All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Note: Measurements were taken of both channels of the Parasound Halo A 23+ at 120V AC line voltage, both channels driven, at the balanced and unbalanced inputs. Except as noted, discussed below are the results for the unbalanced inputs and the left channel.

### Power output (stereo mode) @ 1kHz

- Power output at 1% THD+N: 191.9W @ 8 ohms, 275.1W @ 4 ohms
- Power output at 10% THD+N: 229.3W @ 8 ohms, 337.6W @ 4 ohms

### Power output (mono mode) @ 1kHz

- Power output at 1% THD+N: 526.1W @ 8 ohms
- Power output at 10% THD+N: 693.4W @ 8 ohms

### Additional data

- Input/output polarity: noninverting
- AC-line current draw at idle: 60.0W, 0.73A, 0.68PF
- Gain: output voltage divided by input voltage, 8-ohm load
- Stereo mode
- Balanced input: 28.5X, 29.1dB
- Unbalanced input: 29.2X, 29.3dB

- Mono mode
- Balanced input: 57.6X, 35.2dB
- Unbalanced input: 56.4X, 34.7dB

- Stereo mode
- Input sensitivity for 1W output into 8 ohms
- Stereo mode
- Balanced input: 99.2mV
- Unbalanced input: 96.9mV

- Mono mode
- Balanced input: 49.1mV
- Unbalanced input: 50.1mV

- Stereo mode
- Output impedance @ 50Hz
- Stereo mode: 0.005 ohm
- Mono mode: 0.009 ohm

- Input impedance @ 1kHz
- Stereo mode
- Balanced inputs: 97.0k ohms
- Unbalanced inputs: 50.0k ohms

- Mono mode
- Balanced input: 97.0k ohms
- Unbalanced input: 50.0k ohms

- Stereo mode
- Output noise (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
- Wideband: 0.335mV/0.244mV, -78.5dBW/-82.0dBW
- A weighted: 0.116mV/0.085mV, -87.7dBW/-90.4dBW

- Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- Wideband: 0.322mV/0.228mV, -78.9dBW/-81.9dBW
- A weighted: 0.116mV/0.082mV, -87.7dBW/-90.8dBW

- Output noise (mono mode), 8-ohm load, balanced inputs terminated with 600 ohms
- Wideband: 0.454mV, -75.9dBW
- A weighted: 0.189mV, -83.5dBW

- Output noise (mono mode), 8-ohm load, unbalanced inputs terminated with 1k ohms
- Wideband: 0.438mV, -76.2dBW
- A weighted: 0.179mV, -84.0dBW

### Measurements summary

The Halo A 23+, an update of the Halo A 23, is the lowest-powered amplifier model in Parasound’s Halo line. Because the A 23+ can be switched between stereo and bridged mono, some measurements were taken in both modes. In the charts below, the suffix *A* indicates measurements taken in stereo mode, the suffix *B* measurements taken in bridged mono.

Charts 1A and 1B show the Halo A 23+’s frequency response with varying loads. Chart 1A shows both channels, as between them there is a small difference in gain. Because the A 23+’s output regulation is so tight, only the 8-ohm loading is shown; the other loadings look the same. Note the greater high-frequency rolloff in bridged mode, due to the series connected nature of the load in bridged-mono mode.

Chart 2A illustrates how the Halo A 23+’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output load with loads of 8 and 4 ohms. Chart 2B shows only the results in bridged mode for a load of 8 ohms -- the Halo A 23+ is not specified for use with 4-ohm loads in bridged mode.

The Halo A 23+’s THD+N as a function of frequency at several different power levels is plotted in Charts 3A and 3B. The increase in high-frequency distortion with frequency is moderate, and distortion remains reasonably low through most of the power range in both stereo and bridged-mono modes.

Chart 4 shows that the Parasound’s damping factor vs. frequency is of a value and nature typical of many solid-state amplifiers: high up to 1-2kHz, then rolling off with frequency. Not unexpectedly, the damping factor was lower in bridged mono, due to the fact that in this mode each channel’s output impedance is doubled.

Chart 5, the spectrum of the residue of harmonic distortion and noise of a 10W, 1kHz test signal, reveals a lot of line-frequency harmonics of significant amplitude. The signal harmonics are dominated by the second harmonic, with higher harmonics of significantly lower amplitude.

### Chart 1 - Frequency response of output voltage as a function of output loading

Chart 1A - stereo mode

Stereo mode

Red line = Lch 8-ohm load (open circuit and 4-ohm loading look the same)

Blue line = Rch 8-ohm load (open circuit and 4-ohm loading look the same)

Chart 1B - mono mode

Mono mode

Red line = 8-ohm load (open circuit and 4-ohm loading look the same)

### Chart 2 - Distortion as a function of power output and output loading

Chart 2A - stereo mode

Stereo mode

(Line up at 70W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 4-ohm THD+N distortion

Third line = 8-ohm THD+N

Bottom line = 4-ohm SMPTE IM distortion

Chart 2B - mono mode

Mono mode

(Line up at 70W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 8-ohm THD+N

### Chart 3 - Distortion as a function of power output and frequency

Chart 3A - stereo mode

Stereo mode

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 160W

Chart 3B - mono mode

Mono mode

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Green line = 200W

Yellow line = 400W

Cyan line = 600W

### Chart 4 - Damping factor as a function of frequency

Stereo mode

Damping factor = output impedance divided into 8

### Chart 5 - Distortion and noise spectrum

Stereo mode

1kHz signal at 10W into an 8-ohm load