NAP-140 Clone Amp Kit on Ebay

[nigel pearson]

Hi Chris you can do all of that . However if you want to remove a DC blocking capacitor best remove the one in the preamp . If you get the slightest problem you will loose your speakers if no DC blocking at the input ( a loose plug for example can be enough, a DIN plug / socket Is better as Naim insisted , they used the make Preh ) .

The 100K is to help keep the capacitor in the power amp and the preamp charged . If you are using a passive preamp you might find raising to 47 K worthwhile . If from a standard preamp even 10 K is OK . You will get slightly more hiss and DC offset if doing this . Do check it's below +/- 100 mV . Matching the input transistors is more critical so not something I would loose sleep over . You could go to 100 K I suspect . Do not change the 4K7 and 330 pF , that is part of the unique sound ( input slew limiting and RF filter ) .The capacitor below is probably better .

BFC246804106 - VISHAY BC COMPONENTS - CAPACITOR, POLYESTER FILM, RADIAL | CPC

Here is a ridiculously cheap one ( Nikkia and Panasonic non polars even better ) .This is a unique situation where this can work . 33 uF is OK and will give a tad more bass ( lots more in the technical sense ) .

33uf 35v Non Polarised Capacitor

The posh version is the type N

black gate electrolytic capacitors page

[nigel pearson]

Ruwa . I investigated your question about the 22 K and LTP input transistors more carefully . I suspect it is to put the second harmonic distortion above the third harmonic slightly . If configured approximately with 1K3 and 0R where the 22 K is located the second harmonic from this stage would be effectively zero ( assuming VAS vbe to be 0.65 V ) . There would be a tiny bit for the VAS second harmonic in addition . Jean Hiraga would endorse this idea I feel , Douglas Self not . It is my ambition to meet Jean one day so that says what I think . If anyone wants to know the Hiraga treatment just ask . I didn't simulate this so forgive the approximations , it was A4 paper and my phone as a calculator .

[Chris Goldring]

Originally Posted by nigel pearson

Hi Chris you can do all of that . However if you want to remove a DC blocking capacitor best remove the one in the preamp . If you get the slightest problem you will loose your speakers if no DC blocking at the input ( a loose plug for example can be enough, a DIN plug / socket Is better as Naim insisted , they used the make Preh ) .

The 100K is to help keep the capacitor in the power amp and the preamp charged . If you are using a passive preamp you might find raising to 47 K worthwhile . If from a standard preamp even 10 K is OK . You will get slightly more hiss and DC offset if doing this . Do check it's below +/- 100 mV . Matching the input transistors is more critical so not something I would loose sleep over . You could go to 100 K I suspect . Do not change the 4K7 and 330 pF , that is part of the unique sound ( input slew limiting and RF filter ) .The capacitor below is probably better .

BFC246804106 - VISHAY BC COMPONENTS - CAPACITOR, POLYESTER FILM, RADIAL | CPC

Here is a ridiculously cheap one ( Nikkia and Panasonic non polars even better ) .This is a unique situation where this can work . 33 uF is OK and will give a tad more bass ( lots more in the technical sense ) .

33uf 35v Non Polarised Capacitor

The posh version is the type N

black gate electrolytic capacitors page

Thank you for your kind answers Yeah, i got a passive pre, with a 10k TKD and 1uF V-cap copper foils after the pot, so i need the 50k input impedance badly =)

I don't thing anything will happen if i disconnect the RCA interconnect from the amp because of the 50k resistor grounding the Base of the input transistor

I have some BG N caps but they are 4.7uF and i doubt they are any better then the V-cap copper i use as output in the passive pre.. I think i'll try fit som BG where the rather big values are in the amp, like the 47-68uF or so in the feedback and "T5-bypass" and perhaps the 100uF decoupling in the VAS too. Any good idea to use silver mica over ceramic for the "pF-range" caps?

Is it too much to use 100uF as the feedback DC blockage capacitor?

Thanks again and happy building everyone

[nigel pearson]

Hi Chris . I agree , note I wanted to protect the unaware .

Mr Douglas Self recommends going as large as possible on the feedback capacitor ( low frequency distortion more than bass ) . He also recommends some diodes to protect the capacitor if experiencing a blow up ( I beleive that's why , higher voltage cap should be enough ) . As a point of interest signal can be fed into that cap ( where it would go to 0V ) and the input side of the amp grounded . The preamp needs an output impedance of <100 ohms to do that . It is theoretically better ! One needs to phase reverse the speakers if so . I have even used 1000 uF as feedback cap . I did get a problem once where the amp was configured as a linear phase active filter ( yes the amp ) . That required having the sides equal so as not to blow fuses in the PSU . I recon 220 uF worth trying . You might find the mid range better by doing it also !

Silver Mica's are posh ceramic's . Any high grade NPO/COG ceramic's will be close sonically to silver mica , other ceramic's usually are not audio components except where low inductance required ( DAC decoupling perhaps , snubbers ) . There are silver ceramic's used for high voltage ( Murata class Y2 and similar ) they might be OK . I have a hunch as the high voltage requires a good dielectric they might be a gem . They are cheap . Ceramic's are microphonic , try damping them .

[AndrewT]

Originally Posted by Chris Goldring

I don't thing anything will happen if i disconnect the RCA interconnect from the amp because of the 50k resistor grounding the Base of the input transistor

RCA is a connector that makes hot before return and breaks return before hot.


In the process of inserting and extracting an RCA from LIVE equipment, the hot pin can be connected to the hot inside the interconnect. This hot is not screened, nor is it twisted with another equal and opposite current flow.
The hot PIN is directly connected to an aerial, that will inject a large RF signal into the amplifier.

That large RF signal can damage receivers.

The ancient DIN plugs and sockets did not have this inbuilt fault. But we users thought they were unfashionable and demanded that manufacturers adopt a fashionable but cheap and flawed connector.

We consumers are fools.

[nigel pearson]

There are the Neutrik Profi plugs which do not have the problem . They are expensive and not my cup of tea . The cheap Neutrik are superb . Don't forget XLR .

http://www.rapidonline.com/Cables-Co...1-2eccf39f42d8
Gold plated phono plugs Neutrik NYS373
3 Pole Nc3fxy Idc Cable Socket

[AndrewT]

There are many plug/sockets that do not have the Phono/RCA design flaw.
But generally they all cost more.

I would go for XLR.

But more to the point. Live plugging and unplugging is not recommended unless the designer has designed for this operational mode. eg. professional gear that must be kept live while hot swaps are implemented with the audience still listening.

[nigel pearson]

Hi Andrew . I have Pro Audio chums . They use the Profi when forced to use RCA and mostly XLR . The point is if someone trips over the cable when running a 10 000 watt amp it will disconnect cleanly . I just sent one chum a link to prove I am corrupting the world of audio to Pro Audio ideas . Naim were already professional I would say.

[Ian Finch]

The majority of us are stuck with Cinch or "RCA" connectors regardless of fashion. We occasionally see high-budget builds here but balanced or unbalanced XLR, Neutrik etc are the preserve of high-end retail buyers and professional applications where they are justified.

Domestic equipment, even my $4k CD player, comes fitted with RCAs. So do the vast majority of affordable products outside the capability of average DIY. I'm stuck with RCA for compatibility, resale, client and warranty reasons, I've looked around and found typical up-market RCA cables have massive and very tight fitting ground sleeves. Provided you fit these up firmly (I can';t even get some apart!) and don't play about with them whilst the amplifier is on and at full gain, they are safen except as you point out!

In the situation Nigel describes, the "chums" would be absolutely wonderful, if not for the cost but it may not be an issue in showroom or basic installations. Thanks for the reminder.
There's no accounting for other members of the household, unfortunately.

[nigel pearson]

Hi Ian . Everyone I hope you like this ? Hope it's allowed to put links up like this ? . Nostalgia ....! Valuable look inside the great one . Doubtless seen before ?

Wood NAIM NAP 250 Repair and Restoration October 2011 - YouTube