GSP Accession MC Phono Preamp.[Available in optional Black]
Up until now the Accession phono stage preamp was only available for MM and other high output magnetic cartridges.
Customers and enlightened dealers have been in awe over its new sound quality, the way it digs deeper into the music, the sheer fun of it all. The Accession really is an addictive listen.
But now, at long last, the Accession is available for low output moving coil users.
It is well known that low output moving coil can sound overly bright, and I am sure many MC users, having spent such a fortune, are disappointed.
It is not that the technology of the cartridge itself is overly bright although there is evidence that cantilever resonance can influence how it sounds at high frequencies.
The problem is in the handling and amplification of its signal. With such a low output it is competing with electronic noise for its existence. Interference dwarfs it, and It requires such an incredible amount of gain to bring it up to line-level.
The phono preamplifier can only amplify what it is given, and it is given the interference as well as the signal. All amplification stages produce harmonics and these mix with interference to produce new high frequency sounds (heterodyning). And added to that is the high frequency resonance of the cantilever.
The extra gain required by MC can be achieved by a step-up transformer (SUT) or electronically. The SUT can 'consume' more lows than highs in its magnetising current, emphasizing the highs.
The electronic circuit is by necessity high gain, and it also has to be low noise. Low noise circuitry is slow regarding a thing called slew-rate. A reasonably fast slew-rate is required for music to sound like music. There are integrated circuits called op-amps which seemingly contradict what I just said; they are low noise and fast slew-rate, but the slew-rate is enhanced — added-on and applied to its output — the signal still suffers.
The transistor (or discrete) equivalent does not have the input latitude for the high frequency output of the moving coil, in very much the same way as the slew-rate limited op-amp.
Both end up within a negative feedback loop, which by its nature is global (even if around just one op-amp). It minimises distortion which looks good in specifications, and sounds very quiet when not playing music, but it emphasizes any slew-rate enhancement leading to the heterodyned high frequency sounds dominating the music (making it sound bright).
What is needed is a simple local negative feedback stage at the input, which is therefore independent of global negative feedback elsewhere in the phono stage, to lift the signal out of the noise; that has some degeneration which leads to a natural sounding unforced slew-rate; and one that can apply sufficient interference attenuation. This is what the Accession MC does.
It meets the conditions laid down in the rules for our "fast active" circuitry, which has been a core part of our product design from our very beginning. The "fast-active" noise-level (hiss) is defined as only being noticeable when there is no music playing. It isn't heard below vinyl surface noise, and so cannot interfere with the music.
It can be said that input slew-rate is proportionate to noise and vice-versa, and in-fact it is. Input slew-rate isn't enhanced slew rate and sounds much more natural (as in unforced). To get more means accepting just a little more noise, and by our "fast-active" rule our circuitry operates at a slew-rate which makes the music sound more natural.
When you audition the Accession MC, I am confident you will get that involving feeling.
And with the NEW PSU1 Enigma micro-signal power supply those results will be even better!
The standard PSU1 power supply has powered our phono stages, MM and MC, through a number of great reviews since its introduction in 2000.
However, Graham Slee had refused to accept moving coil as superior no matter how hard he tried to the contrary, which simply led to us making better and better MC phono stages, which have delighted our ever increasing customer base... but not him.
During development of the Accession MC he found the much revered technique of PCB ground planes could be improved by also hard wiring ground returns. According to the experts this makes absolutely no difference, but the difference was immediately audible (all Accession MCs are supplied with ground paths hard wired).
So his thoughts turned to the PSU1, and the application of Kirchhoff's current law and its violations.
Something he'd witnessed developing other circuits sprang to mind and investigating the PSU1's energy storage (the reservoir caps) it occurred to him that by fitting capacitors which met very particular rules, the "microscopic" signal currents, which according to him, were not being treated equally, would improve matters greatly.
Frustratingly there was just one value in only one capacitor range capable of meeting those very particular rules. These were obtained and it made such a difference that he now prefers moving coil!
The PSU1 Enigma is equipped with a specially made DC cord, originally auditioned with the standard PSU1 where it made no difference, but it definitely does with the PSU1 Enigma!
|Input and output connectors||360° shielded RCA/phono sockets, hard gold plated|
|Input sensitivity range||0.125mV to 0.84mV (recommended)|
|Output range (for above inputs)||145mV to 975mV|
|Maximum input||4.2mV rms|
|Maximum output||4.876V rms|
|Gain||61.3dB (1161) at 1kHz|
|Input impedance||500, 300, 100 and 75 Ohms (300 plus 100 both on)|
|Output impedance (driving impedance)||750 Ohm fixed OP/ 470 Ohm variable OP (will drive ≥10k Ohms)|
|Noise at output||-65dB A wtd. 20Hz to 20kHz 0dBu out|
|Distortion||typically 0.02% 20Hz to 20kHz|
|RIAA accuracy||± 0.3dB (sampled)|
|Frequency response||20Hz - 100kHz (±0,−1dB normalised)|
|Power supply||remotely powered using Enigma PSU1 linear power supply|
|Size (approx.)||W: 107 x H: 50 x D: 195 (mm) inc. jacks|
It provides 4 cartridge loading options: 1] the standard 100 Ohms many MC cartridges are specified as; 2] 300 Ohms. Why? because it is logarithmically the double of 100 Ohms and our hearing is logarithmic; 3] 500 Ohms - the maximum the design can do without compromising noise; and 4] 75 Ohms by selecting both 100 and 300 Ohms.
A manual volume control active on the variable "var" outputs which can be used if the Accession MC is to drive a power amp directly. Required power amp input sensitivity will depend on the cartridge output, but a 0.3mV cartridge will cause around 350mV at the variable outputs. Also note this volume control can go fully clockwise without adding distortion to the Accession MC outputs (awesome!)
RIAA is the standard recording EQ for most records, so that's right-hand switch down. But you might have (or could obtain) some older long playing classics from the 1940s and 1950s recorded to NAB or FFRR - those were the most popular American and British EQs before RIAA. And what is CA/Flat? It's what the record really sounds like without any equalisation: it is the Constant Amplitude output after applying the Accession's cartridge equalisation to make it Flat.
Adding left and right channels together and dividing by two means mono records played on a stereo cartridge will sound mono, and that's what the Accession mono switch does. Use it to remove the left-right swaying effect a slightly eccentric mono record can have. This A+B/2 switch will not render stereo as true mono, giving a "tunnel" effect to stereo sound, so ensure it's switched up when playing stereo records.
Recording while you listen
The variable output can also be used to feed a digital recorder (or even a tape recorder!) whilst you listen to the record via the fixed output into your line preamp, integrated amplifier or receiver. Use the volume control to set the right input level into your recording device. Quite often a fixed output level is too "hot" for a digital recorder's analogue input and results in hard clipping. Turn the volume control down so you get just the right recording level.
The very best of EMC protection
The shielding provided on the Accession MC safeguards against the intrusion of unwanted electro-magnetic disturbances, which at best would colour the sound and at worst you'd hear interference from other devices. Make sure you use properly shielded interconnects with it so interference hasn't a chance. Our range of interconnects will help you achieve additional immunity.
Unobtrusive compact design
Our eurocard 1U height cases save on space so you can have more things to enjoy without the worry of where to put them. They will stack on top of each other and will even work on their sides. They're remotely powered so won't make other sensitive items hum or buzz.
The Accession MC uses (and is supplied with) our PSU1 power supply which should be placed off-rack, keeping transformer influences away from your sensitive equipment, and most importantly well away from your pick-up cartridge. Remote DC power is the most sensible way to power sensitive equipment. There is no transformer inside your Accession MC to worry about, and no AC on its low voltage cord to induce hum into adjacent cables.