New Current Feedback Amp.

Michel · 16th January 2002, 02:14 AM

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Elso Kwak · 18th January 2002, 07:33 AM

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.

ergo · 18th January 2002, 07:54 AM

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

grataku · 18th January 2002, 03:01 PM

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.

jam · 18th January 2002, 03:23 PM

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

sonnya · 18th January 2002, 03:57 PM

I have build one... It is runing on my system right know!

Sonny

jam · 18th January 2002, 04:05 PM

Sonny,

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

Jam

sonnya · 18th January 2002, 05:23 PM

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

sonnya · 19th January 2002, 09:12 AM

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

jam · 19th January 2002, 01:20 PM

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

16th January 2002, 02:14 AM	#1
Michel diyAudio Member Join Date: Nov 2004 Location: L'Assomption, QC	654H+8AEFHEMNFOKHE dfhasdrt3qwerothasdxcb \kxn cvoahwsroQwbs ksewbrgqioe;tuqe

18th January 2002, 07:33 AM	#2
Elso Kwak Banned Join Date: Dec 2001 Location: Zamboanga, City of Flowers, Mindanao	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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18th January 2002, 07:54 AM	#3
ergo diyAudio Member Join Date: Mar 2001 Location: Tallinn, Estonia	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

18th January 2002, 03:01 PM	#4
grataku diyAudio Member Join Date: Dec 2000 Location: -	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.

18th January 2002, 03:23 PM	#5
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	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

18th January 2002, 03:57 PM	#6
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	I have build one... It is runing on my system right know! Sonny

18th January 2002, 04:05 PM	#7
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Sonny, Which design did you build and how does it compare to what you were using before. Jam

18th January 2002, 05:23 PM	#8
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	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

19th January 2002, 09:12 AM	#9
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	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

19th January 2002, 01:20 PM	#10
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	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