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EQUIPMENT REVIEW

32 | Australian Hi-Fi

ParasoundP3 Preamplifier & Halo A21 Power Amplifier

It is my personal view that the world has too many hi-fi brand-names already, so I am a bit peeved that a company with the street-cred of Parasound seems hell-bent on increasing that number. After more than 25 years in business as plain old ‘Parasound’, this Californian-based company seems to have decided to use different ‘branding’ to differentiate between its different ranges, so the top-line Parasound equipment will be known as ‘Halo’ and the second-string line as ‘NewClassic.’ And if that wasn’t enough, Para-sound’s rack-mount models are known as its ‘ZCustom’ line.

But if you look closely at the Halo logo, you’ll see that Parasound is playing it safe by in-corporating (in smaller type) the words ‘by Para-sound’. Likewise, although the NewClassic line is advertised as ‘ParasoundNewClassic’, when you get to look at a product in the fl esh, the front panel bears only the word ‘Parasound.’

What has not changed is that the famous John Curl is still a part of the design team at Parasound. If your memory needs a little jogging, you may recall that Curl became famous around the world as the designer of the original Mark Levinson JC-2 preamplifi er, which at the time—and for a good number of years afterwards—was widely acclaimed as being the best pre-amplifi er in the world. Cu-riously enough, Curl’s most recent preampli-fi er design for Parasound recycles the famous JC-2 model number (the Parasound JC-2). Curl also designed the Halo by Parasound A21 power amplifi er that is the subject of this review. (It’s my understanding that although he certainly played a signifi cant part in the design of the P3, this preamplifi er is ‘not all his own work.’ )

The EquipmentThe Halo by Parasound A21 is rated at 250-watts per channel into 8-ohms and 400-watts into 4-ohms in two-channel mode. If you want even more power, you can bridge the two channels of the A21 and operate it as a

mono amplifi er, in which case it’s rated to deliver 750-watts into a single 8-ohm load. Although the circuitry is entirely solid-state, Curl has managed to avoid the ‘hard’ sound quality usually associated with high-power solid-state amplifi ers by using metal oxide fi eld effect transistors (MOSFETs) to drive four pairs of 60MHz/15-amp Sanken bipolar out-put transistors. This odd coupling completely removes odd-order harmonic distortion com-ponents while at the same time extending the amplifi er’s frequency response to beyond 100kHz. Ahead of these, Curl uses matched pairs of discrete JFETS in a dual differential cascade confi guration. This means very low noise and that circuit operation is in no way reliant on the output impedance of the source component. Rather than use blocking capaci-tors or trim controls to prevent unwanted direct current (d.c.) from appearing at the speaker terminals, Curl instead uses a fast d.c. servo. This enables speakers to move around their exact midpoint, rather than an arbitrary offset position. It also effectively immunises the circuit against the deleterious effects of age, so that unlike conventional designs that uses trim controls, which allow d.c. drift over periods of time, the A21’s d.c. offset will al-ways be exactly 0V. There are three other lay-ers of protection built in: relays, fuses, and current sensors. As with all high-end designs, Curl uses a linear power supply, at the heart of

32-38,100-101Parasound HFMar08.i32 32 22/02/2008 10:49:30 AM

Reprinted from Australian Hi-Fi magazine

Australian Hi-Fi | 33

Brand: ParasoundModel: P3 Preamplifi er & Halo A21 Power Amplifi erCategory: Pre & Power Amplifi ersRRP: $1,695 (P3)/ $4,295 (A21)Warranty: Three YearsDistributor: Network Audio Visual Pty LtdAddress: Unit 6B, 3–9 Kenneth RoadManly ValeNSW 2093T: (02) 9949 9349F: (02) 9949 6972E: [email protected]: www.networkav.com.au

Parasound P3 Preamplifi er & Halo A21 Power Amplifi er

which is a massive 1kVA toroidal power trans-former and four 22,000µF Elna electrolytics, each of which is bypassed by small-value polypropylene capacitors.

Curl has also elected to include balanced inputs. These are becoming increasingly com-mon on audio components. I must admit that I fi nd this a bit puzzling. While I am a con-fessed fan of balanced connections, this is pri-marily because I much prefer the convenience of the larger, three-pin XLR connector, which I think enables superior terminal mating than standard RCA connectors. I also like the fact that if you experiment with making your own cables (which I do… regularly), XLR connec-tors are far easier to wire up, and you can eas-ily replace various components in the XLR plug, such as pin-blocks, shells, screws and so on. What I don’t agree with is that balanced connectors ‘sound’ better than unbalanced… though I’d add in a caveat that this is only true if you are not experiencing any problems with induced noise or hum that results from your unbalanced leads picking up stray in-terference. If this is the case, balanced lines are by far the best way to go because their design completely eliminates the possibility of any noise or hum inveigling its way into your system. The way this happens is a bit technical, so here’s my ‘Idiot’s Guide’ take on it: A standard unbalanced line has only two conductors, signal and earth (or, if you pre-fer, [+] and [–] ). This means that if the wires carrying these signals pick up another signal, it simply superimposes on whatever’s there and manifests as hum or some other type of interference. A balanced cable has three con-ductors, signal positive (‘hot’), signal negative (‘cold’) and earth, but most importantly, the signal positive conductor is 180 degrees out-of-phase with the signal negative conductor. When a component receives a balanced sig-nal, it looks only for the voltage differences between the two signals and sends only these

signals for further amplifi cation. Since any hum picked up in the line along the way will be identical on all three conductors, it will simply be ignored by the differential circuit.

Looking back, I guess such a long discus-sion is likely a bit over the top in view of the fact that Parasound is not actually asking you to choose between balanced and unbalanced connections, but offering you both. Sure this means you’re paying for the balanced op-tion even if you don’t use it, but in the great

scheme of things, I can’t see that this would impact too much on the RRP. You could al-most make the same case for the bridging option. This, too, adds to the manufacturing cost of the A21, yet my guess is that very, very few people will ever use the bridging option. Why? Firstly, the A21 is already suffi ciently powerful for 99.99 per cent of users and sec-ondly, because using it means you’d need to buy a second A21 and bridge that to drive your other channel—and that doubles the price of your amplifi cation!

Obviously, you need to be able to switch between balanced and unbalanced operation, and between bridged mode and stereo, and all these switches are provided on the rear panel, along with gold-plated RCA and XLR (female) inputs. There are also volume controls (one for each channel), a ‘loop’ output, so you can run the input signal to another ampli-fi er if you want, a ‘Ground Lift’ switch, and a switchable and fully adjustable ‘Automatic Turn-On’ circuit if you plan on positioning the amplifi er remotely from your equipment

rack. The speaker terminals are standard gold-plated multi-way types that will take stripped wire, bananas or pretty much any standard speaker connector.

Parasound P3 Preamplifi erSomeone has gone to a great deal of trouble with the layout of the controls and display on the front panel of the P3. Is it a sort of electronic Feng Shui? Do consumers identify more strongly with preamplifi ers that have

symmetrical control layouts? All questions to which I doubt anyone will have any answers. But it sure looks good, so there’s both rhyme and reason in it.

The photograph accompanying this re-view should be large enough to see what con-trols are fi tted, but if not… Either side of the central display are bass (to the left) and treble (to the right) controls. They’re electronic, so as you press either the ‘Up’ or ‘Down’ but-tons, you’ll see a read-out in the display as to the amount of boost or cut you’ve dialled in. Very nice. If when you press these buttons, nothing happens, you’ll need to fi rst press the ‘Tone’ button just under and to the right of the Bass > button. To the left of this ‘Tone’ button is the source selector control. There are six sources to choose from, plus two in-put/output loops, one of which is identifi ed as a ‘Record’ loop and the other simply as ‘External.’ Obviously, if you’re using external processing of some sort, you’d use this latter loop, while you’d connect a CD-R recorder to the former loop.

“Curl has also elected to include balanced inputs. These are becoming increasingly common on audio components. I must admit that I fi nd this a bit puzzling.”




Parasound has provided extraordinary fl exibility with its inputs. There are two ‘Di-rect’ inputs, which both by-pass most of the internal circuitry, to give the purest signal. One of these (Direct 1) can be driven by a bal-anced or an unbalanced source (selectable via a switch on the rear panel). There is a phono input, but if you have no need for it, you can quickly and easily change it to a standard auxiliary input, again by means of a switch on the rear panel.

Once you have selected your source, you can adjust volume via the front panel control on the far right, or via up/down push-buttons on the infra-red remote control. This remote also adds a Mute feature that’s not available from the front panel but that’s about all. Most of the 35 buttons on the remote can only be

used to control Parasound’s T3 AM/FM tuner.Outputs are also fl exible, with your choice

of balanced or unbalanced. Actually, there’s not really a choice as such, you can use ei-ther or both… if you can think of an appli-cation! There are also external remote jacks (input and output) and 12V triggers (input and output) plus and RS232 port. The fi t and fi nish of the P3 was extraordinarily good, but I did notice that the surface of the right-most balance push-button on my sample had some very slight imperfections, as if there were tiny ‘bubbles’ under the surface of the anodising. Since my review sample had obviously ‘done the rounds’ before I got it, it’s entirely pos-sible this was not a manufacturing fault but the result of poor handling or outright abuse (at least one hi-fi reviewer of my acquaintance has been known to apply heat to determine whether a fi nish is metal or plastic!)

Listening SessionsI couldn’t wait to fi re up the Parasound combo, and was pleasantly surprised right from the get-go by the attractive blue-coloured LEDs that are behind all the knobs, which contrast nicely with the red-illuminated ‘P’ logo. The display is also a bright blue colour, with dot-matrix style lettering. Making tone and bal-ance adjustments is straight-forward, though the display in the ‘balance’ mode is basic in the extreme, looking for all the world like an old ‘Space Invaders’ game from the DOS days. Given all the buttons and lights, not to men-tion the dot-matrix display, I was surprised to fi nd that there doesn’t appear to be an indi-cator to show whether or not the tone con-trols are in-circuit or defeated. Maybe I just missed something. I regret that I made a note to double-check this, but by the time I re-read my note about the need for double-checking,

I’d already returned the amps. It’s of no real consequence—if you’re not sure you can sim-ply press the ‘Tone’ button—but it does seem odd. By contrast, if you press the ‘Mute’ but-ton on the remote, the word ‘MUTE’ is writ large in the front-panel display, leaving you in no doubt as to why there is no sound! I was thrilled to fi nd that switching to a dif-ferent source does not cancel the mute, and that touching either the volume controls on the remote or the front-panel volume control instantly cancels the mute function. This is exactly what should happen, yet few manu-facturers manage to get it right. One thing I am not sure Parasound has got right is the headphone socket on the front panel. It’s a 3.5mm phone socket instead of the more usual 6.5mm one. I know that it looks neater, and that because of the iPod, more and more headphones are now being supplied with the smaller plug rather than the larger one, but it’s not as if there wasn’t enough room on the front panel, is it?

You’ll be pleased to hear that this is where my carping ends, because when it comes to the operation and sound of this duo I could fi nd absolutely nothing to criticise. The con-trols all operate perfectly and precisely and the sonic performance is just out-and-out stunning! In the end I did end up using the balanced connections (and in the case of my CD player, right from the source) for almost all the listening sessions… though I did, of course, end up using unbalanced connec-tions for my turntable listening (so far as I know, no-one has yet developed a phono cartridge with a balanced output!). So, need-less to say, hum and induced noise were not a problem. Indeed I’d go so far as to say that I think this is the quietest pre/power amplifi er combination I have ever auditioned, and this

Parasound P3 Preamplifier & Halo A21 Power Amplifier



Readers interested in a full technical appraisal of the performance of the Xxxxxxxxxxxxxxxxxxxxxxxxxx should continue on and read the LABO-RATORY REPORT published on the following pages. All readers should note that the results mentioned in the report, tabulated in perform-ance charts and/or displayed using graphs and/or photographs should be construed as applying only to the specifi c sample tested.

LAB REPORT


particularly important when you’re playing back at the relatively low volume levels that are more common in domestic living rooms. I did actually check the noise levels when us-ing unbalanced connections and though I couldn’t do an instant A–B comparison, what I did hear convinced me that noise levels were just as vanishingly low with the unbal-anced connections as they were with the bal-anced, so self-evidently the circuitry has been designed for low noise levels right from the outset.

I seem to recall that the ultimate ‘ampli-fi er’ is a straight wire with gain and from what I heard from this Parasound combo, they’d come very close to this ideal, because not only could I not hear any noise behind the signal, I also could not hear any signal distortion. This proved to be the case not only when listen-ing to music, but also when I listened to spe-cially prepared test signals designed to reveal the presence of harmonic distortion, should it exist. No matter what I tried, and irrespec-tive of the volume level, the sound issuing from the Parasound P3 and A21 was as clean as a whistle.

I should say that when I say ‘irrespective of volume level’ I don’t think that in any of my auditions, despite using a variety of speak-ers of varying effi ciencies, I ever came even close to approaching the A21’s maximum output power—not even close! The A21 is an incredibly powerful amplifi er; of that I have not the slightest shadow of a doubt. My own amplifi er is rated at a shade over 120-watts per channel and the A21 just blew it away. Not so much in sheer volume—as I said, I didn’t even begin to approach full volume—but in terms of dynamics. I could be playing both amplifi ers equally loud, but when it came to a crescendo, or even a savage attack on a kick-drum, the A21 handled it so much better, de-livering a free-er, far more ‘natural’ sound. I can only liken it to driving a small-engined car up a steep hill. You can be travelling quite nicely, and it seems as if you could easily go faster, but when you put your foot down, you fi nd that absolutely nothing happens—the car doesn’t speed up at all. Ever had that feel-ing? Now imagine you’re driving a powerful V8 up the same hill at the same speed. If you put your foot down now, the car will rocket up the hill with a vengeance. It’s the same with Parasound’s Halo A21.

This power does not come at the expense of subtlety. I took particular care to listen

carefully to the very tiniest details of perfor-mances, right down to the whisper of pages being turned by performers, faint sounds in audiences, even the breathing of singers not singing at all, but simply awaiting their en-trance, and I could detect no difference in these details between the P3/Halo A21 and the same signal played through headphones… yes, these Parasounds are that good.

ConclusionSometimes I think Parasound is harbouring a death wish because despite the fact that it is building state-of-the-art components, its re-tail prices are consistently so low that many audiophiles don’t even ask for an audition. I should tell Parasound’s execs the true story of a start-up here in Australia that entered the dry-cell market by trying to sell very high-quality alkaline batteries at half the price of the two ‘biggies’ (Eveready and Duracell). The company bombed, because no-one even tried their batteries because they seemed too cheap. The company then re-invented itself and re-entered the market with exactly the same batteries, under a different brand, but this time priced just a few cents below the premium brands. Success was immediate and it’s now in a three-way tussle for the No 1 spot in the AA and AAA categories. So my message to Parasound regarding its P3 and A21 is that these are truly great products and you’d be selling a lot more of them if you set the retail prices a lot higher than you have. My message to you, dear reader, is that you only have a fi -nite amount of time up your sleeve before the good folk at Parasound read this review! Jutta Dziwnik

Readers interested in a full technical appraisal of the performance of the Parasound P3 Preamplifi er and Halo A21 Power Amplifi er should con-tinue on and read the LABORATORY REPORT published on the following pages. All readers should note that the results mentioned in the report, tabulated in performance charts and/or displayed using graphs and/or photographs should be con-strued as applying only to the spe-cifi c sample tested.


“the sound issuing from the Parasound P3 and A21 was as clean as a whistle.”



TEST RESULTS


Test ResultsPower output was massive! As you can see from both the tabulated fi gures and the bar graph results, the A21 exceeded its rated power at all test frequencies and into all loads, registering its highest output (808-watts/29.0dBw) when driving a 1kHz test signal through only one channel into a 2Ω load. When driving a both channels into standard 8Ω loads, Newport Test Labs measured a minimum output (at 20kHz) of 268-watts per channel, 18-watts higher than specifi cation. Under the same condi-tions, the A21 delivers 276-watts at 1kHz.

Measured into 4Ω loads with both channels driven the Parasound Halo A21 exceeded speci-fi cation by a minimum of 41-watts (at 20kHz) and by 50-watts at low and midrange frequen-cies. It delivers nearly 500-watts into 4Ω with only a single-channel driven, which is an indi-cator of the headroom available under dynam-ic conditions. Driven into 2Ω, the A21 com-fortably delivered nearly 700-watts per channel at all frequencies except in the extreme bass, where the amplifi er’s internal protection acti-vated at an output level of 450-watts.

Graph 1 is a spectrogram showing the to-tal harmonic distortion (THD) present in the output of the Parasound P3/A21 combina-tion, at a level of one watt. You can see that there’s a second harmonic at –100dB, a third harmonic at –110dB and a fourth at –112dB. These components are all far below the realms of audibility, either singly or in combination. Look, too, at the noise fl oor, which is sitting at –120dB above 1kHz and for the most part is more than 100dB below reference below 1kHz. Reducing the load impedance to 4Ω has a very small effect on the harmonic distortion com-ponents—such as they are!—with the most signifi cant being an increase in the level of sec-ond harmonic distortion to –90dB (equivalent to a distortion level of 0.003%). This is shown in Graph 2. Overall THD+N at one watt was measured by Newport Test Labs at just 0.006%.

Distortion increases signifi cantly at rated output, as you can see in Graph 3 (which shows the distortion spectrum at 250-watts output into 8Ω) and Graph 4 (400-watts into 4Ω). Although you can now see harmonic dis-tortion components stretching out to the 13th and beyond in the 250-watt/8Ω graph, the sec-ond and third components at 2kHz and 3kHz are both in the order of 90dB down (0.003%), the fourth and fi fth components are in the order of 100dB down (0.001%) and all other components are even further down again. At 400-watts into 4Ω, the second harmonic is at –80dB (0.01%) and the third and fourth have increased slightly in level. More signifi cantly, the structure of the distortion components has changed from being evenly distributed between the odd- and even-order harmonics


Continued on page 100




to favouring the odd-order harmonics. Also, you can see from the sidebands down around the fundamental (1kHz) and stretching up to 4kHz, that the power supply is fi nally running out of puff. This is hardly surprising: dropping 400-watts of power across 4Ω means the A21 is delivering a continuous current of 10 amps. Note also that because of the increased power output, the noise fl oor is even lower again, al-most down at the –140dB limit of the graph. Despite appearances, summing all these dis-tortion components and adding in the noise still gives a THD+N fi gure of just 0.005% at rated output, which is an order of magnitude better than most high-power amplifi ers, in-cluding high-end designs.

The Parasound P3/A21’s frequency re-sponse was outstanding. Newport Test Labs measured it as extending from 1Hz to 59kHz –1dB and from 0.5Hz to 105kHz –3dB. Remem-ber that most manufacturers quote frequency response specs separately for the pre and power amplifi ers. This measurement includes both! The response within the audio band is shown in Graph 5. The black trace shows the response into a standard laboratory test load (a Dale 8Ω non-inductive high-power resis-tor). You can see that it’s incredibly linear, and only 0.04dB down at 7.5Hz and 0.14dB down at 20kHz. Using the normal 20Hz to 20kHz criteria, the frequency response of the P3/A21 would be within 0.07dB. The other trace on the graph shows the frequency response into a load that simulates that of a typical two-way loudspeaker system. This normally causes the frequency response of most amplifi ers to de-viate well outside their specifi cation, but in this case the Parasounds still returned a result of 20Hz to 20kHz ±0.07dB. Notable is the fact that the red trace for the most part does not deviate from the black trace by more than 0.02dB! Indeed, in order to show up such a vanishingly small difference, Newport Test Labs had to expand the vertical (dB) scale of this graph to 0.04dB per horizontal divi-sion, which means it’s far more ‘zoomed-in’ than you’ll normally see in this (or any other) magazine. The more usual graph presentation is shown in Graph 5a, which has horizontal divisions of 0.2dB. As you can see, only the non-inductive response is shown because at this magnifi cation, it would overlay the other response anyway!

Channel separation was excellent, with a best result at 1kHz of 90dB, reducing to 84B at 20Hz and to 70dB at 20kHz. Remember, these tests are with both the P3 and the A21 being tested as a single entity. Even better was channel balance, which came in at 0.028dB. This would be good in a high-end stereo inte-grated amplifi er, and is unheard-of in a pre/power combination.


“The Parasound P3/A21’s frequency response was outstanding. Newport Test Labs measured it as extending from 1Hz to 59kHz –1dB and from 0.5Hz to 105kHz –3dB.”

Continued from page 38

32-38,100-101Parasound HFMar08.iSec1:100 Sec1:100 22/02/2008 10:53:50 AM


Australian Hi-Fi | 101

TEST RESULTS

Graph 5b simply shows the boost and cut action of the P3’s tone controls. You can see that boost is restricted to around 7–9dB and cut is bang-on –10dB. The boost is quite prop-erly shelved, so using the tone controls won’t mean you are overdriving your tweeters at ultrasonic frequencies (or overdriving your bass drivers at infrasonic frequencies!), which is what happens if there’s no shelving. Using the controls does have a very slight effect on the response at midrange frequencies, but it’s diffi cult to tell what it is from this graph be-cause it appears to me that whoever ran the test at Newport Test Labs failed to properly calibrate the ‘fl at’ response at precisely 0dB, and I doubt that boosting the controls actu-ally results in there being less level at 1kHz!

Intermodulation distortion was almost completely non-existent, as you can see from Graph 6. The two test frequencies of 19kHz and 20kHz are towards the right of the graph, and are reproduced at the correct level. There are two unwanted sidebands appearing at 18kHz and 21kHz, but they’re at –95dB, or 0.001%, so would be inaudible and inconse-quential. As for the main purpose of this par-ticular test, I can’t see any unwanted signal regenerated at 1kHz at all, which is a fabulous result (for the A21 in particular). The small spikes in the noise fl oor at the extreme left of the graph appear to be power supply-related,

with some 50Hz at –97dB and the others more than 100dB down.

You can see that noise is low on the graphs, so the tabulated fi gures should be no surprise, with the A-weighted S/N fi gures coming in at 97dB referenced to 1-watt and a stunningly good 115dB referenced to rated output. I think a signal-to-noise ratio of 115dB is the best I have ever seen from any amplifi er. Sure this fi gure is given a boost because of the very high output of the A21, but it’s still a mag-nifi cent achievement for Parasound. The frequency response into a simulated speaker load should have given you a hint that the A21 had a high damping factor, and this in-deed proved to be the case, as you can see from the table, with the A21 scoring a result of 320 at 1kHz.

The power consumption fi gures show that the duo draws quite a lot of mains power at stand-by (28-watts) and a signifi cant 143-watts when the two are switched on but do-ing nothing at all. Consumption increases to 405-watts when the amplifi er is delivering just one watt to your speakers and to 753-watts when it’s operating at rated power, so it’s not an overly ‘green’ amplifi er and this will certainly be refl ected in your electricity utility bill!

Tested with square waves, the Parasounds came though with all guns blazing. The 100Hz

Parasound Halo A21 Power Amplifi er - Test Results for Power Output

Channel Load (Ω) 20Hz

(watts)

20Hz

(dBW)

1kHz

(watts)

1kHz

(dBW)

20kHz

(watts)

20kHz

(dBW)

1 8Ω 294 24.7 294 24.7 285 24.5

2 8Ω 271 24.3 276 24.4 268 24.3

1 4Ω 490 26.9 495 26.9 484 26.8

2 4Ω 450 26.5 454 26.6 441 26.4

1 2Ω 450 26.5 808 29.0 760 28.8

2 2Ω 450 26.5 690 28.4 684 28.3

Note: Figures in the dBW column represent the output level, in decibels, referred to one watt output.

Parasound P3 Preamp and Halo A21 Power Amplifi er - Test Results

Test Measured Result Units/Comments

Frequency Response @ 1 watt 1.0Hz–59kHz –1dB

Frequency Response @ 1 watt 0.5Hz–105kHz –3dB

Channel Separation 84dB / 90dB / 70dB (20Hz/1kHz/20kHz)

Channel Balance 0.028dB @ 1kHz

THD+N 0.006% / 0.005% 1 watt/rated o/p

S/N Ratio (unweighted/weighted) 91dB/97dB dB re 1 watt output

S/N Ratio (unweighted/weighted) 109dB/115dB dB re rated output

Input Sensitivity (CD input) 104mV/1.6V (1 watt/rated output)

Output Impedance 0.025Ω OC = 2.8447V

Damping Factor 320 @ 1kHz

Power Consumption 28.0/143.0 watts Standby/On

Power Consumption 405 watts /753 watts 1-watt/Rated O/P

Mains Voltage Variation 231–252 volts Min–Max

square wave shows not a skerrick of tilt (indi-cating an extended low frequency response) and no ‘curve’ to the top (showing no phase shift). Indeed it’s almost indistinguishable from the 1kHz square wave, which has such a good shape that it would be easy to swear on a bible that it came straight from a function generator, rather than via the P3/A21 combo. The 10kHz square wave has a rounded leading edge, which is due to the frequency response starting to roll off above 59kHz; otherwise, it’s excellent. The fi nal oscillogram, which shows square wave performance when the amplifi er is loaded down with a parallel capacitance, re-veals that the A21 will be unconditionally sta-ble into any loudspeaker load and in particu-lar will drive electrostatic models with ease. There’s a tiny single-cycle overshoot visible that rises to less than a quarter of the overall wave amplitude, and a complete recovery af-ter the second cycle.

If I had designed Parasound’s Halo A21, I’d be mighty pleased with myself, so Curl deserves an enormous pat on the back, and Parasound is to be commended for manag-ing to deliver such superlative performance at such a low price, but I shouldn’t neglect the P3, which more than played its part in achiev-ing these results… superb performance from both components.

Steve Holding

32-38,100-101Parasound HFMar08.iSec1:101 Sec1:101 22/02/2008 10:54:14 AM


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