naim clones

Some days ago, "carlmart" <[email protected]> asked me about my "naim clones".
Maybe this is of general interest:


Naim clones!

Yes, it is possible to "DIY" them, at least with some care.
Several years ago I was working in a shop (in Vienna, Austria) repairing these amps, so I know them quite good - although NAIM never provided any schematics or spares (a very arrogant company - at least in those days). But for me this amps always were the reference, I rarely heard anything better, at least for this price.
(A highnosed company with an even more highnosed PR, but they make wonderful amps. I would rather like them to be as friendly as there are a few others - I do not have to mention them.)

I always wanted to have something alike, maybe not an exact copy, but an amp "from the same spirit".

So - basically what I build is this:

1. A few preamps, similar to NAP42.5.
But I must admit, I had orginal (swapped, for free) NAC42 mainboards and modified them to 42.5 standards (two 24V supplies).
This preamps have a very delicate and complicated grounding system, which is a bit difficult to copy.

2. Some "HICAPs" , with more or less "high caps".
This is fairly easy, if you have access to high quality parts.

3. Two main amps, a bit similar to a NAP180, one stereo and one in unregulated dual-mono mode.
This amp's circuit details are a bit modified, because it is not possible to get the original power transistors.

They all sound pretty wonderful and musically-dynamic. I still have one setup, which is constantly powered on in my library/listening room and I use it almost every day, together with a LINN LP12, with Ittok and a Goldring Elite, an AT-OC9 or a LINN K9, with an Arcam CD player, a Creek Tuner and DIY speakers made with Audax parts. LS cables is orginal NAIM NACA4, interconnect cables are DIY with belden and other parts. All the setup is modified to some extent (mains filters, cable lineup and grounding).

A few caveats: the gain of the preamp is a bit too high for normal CD use (this could be changed however), it does not always sound friendly with bad recordings or bad sources (because it is a good amp), it does not have the (artificially enhanced) holographic sound some expensive american amplifiers seem to provide.
There are quite a few capacitors (mostly tantal beads, correctly biased) in the signal path, which does not suit to everybody (because caps are considered evil...), and other things.
Generally these amps seem have a great potential for audiphile approved modifications, but some of these mods strangely turn out not to better the performance.

Schematics:
I have drawn quite lot schematics for all NAIM amps up to 72 and 250 and my modifications. But as I mentioned before, some of the parts (transistors) are proprietary and not available for DIY. I also do not have the drawings in digitalized form (not yet).
I hope you appologize, but it is therefore not possible and irresponsible to publish them in the net at this state. I must admit, I never had any idea that someone is honestly interested, because internationally NAIM amps have a very bad or questionable reputation amongst DIYers.
And - last not least - I do not know how NAIM AUDIO will react, AFAIK they have been pretty unfriendly to DIYers in the past. But the circuits are quite simple, more or less standard to some extent, the quality seem to be more in the way how all the parts are selected and the whole thing is made in general.

If - however - there is a great interest, I will try to setup a site and will looking forward to discuss the schematics and the construction details with you !
But be patient, at the moment I am very busy with long term projects (I am a music composer) and html is not my strongest side, to put it mildly...

cheers
Klaus
 

Asen

Member
2001-01-14 1:19 am
Sofia
Klaus

I've heard some Naim stuff. I myself have been using a NACA5 cable in my system for a while which outperformed all the other cables I've been using so far. It's not something exceptional, but it is good for the price.
I like the equipment this firm offers and the CD records they produce. Obviously these guys know about music and its reproduction. Despite of the other amps discussed here, the NAIMs are absolutely cold. The Naim CD players dissipate times more heat then the amps (when idling or at low levels).
I think there will be an interest, so go on...

You mention you've been reparing Naim equipment. In this connection I have a question to ask about the CD mechanism CDM9. If I'm right Naim uses CDM9 in some CD players. Can you tell me is it possible a CDM12 to be replaced by CDM9 direct.

Thanks

Asen
 
Naims are interesting - good to know.

Sorry, folks, I am on holiday for two weeks now.
Please keep this thread open to discuss more details later on.

To Tvi:
Thanks for the urls! This will be of great interest for all naimamp-friends.
I did not know, that this guy had a construction page too. He seems not to link his pages.
But I do definitly not agree with all his mods, specially with the preamps. As I mentioned before, some of this modifications are not in the direction naim amps are strong, and ruin more that they can help.
More about that later.
Yes I know about the Semelab transistors, but can you get hold of them? I couldn't, at least until now.
But Neil McBride's suggestions for transistors are pretty much close to what I did.
But all naim-friends beware! His schematic of the NAP135 is his derivate and definitely not the orginal schematic!

To Asen:
I do not think you can swap the drives in Naim CD Players,
but I will enquire further details with my Naim-importing/selling friends.

To Jason:
Good solution! Why don't you stick with it?
I personally think that Naim preamps sound by far the best
with battery power. I tried that several times with different dry-batteries and lead and NC accus, but
I am just a bit lazy too construct a good charger, because, as you know,
these preamps have to be powered on all the time to sound their best.
I will put a schematic in the net, if time permits.
Basically it is two cheap LM317K (TO3 casing) with textbook components around them.
I do not believe the hype Naim does wonder things to burn them in or what, I think they are carefully selected for noise and other parameters.
If you take for example 100pcs only say 10-20% are up to the (higher) level.
This was out of reach for me, I use components from Linear Technology, they are more expensive, but IMHO better without matching and selecting.

greetings
Klaus
 
Battery powered NAC72

My battery power supply is currently basically 4 Yuasa 12 volt batteries connected to provide 2 * 24volt rails.

I have a case and all the components ready to assemble into the "finished" product, but my hi-fi is currently decommissioned awaiting construction of an extension to the house - until then there is nowhere to put it where the kids (2 & 4 years old) won't tinker with it, so there is no urgency to complete the project.

I am going to use an LM317 regulator to provide standby power to the NAC72 so it will be powered at all times, when i switch to standby power the charger circuit will connect to the batteries. I will have a small bank of Elna capacitors connected to the output of the batteries/standby circuit so switching between the two shouldn't leave me with clicks and thumps in the loudspeakers and the capacitors will overcome the shortcomings of the batteries.

A pair of digital voltmeters in the front panel will tell me when the battery charge has fallen to a level where a recharge is required.

I was interested in the Hi-Cap schematic to see how the standby power could possibly be improved for circumstances where i am forced to use it.
 

ALW

Member
2001-06-12 10:15 am
UK
Power supplies

The regulators Naim utilise in all of their power supplies are LM317's.

They 'select' them for best performance, but do not specifically give information on the selection criteria.

Noise has been mentioned previously, and it's safe to assume that this is at least one of the criteria. I've done extensive tests on my own home-brew PSU's for Naim kit, and have discovered some interesting information, after a similarly minded individual sent me some application notes from one of the engineers at National Semi (I think!).

The output impedance of all three terminal regulators appears inductive, the value of inductance varies with voltage and load current. It is possible to form a series resonant circuit with the output capacitors and it is possible for a noise peak to be created within the audio band. I've done some FFT analyses of my own PSU and was able to create just such a noise peak.

If you do the maths (f=1/2*pi*root(L*C)) one can mathematically derive the frequency of the noise peak, from the capacitor value, for any given set of regualtor operating characteristics.

This also means that the common mod of using low-ESR capacitors can worsen the situation, as the Q of the resonant circuit becomes much greater, increasing the amplitude of the peak, whilst lowering occupied bandwidth.

I also believe that a well designed regulated PSU will outperform a battery PSU any day. My ears tell me this, and I believe it is directly related to poor regultion, and low bandwidth of battery supplies. Noise of a battery supply, when under load, is not lower than a well-designed regulator.

If anyone is interested I have the FFT plots, that I can make available - does this forum allow image posts?

Andy.
 

ALW

Member
2001-06-12 10:15 am
UK
Naim PSU's

Jason,

Most of my Naim power supplies are either standard stock items, modified stock items, or the one home-brew I built whilst educating myself on the intricacies of audio power supplies, whilst trying to save money into the bargain.

When I had a Nait3, I split the pre / power sections (which are, in effect, a NAC92 / NAP90.3) and built a PSU to work with it.

The PSU is a fairly conventional arrangement, consisting of the classic massive toroidal transformer / bridge rec / smoothing.

Running from this raw supply is a dual regulated, dual 24V supply board, consisting of 4 LM317T's, one pair as pre-regulators for the final 24V pair. It is completely star-earthed / star supply with every component having a seperate 0v return.

It has very low measured noise, and sounds great, it's currently powering a NAC42XO (NAC42 with inbuilt active crossover), which then feeds 2xNAP110's. Rather than perform '.5' mods on the pre-amp, I've used one 24V rail for the pre-amp, the other for the crossover as this was simpler to wire and took less work to try.

I've also recently bought a s/h SNAPS and have recapped and modified it slightly to power a Prefix phono stage, fitted to my LP12.

The SNAPS was very cheap (and is a great way to experiment - cheaper than home-brew!), but it looks as is a previous owner had modified / repaired it since one of the regulators had been changed for a cheap JRC part. I've replaced both regulators with LM317AT's (a higher spec part than the standard LM317T) and have modified it for dual-rail operation, changing the rear panel connectors for twistlock DIN's, and adding the 5 pin one required for dual-channel operation. Tantalum caps have been replaced on the regulators with newer AVX tant's.

I've increased the main reservoir capacitance from the standard 10,000uF to 22,000uF, the new device (BHC Aerovox T22) is still 30mm shorter than the part it replaces. I've not gone higher than this as increasing capacitance increases transformer heating (probably not an issue for the oversize toroid used) but will also increase stress on the rectifiers at switch on, and owing to I squared R losses through the reduced conduction angle of the rectifiers.

I select regulators using a PC-based FFT spectrum analyser, running into a very low noise, but inexpensive, Sound Blaster Live soundcard.

Although the current drain of the pre's should be fairly constant (class A with lots of constant current sources) I also have a suspicion that dynamic performance of the regulator, along with it's bandwidth, is an important factor.

I've also tried an active noise shunt circuit, that provided massive noise attenuation, in particular at the low frequqncy end, where capacitors are ineffective. Despite excellent results in SPICE and good measured results it sounded s**t.

There's a lot more to this than measured performance, but I guess it's a start.

My next avenue is to look at capacitance multipliers, as often used on valve designs. Preliminary results indicate superb noise reduction abilities - where have I heard that before ;)

The ultimate piece of test equipment is always your ears, trying to correlate what one hears with measured performance is the hardest part.

Andy.
 

AndreasJ

Member
2001-10-05 12:06 am
Re: Power supplies

Hello Andy.

In your post Power Supplies, you mentioned you believe the output impedance of the LM317 to be inductive.

Could you please elaborate on how you deudced this conclusion?

Lastly, I'm really interested on you FFT analysis. We tried using a Soundblaster card before, but could never quite get the noise floor of the card to be compensated in the mesurements, we always ended up measuring the noise of the circuit and the noise of the card and PC. I would like to know more about measurment system.
We have gone back to using an HP Spectrum Analyser.

On another note, I was talking to a guy from NAIM last year at the CES in Las Vegas, we talked about noise and the power supplies amongst other things, I remember the comment they were testing the LM317 for about 100uV noise level with a few hundred milliamps of load current. But most of the time inductive picked up noise, RF stray fields and the like seemed to swamp the measurements.

In general the noise output of the regulators is highly variable depending on temperature, load current, cosmic rays, you name it. (The cosmic rays isn't a joke, we use a DSP fro TI that has a cosmic ray shield built over the silicon chip!)

Look forward to hear from you.

Thanks,

Andreas.
 

ALW

Member
2001-06-12 10:15 am
UK
Output impedance

Andreas,

>In your post Power Supplies, you mentioned you believe the output impedance of the LM317 to be inductive.

>Could you please elaborate on how you deudced this conclusion?

I didn't deduce it myself, it came from an article by one of the Senior National Semi. engineers, and I have replicated the effect easily myself.

It has nothing to do with long wires, but is simply another way of looking at the fact that the gain of any operational amplifier or regulator is designed to roll of at 6dB / oct.

As for the sound card, the Soundblaster Live is very quiet, and with a low noise (op-amp based) AC buffer can provide very useful measurements of the regulator noise across the audio band. The software is SpectraLAB, which has a fully functional 30 day (I think) version available.

If you can afford an HP analyser though, I wouldn't worry! All of my HP analysers at work are RF, so provide little useful info. across the audio band :(

100uV of noise is easily measurtable with a buffer and a 'scope - take a look at the Linear Technology website, there's an application note that details how to measure the performance of their low-dropout ultra-low noise regulators, specced for 40uV. It uses a battery-powered system, to eliminate ground problems, and a 'scope for display.

For those who are familiar with the Naim product range, in a recent comparison, mny own PSU offered about 75-80% of the performance of a Supercap (in dual-rail configuration) for about 5% of it's price - a Hicap wasn't even close :)

I think a Jung-style super-reg should be a LOT better - I need to try this soon (or a HQ shunt reg.).

Finally, as with all things, the best reg's or cicuit can be totally wasted if the implementation isn't perfect, this is where most DIY designs fall over, through poor layout, wiring and grounding.

Andy.

P.S. I also recently discovered a centre tapped, two diode rectifier arrangement sounds much better than a bridge arrangement. It's less efficient, but sounds much better, not yet sure why, the obvious difference is the connection of the PSU star point to the transformer, and the fact that there's only one diode in series with the transformer.
 

ALW

Member
2001-06-12 10:15 am
UK
Pete

Couldn't agree more with your comments.

I have to say though that Naim do it right, to a level no-one else in my experience does.

No single other manufacturer pursues the objective of a defined earth reference for the entire system in the way Naim do. It's a significant factor on the performance of their systems, and just one of the reasons I've rarely considered anything else, unless it sounds better.

It's also one of the reasons most Naim clones sound nothing like the real thing.

Andy.
 
"No single other manufacturer pursues the objective of a
defined earth reference for the entire system in the way
Naim do. It's a significant factor on the performance of
their systems, and just one of the reasons I've rarely
considered anything else, unless it sounds better."

I'm all in favour of installing a proper grounding system,
and I can see that it offers huge potential advantages when
applied to the whole audio _system_. Naim systems have
historically been particularly vulnerable to mains noise and
also to poor grounding practices in equipment made by other
manufacturers.

Do they common the grounds for the two channels, by the way?

Alex
 
Dhey do actually common the grounds for the two channels, inside the amps of course, but in the cables too. Thats whay Naim uses special cables and DIN plugs and sockets.

I am glad that someone brings up the question of grounding !

We should make this another new thread, I personally think this often forgotten matter is essential for the construction of good (ClassAB - ) amps.

greetings
Klaus
 
Andy,

do you know why Naim uses a unusual kind of rectifying for their bigger amps ?

They use TWO full bridges, but only two diodes are actually used, I suppose one pair for the positive and the other for the negative rail.
(I do not know how the transformer is connected though.)

I read in one of the last interviea of Julian Vereker, that he emphases much on rectification, in his oppinion capacitors via the diodes suppress the switching noise but kill the sound !

Any opinions?

Klaus
 

ALW

Member
2001-06-12 10:15 am
UK
Rectification

Klaus,

I'd suggest the primary reason for their use of centre-tapped dual half wave rectification is that it most definitely sounds better.

As to why it sounds better I'm not yet sure. It improved my DIY supply dramatically over a full wave bridge circuit, it's also less efficient, using only half the transformer secondary each half cycle. For this reason alone there has to be a good reason for choosing it.

They use the same arrangement in ALL PSU's not just the power amps, it also goes someway to explain the much larger than is seemingly necessary toriodals.

As previously alluded to, the connection of the earth to the transformer secondary may be a factor, the bridge arrangement in effect 'floats' the reservoir capacitor on the ends of the diode pairs, with the DHW circuit the negative is connected back to the centre tap.

Andy.
 
Thinking about PSUs and possible methods of rectification I was browsing through old NAIM leaflets and magazine reviews.
And I discovered a little more about the NAIM PSUs than I knew before. I tried to read out from the photographs as many details as possible, but obviously I can be wrong in some part or the other.



1. Andy, you are not exactly correct: NAIM uses the special arrangement only in their bigger amps and PSUs (like the 250, 135 and HICAP; I dont know about the FLATCAP and the SUPERCAP).

The smaller amps use this form:


[IMGDEAD]http://webplanet.lion.cc/uranus/380072/blue/naim_psu3.gif[/IMGDEAD]

(Very bad "CAD design", I know...)

This arrangement is well known, and we do not have to discuss the advantages here.


2. The mentioned bigger amps and psus use the following principle:


[IMGDEAD]http://webplanet.lion.cc/uranus/380072/blue/naim_psu1.gif[/IMGDEAD]


The actual first part of this psu is a little bit more complicated:


[IMGDEAD]http://webplanet.lion.cc/uranus/380072/blue/naim_psu2.gif[/IMGDEAD]

The two transformers drawn are actually only one, of course.



What do we learn from that ?
NAIM always stressed out the fact that their bigger amps and specially their bigger PSUs have a BIG effect on the sound. That might be true because of the special amp construction and the selected regulator ICs, but maybe also have something to do with the design of the psu frontend.
No NAIM amp or psu use some kind of capacitor to suppress the switching noise (I mentioned that before).

1. Do the two-diode arrangement have an effect on the sound, or better: what effect ? We have to pay an efficiency penalty here.
As I just read from the schematic of the Sugden 10W amp in Geoff's JLH Pages, that even Sugden used that kind of arrangement in the seventies.

Andy, you started some interesting interpretations already, please go on.


2. Do the leftover two diodes (of the bridge, connected face-to-face and back-to-back) have an additional positive effect, or are they just used because of the convinience of the availability of power rectifiers ?


I never thought about all that before this came up in this thread. After constructing several "Naim-Clones" until now, I feel a bit ashamed. But it is never too late to learn.

3. Could we use the modern fast and powerful double-diodes for this purpose ? You can salvage them from broken computer-psus, they work at least at low voltages (for class-a amps for example).


Looking forward to your reactions and opinions

Klaus