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Old 16th January 2002, 03:14 AM   #1
Michel is offline Michel  Canada
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Question 654H+8AEFHEMNFOKHE

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Old 18th January 2002, 08:33 AM   #2
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Question Schematics where???

Hi Michel,
Could not find any schematic on the Accuphase site, only product promotion. Could you provide a "deep" link or where do I have to click?
Thanks in advance.
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Old 18th January 2002, 08:54 AM   #3
ergo is offline ergo  Estonia
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I think that the schematics michel mentiones are the ones in product datasheets and are only simplified type. You can get the idea of the cicuit. I have seen the original schematics some time and there really isn't anything mysterious. Just the same schematic + output over current protection included to the output stage. The output transistors and the pre output stage transistors are from Sanken.

Ergo
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Old 18th January 2002, 04:01 PM   #4
grataku is offline grataku  United States
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Elso,
if you want to experiment with CFA look at the Hiraga on Geoff site. Easy to build, hard to get to work (the PSRR is low to nil). I also have an old Aloia article (1981) about a project that looks very 'Accuphase-esque' there was a commercial version of this amp called, I think, ST-200. This latter design was easier to tame. The author claims a max value of 14dB feedback at any freq. I would have posted already if I had a scanner. I built them both and I love them both.
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Old 18th January 2002, 04:23 PM   #5
jam is offline jam  United States
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Check
http://perso.wanadoo.fr/jm.plantefeve/

I would like to hear from anyone who has experimented with current-feedback amplifiers. I am in the process of building one.

Michel

I agree with your comment for the need of a good power supply, do you see any other pitfalls in current-feedback designs. I am aware of their speed and potential for low distortion but that is not usually an indicator of good sound.

Jam
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Old 18th January 2002, 04:57 PM   #6
sonnya is offline sonnya  Denmark
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I have build one... It is runing on my system right know!



Sonny
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Old 18th January 2002, 05:05 PM   #7
jam is offline jam  United States
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Sonny,

Which design did you build and how does it compare to what you were using before.

Jam
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Old 18th January 2002, 06:23 PM   #8
sonnya is offline sonnya  Denmark
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The alexander amplifier started it. But i wanted to have a discrete stage instead of the opamp used in the alexander stage.
The inputstage wich is a buffer looks a bit like the output bufferstage in the Jfet/bipolar amplifier i have made.

It can be made a lot simpler. And i did have problems with the inputbuffer ... It worked like a "mixer" you know the ones they user in FM receivers!!!! I have made lowpass filter in the input to get loose of the problem.

The two currentmirrors in the alexander are betaenhanced with an ekstra transistor. The currentmirrors output is then cascode coupled.

The outputstage is a normal darlington stage with 3 pairs of transistors (2SA1302 and 2SC3281).

It is compensated to drive capacitive load like 100uF||8Ohm without oscillation of course only 2 volt out, not to destroy the amplifier. If i remember right it rings only 2 times on a squarewave and with about 20% overshoot.

BW is around 100KHz.

The sound : Alive with good response i the Bass(1KVA + 2 times 47000uF does it all), detailed Mid and high.

A weak powersupply does have a impact on the sound.

I did have the chance to compare it with a Thule (I think it was a IA100?) on some cheap JBL and got a better Bassresponse.

I have also tried it in compare with an old int. (E-202? it is a long time ago!) Accuphase again same chance like the Thule but also better mid and high. They was compared on my "M1 Super".

If have the design?? yes!!! but i will not give it away.. There is something to chance ... It is not DIY friendly!!!!

Sonny
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Old 19th January 2002, 10:12 AM   #9
sonnya is offline sonnya  Denmark
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Could it not be fun to make a new design from the scratch! ... We could all post our idears .. So that we in the end can end up with a "diyaudio CFB amplifier" ...mmhh Then we need a "project folder" on this webside.

It is only an idear. I would start redraw the inputstage and the current mirror and then post it?

Sonny
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Old 19th January 2002, 02:20 PM   #10
jam is offline jam  United States
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Sonny,

Great idea!

If you could e-mail me at jsomasundram@msn.com there are a few schematics on current feedback designs I could send you.

I had looked at the Alexander design and thought about replaceing the output stage with mosfets but never got around to building it.

Jam
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