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
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
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Ruwa's question
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 .
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 .
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
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 .
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 .
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.
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RCA Plugs
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-C...495/?sid=dd617ea8-0aac-4077-8691-2eccf39f42d8
Gold plated phono plugs Neutrik NYS373
3 Pole Nc3fxy Idc Cable Socket
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-C...495/?sid=dd617ea8-0aac-4077-8691-2eccf39f42d8
Gold plated phono plugs Neutrik NYS373
3 Pole Nc3fxy Idc Cable Socket
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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.
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.
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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.
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.
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.
NAP 250 TOUR
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
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
A most popular part in the DIY circles is the TO-220 MUR 860 8A 600V ''Ultrafast'' from ON Semiconductor. The BYV Vishay (ex Philips design I think) is relatively popular in preamps I have seen, still more hobbyists use MUR 120. Maybe due to availability.
It isn't very long ago I serviced an original ''bolt on'' 250 with blown DO-4 rectifiers. Those through hole mount ones on a bracket. Its owner was adamant about that old version with power transistors wire connected and arrayed on the back panel, being superior to later iterations. He had a full old style Naim system with NAC-32, NAT tuner, Linn Sondek, Dynavector LMC cart, and big IMF Professional Monitor IV speakers kept in excellent condition. The drive was enough with new reservoirs in the amp for Jazz at moderate to high levels. Does his assertion hold water regarding the ''olive oil'' and later NAP-250 iterations? He mainly believed the HF was smoother with the ''bolt on''.
Thanks Salas . I am putting a link in . CPC is a retail company . Just wanted to list it to make sure people are buying at the right price . CPC would be almost 100% genuine parts ( people keep saying about fake parts ) . I say that because I think no one can be 100% sure . Ironically CPC is cheaper than it's trade side for transformers and very good prices . Farnell is world wide , alas CPC not .
I put a link up for a NAP 250 tour . I had forgotten they used Philips SFR25 resistors . MRS 25 are still available if people want to be that authentic ( MRS 25 was the 1% 50ppm version ) .
I think NPO ceramics are fine , still people beleive these things . Don't use polystyrene for the VAS cap as they sometimes fail and will take out the speakers .
MUR860G - ON SEMICONDUCTOR - DIODE, ULTRA FAST 8A 600V | CPC
I put a link up for a NAP 250 tour . I had forgotten they used Philips SFR25 resistors . MRS 25 are still available if people want to be that authentic ( MRS 25 was the 1% 50ppm version ) .
I think NPO ceramics are fine , still people beleive these things . Don't use polystyrene for the VAS cap as they sometimes fail and will take out the speakers .
MUR860G - ON SEMICONDUCTOR - DIODE, ULTRA FAST 8A 600V | CPC
Sorry everyone couldn't resist to reply . Salas . I said the other day I want to see everyone is making NAP 250's by the next day . I'm ready when they are . I think that with that NAP 250 the guy should sell the IMF's and will get good money and buy some mid series Isobarik's ( when they did start to image a bit ) . The system wants a pair . I was looking at a pair of IMF's one day and so was Michael Cain ( Gulp ) , a very impressive person in the flesh . He was still in the Ipcress style and wore a very nice tweed jacket . If Frank Schroeder reads this I know the real look Frank ( he has the same genuine glasses ) . Frank is a valve man so no chance .
Sorry to those who have no clue about ancient Naim amps and will forgive this . I would guess it's the genuine BDY 56 transistors that count Salas ?. Naim would never say what the latter ones were ( Japanese ? ) . Naim amps seldom go wrong so one does not build much knowledge of tweaking . Like RR cars we don't like to change them too much . I said yesterday that smooth style NAC 12 and NAP 160 were magical together and as you describe , JV told me that the bandwidth limits are set by the pre amp and power amp combined and didn't expect other preamps to get that right . DNM did .;
Could be the genuine transistors keeping it steadier than later versions, maybe helping out with the distinct IMF slight treble ''sting'' making it more suitable to his speakers. Alas, with due respect to the venerable designs, listening to his system these days left much to be desired respectively to decent modern offerings. Its like my friend's Norton Commando lovingly preserved bike. What a nice feeling riding pillion on the southern avenue long seaside part of Athens until a GSXR appears and feeds us a ton of dust.
Salas I should give you my email . I don't mind others contacting me and they can even be abusive then ( I hope not ) . You won't believe this I wrote to the son of the designer of the Norton Commando the other week ( Philip Hooper ) . We were talking Scott motorcycles and his late fathers connection with them and George Silk . As I said Clint Eastwood has a Commando he bought in bits . MC was listening to a Tim de Paravacini Luxman Valve amp if interested with the IMF's . The IMF's are too flabby for that Naim system . Norton ES2 was the Nait . Naim NAP 250 is a Vincent if asking . My favorite Jap Bike Honda CB900 FA .
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