · `AMP` · `SPKR`
|
||
|
||
## Signal chain
|
||
|
||
```
|
||
[noise] [amp + brown] [push-pull driver]
|
||
Q1 2N3904 → U1B LM358 −6dB/oct → U1A + Q2/Q3 → 4Ω speaker
|
||
NOISE AMP OUT (Class AB, cool)
|
||
```
|
||
|
||
---
|
||
|
||
## Power · VREF divider (R2, R3, Cref)
|
||
|
||
```
|
||
+12V
|
||
│
|
||
[R2 10k]
|
||
│
|
||
●───────────────┬────────► VREF (6 V)
|
||
│ + Cref 10µF
|
||
[R3 10k] ──┤├──
|
||
│ −
|
||
│ │
|
||
GND GND
|
||
```
|
||
R2/R3 = 20 kΩ across 12 V, midpoint = 6 V. VREF = AC ground (single supply).
|
||
|
||
---
|
||
|
||
## Stage 1 — White noise (R1, Q1, C1)
|
||
|
||
Reverse-biased B–E junction of Q1 into avalanche = broadband white noise. R1 limits
|
||
current; C1 couples it out.
|
||
|
||
```
|
||
+12V
|
||
│
|
||
[R1 100k]
|
||
│
|
||
●──+┤├──────────► NOISE
|
||
│ C1 10µF (+ → emitter side; − → NOISE)
|
||
E
|
||
┌──┴──┐
|
||
GND─B─┤ Q1 │ 2N3904
|
||
└──┬──┘
|
||
│
|
||
C × no connect
|
||
```
|
||
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 + brown shaping (U1B, Rin1, Rf1, Cf1)
|
||
|
||
Single inverting amp, low-frequency gain −Rf1/Rin1 = ×1000, centred on VREF. A feedback
|
||
cap Cf1 across Rf1 makes it a leaky integrator: flat gain below the corner, then −6 dB/oct
|
||
above it. That −6 dB/oct slope turns white noise into **brown**. One stage does gain and
|
||
browning together — no separate integrator needed.
|
||
|
||
- corner fc = 1/(2π·Rf1·Cf1) ≈ **19 Hz** with Rf1 1M, Cf1 8.2nF.
|
||
- below fc: flat ×1000. above fc: −6 dB/oct, reaching unity (×1) at ~20 kHz.
|
||
- so the whole audible band (20 Hz–20 kHz) rides the brown slope; peak gain ×1000 at the
|
||
bottom, rolling off inaudible ultrasonics at the top for free.
|
||
|
||
**Why not a flat ×1000 stage?** LM358 GBW = 1 MHz → a flat ×1000 stage has only 1 MHz/1000
|
||
≈ **1 kHz** bandwidth, collapsing the band (measured ~27 mV pp at AMP). Here Cf1 makes the
|
||
demanded gain *fall* with frequency, so the op-amp GBW is never the limit — the RC feedback
|
||
does the shaping, not the op-amp rolloff.
|
||
|
||
LM358 DIP-8, notch at top, pin 1 top-left. Amp = **unit B** (pins 5/6/7).
|
||
|
||
```
|
||
┌─────∪────┐
|
||
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
|
||
└──────────┘
|
||
|
||
feedback (pin 7 ↔ pin 6): pin 7 ●──[Rf1 1M]────● pin 6 Rf1 ∥ Cf1
|
||
pin 7 ●──[Cf1 8.2nF]──● pin 6 brown slope, corner ~19 Hz
|
||
input: NOISE ─[Rin1 1k]──● pin 6
|
||
```
|
||
DC handling: C1 blocks DC into Rin1, so the op-amp's own offset sees unity gain — output
|
||
sits at VREF (6 V), no railing.
|
||
|
||
Unit A (pins 1/2/3) = the push-pull output driver — see next section.
|
||
Power/decoupling (whole chip, once): pin 8 → +12V, pin 4 → GND. 47µF bulk + 0.1µF at
|
||
pin 8.
|
||
|
||
---
|
||
|
||
## Output driver — Class-AB push-pull (U1A + Q2/Q3), 4Ω speaker
|
||
|
||
AMP is line level; the LM358 can't drive a speaker alone. Complementary emitter-
|
||
followers **inside the U1A loop**: Q2 (NPN) pushes the positive half, Q3 (PNP) pulls
|
||
the negative half. Both halves are actively driven, so there's **no idle resistor and
|
||
near-zero quiescent current → it runs cool.** U1A drives both bases; global feedback
|
||
from OUT hides crossover distortion (no bias diodes needed).
|
||
|
||
Driver = LM358 **unit A** (pins 1/2/3), same chip as the amp.
|
||
|
||
```
|
||
┌─────∪────┐
|
||
bases ─ OUT A 1 ─┤ ├ 8 V+ ──── +12V
|
||
OUT ─ IN− A 2 ─┤ LM358 ├ 7 (OUT B → AMP, Stage 2)
|
||
AMP ─ IN+ A 3 ─┤ ├ 6
|
||
V− 4 ─┤ ├ 5
|
||
└──────────┘
|
||
```
|
||
|
||
Push-pull output stage (totem pole):
|
||
```
|
||
+12V
|
||
│
|
||
C
|
||
┌───┴───┐
|
||
bases ──B──────┤ Q2 │ PN2222 (NPN — sources +half)
|
||
└───┬───┘
|
||
E
|
||
[Re1 10Ω]
|
||
│
|
||
●──────────► OUT ──+┤├──► SPKR ─ GND
|
||
│ Cout 470µF 4Ω
|
||
[Re2 10Ω] (+ → OUT)
|
||
E
|
||
┌───┴───┐
|
||
bases ──B──────┤ Q3 │ PN2907 (PNP — sinks −half)
|
||
└───┬───┘
|
||
C
|
||
│
|
||
GND
|
||
```
|
||
|
||
Connections:
|
||
```
|
||
input: AMP ─────────────● pin 3 (IN+ A)
|
||
drive: pin 1 (OUT A) ───● bases → Q2.base + Q3.base
|
||
feedback: OUT ─────────────● pin 2 (IN− A)
|
||
Q2: C → +12V B → bases E → Re1 → OUT
|
||
Q3: C → GND B → bases E → Re2 → OUT
|
||
OUT node = Re1 ● Re2 ● pin 2 (fb) ● Cout.+ ; Cout.− → speaker → GND
|
||
```
|
||
- Idle ≈ 0 → **cool, no heatsink.** Re1/Re2 = **10 Ω ¼ W** (4.7–10 Ω ok; carry only AC — not hot).
|
||
- OUT sits at ~6 V DC (follows AMP); **Cout 470 µF** blocks it, speaker sees AC only.
|
||
|
||
TO-92 pinout (flat face toward you, leads down): **PN2222 = E-B-C**, **PN2907 = E-B-C**
|
||
(confirm against your batch's datasheet).
|
||
|
||
- PN2222/PN2907 cap ~600 mA → ~1 W into 4 Ω before current-limiting. Plenty for the
|
||
rumble, and cool. Want more power → TIP120+TIP125 pair, or an amp chip.
|
||
- Crossover buzz at low level? Split the bases and add **2× 1N4148** between them for
|
||
bias. Usually unneeded — feedback handles it for a noise source.
|
||
|
||
---
|
||
|
||
## Bill of materials
|
||
|
||
| Ref | Value | Part | Function |
|
||
|-----|-------|------|----------|
|
||
| U1 | — | LM358 (DIP-8) | U1B amp+brown, U1A output driver |
|
||
| Q1 | — | 2N3904 | avalanche noise source |
|
||
| Q2 | — | PN2222 (NPN) | push-pull top (source) |
|
||
| Q3 | — | PN2907 (PNP) | push-pull bottom (sink) |
|
||
| R1 | 100k | resistor | avalanche current limit |
|
||
| R2, R3 | 10k | resistor | VREF divider |
|
||
| Rin1 | 1k | resistor | amp input |
|
||
| Rf1 | 1M | resistor | amp feedback (low-freq gain ×1000) |
|
||
| Re1, Re2 | 10Ω ¼W | resistor | push-pull emitter degeneration (4.7–10Ω ok) |
|
||
| C1 | 10µF | electrolytic | noise coupling |
|
||
| Cref | 10µF | electrolytic | VREF bypass |
|
||
| Cf1 | 8.2nF | film / ceramic | feedback / brown shaping (−6dB/oct, corner ~19 Hz) |
|
||
| Cout | 470µF ≥16V | electrolytic | speaker coupling (big, for lows) |
|
||
| — | 0.1µF | ceramic | LM358 decoupling |
|
||
| — | 47µF | electrolytic | +12V bulk |
|
||
|
||
Chip count: 1× LM358 + 1× 2N3904 + PN2222/PN2907 pair. **No heatsink needed** (Class AB).
|
||
|
||
---
|
||
|
||
## Connection list (authoritative netlist)
|
||
|
||
```
|
||
+12V : R1.1, R2.1, U1.8, Q2.collector, 47µF+
|
||
GND : R3.2, Q1.base, Cref.−, U1.4, Q3.collector, 47µF−, 0.1µF
|
||
VREF : R2.2, R3.1, Cref.+, U1B.IN+(5)
|
||
(src) : R1.2, Q1.emitter, C1.+ (internal raw-noise node)
|
||
NOISE : C1.−, Rin1.1 (after C1)
|
||
AMP : U1B.OUT(7), Rf1, Cf1, U1A.IN+(3) (Rin1.2, Rf1, Cf1, U1B.IN−(6) = summing)
|
||
bases : U1A.OUT(1), Q2.base, Q3.base (driver output → both bases)
|
||
OUT : Q2.emitter→Re1 ; Q3.emitter→Re2 ; Re1.2 = Re2.2 = OUT node
|
||
OUT → U1A.IN−(2) (feedback) ; OUT → Cout.+ ; Cout.− → speaker → GND
|
||
Q1 : collector = no-connect
|
||
```
|
||
|
||
---
|
||
|
||
## Build & test order
|
||
|
||
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 → deep rumble (~volts), darker than the raw Q1 hiss (that's the brown slope).
|
||
4. **Driver (Q2/Q3)** — wire push-pull + feedback. Speaker rumbles. Transistors stay **cool** (near-zero idle). OUT DC ~6 V.
|
||
|
||
## Tuning
|
||
|
||
| Want | Change |
|
||
|------|--------|
|
||
| Louder | ↑ Rf1 (raises low-freq gain; watch clipping) |
|
||
| Darker / deeper | ↑ Cf1 (lowers corner, more brown) |
|
||
| Brighter (toward white) | ↓ Cf1 (raises corner) |
|
||
| Kill crossover buzz | add 2× 1N4148 base-bias diodes |
|
||
| More power | TIP120+TIP125 pair, or amp chip (PAM8403 / TDA2822) |
|