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Old 20th November 2001, 05:22 PM   #1
diyAudio Member
Join Date: Nov 2001
Location: UK
I'm slowly building up a home cinema and music system. So far I've got this little lot together:

Source: PC as a PCM transport / DVD player
DAC / preamp: Tag McLaren AV32R
* Rotel 985 5-channel power amp *
Dynaudio Contour speakers all round (5)
Paradigm Servo 15 sub

It's always been my plan to add a very good power amp to the front two channels as the Rotel, whilst being fine for films, leaves me cold when listening to music. I've auditioned, and until recently have been planning on buying a Chord SPM1200C power amp - nice bit of kit!

I've now decided to go the DIY route for a couple of reasons.. so with that in mind, which type of kit would cut it? I'm pretty much decided on a pure class-A version, but am open to suggestion!
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Old 20th November 2001, 06:52 PM   #2
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Location: Columbia, SC
Start by deciding how much power you want and how much you can afford to spend.

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Old 20th November 2001, 08:30 PM   #3
Super is offline Super  United States
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What's the model of your Dynaudio speakers? I'm assuming you've got the 1.3's all around?

Class A designs give perhaps the best overall quality, but with speakers as inneficient as the Dynaudios, you're going to need a fair amount of power to drive them, and high wattage class A designs don't come cheap. I've heard numerous recommendations of 50 watts solid state being used to drive these speakers. You may want to try looking at some amps with better efficiency than your typical class A design.
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Old 20th November 2001, 08:36 PM   #4
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Talking What I want / what I need!

Thanks Grey for your reply, below are the specs for Chord amp I auditioned. It is more powerful than I currently have call for, but a bit of headroom is always nice for future speaker upgrades!
Here's a detailed PDF:
... and this outlines some of their technology:
(perhaps the high frequency power supplies are a bit non DIY?)

Budget-wise, I'd probably want to budget no more than 500 for the finished article.

Doug Self's trimodal project rather caught my eye @ http://www.signaltransfer.freeuk.com/trimodal.htm, although more headroom would be nice.

************************************************** *********
Chord SPM1200C specs:

Output Power: 330W rms per channel @ 0.03% distortion into 8 Ohms, 550W rms per channel into 4 Ohms, 650W rms into 2 Ohms. Thermal limitation only, 1 channel driven.
Dynamic Headroom 440W rms per channel into 8 Ohms. 780W rms per channel into 4 Ohms. @1KHz, 20 cycles on, 480 cycles off. Peak pulses 8 milliseconds burst 79V peak (the equivalent of 1200W per channel peak into 4 Ohms)
Frequency Response (8 Ohms) -1dB, 0.2Hz to 46KHz -3dB, 0.1Hz to 77KHz
Frequency Response (4 Ohms) -1dB, 0.2Hz to 39KHz -3dB, 0.1Hz to 75KHz
Signal to Noise Ratio Better than -103dB, 'A' weighted two thirds power.
Channel Separation Better than 95dB.
Pre-Amplifier Input Connection 2 x gold-plated, fully balanced XLR sockets. 2 x gold-plated custom phono sockets, unbalanced.
Input Impedance 100kOhms. Unbalanced/Balanced
Input Capacitance < 30pf.
Output Impedance 0.03 Ohms
Output Inductance 2.6mH
Output Connections 8 x 4mm rhodium binding posts (2 pairs Black, 2 pairs Red)
Slew Rate 70V per S, 1KHz 20V square wave
Gain 30dB
Stability Unconditional

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Old 20th November 2001, 08:47 PM   #5
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Hi there, my speakers are 1.8's at the front. I recently downgraded from a behemoth pair of Contour 3's as my amp didn't have the bollo.. errm I mean wherewithall to drive them So I may well change back in the near future
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Old 21st November 2001, 05:10 AM   #6
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Large class A amps are fairly rare. You might try looking at Nelson's Aleph 1.2s (200W/channel). I built a pair of Aleph 2s (100W/channel) for about $400 or so (bought 100 output devices so I'd have plenty to match--you could save money by buying fewer), but I cheated on the heat sinks--mine are water-cooled. If you go air-cooled, it'll cost a bit more.

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Old 21st November 2001, 11:44 AM   #7
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Hmm, I suspect a pure class A design would run too hot for my needs. In the long run, I'd like to upgrade all five channels - and 1500w of heat would probably toast everyone in the near vicinity! I have a garage directly below my listening room, so I could in theory run the amplifiers down there but I probably wouldn't have this option when I move house.

Any other suggestions? Would I be impressed by the kits at http://www.aussieamplifiers.com?

[Edited by jlanng on 11-21-2001 at 09:05 AM]
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