Unbalanced to Balanced Amplifier

Ideal Use Cases

The RDL ST-UBA2 is designed for audio paths that need to convert unbalanced consumer-format signals to professional +4 dBu balanced signals. It accepts two unbalanced line-level inputs and provides three balanced outputs: left, right, and mono sum. This arrangement supports systems that need separate left and right feeds together with a summed mono feed from the same amplifier. Adjustable gain from 2 dB to 22 dB provides flexibility when bringing incoming signals to the required output level.

The model is suited to integrations in which low noise, low distortion, channel separation, and a wide audio-frequency response are important. Its stated input impedance is 10 kΩ, while the balanced outputs have a 150 Ω output impedance.

Why Choose This Model

The ST-UBA2 combines signal-format conversion, adjustable gain, and three +4 dBu outputs in a single model. Its published performance includes a 20 Hz to 20 kHz frequency response within ±0.2 dB, THD+N below 0.02% across that same frequency range, and IMD below 0.004%. Noise is specified below -85 dB when referred to +4 dBu.

Headroom exceeds 18 dB above +4 dBu, giving the amplifier stated operating capacity above its professional output level. Crosstalk is specified below -75 dB at 1 kHz and below -60 dB at 10 kHz. These concrete measurements make it possible to evaluate the model directly against the level, distortion, noise, and channel-separation requirements of an audio system.

Installation and Integration

The amplifier requires ground-referenced 24 Vdc power at 75 mA. A power supply is not included. The listed recommended supplies are the PS-24AS for the USA and the PS-24AX for international use. The stated ambient operating range is 0° C to 55° C, which should be considered when selecting the installation location.

Two unbalanced line-level inputs feed the left, right, and mono-sum balanced outputs. The published input signal range is 20 dBV to -10 dBV, and gain can be adjusted across a 2 dB to 22 dB range. One green LED per channel indicates a 15 dB range below the +4 dBu output level, providing a visible reference during setup and operation.

The product is supplied in a cardboard box with listed package dimensions of 2 x 2 x 4 inches and a shipping weight of 0.205 pounds. The source data also identifies a PDF specification sheet, engineering and panel resources in American DXF format, and high-resolution image resources in TIF format.

Performance Highlights

Across the audible frequency range, the ST-UBA2 is specified for response from 20 Hz to 20 kHz with only ±0.2 dB variation. THD+N remains below 0.02% from 20 Hz to 20 kHz, while intermodulation distortion is below 0.004%. The noise specification of less than -85 dB is referenced to the unit’s +4 dBu output level.

Its crosstalk figures document channel separation at two relevant frequencies: less than -75 dB at 1 kHz and less than -60 dB at 10 kHz. More than 18 dB of headroom above +4 dBu complements the adjustable gain section. Together, these specifications define the amplifier’s signal handling without relying on unspecified processing or enhancement features.

What Makes It Different

The defining feature of the ST-UBA2 is its output configuration. In addition to balanced left and right outputs, it provides a dedicated balanced mono-sum output, with all three outputs specified at +4 dBu. This gives the model a clear role where both individual channel feeds and a combined feed are required.

Its conversion function is supported by measurable audio performance rather than an unspecified feature set. Adjustable 2 dB to 22 dB gain, 10 kΩ input impedance, 150 Ω output impedance, low published distortion, and stated crosstalk performance provide concrete integration details. Per-channel green LED indication adds immediate level-related feedback based on the specified range below +4 dBu.

Final Assessment

The RDL ST-UBA2 is a focused solution for converting two unbalanced consumer-format line signals into professional balanced audio. Three +4 dBu outputs, including mono sum, distinguish its signal-routing capability, while adjustable gain and detailed noise, distortion, frequency-response, crosstalk, and headroom specifications support informed system design. Installation requires a separate, ground-referenced 24 Vdc power supply capable of providing 75 mA.