Parasound Halo Integrated integrated amplifier Measurements

Sidebar 3: Measurements

I measured the Parasound Halo Integrated using my Audio Precision SYS2722 system (see, and the January 2008 "As We See It"). As usual, I preconditioned the amplifier before measuring it by running both channels at one-third power into 8 ohms for an hour. At the end of that period, the top panel was hot, reaching 137.4°F (58.6°C) by the vents over the internal heatsinks.

I began by looking at the Halo's phono-stage performance, taking the amplifier's output from the fixed-level Rec Out jacks with the volume control at its minimum setting, so that the high-level tests wouldn't overload the power-amplifier stage. With the phono input set to moving magnet, the voltage gain was 34.2dB; set to moving coil, it was 53.8dB. Each value is appropriate for that type of phono cartridge. Measured at the speaker outputs with the volume control at its maximum setting, these phono-stage gains were 64 and 94dB, respectively. Both settings inverted absolute polarity. Set to 47k ohms, the input impedance was 47k ohms at 20Hz, 44.5k ohms at 1kHz, and 38k ohms at 20kHz; with this setting at 100 ohms, the input impedance measured 100 ohms at all audio frequencies.

The RIAA response error was respectably low (fig.1), especially in the left channel (blue trace), but both channels can be seen to apply the so-called "Neumann fourth pole," resulting in an output that is up 9dB at 100kHz. While some justify this modification to the RIAA curve on theoretical grounds, I don't like to see it because it boosts the ultrasonic content of unequalized signals such as record ticks and clicks. Channel separation was high, at >70dB above 1kHz, and the signal/noise ratio, measured with the inputs shorted and a 22Hz–22kHz bandwidth, was good, at 69.8dB (MM, ref. 1kHz at 5mV) and 54dB (MC, ref. 1kHz at 500µV). A-weighting respectively increased these ratios to 69.9 and 61dB.

Fig.1 Parasound Halo Integrated, phono input, response with RIAA correction (left channel blue, right red) (1dB/vertical div.).

The Halo's phono stage was extremely linear. Even with a 1kHz signal at 20mV, the MM setting produced just a tiny amount of second-harmonic distortion (fig.2); and with an equal mix of 19 and 20kHz tones at the same equivalent level, there was a negligible amount of intermodulation distortion (fig.3). Correlating with this excellent linearity, the phono-stage overload margin was also excellent, at around 25dB across the audioband at both MM and MC settings.

Fig.2 Parasound Halo Integrated, phono input, spectrum of 1kHz sinewave, DC–10kHz, at 1V into 100k ohms (linear frequency scale).

Fig.3 Parasound Halo Integrated, phono input, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 1V peak into 100k ohms (linear frequency scale).

Turning to the digital inputs, again I assessed their performance at the fixed output jacks. Using my MacBook Pro on battery power to look at the USB input, this operated in the optimal isochronous asynchronous mode, and the Halo was identified as "PARASOUND—Digital Audio" with the manufacturer string "VIA Technologies Inc." The USB input accepted sample rates up to 384kHz, plus, unusually, 705.6kHz, and integer bit depths up to 32. The TosLink input accepted data with a 192kHz sample rate, which is commendable. All digital inputs preserved absolute polarity (ie, were non-inverting).

A full-scale tone at 1kHz resulted in an analog output of 1.92V at the fixed output. Because a tone at –20dBFS with the volume control at its maximum setting produced 18.7V at the speaker outputs, measured into 8 ohms, the digital inputs shouldn't be used with the volume control above 3:00 or so. The reconstruction filter's impulse response is shown in fig.3; the filter is a conventional, finite-impulse-response type with a response that rolls off rapidly above 21kHz with 44.1kHz-sampled data (fig.4, red and magenta traces). With a full-scale tone at 19.1kHz (blue, cyan), the third harmonic lies at –86dB (0.005%), suggesting that the digital circuitry offers low levels of harmonic distortion. This was confirmed by other tests (fig.6). Fig.7 shows the Halo's digital-input frequency response with sample rates of 44.1, 96, and 192kHz via the TosLink input, and 384kHz via the USB input. The ultrasonic output conforms to the same gentle rolloff, but rolls off sharply just below each Nyquist frequency (half the sample rate) at the three lower rates. At the 384kHz rate the smooth rolloff continues, reaching –18.5dB at 190kHz.

Fig.4 Parasound Halo Integrated, digital input, impulse response at 44.1kHz (4ms time window).

Fig.5 Parasound Halo Integrated, digital input, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).

Fig.6 Parasound Halo Integrated, digital input, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 100k ohms (linear frequency scale).

Fig.7 Parasound Halo Integrated, digital input, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red), 384kHz (left gray, right, blue) (1dB/vertical div.).

Channel separation via the digital inputs was good, at >95dB in both directions below 7kHz. Feeding the Halo data representing a 1kHz tone with first 16-bit data (fig.8, cyan and magenta traces), then 24-bit data (blue, red), showed that the increase in bit depth dropped the noise floor by almost 20dB, which suggests that the Halo has better than 19-bit resolution. Repeating these measurements with USB data gave the same result, indicating that the Halo's USB input correctly handles 24-bit data. While many very low-level, power-supply–related spuriae can be seen in fig.8, these didn't affect the Halo's accurate reproduction of undithered 16-bit and 24-bit tones at exactly –90.31dBFS (figs.9 & 10).

Fig.8 Parasound Halo Integrated, digital input, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red) (20dB/vertical div.).

Fig.9 Parasound Halo Integrated, digital input, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).

Fig.10 Parasound Halo Integrated, digital input, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).

Intermodulation distortion via the digital input was negligible (fig.11), as were any jitter-related artifacts with both 16- and 24-bit J-Test data (fig.12).

Fig.11 Parasound Halo Integrated, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 40W peak into 8 ohms (linear frequency scale).

Fig.12 Parasound Halo Integrated, digital input, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit data from SYS2722 via TosLink (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Turning to the Halo's behavior via its line inputs and measured at the speaker outputs, the maximum voltage gain at 1kHz was 39.6dB into 8 ohms via the balanced jacks, and 39.7dB via the unbalanced jacks. The balanced input impedance was 40k ohms across the audioband, and the unbalanced impedance was 24k ohms, again across the audioband. While the balanced input preserved absolute polarity, the unbalanced inputs were inverting.

The output impedance was very low, at 0.09 ohm at 20Hz and 1kHz (including 6' of speaker cable), rising slightly to 0.11 ohm at 20kHz. The modification of the amplifier's frequency response by the interaction between this output impedance and that of our standard simulated loudspeaker was therefore very small (fig.13, gray trace). This graph indicates that the Halo has a wide bandwidth, the response into 8 ohms reaching –3dB at 100kHz. As a result, the Parasound's reproduction of a 10kHz squarewave was excellent (fig.14), with short risetimes and no overshoot or ringing. The traces in fig.13 were taken with the volume control at its maximum setting. Repeating the measurements at lower settings preserved both the close channel matching and the wide bandwidth.

Fig.13 Parasound Halo Integrated, volume control set to maximum, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green) (2dB/vertical div.).

Fig.14 Parasound Halo Integrated, small-signal, 10kHz squarewave into 8 ohms.

There was an audible 0.36dB insertion loss at 1kHz when the tone controls, set to their central, detented positions, were switched into circuit. Fig.15 shows the effect of the treble and bass controls set to their maximum and minimum settings; these are very similar in behavior to the controls of Parasound's Halo P 5 preamplifier, which Art Dudley reviewed in April 2014. The behavior of the Halo Integrated's subwoofer and crossover controls also look very similar to the P 5's.

Fig.15 Parasound Halo Integrated, frequency response at 2.83V into 8 ohms with tone controls set to: flat (left channel green, right gray), and maximum and minimum positions (left channel blue, right red).

Channel separation at 1kHz was good rather than great, at 70dB, decreasing to 50dB at the top of the audioband. The wideband, unweighted S/N ratio, measured with the inputs shorted but the volume control at its maximum setting, was good, at 73dB ref. 2.83V into 8 ohms. This improved to 78dB when the measurement bandwidth was restricted to the audioband, and to 82.5dB when A-weighted. Spectral analysis revealed that AC supply components were at a low level (fig.16).

Fig.16 Parasound Halo Integrated, spectrum of 1kHz sinewave, DC–10kHz, at 1V into 100k ohms (linear frequency scale).

Figs. 17 and 18 plot the percentage of THD+noise in the Halo's output as it drove 8 and 4 ohms, respectively. These graphs show that the Parasound met its specified power of 160Wpc into 8 ohms (22dBW) and 270Wpc into 4 ohms (21.2dBW) at 1% THD+N. Fig.19 plots the THD+N percentage against frequency at a fairly high level: 20V, equivalent to 50W into 8 ohms, 100W into 4 ohms, and 200W into 2 ohms. Fig.19 also shows that the amplifier offers low levels of distortion into the two higher impedances, but begins to stress out into 2 ohms. (The amplifier's protection circuit operated before the 2 ohm sweep was finished.) The distortion signature is strongly third-harmonic in nature (figs. 20 and 21), and intermodulation is also very low, even at high powers (fig.22).

Fig.17 Parasound Halo Integrated, distortion (%) vs 1kHz continuous output power into 8 ohms.

Fig.18 Parasound Halo Integrated, distortion (%) vs 1kHz continuous output power into 4 ohms.

Fig.19 Parasound Halo Integrated, THD+N (%) vs frequency at 20V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta).

Fig.20 Parasound Halo Integrated, 1kHz waveform at 50W into 8 ohms, 0.012% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.21 Parasound Halo Integrated, spectrum of 50Hz sinewave, DC–1kHz, at 50W into 8 ohms (linear frequency scale).

Fig.22 Parasound Halo Integrated, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 100W peak into 4 ohms (linear frequency scale).

The headphone output preserved absolute polarity, and was sourced from a 10 ohm impedance.

Like other Halo-series components from Parasound we have reviewed, the Integrated is a well-engineered, well-performing product.—John Atkinson

Parasound Products, Inc.
2250 McKinnon Avenue
San Francisco, CA 94124
(415) 397-7100

Ishmael's picture

Herb, I think you may have been given bad info somewhere along the line. Your Burson does not use a TI chip for the headphone out. In fact Burson is very anti-opamp, and has been pushing that agenda for some time. I believe the Halo integrated uses the same headphone stage as Parasound's Zdac v2 incorporating a TI TPA6130a2 chip. Other than that, a very enjoyable write up.

Long-time listener's picture

Looking at the graphs showing the tone controls, I've realized this is not an amp I want to buy. The fashion in tone controls these days is to "keep them out of the midrange" by boosting mostly the extreme highs and lows. But the result is that all you get is a lot of extra hiss in the high treble along with some awful, thudding, one-note bass. I've had several amps with tone controls like this and I hate them.

To actually hear a subjective increase in bass or treble, tone controls need to center more on the mid-bass (100 Hz) and mid-treble (10 kHz), and should level off below and above those that points. This doesn't affect the midrange, except in the sense of providing a nice transition to it. The tone controls in this amp are useless. Fashions come and go; this one has never made any sense.

nick22samm's picture

I couldn't disagree more. Like most, I prefer to bypass the tone controls, but they are far from useless, and how important and useful a function they serve will be HEAVILY dependent on the rest of your equipment, the albums you're listening to/how they were mastered, and your preferences. Boosting treble a bit for certain albums, especially with my paradigm studio speakers, has proven to be an invaluable asset that brings the sound quality to a whole new level, allowing the entire system to work together in a way that produces sound rivaling systems and speakers 10 times the cost. It has also allowed tweaks to allow me to get a poor mastering of one album to sound identical to that of a known to be better master of the same album, in the same or different format. Some "audiophile," tenets really need to go away and people need to be more open to various features, formats, etc, instead of sticking to their preconceived beliefs with greater conviction than religious zealots.

the short of it: the tone controls are not useless, they're very valuable; and with true bypass inherent in its circuity, the worst-case scenario for its biggest opponents is simple: don't use it

Long-time listener's picture

You're not reading what I wrote. I said the tone controls "in this amp," are, for me, useless. I didn't say ALL tone controls are useless. I'm VERY heavily in favor of them. But again, if they only boost the very lowest bass and the very highest treble, it only results in a dull, thudding bass or extra hiss and brightness. Tone controls whose action includes a boost in the mid-bass and mid-treble as well as the further extremes are much more musical, and are the ones I favor.

nick22samm's picture

doing vinyl rips with and without tone controls on, set to various degrees, and comparing them to one another, as well as needledrops with the tone controls off, has completely debunked your assertion, verified not just by listening but comparing the visual audiowaves of each recording at the same point in the song to one another. And certainly no highlighting hiss unless completely maxing out the treble, or using it on an already hot or treble-heavy album/master

Allen Fant's picture

Very good review -HR.
the specs certainly make this integrated powerful. Maggies aside, the ultimate speaker to drive would be the Thiel Cs 2.4 or Cs 2.7.
These too, are current-hungry monsters that deliver the audio "goods" when fed properly.

wgb113's picture

My two primary transducers of choice. I wonder how the Halo would match up with my McIntosh MA6300 & Oppo HA-1 combo. Could be nice to "downsize" and have more flexibility in the subwoofer integration department.

tschwagerl's picture

thanks for taking the time to write about several different type of speakers paired with this particular amp. I wish more reviews would write little paragraphs detailing the differences between each one (what you liked and didn't like). Most helpful when trying to find the right combination.

schmonballins's picture

I know it's late to comment on this review, but I have owned my Halo Integrated for over a year and this review is entirely accurate. I have my Halo Integrated paired with PBN Audio's Montana EPS Speakers. This amp makes those speakers sing. I use every part of this amp, and I must say that this review is accurate. I just wanted to make a plug for this amp powering some more "affordable" Montana Speakers. It is a great pairing, I know that I am late to comment. Most people buying Montana speakers have a bigger budget for all of the other components, but if you are looking for a pair of used EPS speakers or EPS2s they can be had for around 5K, plus the 2.5K for this amp, you have an amazing stereo for less than 10K.