A warm good afternoon to all!
Both 2023 and MKII versions of the SPARTAN 15 phono preamp, sharing the same MM section as the ASR-reviewed SPARTAN 20 design, are now sold out and discontinued. As with the SPARTAN 5, I'm releasing the full designs files both on ASR and my own website for general interest, DIY, third-party repair and posterity.
The files are included below, but no official BOM document exists are most of the parts were shared with the PRO series and the remainder were simply topped up visually via the transparent draws of a parts cabinet for the two-year product run!
I'm currently writing full technical articles for the MC PRO and SPARTAN 30 lines, at a considerably deeper level than the SPARTAN 5 write-up. As the SPARTAN 15 is already part of the 20 design that will have its own article, it might be a lot more fun just to answer questions directly from forum users and have a bit of a discussion thread rather than repeating the same thing twice.
So, fire away with the questions if you have them! I'm more than happy to discuss all of the design decisions of this would-be Golfing Panther circuit. I was rather up against it when I designed it, so anyone can make it with very basic electronics tools. A quick excerpt from the original 2023 press-release summarises the design quite nicely, despite the presence of "marketing copy":
Hand made in Kent, England using all through-hole technology, the SPARTAN 15 hangs a deep black background behind the music. The ultra-quiet classic Japanese 2068 amplifier ICs are specially chosen to match up to MM cartridge impedances, yielding a signal-to-noise ratio of 78dB. Hyper-accurate RIAA equalisation to 0.1dB has been implemented using 1% tolerance film capacitors to eliminate the colouration and channel balance issues of more common designs based on 5% parts, resulting in a perfectly balanced tonal character with great imaging.
Fully defeatable low frequency crossfeed reduces vertical noise to reveal new bass detail on stereo discs, particularly noticeable with headphones on. A superior 3rd order subsonic filter is used to prevent the nasty shimmering effects of infrasonic intermodulation distortion in loudspeakers caused by over-excursion. Polypropylene film capacitors in the filter are hand-matched during assembly to create an ultra-flat in-band response with none of the usual low-end inconsistencies that give such filters a bad name. Full mono switching on the front panel is included for greatly reduced noise and distortion on mono pressings.
Like its predecessor, the popular SPARTAN 10, special gain structuring is used to share the burden of amplifying the tiny cartridge signal by 110 times at 1kHz (40.8dB). By making up the final 10.7dB of gain in the second stage, the input stage only does a third of the work compared to a single stage design, producing less than 0.0006% THD from 40Hz to 22kHz, for a listening experience completely free of grain and harshness.
A maximum input of 95mV at 1kHz, rising 900mV at 20kHz thanks to the active equalisation, makes overload impossible with standard MM cartridges, keeping transients sharp and clear even at diabolical levels. At the other end, the socketed ICs can drive over 10V RMS into 3 standard 10kΩ line loads in parallel without loss of linearity, due to the extra headroom afforded by the upgraded ±17V internal power supply rails. Using a split double rail design also keeps distortion-causing non-linear amplifier power currents out of the ground path.
Both 2023 and MKII versions of the SPARTAN 15 phono preamp, sharing the same MM section as the ASR-reviewed SPARTAN 20 design, are now sold out and discontinued. As with the SPARTAN 5, I'm releasing the full designs files both on ASR and my own website for general interest, DIY, third-party repair and posterity.
The files are included below, but no official BOM document exists are most of the parts were shared with the PRO series and the remainder were simply topped up visually via the transparent draws of a parts cabinet for the two-year product run!
I'm currently writing full technical articles for the MC PRO and SPARTAN 30 lines, at a considerably deeper level than the SPARTAN 5 write-up. As the SPARTAN 15 is already part of the 20 design that will have its own article, it might be a lot more fun just to answer questions directly from forum users and have a bit of a discussion thread rather than repeating the same thing twice.
So, fire away with the questions if you have them! I'm more than happy to discuss all of the design decisions of this would-be Golfing Panther circuit. I was rather up against it when I designed it, so anyone can make it with very basic electronics tools. A quick excerpt from the original 2023 press-release summarises the design quite nicely, despite the presence of "marketing copy":
Hand made in Kent, England using all through-hole technology, the SPARTAN 15 hangs a deep black background behind the music. The ultra-quiet classic Japanese 2068 amplifier ICs are specially chosen to match up to MM cartridge impedances, yielding a signal-to-noise ratio of 78dB. Hyper-accurate RIAA equalisation to 0.1dB has been implemented using 1% tolerance film capacitors to eliminate the colouration and channel balance issues of more common designs based on 5% parts, resulting in a perfectly balanced tonal character with great imaging.
Fully defeatable low frequency crossfeed reduces vertical noise to reveal new bass detail on stereo discs, particularly noticeable with headphones on. A superior 3rd order subsonic filter is used to prevent the nasty shimmering effects of infrasonic intermodulation distortion in loudspeakers caused by over-excursion. Polypropylene film capacitors in the filter are hand-matched during assembly to create an ultra-flat in-band response with none of the usual low-end inconsistencies that give such filters a bad name. Full mono switching on the front panel is included for greatly reduced noise and distortion on mono pressings.
Like its predecessor, the popular SPARTAN 10, special gain structuring is used to share the burden of amplifying the tiny cartridge signal by 110 times at 1kHz (40.8dB). By making up the final 10.7dB of gain in the second stage, the input stage only does a third of the work compared to a single stage design, producing less than 0.0006% THD from 40Hz to 22kHz, for a listening experience completely free of grain and harshness.
A maximum input of 95mV at 1kHz, rising 900mV at 20kHz thanks to the active equalisation, makes overload impossible with standard MM cartridges, keeping transients sharp and clear even at diabolical levels. At the other end, the socketed ICs can drive over 10V RMS into 3 standard 10kΩ line loads in parallel without loss of linearity, due to the extra headroom afforded by the upgraded ±17V internal power supply rails. Using a split double rail design also keeps distortion-causing non-linear amplifier power currents out of the ground path.
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