NAP-140 Clone Amp Kit on Ebay

[nigel pearson]

See t/f if in UK

http://cpc.farnell.com/multicomp/mct...20This%20Range

[Ian Finch]

Originally Posted by nigel pearson

.... I never missed the opportunity to pump him (JV)for information ....

Here is a curly question about NAIM preamps -early ones which had no clear model number, but were quite shallow in the case and sported largish plain knobs. Now, who was the clown who specified a DIL reed relay as the mute switch?

When the preamp was placed on hard surfaces such as a table, glass shelf etc. the audio would change from wonderful to old 78 record player in a flash, due to acoustic feedback so I do mean clown, for lack of testing. It was amusing, when some years later, the manufacturer and the UK hi-fi toy industry generally, began to promote Aerolam table tops, coned feet and special isolating shelving for every bit of kit. 'Not funny really, at the prices asked.

[nigel pearson]

That's very interesting Ian . I had a NAC 12 which by then didn't have that .

If you ever get smooth box NAC 12 and NAP 160 together they have a magical sound . I don't find them as good used with other Naim bits . For example swap to NAC 42 . The other Naim products are not affected by this including later NAP 160 .

My noise gate used a comparator and a simple relay also ( shunt ) . It was very reliable and apart from the click it was difficult to detect .

The guy in Australia I seem to remember was Warren Stolmark or something doing Naim . My freind Martin Renwick wanted to do it . He would have been great .

I have a Linn pre amp somewhere , it was made by Naim .

If you ever want to talk 78's I'm very interested ( or ancient stuff ) . Not on this forum .

[Ian Finch]

Originally Posted by nigel pearson

....smooth box NAC 12 and NAP 160 together they have a magical sound . I don't find them as good used with other Naim bits . For example swap to NAC 42 . The other Naim products are not affected by this including later NAP 160.....

Thanks for that experience. I do wonder because of the secretive Naim policy about even its early IP, or any avenue for criticism. It's easy to read a NAC 42 from the cloner's Ebay sites but I imagine the preamp circuits change a lot with time and market needs. The schematic and PCB only describe the main line-level amplifier which may have sat before the volume control so it is difficult guessing what you really have and how much you don't when you pay for these.clones.
Any comments on topology changes would be priceless.

[nigel pearson]

Ian . I will be honest with you and say I am not the worlds greatest fan of the pre-amps . Although they are super competent designs . The Martin Renwick I refer to introduced me to DNM pre amps of the 1985 vintage which I preferred used with NAP 250 . I think he was importer for Australia of DNM .

I did draw the pre amps years ago and have lost them . Do you guys insist on using tantalum caps like Naim did ( do ? ) .

One tip with NAC 32.5 and similar . Leave the screws slightly loose into the feet . That was discovered by accident and makes the pre amp less microphonic .

Sorry to hog the thread every one . .

It must be 1.40 in Aus , hope I'm not keeping you up ?

Just had another look . Nice simple distortion cancelling design , some of this I remember now . I tried to find the Stan Curtice stuff on this ( he designed Rotel RA 820 ) . Perhaps with better components it could come alive . The power supply doesn't look right although doubtless good .

[Ian Finch]

Not at all (only 11.40 ) - Warren Stolmack, I recall as a name only, Martin, no but we have >800km between the
largest cities and it's possible the agent operated from Melbourne as now - since it's the bastion of stereo hi-fi here.
Thanks for the comment -'would like to explore that and the DNM matter at some other time.

P.S. Member ljm-ljm produced that schematic and board so we can't say where in the PSU Naim started or finished.
Perhaps he will post.

[nigel pearson]

[IMG][/IMG]

Ian , I am very mindful of keeping things cheap . One of the debates raging in audio is what type of power supply rectifier diodes to use . Naim would have used simple big versions of what I show here in a 35 amp bridge rectifier .

Regulations came in some years ago to suppress the diode noise . The simple 10 nF I show across each of the 4 diodes is what the testing house recommended .

Many say this ruins the sound ( me ) . The 470R and 3n9 ceramic is an attempt to please everyone . In theory it should be better . Carbon composition resistors are best and solder close to the diodes ( difficult ) .

The last example with 10nF 110R and 68 nF is supposed to be the best .

Unfortunately this solution was for a particular transformer . However it must be better than nothing .

I am research this at the moment so would love any feedback . The little neon bulb idea is just a bit of fun . The dotted resistor for
valves .

People pay money for mains conditioning equipment only to have a nasty little radio transmitter inside the amplifier , the rectifier diodes .

Some use fast / soft recovery diodes without suppression .

[Chris Goldring]

Hello,

Is it possible to increase the input shunt resistor (22k as standard) to something like 47-50k? and also remove the 100k+10uF RC filter? (my source is capacitive coupled at the output)

Regards.

[Salas]

Are fast/soft good enough on their own without rc snubbing them?

[nigel pearson]

Hi Salas . That's the question I had hoped for ! I suspect 470 R and 470 pF is about right for an ultra fast diode . I think the diode is BYV 28 200 I am playing with . What I suspect is that we can come up with a generic value which reasonably ignores transformer leakage inductance and capacitance . I want to keep away from a mathematical discussion as I feel this can be arrived at empirically and would be fun for the penniless to pursue . Note I stress carbon composition resistors and ceramic capacitors ( NPO / GOG ) . That's about 720 kHz and a sensible rise time . What should be noticed is better HF clarity . BYV 28 200 is a bit small for a power amp I should point out ( probably just about OK , cheap and very good ) .