This review page is supported in part by the sponsors whose ad banners are displayed below |
 |
 |
Testing methodology. I compared the Soulution 720 to my reference Ayon Audio Polaris III custom version, as well as other linestages reviewed for the same issue of HighFidelity—the ModWright LS 36.5, Audio Research Ref5 SE, Avantgarde Acoustic PRE, Octave Jubilee—and direct coupling my Ancient Audio Lektor Air V-edition CD player to my Soulution 710 power amp. The 720 drove two the Soulution 710 and Leben CS-1000P. It connected to the AC mains via a Harmonix X-DC350M2R Improved-Version power cord and sat on its own feet on the Base IV rack.
|
 |
The review was an A/B comparison with A and B known. Music samples were two minutes long but I also auditioned whole albums. Coupling was via RCA cables on both source and power amp sides. Though the 720 offers XLR balanced inputs its circuit is unbalanced. RCA cables sounded better than XLR. It’s important to properly warm up this machine. An hour should be sufficient to stabilize the temperature and parameters of active amplification and power supply components.
|
 |
Design. Front and rear panel. The Soulution 720 is a transistor preamplifier with built-in phono stage. Its modern industrial design is characteristic for this manufacturer and often compared with cubist works or possibly designs from Kelvin Klein. It is a very large and heavy device with flat aluminum planes and a large window on the front panel which is largely decorative since its red dot matrix display and the three LEDs behind it only take up some of its space.
|
|
|
Adjacent to the display are three buttons for power from standby, mute and prog which changes device mode from normal (operating mode) to programming mode where we can individualize settings. We can choose the active input after power on, which input gets associated with the monitor loop, set the power-on level, display brightness, maximum volume, channel balance, input names, frequency extension (if we have a SACD player), input gain as well as phono stage settings. This is a modern highly versatile machine.
|
 |
On the right side we have two rotary knobs for input selection and volume control. They also work as buttons to confirm our menu selections. Volume can be controlled over an 80dB range in 1dB increments. The 720 is an unbalanced preamplifier hence the most important sockets are the four RCA connector pairs rather than the two XLRs. One of those RCAs is a phono input. The linestage 721 version costing 15.000 PLN less turns the phono input into a standard line-level. The phone input connectors in the 720 are shorted by special RCA plugs to reduce input noise. Above each phone connector there is a hot-pluggable input load module with a handle that may be changed. And there’s a ground terminal. We also get three pairs of outputs – a fixed RCA monitor loop and two pairs of variable outputs, one RCA, one XLR. Next to the XLRs are ground lift switches.
|
 |
On the far left side we have the IEC power inlet with a mechanical power mains switch and high-quality Neutrik RJ45 Ethernet ports acting as system links between various Soulution components. We also get a multi-pin (remember a DB-25 parallel printer port?) DC-out power connector for Soulution’s outboard phono stage.
|
|
|
Interior. The enclosure is made up of very thick rigid aluminium plates with invisible fasteners which are all located on the bottom. This is no preamp with NOS components. It’s an ultra-complex design based on the same philosophy as the 710 power amplifier – a hyper-short signal path over several gain stages. The remainder of parts are for the power supply, parallel and control circuits which spread out over several PCBs with the largest one housing the gain circuits. Each input sports a Burr Brown OPA627 buffer from whence the signal is sent to a stepped attenuator on ultra-precision Dale resistors switched by reed relays (far superior to normal relay switches) as also championed by McIntosh and Linear Audio Research from Poland. The next step for the signal is an individual gain stage for each input—also on a three-stage resistor ladder—and finally we come to the output gain stage. Its input is based on the OPA627 and AD817, the latter from Analog Devices. The output is driven by pairs of 2SA1606+2SC4159 Sanyo transistors mounted on a common heat sink. They are bipolar epitaxial planar silicon transistors.
|
 |
The power supply looks absolutely brilliant. It’s actually four separate power supplies with many secondaries. The largest powers the main PCB. It sports a large toroid transformer that does not reduce the mains voltage to the usual dozen or so volts but powers a very large switching power supply coupled by thick stranded copper wires to the main PCB. The stranded wires are soldered to thick copper rails running along the entire PCB distributing power. There is a separate power supply with two smaller transformers and another small switching power supply for various auxiliary systems. Everything looks very impressive. Perhaps that’s what's really behind such impressive dynamics and low noise – the 720 boasts a staggering 130dB signal to noise ratio. All power supplies are fully shielded; the toroid has its own shield and the switching power supply is mounted on a thick aluminium plate. The phono stage occupies a separate small PCB. Its gain stage is based on several OPA627 chips, two of which sport small heat sinks. RIAA equalization circuit is built on high-quality BC foil capacitors. In general there are no ’ordinary’ parts in sight. All are very expensive Dale resistors, Wima capacitors etc.
Remote control. The wand is the same as for the Soulution SACD player – a small but very handy plastic device.
|
|
opinia @ highfidelity.pl |
Technical specifications according to the manufacturer:
Power Consumption: 60W (<0.5W in standby)
Gain: XLR: +9.5 to +18.5dB; RCA: +3.5 to +12.5dB; phono: +54 to +60dB
Frequency response: DC – 1MHz
Slew Rate: 400ns
Distortion (THD): <0.0006%
Signal to Noise Ratio: 130dB
Channel Crosstalk: 105dB
Input impedance: XLR 2kΩ, RCA 47kΩ, phono adjustable
Output impedance: XLR 2Ω, RCA 2Ω, monitor loop 100Ω
|
 |
 |
|
 |
