CONTACT DETAILS
Brand: Parasound Model: Halo Category: Amplidac RRP: $4,995 Warranty: Three Years Distributor: Network Audio Visual Pty Ltd Address: Unit 6B, 3 – 9 Kenneth Road Manly Vale NSW 2093 T: (02) 9949 9349 E: info@networkav.com.au W: www.networkav.com.au
• High power, low distortion • Tuneable subwoofer output • Built-in electronic x/o • On-board DAC • 3.5mm headphone socket • Using headphones disables spkrs
LAB REPORT ON
Newport Test Labs measured the power output of the Parasound Halo at 1kHz as being 176-watts both channels driven into 8 loads, and 262-watts both channels driven into 4 loads, both figures being just a little higher than Parasound’s specification of 160-watts into 8 loads and 240-watts into 4 loads. The reason for Parasound’s lower specification becomes clear when you look at the tabulated figures (or the relevant bar graphs), which show that at 20Hz, the Parasound Halo was only able to deliver 166-watts into 8 and 245-watts into 4 . Parasound deserves congratulations for the honesty of its power output specification. Many of its competitors are now quoting the output power at 1kHz with only a single channel driven as their ‘power output’ specification—a trick that’s illegal in the USA and Australia, but I don’t know about other jurisdictions. There are no 2 power output results shown because when Newport Test Labs connected the Parasound Halo to a 2 test load, the Halo’s internal protection circuit triggered after an output of only tens of watts had been attained. This was no doubt because, unlike music, test signals are continuous, which presents maximum load. However, I would recommend that users avoid using the Halo with loudspeakers whose impedance dips below 2 .
The frequency response of the Parasound Halo was very flat and extended… at least when the tone control circuitry was defeated. With the controls at this setting, the Halo’s low-frequency response was down 1dB at 8Hz and 3dB at 4Hz, and its high-frequency response down 1dB at 55Hz and 3dB down at 103kHz. The response across the audio band is shown in Graph 5, both into a standard 8 resistive laboratory test load (black trace) and into a load that simulates that of a two-way bass reflex loudspeaker ( Newport Test Labs uses Ken Kantor’s circuit, with John Atkinson’s modification that includes Zobel impedance compensation in the treble.) You can see that the two traces track each other perfectly, which is an excellent result that means the amplifier will sound exactly the same irrespective of the impedance magnitude of the loudspeakers you use.
The response rolls off as expected at low and high frequencies, to be 0.5dB down at 20Hz and 0.3dB down at 20kHz, which puts the normalised frequency response at 20Hz to 20kHz ±0.25dB. Channel separation was measured at discrete frequencies, and was 95dB at 20Hz, 73dB at 1kHz and 51dB at 20kHz. The result is obviously the poorest at 20kHz, but 51dB is still more than adequate to ensure perfect channel separation and stereo imaging. Inter-channel phase errors were, perhaps, just a touch higher than I’m used to seeing, particularly the 1.97° result at 20kHz, but still low enough not to be audible, even under controlled listening conditions. Channel balance was an outstandingly good 0.08dB.
The Halo’s frequency response is not nearly as good when the tone control circuit is
The frequency response of the Parasound Halo was very flat and extended … at least when the tone control circuitry was defeated
engaged, as you can see from Graph 6, which compares the ‘in-circuit’ (red trace) and ‘out-of-circuit’ (black trace) responses. Firstly, inserting the tone control circuit reduces the overall gain by around 0.4dB across the midrange and high frequencies, and a bit over 1dB at low frequencies. This means that if you switch between one and the other while playing music, the ‘defeat’ position will appear to deliver ‘better’ sound, but this is simply because the music will be louder, which the human ear detects as appearing ‘better’ rather than simply ‘louder’. But with the controls in-circuit, the amplifier will also appear to sound slightly bass-shy as well, despite the fact that the overall frequency response with the tone controls in-circuit is still a very creditable 20Hz to 20kHz ±0.5dB.
As for the tone controls themselves, their action is shown in Graph 7. The bass tone control affords much more boost and cut than is usual, delivering around 16dB of boost and cut at 20Hz (10–12dB is more usual). At high frequencies boost and cut is still fairly extreme, at around ±13dB. The boost on both controls is partially shelved— full shelving would have been preferable, and both controls will have an effect on the midrange, whereas it would have been better if they didn’t. My advice would be that if you are using the tone controls, do so sparingly, perhaps not using more than around half the available range and, if you are not using the controls, ensure the tone control circuit is defeated.
Harmonic distortion was very low, with Newport Test Labs measuring overall THD+N at 0.006% at an output of one watt, and just 0.018% at rated output. Spectrum analysis of the individual distortion components that delivered this result is shown in Graphs 1 through 4. At an output of 1-watt into 8Ω (Graph 1), there was a second harmonic distortion component at –100dB (0.001%), a third harmonic at –102dB (0.0007%), a fourth at –112dB (0.0002%) and a fifth at –120dB (0.0001%). If there were any higher-order components, they were buried in the noise floor. Reducing load impedance to 4Ω (Graph 2) resulted in slight increases in the levels of the first five distortion components and the addition of sixth, seventh and eighth-order components but with the exception of the first two components (the second at –97dB or 0.0014% and the third at –95dB or 0.0017%) all were more than 110dB down (0.0003%).
Harmonic distortion increased when the amplifier was operating at its maximum output into 8Ω and 4Ω loads, as you’d expect, and the distortion spectrum was similar for both loads, both in its spectral distribution and level. In both cases the third harmonic dominated, at a level of around –76dB (0.0158%), with a second at around –95dB (0.0017%) and the higher-order components at around 100dB down (0.001%) or more.
As for the tone controls, my advice would be that if you are using them, you should do so sparingly
You can see that the noise floor is mostly down below –120dB at frequencies above 4kHz. The ‘grass’ on the noise floor at lower frequencies is a sign that the Parasound Halo’s power supply is at its limit delivering rated power into these loads.
Intermodulation distortion is shown in Graph 8. There are only four sidebands either side of the two test signals at 19kHz and 20kHz, which is excellent performance, and
the levels are quite low, at around –95dB (0.0017%) for the 18/21kHz signals and at around –105dB (0.0005) for the 17/22kHz signals. There is an unwanted difference signal generated down at 1kHz, as you can see at the left of the graph, but it’s 95dB (0.0017%) down, therefore would not be audible.
The Parasound Halo’s 100Hz square wave shows the considerable tilt one would expect from the –3dB downpoint being at 4Hz, but there’s no bending to indicate any phase shift, which is excellent. The 1kHz square wave is very close to perfect, also an excellent result. The 10kHz square wave shows some rounding, the result of the Halo’s high-frequency response being 3dB down at 103kHz, but is otherwise excellent. Performance into a highly reactive load was fairly typical of a solid-state amplifier, with a half-height overshoot and a few cycles of quickly-damped ringing, so the Halo will be perfectly stable when driving highly reactive loads.
Signal-to-noise ratios were very high when referenced to either one-watt (where the Halo returned figures of 80dB unweighted and 86dB A-weighted) or rated output, where it returned figures of 94dB unweighted and 100dB A-weighted). All are excellent results, and most particularly the A-weighted result at rated output: Not too many integrated amplifiers can break into the three-digit range, and most particularly not if they contain digital circuitry!
Newport Test Labs found the line inputs of the Halo were quite sensitive, requiring only 28mV to deliver 1-watt at the speaker terminals, and only 362mV to deliver rated output. Output impedance was only 0.02 at 1kHz, resulting in an excellent damping factor of 400, which means the Halo will easily be able to control the back-emf from even the largest-diameter bass driver.
Tests on the Halo’s DAC showed that it performs well, but does not represent the state-of-the art so far as digital-to-analogue conversion is concerned, as you can see from the tabulated results. The signalto-noise ratio was 116dB, with crosstalk hovering either side of 100dB. THD (shown in Graph 9) was low, less than 0.01% right across the frequency band and IMD also low, at close to –100dB (0.001%). Phase was within 0.2 degrees and the circuit was non-inverting.
Standby power consumption was measured at 0.29-watts, so the Parasound Halo conforms to the latest Australian standard, and will also pull only a fairly modest 82-watts from your mains when operating at normal listening levels.
Overall, the Parasound Halo performed very well in all Newport Test Labs’ tests and has well-designed, non-intrusive protection circuitry, which is a reassuring but oft-omitted feature. Recommended. Steve Holding
Overall, the Parasound Halo performed very well in all Newport Test Labs’ tests
Readers should note that the results mentioned in the report, tabulated in performance charts and/ or displayed using graphs and/or photographs should be construed as applying only to the specific sample tested.