#2 Audio

Stereo Audio Amplifier (TDA2030 + TL072)

A stereo audio amplifier circuit running on a single 24V supply, built around a TL072-based preamp/volume stage feeding two independent TDA2030 power amplifier channels.

Features

• Stereo (L/R) audio input via 3.5mm TRS jack (J3)
• Synchronized volume control using a dual-gang potentiometer (RV2, 100k)
• Independent TDA2030 power amplifier IC per channel
• Short-circuit / inductive back-EMF protection (1N4001 diodes)
• Zobel network for high-frequency stability
• Single 24V DC supply input (J1, DC jack)

Block diagram

                 ┌───────────────┐        ┌───────────────┐
                 │  Power supply │        │  Audio input  │
                 │  24V DC (J1)  │        │  J3, stereo   │
                 └───────┬───────┘        └───────┬───────┘
                         │                        │
                         └───────────┬────────────┘
                                     ▼
                        ┌─────────────────────────┐
                        │        Preamp            │
                        │  TL072 (U2) + RV2 volume  │
                        └────────────┬─────┬───────┘
                                     │     │
                    ┌────────────────┘     └────────────────┐
                    ▼                                        ▼
        ┌───────────────────────┐                ┌───────────────────────┐
        │   Left channel amp    │                │   Right channel amp   │
        │       TDA2030         │                │       TDA2030         │
        └───────────┬───────────┘                └───────────┬───────────┘
                    ▼                                        ▼
                 LS1 speaker                            LS2 speaker

How it works

1. Power supply — 24V comes in through J1 (DC jack). C3 (2200µF) provides low-frequency bulk smoothing, C2 (100nF) filters high-frequency noise.
2. Audio input — J3's Tip (T) and Ring (R) pins feed the left and right channel input capacitors (C1, C7 — 4.7µF) respectively.
3. Preamp stage — Both op-amps of the TL072 (U2A, U2B) operate as inverting amplifiers. Since the supply is single-ended, an R3/R4 (4k7/4k7) divider (filtered by C6) creates a mid-supply bias voltage for the non-inverting inputs. RV2 (100k, dual-gang), in series with R7/R8 (2k2), adjusts the feedback resistance and therefore the gain of both channels in sync — this is the volume control.
4. Power stage — Each channel is amplified by its own TDA2030 IC. R9/R10 (100k/100k) set the DC bias divider; R11/R12/C12 (4k7/150k/2µF) form the feedback network giving an AC gain of roughly 1+R12/R11.
5. Protection and stability — D5/D6 (and D7/D8) diodes protect against inductive back-EMF from the speaker; R13+C13 (1Ω + 220nF) form a Zobel network that prevents high-frequency oscillation.
6. Output — C14/C22 (2000µF) output capacitors block the DC bias before the signal reaches the LS1/LS2 speakers.

Bill of materials (BOM)

Power and input

Preamp (TL072 — U2)

Left channel power stage (TDA2030)

Right channel power stage (TDA2030)

Mirrors the left channel topology: R15/R16=100k, R17=4k7, R18=150k, R19=100Ω, R20=1Ω, D7/D8=1N4001, C17=22µF, C18=1µF, C19=100µF, C20=2µF, C21=100nF, C22=220nF, C23=2000µF, LS2=Speaker.

Note: Values above were read from the schematic image. Cross-check against the original schematic file (KiCad .kicad_sch / netlist) before manufacturing.

Approximate specifications

• Supply voltage: 24V DC
• Channels: 2 (stereo)
• Power IC: TDA2030 (~14W/channel into 4-8Ω per datasheet — actual figure depends on heatsinking and load impedance)
• Input: 3.5mm TRS stereo line level

Known limitations / notes for improvement

• RV2 sits inside the op-amp's feedback loop; a wiper contact dropout could push the stage into open-loop operation — moving to a passive input attenuator would be safer.
• No fuse or reverse-polarity protection on the supply input (J1).
• No power-on/off "thump" protection (mute/delay circuit) for the speakers.
• TDA2030s require adequate heatsinking — not shown in the schematic, needs to be addressed in the mechanical design.

License

No license has been chosen yet — add one as needed (e.g. MIT, CC-BY-SA).