Manley STEELHEAD RC - Manual (Page 5)

5
FEATURES AND APPLICATIONS
1. HIGH PERFORMANCE FRONT END
The STEELHEAD RC preamplifier makes the best use of active and passive component and circuit
developments generated over the past half-century. The hybrid cascode gain blocks simultaneously deliver
wide-band high-gain, low noise and low distortion performance without having to resort to heavy-handed
amounts of negative feedback. Or overly complex circuit topology. The multiplicative aspect of the cascoded
device’s output (anode) impedance means that the most important characteristics of each gain stage are pre-
served even though the local negative feedback present in each block is very small. This approach makes the
amplification factor of each stage insensitive to tube gain or transconductance variations which occur due to
device production tolerance allowances or aging.
Other uncommon traits include high quiescent and operating current in each gain stage. This lowers
the static and dynamic impedances found within each stage and raises system bandwidth. Musical material
which would cause a cave-in of the typical current-starved 12AX7-based preamplifier circuit are conveyed
unflinchingly by these amplifier stages.
2. ACCURATE “4-CORNER” RIAA EQUALIZATION
In the spirit of high fidelity, all four RIAA phono equalization corner frequencies or time constants
have been specifically addressed in the STEELHEAD preamplifier. Historically most designs have concen-
trated on the “big three” time constants of 3180, 318 and 75 microseconds. This ignores the fourth corner
of about 3.2 us, which when ignored causes most phono stages to continue rolling off the highest octave
signals coming from the phono pickup, rather than turning the final “corner” and shelving to flat response at
about 50 kHz. Careless removal of upper octave bandwidth causes the recovered audio to become somewhat
lifeless and remote, with needless loss of impact, detail and percussiveness. Ironically this signal content is
precisely what is omitted from all currently popular digital audio delivery formats, and is one of the chief
culprits behind the homogenous upper octave sonic characteristics of those formats.
As with all equalizing amplifiers intended to correct a given form of frequency-selective emphasis
curve, care must be used when building the restorative compensation networks. Great care must be exercised
if the goal is to produce a highly accurate passive network coupled to low-feedback amplifiers. And experi-
ence has shown that the effort spent in faithfully adhering to the inverse RIAA equalization curve produces
results that easily justify the additional procurement and manufacturing costs. To this end, only hand-select-
ed and/or 1% tolerance components are used throughout the RIAA equalization network. Add to that the
factory-set variable capacitors, and the result is very high equalization accuracy where small component and
circuit layout variations that other manufacturers ignore are netted out. This yields impeccable inter-channel
phase and gain matching at any gain setting. In short, the STEELHEAD will magnify the differences in the
character and personality of your vinyl recording collection, cartridge, tonearm and turntable. A microscope
for the ear! Be prepared to hear previously undiscovered musical content as you play back your favorites!