REVIEW: HESCHL AUDIO LABS HAL350 DAC AMPLIFIER

Mark Gusew's avatar

by Mark Gusew

20th June, 2019

REVIEW: HESCHL AUDIO LABS HAL350 DAC AMPLIFIER

Setting out to design, develop, and manufacturer a new amplifier today is much harder than you can imagine, especially when the market has thousands of excellent amplifiers already. What drives a person to create another one? All this and more will be revealed. 

Heschl Audio Labs

HAL350

DAC Amplifier

AUD $24,999 RRP

First, meet Rod Harris. A mild-mannered electronics genius, with far more than a casual interest in music and electronics. 

Rod started by repairing audio equipment, getting an understanding of how things tick and then began designing amplifiers and speaker systems for fun in his spare time. 

His designs were good as he was soon being asked to develop custom solutions for others. After spending time working in the professional recording studio industry with high end pro audio equipment, he lamented that folks at home weren’t fully hearing the quality of the music produced by the studio. Realising that even some well known ‘high-end’ equipment didn’t sound real, he set out to create products that make you forget about the electronics and allow the listener to focus on the music.

So Rod spent years perfecting circuit topology, the choice of individual components, and the way that they all interacted with each other in a synergistic manner. 

Rod told me that every resistor, capacitor or any other component has a ‘sound’ and that there is a myriad of choices to be made in balancing the overall voice of any component. 

The result of all of that effort is the newest integrated amplifier on the Australian market, the Heschl Audio Labs HAL350, the subject of this review. 

Heschl Audio Labs is made up of three self-confessed audiophiles - Dan, Simon and Rod, with its headquarters at Queensland’s sunny Gold Coast.

The brand was named after the Heschl gyri, which is the part of the human brain that processes incoming auditory information. 

Without it, you hear no sound and research has shown a musician’s Heschl’s gyri is typically larger than most.

The Heschl HAL350 is an all-new design, and to the best of our knowledge, something rarely seen. Rod (the chief designer) did not use audio or amplifier designs from a textbook but instead created the circuit designs himself. Just stop and think of the immensity of that. 

Each of the components that are required inside an amplifier, like the power supplies, preamplifiers, DAC, control systems and output stages are items that demand intelligent design, careful choice and lots of experimentation. To create the best sounding amplifier, you have to use all of the best ingredients. 

Heschl Audio Labs' HAL350 sells for $24,999 RRP in Australia, so you would expect it to be a technical tour de force. Let’s delve deeper.

Design

The HAL350 was designed with modern digital sources in mind. Described as a DAC Amplifier, with the majority of music consumed today being in a digital format, the high-quality DAC that is fitted on-board as an integral part of the design makes perfect sense.

Rod selected a discrete R-2R or ladder DAC design, with an FPGA based FIFO buffering/reclocking stage and custom digital filters. It has 28-bit resolution. The DAC is capable of up to 24-bit/384kHz data from its galvanically isolated USB input and up to 192kHz on its single coaxial RCA (S/PDIF) and optical (Toslink) inputs. 

The DAC utilises proprietary voltage regulators that are super low impedance and high in bandwidth. An ultra-clean low noise power supply for any DAC is critical for sound quality, as minutely stepped voltage is effectively what you are hearing. 

The other remaining input is a single RCA or unbalanced input. Heschl believes that a single input is all that is required, and typically it will be a phono input from a high-quality stand-alone phono stage. Incidentally, Heschl does offer an option for a balanced XLR input for those that would prefer it. 

The HAL350 is a large, tall amplifier, measuring (W x H x D) 435 x 250 x 408 mm and weighing a back-breaking 38.5 kg. It’s only available in black and looks somewhat imposing and menacing. There is a display window with a white OLED screen that is clear and easy to read, even from a distance. 

The large volume dial is smooth in operation, and inputs are chosen by pushing the dial inwards for selection. It feels modern and works very well. The volume adjustment is a purists dream; an R2R attenuator controlled in the digital domain with 64 steps (1db per step) and utilises seven precision relays for perfect channel matching. There is a soft clicking sound as you adjust the volume setting as the relays work to vary the output. 

At the heart of the amplifier is the oversized power supply. Once again, this is Rod’s design. A massive 2KVA toroidal transformer is fitted, with extra turns per volt and additional electrostatic shielding between the primary/secondary and outside. FRED diodes (Fast Recovery Epitaxial Diodes) and large storage capacitors complete the story. 

There is no mains power switch at the rear of the amplifier; the front panel switch powers the amp up. The detachable power cord is unusual in that it isn’t the standard IEC C13 connector at the amplifier end, but rather a 16A Neutrik speakON connector. Frankly, I like it. It’s rugged and has a locking device to guarantee a safe, secure power connection. Traditional IEC mains connectors can have a somewhat poor fit, but the speakON is a far more positive fit, and it locks, so the cable can never fall off. The cable is supplied by the Australian manufacturer, EGM Audio, with 14AWG 2.5mm cores, with the same gauge used internally. 

The power amplifier is also unique in using a very high 330v in the Class A driver stage, more akin to voltages used in tube amplifiers rather than in solid state designs. The output stage is Class AB and uses sixteen switching FET’s. A high impedance feedback loop is used. Rod says that the amp was designed like a valve amp in some respects, but without the valves and their inherent limitations.

The HAL350 delivers a minimum of 350 watts per channel continuously into an 8ohm load and 600 watts into 4ohms. Moreover, it is stable with any load 2 ohm and above, allowing a vast choice of loudspeakers, even those ‘difficult to drive’ ones.

It does seem that every aspect of the design and execution of this DAC Amplifier has been thoroughly thought out. Simon Garcia, Heschl’s Head of Sales, told us:

We have designed our HAL350 flagship amplifier from the ground up, incorporating a minimalist design philosophy using a synergy of high-quality components all individually matched and tuned together as one. It is the result of many years of research, prototypes and perseverance.

So far, it looks like that effort is paying off.

In Use

With only one digital input and a single line-level input available, making the connections to the HAL350 is very straightforward. As soon as the front panel switch is pushed, the unit comes out of standby, and a pleasing white backlit circle starts to glow as the display springs to life. The amplifier has been designed with soft start relays to gently start and bring on-line the various internal components with longevity in mind.

There are several ways to control this amplifier. First off is the usual single multi-function volume control on the front panel. For those of us that prefer remote control, a small Apple Bluetooth remote control was included with my review sample, which proved simple and effective. Otherwise an infrared remote with RC5 control protocol can be used, although it is not supplied.

Alternatively, you can use a remote control app from Heschl available for iOS and Android on a smartphone or tablet via Bluetooth. Included is gesture control where you can shake your phone to mute/unmute the sound. Cool.
 
The OLED display can be switched off if preferred, and via the menu is an internal temperature display and monitoring function. Comprehensive self-protection is inbuilt to keep the amplifier working safely for many years. If the protect circuit detects any DC offset or other faults, it will illuminate the protect indicators at the rear of the amp and disconnect the speakers. 

If your audio is sent via a USB input from a Windows-based computer, you will need to go to the Heschl USB Driver web page and download and install the driver. If you use an Apple Mac, a driver isn’t necessary.  

Listening

So how does the Heschl HAL350 sound? Most of my listening was via a Melco N1Z/2 music server with USB to the Heschl DAC. Immediately apparent was a sound that is clear, open and spacious, with power and finesse in equal portions. 

The HAL350 has the unique ability to fill the room with a huge soundstage, in the same way that I'm used to good tube amplifiers doing so. If you have never heard the difference that a high-end amplifier can make to the sound of your music, then let me assure you that something of this calibre quickly convinces you that not all audio equipment sounds the same.

I have to say that it was unexpected on my part of just how large and three dimensional the soundstage sounds. I can see myself getting addicted to the feeling of spaciousness and ease that the HAL350 delivers. 

Rod told me that one of his design criteria was to create a product that would have some of the favourable sonic aspects of tube gear, like the openness, large soundstage and presence, but without the power restrictions and fragility of valves. I think that he has succeeded splendidly. 

I’ve heard valve amplifiers project an incredibly large soundstage but with an inherited sound that is too warm, burnished and with added colour - which in my book is distortion. The HAL350 delivers a big soundstage without those drawbacks with absolutely no audible distortion or an overly forward sound. It just sounds right, musical and nimble, with good speed and pace.

Tonally, the HAL350 is very neutral and balanced, with a sweet extended treble, rich and textural midrange and full and balanced bottom end. No particular area especially dominates, and it sings with a single voice, harmoniously. The bass does not have the greatest guttural extension known to man, but this is not a complaint but rather an observation. The bass is perfectly adequate and in proportion to the rest of the sound.   

As a result of the balanced tone, presence and neutrality, music is played with an accuracy that I am confident portrays the artist’s intent. It’s so clean that all the detail that's often hidden within tracks is unlocked, on show and easily heard. It has the effect of bringing the listener closer to the performance.

With 350 watts of continuous power available per channel, there is no shortage of grunt or volume available. It seems limitless. It doesn’t get uncomfortable at all when the volume is loud enough to make you feel like a cheeky schoolboy. 

Without question, the HAL350's built-in DAC plays a significant role in the overall sound quality, confirmed when I connected an external DAC of known sound quality through the Heschl's RCA inputs. The internal DAC complements the amplifier very well in sounding neutral, open, and with tons of inner detail. 

It's also very quiet, with dark backgrounds and silence between the notes. It's safe to say that you would need to spend many thousands on an external DAC that would be as good, and even more in worthy cables. As an integrated amplifier with an internal DAC, the HAL350 makes a lot of sense as a complete package.  

As excellent as the HAL350 is for digital music, the thoughtful provision of the RCA input caters for the analog enthusiast to add a good turntable and phono setup which I have no doubt would be similarly spectacular.

Conclusion

Heschl has made a stellar effort to produce something as good as the HAL350 for its first release. Starting with a clean sheet design approach and ending up with a product that sounds as good as it does really is a big deal. 

In my opinion, Heschl Audio Labs deserves a standing ovation, and the tireless work devoted to making the HAL350 sound the way that it does should be celebrated. 

Heschl’s world-class HAL350 is a viable alternative to those that prefer some of the best aspects of the sound of a triode valve amplifier but with the low running costs, reliability and convenience of a solid state design. Not to mention the advantages of having 350 watts of power available. 

Where you save on cables and purchasing an external DAC, the limitation of just one analog input may prove a difficult obstacle to overcome for some buyers though.

The HAL350 demands the best auxiliary equipment that you can get your hands on and gives back such an intimate relationship with the recording artist. Give me more.

For more information, visit Heschl Audio Labs.

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Mark Gusew's avatar

Written by:

Mark Gusew

Starting his first audio consultancy business in the early ’80s whilst also working professionally in the electronics industry, Mark now splits his time between professional reviewing and AV consultancy.

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