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.
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 thecurrent 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.
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.
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.
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.
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.
in this case I don't find anywhere service manuals and schematics, but I have found a PDF URL in German language
"Leonardo daVinci and the LEF topology"
www.hifi-weiler.de/fileadmin/media/LEF-Technik.pdf
I think, translation about google's language tools is possible.
There are a detailled circuit describtion and I will try to create (in the next time) by simulation a circuit example (pre- or power amplifier) in order to this describtion. But I guess already now, that is close to the concepts of "Stasis" so as the MJR-Amp
"Leonardo daVinci and the LEF topology"
www.hifi-weiler.de/fileadmin/media/LEF-Technik.pdf
I think, translation about google's language tools is possible.
There are a detailled circuit describtion and I will try to create (in the next time) by simulation a circuit example (pre- or power amplifier) in order to this describtion. But I guess already now, that is close to the concepts of "Stasis" so as the MJR-Amp
still no schematics online of the Amp 71?
some people claim, that was the ultimatest virtually Class-A topology of the world. Here some URLs:
CEC ƒvƒŠƒ�ƒCƒ“ƒAƒ“ƒvAMP71‚ÌŽd—l
CEC AMP 71 (Carlos explain the theory of operation)
CEC DAC
some people claim, that was the ultimatest virtually Class-A topology of the world. Here some URLs:
CEC ƒvƒŠƒ�ƒCƒ“ƒAƒ“ƒvAMP71‚ÌŽd—l
CEC AMP 71 (Carlos explain the theory of operation)
CEC DAC
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.
last month I have receive the same CEC Service Manual from two persons: first as PDF from a diyaudio member by email attachement and second as printed version from a friend of me, which was come back from working in Japan. THE headline of service manual is follow: CEC Balanced Amplifier "AMP 3" - and from the schematic (power amp section) CEC AMP 1 balanced integrated amp Number CEC-1001-93. There is noted "CONFIDENTAL".
The input stage consists of a single stage (INSTEAD A DIFFERENTIAL STAGE) amplifier in push-pull followed from a push-pull VAS-Stage (2SJ76/2SK213) with integrated Vbe multiplier for adjust idle current of 120 mA through the output buffer (true complentary push pull, 2SC2921/2SA1215). The NFB goes like by the STASIS from the VAS-Stage to the EMITTERS of input stage (in the same manner like Musical fIDELITY A1/A100/A200). Thus the output stage isn't in the feedback loop.
According the schematic the supply voltage is 2x18VAC (aproximately +/- 24-26VDC). The power amp section exist four times for bridge mode.
I miss emitter resistors in the output stage and the fast fuses in the collector line means two fuses in the signal pad (because the absense of caps behind the fuses resp. at the collectors).
There must be several misprints arround the VAS stage (PP current source), thus i am not able to determine the appropriate current value - but I assume approximately 100 mA (necessary because the output buffer isn't triplet/darlington - this fact is very special for me).
The describtion by the URL
CEC AMP3300R
isn't suited to the schematic - maybe there are a wide range of others or "LEF" is only a name for marketing as Mr. Bob Cordell mentioned by one of the LEF threads here on diyaudio.
The different to Musical Fidelities A1 is actually very low. In the A1 is the output stage the VAS stage at the same time. If one replace the both emitter follower stages behind the input stage of the A1 and the output stage by one pair medium power lateral mosfets for the VAS stage include Vbe multiplier and add a pair of BjT power devices from SANKEN in a MT200 outline (not darlington or triplet) one will get the mentioned CEC topology.
I am still looking for the LEF topology.
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In this case I have found a description concerning LEF by the B.M.C. Amp C1 under
B.M.C. Audio Amplifier C1 integrated amplifier | Stereophile.com
Here I read follow:
The Unique Circuit
When we met following his visit, at the 2012 Consumer Electronics Show in January, Carlos Candeias told me that the Amplifier C1's circuit is neither class-A nor class-B; instead, he calls it Load Effect Free (LEF). He doesn't use energy-wasting class-A operation to eliminate crossover distortion and have transistors operate within a more or less linear range, because such designs still usually require some global feedback to further reduce distortion. If the distortion never happens in the first place, due to the choice of transistor operating characteristic, it doesn't need to be corrected.
Unfortunately the measuring results under
http://www.stereophile.com/content/bmc-audio-amplifier-c1-integrated-amplifier-measurements
indicates for me a harsh sound in the high frequency area above 2 KHz, and below 8 ohms load impedance (go to fig. 10). This is typical and usual at all class AB models with low idle current through the output stage.
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any news ?
a friend of me, who use this model, want to remove the bad character of distortion in Fig. 10 unter
B.M.C. Audio Amplifier C1 integrated amplifier Measurements | Stereophile.com
and therefore a schematic diagram is necessary.
a friend of me, who use this model, want to remove the bad character of distortion in Fig. 10 unter
B.M.C. Audio Amplifier C1 integrated amplifier Measurements | Stereophile.com
and therefore a schematic diagram is necessary.
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