| MarcinG |
Hello,
I have just read some piece of information I found interesting. It is taken from http://www.rcm.com.pl/cec/cec_main.htm , and it concerns CEC's new integrated amp, AMP71. The original text is in Polish, here is my (poor :() translation. I may have messed it a bit, I believe HPotter would do a better job. Anyway, here it is:
AMP71 works in Class-A, giving 200wpc max, without generating huge amount of heat. Enough to say, that heatsink temperature of a working amplifiers does not exceed 40 deg. C. What's more interesting, all A class amps, with power exceeding humble 30wpc, have large cases with enormous power supplies. AMP71 has traditional ps with 160000uF caps and two highest (:)) quality toroid transformers (650W each). Using two toroid is caused by fully symmetric design, including speaker terminals, not connected to the ground. Basic idea is very simple from theoretical point of view, yet its implementation is not that simple. To make long story short, signal is amplified by single bi-polar transistor, working in pure class A. It amplifies signal from input, which basically means that AMP71 does not contain pre-amp section, and the whole amplification is done by single gain stage without feedback. (...) The most interesting part is how to gain 200W in class A using only one gain stage. As we were said by designer, Mr. Carlos Candeias, gain is set between 40 and 50, and with given 100mV input sensitivity results in 5V max on the output. So where is that 200W coming from? The gain transistor is supported by current source made of 8 transistors per channel, that can easily generate 200W while working in A class (its very high impedance does not influences the signal). Roughly speaking, the power transistor works as switch controlling the
current transistors. The whole process is controlled by detecting output signal and informing the current source about changes, that are apropriately amplified. (...)
Does it sound familiar? Any comments, guys?
Regards,
Marcin. |
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| dieringe |
it sounds like a zen with aleph current source, doesn't it?
(I mean I haven't listened to it) |
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| Nelson Pass |
Actually sounds more like a single transistor driving a
complementary version of the Aleph current source. In
this design the N channel current source of say, the Penultimate
Zen, is complemented by a P channel current source and
together they form a push pull version of the current source.
If you set their current gain very high, they don't load the
single transistor very much, and so it works.
My experience with this circuit is that it can be made quite
good in performance, but as a practical matter the current
sources must be run pure Class A to avoid high distortion.
In the case of the CEC, this implies about a 900 watt idle.
Given the description I would be skeptical that you would
want to refer to the amp as Class A or single stage. |
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| MarcinG |
| Actually, at first glance it looked to me exactly like Dieringe has said... but The One And Only must be right ;) ! I wonder what does the amp sound like? |
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| Nelson Pass |
If you want to see yet another variation of this concept,
check out the Stasis patent #4,107,619. In this approach
a small amplifier stage connected directly to the load is
"current bootstrapped" by an external circuit.
Same basic idea.
Certainly you can operate this small amplifier stage, perhaps
a single transistor, in Class A, but when 95% of the current
to the load comes from an AB power circuit, you are seriously
stretching the idea of single-stage Class A.
:bigeyes: |
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| djk |
| The AMP71 looks great! But the heatsinks don't look any bigger than the ones on my old class AB design 100W Hafler DH200. I only see what looks like four pair of IRFP type devices. |
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