Post by MartinT on Jun 12, 2015 22:31:55 GMT
How I Arrived at my Power Amp
My first proper amplifier was a Linsley-Hood 75W, following the Wireless World design and built using the Powertran Mk. I kit, later heavily modified to be a power amp only. There was a lot about that quasi-complimentary push-pull circuit that was elegant and it worked well using the specified 15A BDY56 NPN transistors. It lasted me all the way through to when I finally bought the Croft preamp (see previous article). I then had a foray into building a high power MOSFET amp using the Hitachi MOSFET application note. That taught me a lot: high power is NOT the same as big dynamics or the ability to swing volts fast. It sounded as flat as a pancake, despite having 2 x 625W toroids and some big reservoir capacitors. The retail Hitachi MOSFET power amp measured well but sounded awful, too!
After that, I ventured into valve power amps for a while. I bought a Rogers Cadet III which was fun but underpowered, a Leak Stereo 20 which was epic in the midrange, and which I modified for better performance, but which was ultimately also underpowered. Then came the chance to buy a Croft Series 4 from Audio T in a strange deal where they seemed to have fallen out with Glenn Croft and wanted rid of it, while Glenn himself called me and tried to sell me his OTL model instead. Not being a complete fool, I stuck to my guns and bought the 4, which I later had upgraded to a 4S. This was a good all-round power amp which I felt never sounded as good in 4S mode as it had originally. I put it down to the somewhat harder sounding 6550 valves compared with the lovely original EL34s.
My final valve setup used the Leak for mid/treble duties and the Croft for bass in a bi-amp configuration. This was the best I ever got from valves - liquid, organic, but certainly not the last word in detail, transparency or dynamics.
At that time, about 16 years ago, I was scouting around for a power amp to really drive my speakers hard, to run in balanced mode and make best use of the Pass X2 preamp, and to be virtually bullet-proof. Valves were out. I tried a Linn Klimax and a few others and honed in on a Chord SPM-1200C, which appeared to fit the bill at the Reading Hi-Fi demo. A home loan later, and I realised it was just what I had wanted: highly transparent, detailed, neutral, with plenty of reserve power and could be left switched on with very little standing current. Best of all, it's solid state and bullet-proof. The high frequency switched mode power supply guarantees very fast recovery times since the reservoir charge cycle is so short. Midrange detail in the vocal area is wonderful without any harshness, treble is extended and bass has real impact and goes down to very low frequencies (as witnessed when playing a warped record). Just one observation: it needs warming up to sound of its best.
It was just one step up about two years later to upgrade to the 1200E when it was released, using dual tracking power rail technology to provide more instantaneous current through an even stiffer power supply. Some 13 years later and I still haven't heard a better power amp, having had all manner of models pass through my system, including some fascinating ones like the Sanders Magtech, Parasound A21 and Tube Distinctions Copper (which remains the best valve amp I've heard in my system).
Quite recently, I decided to remove the Integra legs, which appear to be for looks only. I'm glad I did: they had worked loose over the years and must have been resonating. That plus the use of RDC cones for supports further improved its transparency. The Chord remains in my system simply because I have not found its limits: every time I upgrade the system, it just carries on raising its game and getting better. Its symbiotic relationship with the Pass preamp, in balanced mode, means that I am very loath to mess with the core system. Change one of these items at my peril! Happily, I don't feel the need to.
My first proper amplifier was a Linsley-Hood 75W, following the Wireless World design and built using the Powertran Mk. I kit, later heavily modified to be a power amp only. There was a lot about that quasi-complimentary push-pull circuit that was elegant and it worked well using the specified 15A BDY56 NPN transistors. It lasted me all the way through to when I finally bought the Croft preamp (see previous article). I then had a foray into building a high power MOSFET amp using the Hitachi MOSFET application note. That taught me a lot: high power is NOT the same as big dynamics or the ability to swing volts fast. It sounded as flat as a pancake, despite having 2 x 625W toroids and some big reservoir capacitors. The retail Hitachi MOSFET power amp measured well but sounded awful, too!
After that, I ventured into valve power amps for a while. I bought a Rogers Cadet III which was fun but underpowered, a Leak Stereo 20 which was epic in the midrange, and which I modified for better performance, but which was ultimately also underpowered. Then came the chance to buy a Croft Series 4 from Audio T in a strange deal where they seemed to have fallen out with Glenn Croft and wanted rid of it, while Glenn himself called me and tried to sell me his OTL model instead. Not being a complete fool, I stuck to my guns and bought the 4, which I later had upgraded to a 4S. This was a good all-round power amp which I felt never sounded as good in 4S mode as it had originally. I put it down to the somewhat harder sounding 6550 valves compared with the lovely original EL34s.
My final valve setup used the Leak for mid/treble duties and the Croft for bass in a bi-amp configuration. This was the best I ever got from valves - liquid, organic, but certainly not the last word in detail, transparency or dynamics.
At that time, about 16 years ago, I was scouting around for a power amp to really drive my speakers hard, to run in balanced mode and make best use of the Pass X2 preamp, and to be virtually bullet-proof. Valves were out. I tried a Linn Klimax and a few others and honed in on a Chord SPM-1200C, which appeared to fit the bill at the Reading Hi-Fi demo. A home loan later, and I realised it was just what I had wanted: highly transparent, detailed, neutral, with plenty of reserve power and could be left switched on with very little standing current. Best of all, it's solid state and bullet-proof. The high frequency switched mode power supply guarantees very fast recovery times since the reservoir charge cycle is so short. Midrange detail in the vocal area is wonderful without any harshness, treble is extended and bass has real impact and goes down to very low frequencies (as witnessed when playing a warped record). Just one observation: it needs warming up to sound of its best.
It was just one step up about two years later to upgrade to the 1200E when it was released, using dual tracking power rail technology to provide more instantaneous current through an even stiffer power supply. Some 13 years later and I still haven't heard a better power amp, having had all manner of models pass through my system, including some fascinating ones like the Sanders Magtech, Parasound A21 and Tube Distinctions Copper (which remains the best valve amp I've heard in my system).
Quite recently, I decided to remove the Integra legs, which appear to be for looks only. I'm glad I did: they had worked loose over the years and must have been resonating. That plus the use of RDC cones for supports further improved its transparency. The Chord remains in my system simply because I have not found its limits: every time I upgrade the system, it just carries on raising its game and getting better. Its symbiotic relationship with the Pass preamp, in balanced mode, means that I am very loath to mess with the core system. Change one of these items at my peril! Happily, I don't feel the need to.
