What is the RDL TX-PA40D?
The RDL TX-PA40D is a 40 W stereo Class D utility amplifier delivering 20 W RMS per channel into 8 Ω or 15 W per channel into 4 Ω. It is suited to fixed-gain applications where level is controlled by other equipment, such as projectors with variable audio outputs. A studio-quality compressor/limiter controls clipping, and the power supply with North American cord is included.
How does it work?

The TX-PA40D has two unbalanced line-level inputs on gold-plated RCA jacks. Recessed front-panel trimmers set the output level for each channel across typical unbalanced signal levels. Each output drives a 4 Ω or 8 Ω speaker, or several speakers presenting that load, with impedance selected on the front panel. A front-panel switch sums the inputs to mono when speaker placement does not suit stereo. The stereo analog compressor/limiter prevents clipping and, with higher input gain, raises average output beyond a standard 40 W amplifier. A red LED flashes at the compression threshold and stays dimly lit between flashes while compression is active. Compression uses three dynamic time constants and keeps audio clean for input overloads of up to 20 dB. The included supply accepts 100 to 240 Vac and powers the module at 24 Vdc, and the amplifier has thermal and short-circuit protection. The compact TX chassis mounts with RDL accessories such as the RDL TX-HRA3 or RDL TX-RA5.
What are the key features?
- 40 W stereo Class D — 20 W RMS per channel into 8 Ω or 15 W into 4 Ω.
- RCA inputs — Gold-plated left and right unbalanced phono jacks.
- Stereo or summed mono — Front-panel switch matches the speaker layout.
- Compressor/limiter — Controls clipping and maximizes average output.
- Selectable impedance — Outputs drive 4 or 8 ohm speakers.
- Supply included — 100 to 240 Vac supply with North American cord.
Where is it typically used?
- Conference room
- Boardroom
- Training room
- Huddle room
Technical Specifications
| Model | TX-PA40D |
| Inputs (2) | Line level (-10 dBV nominal unbalanced), Left and Right |
| Input Impedance | 10 kΩ unbalanced |
| Gain Adjustments (2) | Single turn, one per channel |
| Minimum Input Levels | -18 dBV (to cross compressor threshold) |
| Maximum Input Levels | +15 dBV |
| Frequency Response | 20 Hz to 20 kHz (± 1 dB, 4 or 8 Ohms)* |
| THD+N | < 0.1% (1 kHz, 1 W, 4 or 8 Ohms); < 1% (50 Hz to 20 kHz, 8 Ohms)* *measured at compressor threshold level equaling 12 W RMS (8 Ohms) output power |
| Compressor | Threshold nominally 2 dB below rated output, automatically adjusting attack and release times |
| Crosstalk | Better than 60 dB (1 kHz, no compression) |
| Noise | < -75 dB (below 20 W RMS) |
| Selectors | Slide switches: Output Impedance 4 Ohms or 8 Ohms; Input Mode SUMMED MONO or STEREO |
| Output Power | 20 W RMS into 8 Ω per channel, 40 W RMS total; 15 W RMS into 4 Ω per channel, 30 W RMS total |
| Output Circuit | Class D |
| Ambient Operating Environment | 32° F to 104° F (0° C to 40° C) Maximum; 68° F (20° C) recommended |
| Indicators (2) | Red LED: THRESHOLD LED indicates compressor activity Blue LED: POWER on |
| Power Requirement (Supply Included) | Input: 100 to 240 VAC, 50 to 60 Hz, 1.5 A, IEC C14; Output to module: 24 Vdc |
| Dimensions | 3.17" (8.05 cm) W; 1.76" (4.47 cm) H; 2.06" (5.23 cm) D |
Frequently Asked Questions
What power does it deliver?
20 W RMS per channel into 8 Ω (40 W total) or 15 W RMS per channel into 4 Ω (30 W total).
Does it have remote volume control?
RDL designs the TX-PA40D for fixed-gain use where level is controlled by other equipment. For remote VCA level control, RDL offers the RU-PA40D.
What inputs does it have?
Left and right unbalanced -10 dBV inputs on RCA jacks.
Is the power supply included?
Yes, with a North American cord. The TX-PA40DE export model excludes the cord.
Can it run in mono?
Yes. A front-panel switch sums the inputs to mono.
What warranty does it carry?
This product is covered by a 7-year RDL warranty. For warranty claims, RMAs or support, contact Creation Networks at (888) 230-3661 or sales@creationnetworks.net.
Can Creation Networks help design the system?
Yes. Our team specifies, programs and installs classroom and conference room audio systems for commercial projects nationwide. Call (888) 230-3661 for a quote or design review.
At Creation Networks, we do everything we can to create an excellent customer experience. This includes fast shipping and easy returns.
- Most in-stock orders placed Monday-Friday ship within 24-48 hours. General restrictions apply; please see our full shipping policy here.
- We offer a 30-day return policy from the delivery date on many products. Product restrictions apply. Restocking fees for the return of open-box items. Please see our full return policy here for more information.
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