Arkless Electronics
14-10-2012, 13:59
The Arkless Electronics modifications to the Cambridge Audio 640P/651P are extensive and result in a unit which is.....well actually pretty much an Arkless Electronics phono stage in a Cambridge audio box! The stock 640P/651P power supply is retained.
So what do the mods actually consist of?
Starting at the beginning (from the signals point of view)
• The MC input is now used for both MC and MM cartridges. The standard input capacitors of 220pF are a bit excessive for some MM cartridges and are replaced with 100pF
• The MM input sockets are now utilised to allow any cartridge loading by the use of loading plugs. By this means the inputs can be loaded with any desired combination of resistance and capacitance to suit any model of cartridge. As standard, a set of loading plugs offering 100 Ohms in parallel with 1nF are supplied and will be a good match for the majority of MC cartridges. Without the plugs the cartridge sees 47K and 100pF which will suit most MM cartridges.
• Customers can of course specify any loading to be supplied instead of the standard one, and if familiar with the art of soldering can of course change the plugs to their own requirements. Extra loading plugs to any customer specified value can be supplied (at extra cost) at any time.
• The original input stage is disconnected and is replaced in its entirety with an Arkless Electronics designed low noise stage which allows direct coupling of the cartridge to the first stage, thereby removing all capacitors from this delicate part of the signal path.
• Output is much higher than before. Output level could be a bit marginal with low output cartridges in original 640P/651P.
• Gain is set for either MC or MM cartridges by removing the lid and cutting one wire loop per channel. Simply solder the ends of the loop together again to go back to MC..... Customers can of course specify whether the amp is to be set to MC or MM as supplied.
• The stock MM stage is completely disconnected.
• The original MC/MM switch is removed and bypassed.
• The input stage is direct coupled (avoiding yet another electrolytic capacitor in the signal path) to the RIAA equalisation stage, which has been completely recalculated to give tighter accuracy to the RIAA standard and impedance levels more conducive to good sound. The capacitors used in the RIAA network are a critical aspect of the design of any phono stage and Arkless Electronics have had close tolerance polystyrene capacitors made to order for this application.
• The original NE5532 op-amps in the RIAA stage are replaced with much better quality items from Burr Brown.
• The grounding regime of the amp is changed to improve sound quality.
• The original subsonic/warp filter is left in place untouched and can still be used if needed when having a party or whatever..... It is however highly recommended that this filter is not used in normal use as it is highly detrimental to sound quality. The switch can be permanently bypassed if so specified by the customer, as can the relay used in the anti- thump switch-on delay.
And the cost of all this? You send me your original 640P/651P for modification and then it's £140 not including postage.
For this your 640P or 651P is transformed into a unit well capable of standing comparison with well known phono stages in the £500 - £800+ range... Bargain!
So what do the mods actually consist of?
Starting at the beginning (from the signals point of view)
• The MC input is now used for both MC and MM cartridges. The standard input capacitors of 220pF are a bit excessive for some MM cartridges and are replaced with 100pF
• The MM input sockets are now utilised to allow any cartridge loading by the use of loading plugs. By this means the inputs can be loaded with any desired combination of resistance and capacitance to suit any model of cartridge. As standard, a set of loading plugs offering 100 Ohms in parallel with 1nF are supplied and will be a good match for the majority of MC cartridges. Without the plugs the cartridge sees 47K and 100pF which will suit most MM cartridges.
• Customers can of course specify any loading to be supplied instead of the standard one, and if familiar with the art of soldering can of course change the plugs to their own requirements. Extra loading plugs to any customer specified value can be supplied (at extra cost) at any time.
• The original input stage is disconnected and is replaced in its entirety with an Arkless Electronics designed low noise stage which allows direct coupling of the cartridge to the first stage, thereby removing all capacitors from this delicate part of the signal path.
• Output is much higher than before. Output level could be a bit marginal with low output cartridges in original 640P/651P.
• Gain is set for either MC or MM cartridges by removing the lid and cutting one wire loop per channel. Simply solder the ends of the loop together again to go back to MC..... Customers can of course specify whether the amp is to be set to MC or MM as supplied.
• The stock MM stage is completely disconnected.
• The original MC/MM switch is removed and bypassed.
• The input stage is direct coupled (avoiding yet another electrolytic capacitor in the signal path) to the RIAA equalisation stage, which has been completely recalculated to give tighter accuracy to the RIAA standard and impedance levels more conducive to good sound. The capacitors used in the RIAA network are a critical aspect of the design of any phono stage and Arkless Electronics have had close tolerance polystyrene capacitors made to order for this application.
• The original NE5532 op-amps in the RIAA stage are replaced with much better quality items from Burr Brown.
• The grounding regime of the amp is changed to improve sound quality.
• The original subsonic/warp filter is left in place untouched and can still be used if needed when having a party or whatever..... It is however highly recommended that this filter is not used in normal use as it is highly detrimental to sound quality. The switch can be permanently bypassed if so specified by the customer, as can the relay used in the anti- thump switch-on delay.
And the cost of all this? You send me your original 640P/651P for modification and then it's £140 not including postage.
For this your 640P or 651P is transformed into a unit well capable of standing comparison with well known phono stages in the £500 - £800+ range... Bargain!