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Old 6th October 2009, 10:14 PM   #1
Krisfr is offline Krisfr  United States
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Default State of the Art TODAY

I am new here, the last amp I built from Scratch Stereo wise was 100 watt Leach. I am curious why the topology that amp had does not show up on ANY of the schematics I have seen here. Fully complementary (dual long tail pair) seems to gone out of style and bi-polar transistors followed right behind. Is there a summation of the acceptable starting points of design today to be called State of the ART? Are any examples of the new SOTA in the 100 to 250 range exampled out on the Forum?

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Old 7th October 2009, 06:47 AM   #2
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Quote:
Is there a summation of the acceptable starting points of design today to be called State of the ART?
First one must ask what is SOTA ? By definition ALL the amps here are NOT , with MOSFET class D designs being the "new tech".

If one looks at 2009 "mid- fi" , IC driven output stages or (in the case of sherwood) fully discrete doug self type amps with the most modern semi's are the rule.
As far as the designs here at DIYA , at least the Class B ones, if you use the most modern components and precise layout ,these are SOTA for that particular design.

The leach is a good amp, but based on old devices. Without a redesign it can not be SOTA. The RMI/patchwork , supersym , symasym , Syn08's amps all use the latest fairchild and ON semi discretes. The DX and quasi amps use 20 year old semi's but could be upgraded. But back to the SOTA ??? , if a amp sounds good ... Who cares ? ALL the class b amps here can be traced back to RCA or japanese designs with very few exceptions.
OS
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Old 7th October 2009, 12:52 PM   #3
Krisfr is offline Krisfr  United States
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I am very appreciative of you taking time to answer my post.... The direction I would like to head in is to build the "best" amp I can to re-wet my feet in the DIY mode. I am torn between practical and SOTA considerations. The topology vs. the devices available at a reasonable price. The integration of enhancing digital control integration and refinements in design techniques such as spice and printed circuit board simulations in the analog arena. Forgive my rambling, but I will look at the suggestions you gave and dive into "something" to get back into what makes me wiggle my toes; listening to the labor of my mind and hands while getting the compliments of my friends and family. I did not have time as the years went by, but I am blessed to have a few moments now. Thanks
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Old 7th October 2009, 06:27 PM   #4
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Quote:
The direction I would like to head in is to build the "best" amp I can to re-wet my feet in the DIY mode.
Here are the best , most reliable I have actually built. I now split the design into output stage / input voltage amp (separate boards , too).

(attachment 1 is the OP stage) , it uses modern on semi discretes and will be faithfully driven by any voltage stage.
(attachment 2,3,4 are the "big 3" input/ voltage stages) all will run the above Op stage. you can be anal and make the OP stage modular to accept all 3. My next project will be SMD based and I will have the option of "plugging in" all 3 .
attachment 2 is the symasym based one I use now, 3 is self based, and 4 is bootstrapped (old RCA design).. all are "single ended" current sourced input stages. All these have a unique sound , which is a very subjective topic , I just like attachment 2 (real clear vocals/highs).


OS
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Old 9th October 2009, 12:06 PM   #5
Gordy is offline Gordy  United Kingdom
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Krisfr, one place to start would be to investigate operational amplifier design (yup, those little chips), and see what's going on with those guys as they seem to be employing some fancy circuit design to get their distortion levels down.

Some folk think that current (as opposed to voltage) feedback is a good direction, so that might make some interesting reading for you.

Also read up on D. Self, because he may only have one main approach, but he seems to do it very thoroughly.

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Old 9th October 2009, 12:39 PM   #6
Krisfr is offline Krisfr  United States
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I know what you mean about the operational amplifier circuits, I had the pleasure of working with Bob Pease at National Semi in the linear IC department in the 70's. I learned a lot there and even though I was working on a Automotive Ignition IC, noise reduction techniques had their place in those circuits too.

I developed a circuit to transfer the thermal information from the output transistors back to the feed back circuit ( to control the bias ) with an opto-isolator that I will share a little later. It uses an op amp or two.

To me the power amp is a HUGE op amp.

I remember reading some articles in Wireless World in the 70's and or 80's by Self ( I think, as I grow older my memory fails me) that impressed me. I will gather some more info before diving head first into this journey. I must strike the inevitable balance between more analysis and DOING something to move forward and learning by doing.

Laying out the PC boards with Black tape and being extra careful of the ferric chloride stuff while maintaining registration of the top and bottom side of the intended PC board is a thing of the past I will give up. Laying out a board on the internet with a computer is but a dream of the past. Having the 4 layer board delivered to your door in less than a week is priceless.....

We live in exciting times, I just wish my DAD was here to see just a glimpse of what we take for granted.

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Old 9th October 2009, 01:18 PM   #7
Gordy is offline Gordy  United Kingdom
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Quote:
Originally Posted by Krisfr View Post
We live in exciting times, I just wish my DAD was here to see just a glimpse of what we take for granted.
Yes, I have thought the same. I am sure that just one glimpse of my 50" television would have been enough to stop my father in his tracks.

Extending the thought momentarily to beyond departed family; I would like to be able to escort Leonardo da Vinci on a tour of today's world. What would he make of it all, and what possibilities would he see in our current technology?

But back to reality... if you do decide to catch up with Self his book is The Audio Power Amplifier Design Handbook, 4th Edition, ISBN 0-7506-8072-5
and his site is here: http://www.dself.dsl.pipex.com/ampins/ampins.htm
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Old 9th October 2009, 03:12 PM   #8
jaycee is offline jaycee  United Kingdom
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It seems to me that "State of the Art" now is about price and size. To this end, we're talking about Class D type amps. It seems that what matters now is form and low energy consumption, and THD/sound quality be damned.

The Leach circuit is still a valid topology and works well with modern devices and layout techniques - this is already pursued by Jens Rasmussen here.
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Old 10th October 2009, 03:37 PM   #9
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The present challenge and excitement seems to be getting the most out of a B&O ICE module but that may have already turned into yesterday's news.
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Old 10th October 2009, 10:16 PM   #10
jkeny is offline jkeny  Ireland
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Quote:
Originally Posted by ostripper View Post
Here are the best , most reliable I have actually built. I now split the design into output stage / input voltage amp (separate boards , too).

(attachment 1 is the OP stage) , it uses modern on semi discretes and will be faithfully driven by any voltage stage.
(attachment 2,3,4 are the "big 3" input/ voltage stages) all will run the above Op stage. you can be anal and make the OP stage modular to accept all 3. My next project will be SMD based and I will have the option of "plugging in" all 3 .
attachment 2 is the symasym based one I use now, 3 is self based, and 4 is bootstrapped (old RCA design).. all are "single ended" current sourced input stages. All these have a unique sound , which is a very subjective topic , I just like attachment 2 (real clear vocals/highs).


OS
Os,
Nice overview of designs, thanks for the schematics (when I try to go to your homepage - I'm asked for username/password - is this open access?). I was hoping to follow up on any pcbs, mods for SC5200/1943 o/p transistors, etc

About SMD parts - are you not worried about the thermal drift effects - particularly on SMD resistors

Last edited by jkeny; 10th October 2009 at 10:40 PM.
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