Фонокорректоры — Boulder 508

The 508 is a transistor phono stage built by Colorado-based Boulder Amplifiers, and it opened the firm's lower-priced 500 series. At launch it carried a USD 5,000 price, making it the least expensive Boulder component of its time, and the figure later rose to USD 5,900. The idea behind it was a short, direct signal path with almost no user settings, in contrast to the heavily configurable phono stages further up the Boulder range.

Key specs that matter

The circuit is balanced from input to output and uses XLR connectors only, with one pair of inputs and one pair of outputs. A rear toggle sets the cartridge type, MM or MC. In MM mode gain is 44 dB with a 47 kOhm input impedance, while MC mode gives 70 dB of gain into a 100 ohm load. Output impedance is 100 ohms balanced, and RIAA accuracy is held within 0.5 dB from 20 Hz to 20 kHz by an active two-stage equalisation network. The case measures 292 x 58 x 241 mm and weighs 5.2 kg. The mains input accepts 100 to 240 V.

Engineering and use context

Boulder cuts the case out of one 6061-T6 aluminium billet on Boulder's own CNC equipment, then it is bead blasted, sanded and anodised, with the anodising handled by an outside vendor. Inside, a self-regulating power supply sits in its own partitioned compartment to keep mains noise away from the audio board. That board is densely populated with surface-mount parts placed by Boulder's in-house pick-and-place machines, which leaves almost no internal wiring and cuts parasitic capacitance and lead inductance. A built-in low-cut filter removes excess low-frequency energy from warped records. The front panel carries only a power toggle, a mute button and a single white LED, and there is no remote control. Boulder states that the efficient supply allows the unit to stay powered at all times, avoiding warm-up periods. The rear panel also holds a ground screw beside the inputs, an IEC socket and a fuse.

Pairing

Gain and loading are fixed, so the 508 suits typical MM cartridges and MC designs that work well into the fixed MC load, while cartridges with very low output may require an external step-up device. Turntables with RCA tonearm cables connect through the supplied pair of RCA to XLR adapters, and a preamplifier with only RCA inputs needs a second pair. A balanced line stage such as the Boulder 1110, with five XLR inputs, keeps the whole chain differential.

Alternatives

The Boulder 808 Phono Preamplifier builds on the 508 with MC and MM loading set by removable Personality Cards, a mono mode and a switchable low-cut filter in a 4.76 kg chassis.