Audiophile Home Theater

Sigma SSP Multichannel preamplifier-processor, Sigma AMP2 and AMP5 amplifiers from Classé Audio

Audiophile Home theater By Michel Laliberté After its stereophonic immersion at Adrien Rouah’s (see TED Magazine April-May edition) the Sigma system has found its way to my house with the addition of the Sigma AMP5 in order to build the most affordable 7.1 system from Classé.

TED Magazine, June-July 2015

What is the goal? The Sigma system is aimed at audiophiles who will use their system for music listening in stereo or to watch a multichannel movie in a multifunction room. This person wants something better than a mass produced receiver but does not necessarily have deep enough pockets to be able to afford the pinnacle of high-end products. As a matter of fact, even if we cannot speak of bargain products here, the fact remains that the Sigma series is 50% less expensive than the flagship products from this company. So, in a 5.1 configuration, a Sigma SSP combined with an AMP5 represents a $10,000 dollars investment. An additional $9,000 dollars would be required to buy an SSP-800 and a CA-5300. You will not find cheaper prices if you look at the Canadian competition: a Bryston SP3 and a 9B will cost $19,000 and with Anthem, a D2V and P5 will cost $21,800. Design, choices and decisions Classé has been able to exert a control on the price of the Sigma series by attacking several aspects of the design and making sensible choices without any compromises towards sound quality. We can immediately notice the simplicity of the video stage of the SSP offering only HDMI v1.4 connections. Eight inputs for one output without upscaling. The expensive and obsolete analog video section is absent and before implementing HDMI 2.0, a decision has been taken to wait until native 4K material becomes available. By that time, the HDMI 2.0 standard might also become obsolete. This is why a modular approach has been taken to enable hardware updates of the video board if the need becomes essential. In the meantime, let your Blu-ray player or your TV do the video conversion. However, the omission of a second HDMI output is disappointing. I have in my “multimedia room” a TV and a projector and the idea of having to use an external HDMI splitter hanging behind the SSP makes me curse. Analog stereo audio inputs are limited to three amongst which one is a balanced XLR pair. This is amply sufficient. And if vinyl is a part of your diet, the same optional phono module used for the CP-800 is also available for the SSP. For digital audio, 3 coaxial SPDIF inputs and 2 TOSlink optical inputs complement the HDMI inputs. Well in tune with its time, the SSP enables USB connection of an iPod, iPad, iPhone from the front panel and another USB port located on the back panel is available for a PC used as a music source. This input is good up to 24 bits and 192 kHz. An Ethernet port is used for streaming music from a computer, a NAS music server or using Apple’s AirPlay. The Sigma SSP has eight analog audio outputs. Using both balanced and unbalanced on RCA and XLR connectors we find the right and left channel . The remaining outputs for center, sub, left and right surround and auxiliary 1 and 2 are all on RCA sockets. The latter can be configured in

four different manners: stereophonic surround for the rear speakers, height channels, stereophonic conversion of the main source or mirror image of the left and right channels for bi-amplification. If you are using two subwoofers, a “Y” splitter will be required. The Sigma SSP decodes any audio formats up to 7.1 channels. No Dolby Atmos or Auro 3-D for the time being: too little available content to justify it. Once again, the modular approach of the Sigma SSP will enable replacing the multichannel decoding board. For this application, Classé does not use an internally designed circuit for this process but a Momentum Data Systems DAE-82 card based on the Texas Instrument microprocessor (from the DA 810 series). A nice way to save a few dollars. Another saving: the Texas Instruments PCM1792 reference digital to analog audio converters used in the SSP-800 are replaced here by Wolfson 8741 which are also excellent but less expensive. Design is an art, it marries a goal, a price and compromises. At the bottom of the ladder it is possible to find many affordable class D designs offering advantageous performance and efficiency compared with class A/B. However, if the price is increased, class A/B tends to dominate by offering a superior sound quality. By increasing the price again, we reach a zone where it is now possible to attack the main deficiency of class D amplifiers: Dead Band Time, this short period when both phases of the amplifier are dead (off) produces a lot of distortion similar to the switching distortion found in class A/B amplifiers except that dead band time distortion is more difficult to eliminate. Classé’s know how illustrates here how an in-house developed solution has solved the problem. As a result, Classé now has a circuit that has a dead band time below 3 nanoseconds thus minimizing the use of a negative feedback loop and bringing the filter frequency well above the audible band. A class D amplifier implies the use of a Switch Mode Power Supply (SMPS) this is another area where Classé has heavily invested for the past ten years already. An SMPS first appeared in the CP-800 preamp, then in the CA D-200 amplifier and now in every Sigma component. Once every technical difficulty has been mastered, a well-designed switch mode power supply can yield a superior signal to noise ratio compared to a linear supply while being less sensitive to voltage variations from the AC mains and while also rejecting only negligible amounts of interference in the AC mains. Above all, it can reach an efficiency of 95%. Or if you prefer, only 5% of the consumed energy is transformed into heat. Linear power supplies will never go above an efficiency of 60% and are much bigger and heavier. So, Classé estimates having reached an optimal compromise between power, performance and price and in addition offers huge energy efficiency in compact and elegant boxes that generate very little heat. While the design is Canadian, the assembly is done in the B&W manufacturing plant in China.

Configuration Classé, just like many high-end manufacturers, resists the temptation to use an automated calibration system. Everything is done manually. It takes more time but with the right tools the results are less extravagant. Using a spectrum analyzer, ironing out the frequency response is a charm using the nine parametric bands available for each channel including the subwoofer. I often repeat that equalization is not a panacea but used intelligently it enables correcting and diminishing the unavoidable aberrations, especially in the low frequencies in a small room. Every mixing studio that I have visited uses equalization to even out and perfect the frequency response of their playback system. If the professionals can use it sparingly , why not us at home? In addition to equalization, Classé allows six speaker configurations. It is possible to define for each of them the number of speakers and the frequency and slope of the filters for each channel if bass management is activated. Each configuration also allows discrete levels and distance adjustments for each channel. As an example, it is possible to create a profile for a stereo configuration using two speakers without bass management for vinyl listening, a 5.1 configuration without bass management to listen to multichannel SACD and a 7.1 configuration with bass management to watch a Blu-ray disc. The possibilities are endless and will enable optimization of your speakers for each type of listening session. Every parameter of the Sigma is accessible from the tactile front panel screen and its menus. The menus can also be routed via the picture from the HDMI output and navigating the menus is done via the little remote control. Don’t get fooled by its small size and its eleven keys, you can do everything with it: 3 keys are used respectively for on/off, source selection and mute. The two volume controls and the 3 transport keys have a second duty to become navigation keys for the menus. Finally the last 3 keys are assignable and give access to the functions chosen. In my case, I have assigned F1 and F2 to my two main sources and F3 was used to activate the main page of the SSP’s menus. For even more control, the Ethernet port will assign an IP address to the SSP and with the free Classé app available from the Apple App Store, your iPod Touch, iPhone or iPad, the dashboard of the SSP is virtually imported giving full control of the preamp while accessing your music files through your domestic network. Listening It is often in the upper range that class D amplifiers will expose their weaknesses so we will start with SACD multichannel music with Yannik Nézet-Séguin directing the Orchestre Métropolitain du Grand Montréal interpreting Prélude àl’après-midi d’un faune from Debussy. I have chosen this piece for the smooth and velvety flute intro, without any harshness. Shortly

after there is a precise and well defined harp. The soundstage is wide, deep and very stable. The Sigma system offers a superb musicality and cannot be faulted in the upper frequencies. Let’s go a little bit lower in the spectrum with Diana Krall in SACD 5.1. All along The Girl in the Other Room album, her voice is natural and sibilance is well controlled. The upper medium shows a nice presence and never falls into aggressiveness. The articulation of the piano and the bass is beyond reproach. The fine tuning performed by the parametric EQ at the bottom of the spectrum smooths out resonant frequencies in my room and improves the realism of the double bass. With Sing Sang Sung from Big Phat Band in Dolby Digital 5.1, the Sigma AMP5 exhibits his “muscles” and “cardio” with masses of power and never runs out of breath. The top of the spectrum is sparkling and the sheer limpidity of the trumpet and clarinet solos makes us forget we are listening to Dolby Digital through a class D amplifier. To my surprise, the bottom of the spectrum does not have the same articulation, the same control, the same solidity as the very best class A/B amplifiers (a lot more expensive) that I have had the chance to try. Little hypothesis: the passive components used to filter out the switching frequency of the amplification stage increases the output impedance and consequently reduces the damping factor. Let’s finish with The Lone Ranger in Blu-ray with a soundtrack in DTS HD Master Audio 7.1. The chase in the train in chapter 21 is a torture test with all seven channels used at their maximum. Even without the bass management activated, it is power, power, power. The power supply never gives up and the incredible dynamic range never collapses even at very high volumes. The soundtrack, at the same time heavily charged and full of details is displayed to its full advantage thanks to the tonal equilibrium reached with all the possible adjustments allowed by the Sigma SSP. The video section is transparent. The absence of conversion accelerates switching between sources and seems to preserve better the synchronization between sound and picture. To conclude: at the threshold of very high end I really liked this Sigma system. This processor really offers all the flexibility anyone could dream of and the omission of some inputs that simplifies the layout of the back panel and will most likely never be used is amply justified. The multichannel audio performance is beyond reproach and I do not think that the absence of Dolby Atmos or Auro 3D decoding will be a factor for the targeted customers of these products. What can we say about all these configuration menus except that, even if they require time, a basic expertize and specialized measuring instruments, they enable reaching accurate and convincing results. And these results are what Classé retailers will be please to help you reach.

On the amplification side, Classé pushes class D amplifiers to new summits. If on a few aspects they do not reach the performance level of the very best class A/B amps, they are coming very close and at half the price they definitely win the war over weight and energy efficiency. Between a $3,000 dollars receiver and a system built from separate components for $20,000 dollars, there is a nice place for the Sigma series. Classé proposes a price to performance ratio that will allow many cinephiles/audiophiles to afford a distinctive product and to taste what very high-end is.