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Old 5th February 2008, 11:47 PM   #1
eicen is offline eicen  Denmark
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Default Ultra low distortion amp

I'm sorry if this topic have been answerred a billion times before, but i just got tired of spending every evening in over a week, searching for an answer on the wild wild web.

I'm in need of a schematic for an high end amplifier for my control room in my studio.

I personally know the man behind AudioTechnology in Denmark. Therefore i got the pleasure of buying my speaker units from him, with huge discount. Along with blueprints and cross-over's for some awesome ultra-linear speakers.
Never heard anything like 'em.

Now I need an amplifier to match the speakers. Anything else would be a shame

I've been searching mostly for ultra-low distortion schematic's, regardless of the output power (though about 100W would be the preffered amount.)
And i actually found one.. with lovely specs: ( www.littlefishbicycles.com/poweramp/ ) I was in heaven for 15minutes, untill i discovered, that almost every transistors and FETs were no where to be found at dealers in Denmark.

Also it would be preferred, if it was built around more common (and cheaper if possible) components

Anyway, I was hoping that some of you guys could give me a hint of where to find a schematic which stands up to my requirements (or at least closely or partly)

THD between 0.001%-0.01%
SNR at around 110db
Slewrate as fast as possible

I know that the requirements are a bit hard, and maybe it may not be possible at all. But at least I think posting this forum maybe could solve it for me.

By the way.. I'm sorry if my english is rather poor, but I'm not very good at languages.

Best Regards
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Old 6th February 2008, 10:02 AM   #2
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Location: Budapest, Hungary

The listed parameters are not tightly related to the sound of the amplifier. An amplifier that measures perfectly may still sound terrible and vice versa. Others hopefully recommend an amp that measures and sounds well.

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Old 12th February 2008, 11:32 AM   #3
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Check out the studio 350 amp by silicon chip:

Click the image to open in full size.



I built a pair just recently, and it sounds amazing - every frequency is crystal clear at all volumes below omgmyearsarebleeding.

This is one of those beauties that produces sound so pure that you can't tell how loud it is until you try to speak

pcb diagram:
power diagram:
pcb pattern:

I bought my kits from Altronics and various other bits from Jayjar and built myself a stereo 350w amp for around au$500 (about us$450, 310 euro)
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Old 12th February 2008, 01:04 PM   #4
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Location: Canandaigua, NY USA
IMO, measurements *can* tell you just about everything you'd want to know about an amplifier, unfortunately not the common THD and response measurements that are easy to make and that everybody talks about. You need to know more about things like harmonic structure, dynamic stability and RF susceptibility. Then you need to come to grips with the fact that perfect signal reproduction *may* not sound as good as signal reproduction with some carefully designed "flaws". If you just want to know how to design an ultra-low distortion amp, I'd highly recommend Doug Self's book on amplifier design. It has some schematics that are close to what you asked for, and the semiconductors can easily be substituted as they are non-critical (as should be the case with any good design).
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Old 12th February 2008, 01:23 PM   #5
tinitus is offline tinitus  Europe
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From my very limited experience the best amp will be 1ohm stable
sometimes we know very little, and sometimes we know too much
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Old 12th February 2008, 02:37 PM   #6
eicen is offline eicen  Denmark
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Thank you very much for your replies.

I think what i really want is a flat frecuency responce.. This might be a bit more important than the THD.
Also the damping factor has to be quite good..

I'm actually not looking for an amplifier with "great" colored sound. Since the amp is going to be used for reference audio, and for mixing purpouses, it has to be as clear and transparent as possible.

It looks like a relatively easy build, and the THD-curve looks acceptable. Can you inform me about other data's on the amp?

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Old 13th February 2008, 05:32 PM   #7
steenoe is offline steenoe  Denmark
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If you need an amp that can drive a 1ohm load, maybe you need a new pair of speakers instead??

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Old 13th February 2008, 06:59 PM   #8
eicen is offline eicen  Denmark
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Old 13th February 2008, 08:37 PM   #9
tinitus is offline tinitus  Europe
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Jan claims his LYNX amp to be stable in 1ohm

BTW... an amp with good sonics is not a "coloured" amp, but an amp that is capeable of revealing the musical colours in the recording...if your speakers can do it too
sometimes we know very little, and sometimes we know too much
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Old 17th February 2008, 03:56 AM   #10
eicen is offline eicen  Denmark
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I have bought access to both of the studio 350 articles, cause it seems to be an quite good and easy build. And also not to expensive..

My only problem is that i dont have any 50V-0V-50V transformers.

And since i'm running at a pretty tight budget, and i've recently invested in some other studio-gear, there isn't any room for new investments.

I'd really like to use some of the transformers that i have in "stock".

2 pcs Holden & Fisher LTD 1000VA, 4 x 65Vac ~ 2 x 92Vdc rectified
2 pcs Unknown 500~800VA, 2 x 70Vac ~ 2 x 99Vdc rectified
2 pcs Unknown 400VA, 2 x 25Vac ~ 2 x 35Vdc rectified

My idea is to make 2 mono-blocks, so I'll need a transformer to each amp.

Is it possibel to make a simple mod to the SC Studio 350 amp, to fit any of the transformers that i already have??

I also have 8 pcs of 15000F 100Vdc Caps, that i want to use in this project.
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