Arkless Electronics
Trade: Amp design and repairs.
This started as a reply to a PM.... then I posted it as an addendum to another thread where the subject had come up... and ended up adding further to it... Eventually it occurred to me that it could do with its own thread.
This range of amps, designed by Tim de Paravicini, rarely gets mentioned and has an often deserved reputation for unreliability. However, I put it to fishies that when suitably fettled they are not only very reliable but are more than a match for the usual forum fodder of Quad, Naim and Rega, which one could be forgiven for thinking are the only second hand amplifiers in existence!
The same basic design of power amp was used in everything from the B200 integrated to the SA470 beast and basically the more money one spent on this range the more output mosfets were used, the bigger the power supply and the more biased into class A they got... in rough order of expense and "goodness" it went:
B200 integrated (B200, P140 and P150 basically the same power amp section but you get a pre thrown in with B200)
P140 (power amp section only of B200)
P150 (identical to P140 but has "MkII" mod to reduce hiss. I'll come back to this)
All the above have a rather small mains transformer for the output power but quite a lot of reservoir capacitance so they are a case like the one described by "JimAudiomisc" the other day in that whilst rated at 75WPC they can give more like 200W for very short peaks... this also means that when used as paralleled monoblocks (see below) RMS power goes up to about 110W rather than staying the same (75W). The doubled up mosfets mod adds to this and about 120W then available as paralleled monoblocks.
P170 older version without a couple of minor "improvements" but bigger power supply and more output devices.
Studio T Similar to P170 but IIRC even bigger PSU
P180 A bit of an odd one this... Basically an A370 built down to a budget and without much class A bias (or heatsinking!) but you get the 5 pairs of mosfets per channel. Has a separate power supply and there was an extra "choke regulated PSU" available which if anything held it back a bit. In effect the £3K A370 with much smaller PSU, very little class A bias and vastly under heatsinked but was more like £900 IIRC. Bit of a curates egg... can sound fantastic but if thrashed can have overheating issues....
P270 An A370 with 3 pairs of mosfets rather than 5 and smaller PSU but still quite a beast.
A370 5 pairs of mosfets, huge beast of a thing, 2 x 1KW mains transformers,
big heatsinks 220WPC class A to 18WPC
SA470 11 pairs of mosfets, two man lift etc.... Very few made.
There were P140 X and P150 X later on IIRC but I don't know what precisely the differences are to the earlier versions... probably a last run with left over parts and they added the x for marketing reasons! I had left MF when these were around and have never worked on one.
In original form they share a foible of being a bit hissy. It wouldn't bother me personally as it's not loud and even very quiet listening masks it but with nothing playing it's certainly noticeable. If you have 103dB/W horns I guess it would be a problem! A modification with a couple of transistors solved it and it was gradually incorporated into the range. B200 I don't recall its name changing at all, P140 became P150, P270 and A370 became "MkII" versions. P170 and Studio T are older and had finished production by this time.
A generic version of the topology, most similar to the P170, was made for Bose and sold as a Bose Professional product but I suspect only small quantities were made and in fact it may never have been taken up by Bose after say 20 evaluation units had been shipped... More vague on this but some Studio T's may have been sold as Bose also (virtually the same inside but very different styling).
The problem with all of them is they run hot and were built with basic bog stock electrolytics that were only just up to the job....in fact not quite even up to the job as they used 63V rated caps and put 70V across them!! so even if you find any of the above amps actually still working they will be on their last legs... Don't let this put you off though because....
A rebuild with 105C rated top quality electrolytics and general service makes them reliable Quad and Naim etc slayers! They really are considerably better sounding than the forum regular fave rave power amps at and around this price bracket
Other mods are available such as doubling up output mosfets. P140/150 also can be used as monoblocks and have a mono button for this. When used as monoblocks they are paralleled, not bridged, so power goes up only a little but real world load driving ability is much increased (doubled). A pair of P140/150's used as monoblocks is quite formidable!
A mate of mine has been using a pair (with full mods by myself including doubled up mosfets) for about 20 years plus of daily use without any issues and is presently using them to drive his ATC SCM40's.
This range of amps, designed by Tim de Paravicini, rarely gets mentioned and has an often deserved reputation for unreliability. However, I put it to fishies that when suitably fettled they are not only very reliable but are more than a match for the usual forum fodder of Quad, Naim and Rega, which one could be forgiven for thinking are the only second hand amplifiers in existence!
The same basic design of power amp was used in everything from the B200 integrated to the SA470 beast and basically the more money one spent on this range the more output mosfets were used, the bigger the power supply and the more biased into class A they got... in rough order of expense and "goodness" it went:
B200 integrated (B200, P140 and P150 basically the same power amp section but you get a pre thrown in with B200)
P140 (power amp section only of B200)
P150 (identical to P140 but has "MkII" mod to reduce hiss. I'll come back to this)
All the above have a rather small mains transformer for the output power but quite a lot of reservoir capacitance so they are a case like the one described by "JimAudiomisc" the other day in that whilst rated at 75WPC they can give more like 200W for very short peaks... this also means that when used as paralleled monoblocks (see below) RMS power goes up to about 110W rather than staying the same (75W). The doubled up mosfets mod adds to this and about 120W then available as paralleled monoblocks.
P170 older version without a couple of minor "improvements" but bigger power supply and more output devices.
Studio T Similar to P170 but IIRC even bigger PSU
P180 A bit of an odd one this... Basically an A370 built down to a budget and without much class A bias (or heatsinking!) but you get the 5 pairs of mosfets per channel. Has a separate power supply and there was an extra "choke regulated PSU" available which if anything held it back a bit. In effect the £3K A370 with much smaller PSU, very little class A bias and vastly under heatsinked but was more like £900 IIRC. Bit of a curates egg... can sound fantastic but if thrashed can have overheating issues....
P270 An A370 with 3 pairs of mosfets rather than 5 and smaller PSU but still quite a beast.
A370 5 pairs of mosfets, huge beast of a thing, 2 x 1KW mains transformers,
big heatsinks 220WPC class A to 18WPC
SA470 11 pairs of mosfets, two man lift etc.... Very few made.
There were P140 X and P150 X later on IIRC but I don't know what precisely the differences are to the earlier versions... probably a last run with left over parts and they added the x for marketing reasons! I had left MF when these were around and have never worked on one.
In original form they share a foible of being a bit hissy. It wouldn't bother me personally as it's not loud and even very quiet listening masks it but with nothing playing it's certainly noticeable. If you have 103dB/W horns I guess it would be a problem! A modification with a couple of transistors solved it and it was gradually incorporated into the range. B200 I don't recall its name changing at all, P140 became P150, P270 and A370 became "MkII" versions. P170 and Studio T are older and had finished production by this time.
A generic version of the topology, most similar to the P170, was made for Bose and sold as a Bose Professional product but I suspect only small quantities were made and in fact it may never have been taken up by Bose after say 20 evaluation units had been shipped... More vague on this but some Studio T's may have been sold as Bose also (virtually the same inside but very different styling).
The problem with all of them is they run hot and were built with basic bog stock electrolytics that were only just up to the job....in fact not quite even up to the job as they used 63V rated caps and put 70V across them!! so even if you find any of the above amps actually still working they will be on their last legs... Don't let this put you off though because....
A rebuild with 105C rated top quality electrolytics and general service makes them reliable Quad and Naim etc slayers! They really are considerably better sounding than the forum regular fave rave power amps at and around this price bracket
Other mods are available such as doubling up output mosfets. P140/150 also can be used as monoblocks and have a mono button for this. When used as monoblocks they are paralleled, not bridged, so power goes up only a little but real world load driving ability is much increased (doubled). A pair of P140/150's used as monoblocks is quite formidable!
A mate of mine has been using a pair (with full mods by myself including doubled up mosfets) for about 20 years plus of daily use without any issues and is presently using them to drive his ATC SCM40's.