First NAIM after 50+ years of Quad and Krell

It's worth repeating this.  Very important on Naim amps only ever to take a high level signal for a subwoofer from the speaker end of the chain, not the power amp end. Even a Nait 5i requires this, otherwise performance suffers markedly and may even cause instability or damage. 

Anyway, I'm sorry to hear about your 77 amplifier.  It may well be suffering from ESD (Electrostatic damage) on its control chips.  This is a particular problem with electronics running microprocessor parts, such as logic control systems - it's a slow burn issue and usually results from someone opening up and touching circuit boards etc.. without taking proper ESD precautions.  The chips then slowly break down and you only discover a problem weeks, months or sometimes years later.  Has your amp ever been opened up?

Just out of interest - why given that they are connected by (in my case) low resistance speaker cables?

Because Naim amps don't have inductors on their outputs, relying instead on the speaker cable to provide adequate inductance for stability.  It's an elegant way of keeping an extra element out of the signal path - you can always easily hear the effects of inductors on the sound.

For some reason taking a reference signal for the sub off the amp outputs can cause upset.  However, taking from the speaker end (provided you have followed Naim's recommendation re. cable length and type) it can't been "seen" by the amp.

The amp was opened up some 8 years ago by Fidele Audio in Scotland to replace the fast switching coupling IC's with audiophile quality, low noise ones, put in better op-amps and replace the PSU caps with Blackgates. Knowing the person who did it for me (Peter Hickman), I would be very surprised if he did not take full ESD precautions. 

Richard, 

Many thanks for the explanation. 

It's worth reading up on old posts about people who have accidentally connected the wrong way and wondered why they have poor sound and/or problems and then reluctantly re-wired the sub from the speakers with a huge sound improvement as a result.  

In fact, one such that I recall not so many years ago, was a Naim Nait5i owner...

Well, the behaviour you cite is classic ESD.  Of course, it may well just be an unfortunate coincidence.  Anyway, I guess it's all water under the bridge.  However, not everyone realised 8 years ago what we now know about ESD problems in electronics.  In fact, even today, there are still those who ignore taking any ESD precautions when opening up a piece of electronics.

Richard,

It has also been suggested to me that it may be the control system IC’s acting up and specifically, that two electrolytic caps C56 and C57 in the strange reset circuitry linking the two cpu’s 80C32 and PSD311 may need replacing. Alternatively sometimes it is the programming deteriorating, which needs a new ROM chip with the correct programming. In any case given it is 20 years old, I am not going to spend a fortune finding out. I will leave that to the next owner :-) Better to move on. 

Yup, could be.  However, as you say, it's time to move on and the Nait 5i is a great amp to move on to.

It was actually much easier to wire the Neutrik Speakon plug subwoofer cable to the speakers end, as there are 4 x 4mm sockets there on each speaker with plated brass links. I have loads of old 4mm plugs, so that saved having to piggy back onto the 4mm plugs at the amplifier end. In general I am not a big fan of plate links and on my higher power main systems, I replace them with proper cable links from Rivercable but at the lower power I use in my bedroom, I would doubt if I would hear any difference. 

Well the Nait 5i-2 has arrived after waiting 2 and a half days for ParcelForce to deliver on a 24 hour delivery. Two things that I find disappointing. The first is that I understand that it is supposed to be left on 24/7 and has no stand-by setting or switch which is not very "green" and that I cannot switch off the  lit up Naim logo on the front, when I turn off the rest of the display with the remote, so this green light is going to be glaring into my face all night (it is on my bedroom system right beside my bed). I am not going to scrabble around on the floor every night trying to reach the mains switch at the back and covering up the logo with black tape, is a bit of a bodge. 

The second issue is the horrendous amount of hum. There is far more hum than my previous and elderly Quad 77 Integrated. There is even more hum than a cheap Sony AV amplifier, which I plugged in to see if it was a problem on my mains or the DAC. The Sony had next to no hum at all. I have tried three different sets of interconnects to my Beresford Cayman DAC, a Chord set, a QED Arctic set and an Ecosse set, all with no improvement. I thought I had some silver Litz braid interconnects but they must be at my French house. As it is a new amplifier, should I just wait to see if it improves as it runs in or should I send it back as faulty. It certainly is not liveable with long term. I have no problems with the Krell Integrated on my main system, so again I don't think I have a mains problem. My house is within 40 metres of the electricity mini sub station, which reduces the voltage from 11kV, and I am the only house on that phase.

I saw another thread which claimed that Naim deliberately choose to make amplifiers that are prone to hum, so that you could choose how to minimise it. This sounds like a total load of specious garbage to me. No responsible or sane manufacturer has make amplifiers that hum as standard since before WW2. 

You can switch on or off by the power switch on the back of the NAIT.  The green logo cannot be defeated when the amp is powered up - safety regs require it top be so.

Are you saying you get hum through the speakers/system or is it physical hum from the transformer?

What were your impressions of the Nait 5i when you went to demo it at the dealer?

Richard,

It is hum through the speakers. I did not demo it as it was up in Sheffield. I was just going on Naim's excellent reputation and glowing reviews of the 5i/5i-2 and 5i-S. 

It seems very sensitive to any PSU's (e.g. the one for the Beresford DAC) and any wall warts for things like my cordless phone and Oregon weather station, nearby. I have moved the Beresford power supply about three feet away and that has reduced the hum by well over 50%. I will need to get a longer extension/socket block for all the wall warts so that I can move those away as well. Is it normal for Nait's to be that sensitive to magnetic fields? The Nait is plugged directly into the wall socket and not via an extension or power cleaner. 

I have sorted the hum completely with the first class assistance and advice of Stan Beresford, who designed the Caiman DAC. He explained about the double earth system of Naim amplifiers and that a link wire between the two casings of the DAC and the amplifier would cure the problem. This was 100% successful. Given that this seems to be a known issue and that there are quite a lot of threads on hum issues on this forum, I am surprised that Naim don't put an casing/earth terminal on the back, like Meridian does and Quad used to (I don't think the 99/909 I used to have did.)