The Labworks Inc. PA-138 is a linear power amplifier for laboratory and vibration testing applications. It delivers continuous high-quality amplification into low-impedance loads with switch-selectable output modes: voltage source or current source. The unit integrates signal monitoring, proportional current output for force measurement, automatic thermal and over-current protection, and user-configurable external interlock circuitry. Dual-speed forced-air cooling maintains stable operation under continuous duty, with noise levels below 45 dB at low fan speed and below 55 dB at high fan speed.
## Technical Specifications
**Output Voltage (Continuous)**
• Open circuit (DC – 0.1 Hz): 45.0 Vdc/pk
• Open circuit (10 Hz – 20 kHz): 31.0 V rms
• 4 Ω load (DC – 0.1 Hz): 36.5 Vdc/pk
• 4 Ω load (10 Hz – 20 kHz): 26.0 V rms
• 2 Ω load (DC – 0.1 Hz): 22.0 Vdc/pk
• 2 Ω load (10 Hz – 20 kHz): 23.5 V rms
• 1 Ω load (DC – 0.1 Hz): 11.0 Vdc/pk
• 1 Ω load (10 Hz – 20 kHz): 20.0 V rms
**Output Current:** 20 A rms (continuous)
**Electrical Performance**
• Maximum continuous dissipation: 450 W
• Voltage source frequency response (DC – 10 kHz): –0.6 dB
• Current source frequency response (DC – 2 kHz @ 4 Ω): –2 dB
• Maximum current gain: 22 A/V
• Maximum voltage gain: 34 dB
• Input impedance: 10 kΩ
• Input power: 1,000 VA maximum
## Key Features
• Peak voltage and RMS current bar graph metering
• DC and AC coupled signal inputs
• Proportional voltage output for current monitoring and modal testing
• External interlock circuit with TTL compatibility
• Automatic over-current and over-temperature protection
• Two-speed fan with automatic thermal management
## Typical Applications
Vibration system excitation, modal analysis, force monitoring, laboratory signal amplification requiring continuous output into low-impedance loads.
## Compatibility & Integration
Accepts DC and AC coupled inputs. Configurable output impedance supports voltage source or current source operation. Full external interlock capability enables integration with user-defined safety and control logic.
