I've noticed that there are a lot of Naim NAP 140 clone power amplifier kits being sold on the internet, and was wondering if anyone has heard them?

From what I gather the NAP 140 was based on a 1970's RCA power amp design but with different component values. This might explain why the clone makers have avoided any legal issues. Some people have also mentioned that some of the component values in the clone kits are also different.

Edited by user 28 October 2011 13:10:07(UTC)  | Reason: Not specified

I ran a genuine '140 for a while. Was never that impressed. I remember that it did sound significantly better with the current limiting removed, so it must have been intruding. Some nice low-value paralleling caps on the PSU caps helped as well, though I remember they were a bit of a squeeze. Then for a while I used it on treble with a pair of DIY '135 "McBride clones" on bass. Sounded fairly good, but eventually dumped the lot for the DIY Tripath approach, a significantly superior (sounds better, timing's better, much safer) solution IMHO. As indeed did Dr McBride :-). Have still got them all somewhere in the garage, but I suspect I'll have gutted them to get the expensive caps out...

If it was the original 2SC2837 transistors, they are not particularly robust - indeed a bit marginal for 4ohm speakers with much reactive content, hence the fairly draconian current limiting ,with only a single-slope safe-area limit. Designed when the norm for speakers was a reasonably kind 8ohms. With a few zeners and resistors you could give it a dual or triple slope safe-area limit with much better current delivery without risking blowing it up. I wouldn't care to run it without any limiting - it only takes a slip with a wire or a heavy bass content at full volume into a nominal 4 ohm speaker to overdo things. I suspect the various clones went for tougher output devices - 2N3773 turned up a lot in power amps of the period.

Can't remember what I used now when I built my NAP135 clones - it was a very long time ago - but I've just looked in the cupboard and found a bag of unused TIP35Cs, so I could have used those, or perhaps they're unused because I bought them and then chose not to. Who knows? I was driving benign loads - ES11s and then ProAc Response 3.5s, so high current wasn't really a necessity. Anyway, I do remember that Naim's rather lovely high-current +/-40V regulator circuit saved my bacon on more than one occasion in terms of accidental shorts! It generally shuts the rails down in time to save your output transistors, which is nice... The 140, of course, doesn't have one of those.

To be honest, all this was a major contributor to why I eventually dumped the lot and went for the Tripath solution. As the older and .... I won't say "wiser", let's just say "less gung ho" ... I got, the less comfy I felt about leaving all this lot powered up 24/7 in my living room[1] while we slept upstairs and teething kittens roamed the house... I was aware of just how much less "safe" my clones were than Naim's original, and eventually fear caught up with me. The Tripath boards astounded me with how good they could be got to sound (they had enthusiastic "audiofile" apps support back at base in California, real shame they went belly-up) and their short-circuit protection and current-limiting Just Works, as my little boy has subsequently proven...

[1] And yes, it did have to be powered 24/7, else it sounded like a bag of nails... The Tripaths, by contrast, can be left with the Very Big Linear PSU powered, but the output stage muted (which seems to turn off all the output stage's warm-running driver circuitry as well) so it sleeps safely and relatively greenly, and sounds just fine on being un-muted from "cold"...

Edited by user 30 October 2011 15:21:59(UTC)  | Reason: Not specified

But what sort of control do you need? My stand is a metal framed affair on a suspended wooden floor with numerous Naim amps on. The rack has glass shelves. Would I need to deal with the same issues as a wooden stand with wooden shelves on a concrete floor with a class D amp with SMP? Or with a valve pre-amp? Close or far away from speakers? wall or floor shelf? Aesthetics? Cost?

Of course if vibration control was tackled by the initial equipment manufacturer this would help but they would be some market resistance to it (ie would YOU pay for it?!?!) and not all manufacturers might agree it is necessary.

Edited by user 02 November 2011 21:53:29(UTC)  | Reason: Not specified

Vibration control within an amp is a matter of sound design - there's no need for fancy feet, rubber bits, ebony bits etc etc, just proper attention to component selection, PCB design, physical construction. It's a routine thing in some of the fields of design I have worked in, where sensitive electronics are mounted on bits of equipment which have collosal vibration levels - for instance compressors running at 60,000 rpm, cutting-heads of oil-well drills, probes in the wake of a warship with twin 28,000bhp motors at full throttle, and have managed to get induced vibration effects to well below the lsb of a 16-bit aquisition system (-96dB). Similarly when I was designing active speakers I specifically tested for the INAUDIBILITY of vibrational effects on the commercial amps I used as well as my own designs. I am sure if it was possible 30-40 years ago it should be a doddle for current designers. Of course if you insist on using valves then you really are cutting off your nose to spite your face - there are huge problems with pickup, especially as the audio field usually uses B9A-based and similar valves. But you will need to attack this at the amp design stage, not try and cure the problems externally.

But the real question is - do these effects actually exist? Are they actually audible? There's loads of anecdotal evidence, on this site as well as lots others, where people have listened with and without various shelves, brackets, pods etc. and claim to hear differences. But of properly conducted blinded, randomised placebo-controlled trials virtually nothing. And of course if a particular aftermarket accessory cures the faults on one particularly susceptible product, you can assume nothing at all about its effect on another product, which if it has any of these faults at all will probably lie in a completely different area.

And of course the manufacturer is in an awkward position - if he has eliminated any vibrational pickup effects and then points out this fairly routine achievement in his publicity material "Will work perfectly on any shelf, any floor. No need for fancy feet, special mains cable" he alienates the dealers who actually make a handsome profit from these aftermarket products.

I wish at this point to use in a completely inappropriate and twisted manner a quotation from Stereophile magazine

"All important differences between hi-fi components can be measured; most differences that can be measured don't actually matter because they are below the limit of audibility, as proven by double-blind listening tests; thus, at least for amplifiers, all competently designed amps sound the same."

Andrew

You've mis-summarized:

1. The problems are PROBABLY imaginary in the first place
2. IF they're not, then they are easily dealt with by any competent designer
3. Agree
4. Double blind testing will tell IF there's a problem - it's only worth trying to solve problems that actually exist.

It's very hard to know, though I suppose one could do such tests. But there's not really much point - if you design an amplifier from first principles to have an output which is an exact copy of its input except that it's more powerful, (or at least, nobody in a db test can tell the difference), only amplifies signals within the audio band and to be non-susceptible to vibrational input or inteference - radiated or conducted - (again, low enough that nobody can actually tell in a db test), and it passes its db tests, then there's not really much point in spending more design effort trying to degrade the design until it fails and then going back one step. Especially if you're selling into the HiFi rather than mass market, because quantities are low (thus not worth spending more development time to spread across these small numbers) and the small changes in bought-in cost will not have a significant effect on the selling price.

Effectively this is the market I work in, designing products where performance is all, numbers by mass-market standards are infinitessimal and development cost tends to dominate the costings. You go for broke straight away, using the best suited technology for the application, taking all sensible precautions against emc, vibration, over/undervoltage, over/under temperature etc etc. If the prototype works to specification, the last thing you do is to go back and see what you could degrade, becasue nobody would pay you for doing it.

Speakers are another matter- they are still so far from theoretical perfection that the whole design excercise is about playing advantages and disadvantages of technologies, material, geometries, material costs etc against each other to get the best compromises possible within cost and the end-users' environment. But you still need to use db testing - or at the very least single-blind testing - to see if your pet solutions produce differences, improvements or degradation. The hardest thing is to tell whether things that the user says sound "better" (single or db) are actually any nearer to what's within the source - because hardly anyone has any real knowledge of what the original is actually like.

This just means that your "good" amplifier had a very poor power supply rejection ratio (PSRR). This is all this test proved - it doesn't enable one to generalise about the effect of these caps on any other amplifier. With attention to detail it is possible to achieve -120dB over the audio range. The 140 circuit that started this thread inherently doesn't have a very good PSRR, especially with reference to the positive rail - it's necessary to seperately decouple the rail to the driver with resistor/inductor and decent low ESR cap(s). The makers of PA chips have long realised this - you will find most bring out the driver and front-end rails seperately from the output devices, just so that you can apply this seperate decoupling. For the same reduction of power-supply effects this is MUCH cheaper than throwing massive capacitors at the main power supply.



No there isn't a fortune to be made. There are almost certainly quite a few amplifiers already on the market at moderate cost whose output is completely indistinguishable from the input when driving real loudspeakers. But how would you ever prove it to the customer? Virtually all mags use hopeless testing techniques, non-blinded, judged against a purely imaginary view of what the source material SHOULD sound like, judged on things like Pace, Rhythm and Timing without any idea of the Pace, Rhythm and Timing of the original. Equally, all retailers demonstrating can do is play music from an arbitrary source through an arbitrary set of speakers, all coloured by the retailer's own expectations (and probably his commision level). Almost certainly I have designed amplifiers whose performance if used as a Hifi amp (and a lot aren't, they are driving far more vicious loads than any loudspeaker, and over a wider frequency range) would be "perfect", if you mean that no-one could distinguish its output from its input (the very definition of HiFI, surely?). But I long ago gave up on any idea of making money from selling into the Hifi market - you need lots of skills in the styling and advertising-puff area. The latter I find particularly hard to do, selling pseudo-theories and "specialist"-name components into a market that has very little judgement of its own and is almost certainly not looking for Fidelity. I always remember when a fellow engineer ( a mechanical design engineer) left to work as a salesman for a large pneumatics company, my boss saying to me " **** will make a very good salesman - he's got just the right amount of insincerity"
My customers employ me (I now design on a consultancy basis rather than as a direct employee) to design products which meet their specification without any preconceptions as to how I would do it, and for as little expenditure (of course!) as possible. This means that there is a heavy emphasis on right-first-time, because a protracted development time would cost lots of money. Luckily they don't want lots of unnecessary flashy tooling, themed styles etc. Just the actual performance.