Michael Fidler Releases Spartan 15 MKII MM Phonostage
All Image Credit: Michael Fidler/Classic Audio
Michael Fidler of the UK has just released the new SPARTAN 15 MKII MM phono stage through Classic Audio Ltd. The SPARTAN 15 MKII moving magnet phono stage builds on the earlier SPARTAN 15 and SPARTAN 10 models. The updated design features an improved power supply used in his PRO series for higher output, with all-new parts in a total re-design of the original circuit. Precision RIAA equalization, low noise, and LF X-Feed are retained with extra settings at 100 and 200Hz. This phono stage is also hand assembled in Kent, England, and comes at a similarly competitive price point to the original SPARTAN 15.
The SPARTAN 15 MKII delivers a dynamic range of over 110dB from the ultra-quiet background of the new NJM2068 amplifier IC’s. Panasonic electrolytic capacitors and film resistors ensure long-term stability, while 1% tolerance film capacitors in the active RIAA stage hold replay to ±0.1dB of the reference curve, all said to assist in “eliminating mid-range coloration and channel imbalance”.
New SPARTAN MKII fiberglass double-sided PCB with through-hole technology and 3% silver solder.
The designs 40.8dB (110x) gain is shared between the input and output amplifier stages. This lowers the input-stage workload by 70%, keeping distortion under 0.0006% from 40Hz to 22KHz, and by applying the final 10dB of gain after the subsonic filter, surface disturbances are said to be excluded from the final headroom.
Even the best turntables create rubble at frequencies below 20Hz and even if they didn’t, the cutting lath and other sources can inject low frequency noise into the vinyl cutting process. Vinyl playback also has its challenges with warps and arm resonances all of which can cause overloads to bass and subwoofer drivers and pre-amplifier circuits causing distortion and overloads. A fixed subsonic filter that uses a 3rd order 18dB/octave high-pass filter with a cut-off frequency of 22Hz is used to attenuate signals below 10Hz, making certain that they can’t cause any trouble further down the signal path. Hand-matched polypropylene film capacitors in the filter network ensure the desired response doesn’t change more than 0.1dB at 40Hz.
A unique feature of the Spartan is the defeatable low-frequency crossfeed arrangement, which now supports a switchable 100/200Hz turnover frequency. This new design is said to “cancel low-frequency ‘vinyl-roar’ while retaining the same level of stereo separation on the record at mastering, unveiling bass detail previously hidden in the noise”.
Mono recordings are also catered for with a front panel switch that provides summing of the two channels when enabled.
Ensuring that noise is kept to a minimum the internal discrete, ±17V DC analog power supply uses an external 9VAC linear transformer rather than a noisy switched mode power supply. This approach ensures that any interfering magnetic fields and electrical noise are kept well away from SPARTAN 15 MKII. Internally, the split ±17V rails are regulated with precise reference diodes, providing a fast and stable headroom independent of temperature. Both positive and negative rails are full-wave rectified, ensuring no direct current can unbalance the transformers core, allowing it to always operate in its magnetic “sweet spot”. The design includes both an over-voltage resettable protection circuit and a start up circuit that controls a mute relay while the electronics stabilize, thus preventing any unpleasant and damaging thuds and bangs when switching on and off.
External transformer and power supply
Finally, the design is housed in a sleek and substantial sandblasted black aluminum case with a CNC milled 6mm scratch-resistant aluminum front panel and white silkscreen lettering
Features At A Glance:
- New NJM2068 amplifier IC’s
- Strict RIAA equalization to ±0.1dB for far less coloration and channel mismatch than others at ±0.5dB
- Ultra-low distortion by splitting the final gain between two optimized amplifier stages for better linearity
- Vanishingly little background noise from dead quiet input amplifiers, specially matched to MM cartridge impedances
- LF X-Feed cancels low-frequency vertical surface noise while preserving mastered stereo separation and bass response
- 23Hz 18dB/octave subsonic filter removes surface disturbances with hand-matched capacitors to preclude tolerance effects
- Mono switching greatly reduces noise and distortion on mono and heavily worn discs for better clarity and enjoyment
- Linear split power supply with start-up mute, elevated from ±15V to ±17V for even more headroom with no switching noise
Specifications:
- Gain at 1kHz, 10kΩ line load: 40.8dB, 110x
- RIAA accuracy: ±0.1dB, 40Hz to 22kHz
- Channel balance: ±0.1dB, at 1kHz
- Crosstalk: <72dB 20Hz to 22kHz
- SNR, ref 5mV, cartridge load: 78dB, 7900x, 220Hz to 22KHz
- Overload margin, ref 5mV, at 1kHz: 25.5dB, 19x
- Maximum input at 1kHz: 94mV RMS
- Maximum input at 10kHz: 450mV RMS
- Maximum output, 3kΩ line load: 10V RMS, 20Hz to 60kHz
- THD, 5kΩ line load: <0.0006%, 40Hz to 22kHz, 10V RMS output
- Input capacitance: 120pF
- Input impedance: 50kΩ, ±1%
- Output impedance: 100Ω
- Minimum line load impedance: 3kΩ
- Subsonic filter: 22Hz, 3rd order, -20dB at 10Hz
- Low-frequency crossfeed: 100/200Hz, 7/12dB rejection at 50Hz
- Power supply: Split linear ±17V
- Power consumption: 2W at full output, 0.2W standby
- Dimensions (W*H*D): 172*60*110mm
MSRP (Direct: incl. P&P):
- US: $490.00
- UK: £360.00
- EU: €440.00
For more information visit the Michael Fidler UK web site.
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