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Old 30th January 2010, 10:37 PM   #1
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Default NAD 310 - need some info

Hey guys,
i just need some basic info on my NAD 310 integrated amplifier, which by the way serves me well, since i began very interested in it`s circuit topology.. i know that it`s a hybrid (NMOSFET w bipolar) design but i cant` really understand how it operaters in this particular model.. is it like a class AB or something else.. so if anyone here could give me some info about this "strange" transistor implementation, i would be very happy..

Here`s the schematics picture..
http://img526.imageshack.us/img526/9...d310schxb3.jpg

Cheers,
Filip
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Old 1st February 2010, 07:29 AM   #2
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This is a very interesting circuit... it's single ended AC coupled which is the obvious feature... less obvious is the fact that this "single ended" input stage, as opposed to a long tailed pair generates even harmonic distortion... which is great for sound quality.
The output stage is class ab and very unusual in that it eliminates a push pull driver stage... I think that's the reason for "having" to use a FET as the top device, as it's drive requirements are modest. Again this will generate distortion... but it's the "right" sort. I imagine it sounds fantastic... very musical.

Even more unusual... I might post a link to this is the "cross coupling" between channels. Look at the output and R255 and C225 and R256 and C226... why ?

Edit... have linked another thread to this one. It's worth discussing

Last edited by Mooly; 1st February 2010 at 07:37 AM.
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Old 1st February 2010, 11:27 AM   #3
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The link is now showing up for me. But going by what you have said in the other linked post, I wonder if only HF is cross-coupled between left and right channels, not having seen the schematic, then it might be for the "wide-stereo" effect which was prevailent in some Japanese equipment of the early 1990s.
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Old 1st February 2010, 11:39 AM   #4
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It's very strange for sure...
I know the "wide stereo" effect you mean, isn't that done with out of phase signals though, this is more like deliberately introducing a known level of crosstalk, which in itself should be inaudible.
I have wondered how important having the same level of crosstalk between L-R and R-L is for image stability. Could this be something to do with that, to reinforce the stereo image although the effect at those frequencies would be minute I would think.
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Old 1st February 2010, 11:40 AM   #5
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Samuel,
Is the circuit not showing for you ?
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Old 1st February 2010, 11:44 AM   #6
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This is the part,
Attached Images
File Type: jpg Crosstalk.JPG (118.8 KB, 321 views)
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Old 2nd February 2010, 01:27 PM   #7
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Well, thank you guys for your kind explanation.. so, if i`m guessing it right, input is basically a class A (?) and the output is class AB but without the usually required "push pull" implementation.. very strange i guess... now i`m even more confused..
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Old 2nd February 2010, 02:54 PM   #8
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I`ve found something interesting on net.. Review | NAD 310 integrated amplifier Geoffrey Horn for themselves and a considerable number of friends, particularly amongst the student community, by marketing a range of high fidelity units, or 'separates' at very low prices. These units invariabl

it`s a 310`s review in which there is the original NAD`s quote about little 310 :
"(Previous) circuitry, being the most limiting factor, was disposed of, to be replaced with a single ended, pure 'Class A' driver stage. This in turn drives a complementary set of output transistors, one N channel MosFet and the other a state-of-the-art PNP bipolar transistor. Through careful and limited local feedback around these transistors their characteristics are accurately matched. The result is an amplifier with approximately half theumber of components and an increase in efficiency of almost 20% when compared to other amplifiers of similar price or specification. This reduction permits the use of higher quality cornponents ..."
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Old 2nd February 2010, 06:07 PM   #9
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That's a real bit of "marketing talk" It is non the less an unusual design.
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Old 3rd February 2010, 11:46 AM   #10
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Ok.. thank you Mooly!

Anyway, i was thinking about refreshing this little gem with some new capacitors.. the original values for 4 main caps are 4700/63v/85 c .. do you think i should better get some increased values caps? I also think they should be upgraded with some 105 c values because the one cap that sits close to the transistor layout gets hotter than the other (because of the unusual caps design in the preamp section)... what do you think about all of this?

Cheers,
Filip
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