Thanks! Actually I meant a slow-blow fuse. Here in Germany "T" stands for "träge" which is slow-blow. So I think I should be fine with that?
That'll be fine then.
Another thing I do when first powering up a circuit is to put a power resistor of a few ohms in series with one of the psu wires to the circuit and clip a voltmeter across it. This is a precaution against a short or other cause of excessive current. You can power it up like this and check voltages and set the bias current.
Also, tantalum capacitors are fragile when it comes to being reverse biased. If there is a fault that causes the output to go positive your C2 caps could be killed, or worse damaged without you realizing. So I advise putting a non-polarized electrolytic instead of C2s temporarily just until you know it works ok. Or you could put a temporary diode across them; they should survive 0.6V if their voltage rating is high, like 35V.
Good luck.
I was always told 'F' for fast acting and 'T' for time delay to remember.
I think traderbam has given you good suggestions. I would go a little further with precautions because I had no problem with a 500VA transformer and ordinary "F" type glass fuse - these are seldom specified but the plain length of tinned copper wire inside is an obvious clue.
After checking that the transformer takes mains power to the primary without secondary connections (don't assume transformer lead colours are standard) I would only connect one set of secondary winding leads from the PCB and tape the others to prevent shorts. Buy a small number of fuses, as you may need them. Inrush current can be a problem with some low resistance toroidal transformer types and this can be a problem if the manufacturer is unaware of the application but I don't have much experience there - only seen it a few times when I was amazed to see fuses many times the usual size for a 300VA toroid. Inspect the board for shorts with a magnifier after soldering the power supplies, looking for shorts and wrong orientation of rectifiers and caps. The tracks are very close in some places and it's easy to miss shorts and confuse markings.
NAP models including this one, are now dual mono, so you can power up one amplifier quite independently of the other and you don't need to connect the preamp supply winding at all. Fit the secondary power leads to just one channel and check that it powers up and amplifier voltages are as expected - around +/-40V if your transformer is specified for a 230V supply, I'd guess. This will vary according to the actual local supply and transformer spec.
If you have problems even with one channel, you can try the other and so eliminate the possibilities. First though, be certain that AC voltages and the centre taps are correctly identified before connecting anything and then that your wiring matches with the board.
After checking that the transformer takes mains power to the primary without secondary connections (don't assume transformer lead colours are standard) I would only connect one set of secondary winding leads from the PCB and tape the others to prevent shorts. Buy a small number of fuses, as you may need them. Inrush current can be a problem with some low resistance toroidal transformer types and this can be a problem if the manufacturer is unaware of the application but I don't have much experience there - only seen it a few times when I was amazed to see fuses many times the usual size for a 300VA toroid. Inspect the board for shorts with a magnifier after soldering the power supplies, looking for shorts and wrong orientation of rectifiers and caps. The tracks are very close in some places and it's easy to miss shorts and confuse markings.
NAP models including this one, are now dual mono, so you can power up one amplifier quite independently of the other and you don't need to connect the preamp supply winding at all. Fit the secondary power leads to just one channel and check that it powers up and amplifier voltages are as expected - around +/-40V if your transformer is specified for a 230V supply, I'd guess. This will vary according to the actual local supply and transformer spec.
If you have problems even with one channel, you can try the other and so eliminate the possibilities. First though, be certain that AC voltages and the centre taps are correctly identified before connecting anything and then that your wiring matches with the board.
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You are right: Fuse Markings Explained
It's been a while since I bought a fuse, thankfully, and when I search for type T fuses I first got class T industrial which are fast blowing and I assumed T meant fast blowing in general. No.
It would be helpful, though many newcomers arrive without preconceptions of what Naim Audio or the NAP140 model is about - at least to those diehard owners and enthusiasts with deep pockets and high regard for the brand. It might take a bit of preamble to set out the aims for what you envisage as essential for a clone plus relative costs since some components can be prohibitively expensive or too difficult to source from specialist sellers.
I think many would read a new thread if it stayed clean of off-topic ramblings and could be read without having to glean the few percent of useful comment first. That's a problem with this thread - too big to search anymore. If readers thought there was going to be a straightforward build guide or wiki for the kits generally, it would be strongly attractive, though many will find that their kit is different, has these different parts etc. and they don't want to spend more on extras than than the kit is worth. Some just want personal affirmation that they are on the right/wrong path when they make ground connections, replace the burnt semis or use a certain grade of capacitor, choose a transformer, set quiescent current - basic stuff.
Better, would be a guide suggesting levelled upgrades; the whys and hows to turn a "sows ear" of a kit into a "silk purse" clone. The trick will be to open a new thread with a title that means what it says. If it is personal opinion about Ebay kits or the components, then let that be said clearly with reference to real kits and bits, as we find them now. If we expect builders to aspire to the quality of the original product, then that should also be clear as there can be prohibitive cost barriers when the Ebay clone concept is dropped and we begin with just the convenient, cheap PCB but fit premium components of choice.
I think many would read a new thread if it stayed clean of off-topic ramblings and could be read without having to glean the few percent of useful comment first. That's a problem with this thread - too big to search anymore. If readers thought there was going to be a straightforward build guide or wiki for the kits generally, it would be strongly attractive, though many will find that their kit is different, has these different parts etc. and they don't want to spend more on extras than than the kit is worth. Some just want personal affirmation that they are on the right/wrong path when they make ground connections, replace the burnt semis or use a certain grade of capacitor, choose a transformer, set quiescent current - basic stuff.
Better, would be a guide suggesting levelled upgrades; the whys and hows to turn a "sows ear" of a kit into a "silk purse" clone. The trick will be to open a new thread with a title that means what it says. If it is personal opinion about Ebay kits or the components, then let that be said clearly with reference to real kits and bits, as we find them now. If we expect builders to aspire to the quality of the original product, then that should also be clear as there can be prohibitive cost barriers when the Ebay clone concept is dropped and we begin with just the convenient, cheap PCB but fit premium components of choice.
This would be very helpful indeed!
And here’s my next question
Did I get it right that the mains earth is the only connection that is made to the chassis? The 4 pin DIN connector cable shell touches the chassis, too, of course, but is not connected with the ground pin of the connector, right?
Or in other words: The PCB ground and all cable grounds and input/output jack grounds are isolated from the chassis?
And here’s my next question
Did I get it right that the mains earth is the only connection that is made to the chassis? The 4 pin DIN connector cable shell touches the chassis, too, of course, but is not connected with the ground pin of the connector, right?Or in other words: The PCB ground and all cable grounds and input/output jack grounds are isolated from the chassis?
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It could be described but a diagram is much easier to understand. The mains protective earth connection is critical to safety and must be done with an approved fastening method. The amplifier is sometimes also connected on the same bolt etc. but is best grounded with a similar fastener, at some distance away.
Have a look at this article, written for DIY builders: Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
Have a look at this article, written for DIY builders: Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
Thanks! Yes, the safety earth is clear and to avoid ground loops is clear, too. I have built a few 50W guitar tube amps and one small 3W PCL86 HiFi amp so far and in all of these the signal ground and PSU ground were all connected to the chassis, too (some used star ground, some used other grounding schemes, but all connected to the chassis), so that’s not completely new for me, but I have read here in this thread that Naim uses floating grounding.
So should I just try it out and maybe add a switch to connect the PCB ground to the chassis and see what works better?
7.The grounding, the Naim magic!
Read the user manuals available on their site. They mention that the Naim equipment is grounded only in one point, usually the source, hence the CDP. Mine has huge thick AC cord. All other AC plugs of your equipment contain only safety grounds (only the enclosure chassis is grounded). The boards themselves are using “floating” grounding, which means they are at 0V potential, but not connected to ground until you put your whole system together and then everything is grounded via your source. To make this work use only isolated from the chassis RCA chinches (with plastic washers). You can keep everything “neutral” in your amp in one point – the reservoir capacitors common point.
Have in mind that in this kit the input “neutral” is not connected to the output (speaker “neutral”). You have to connect them or better, to pull wires from each of them to the capacitor's common. If not, you should expect some big DC voltage on your speaker output. I realized this from experience
My ground configuration is slightly different from the original Naim idea. I've put a 15 ohms resistors between the amp's input and output “neutrals”, and I grounded in the AC plug the capacitors' common. This way I have de facto properly grounded amp, but the inputs are not grounded there, because the 15 ohms resistors should force the inputs to be grounded through the source (my CD5i) less resistive path to ground, travelling into the interconnect cables shielding etc. etc.
I don't know which way is best, but I don't have any hum, and in the speakers I find only very quiet and uniform white noise.
The important thing is to avoid ground loops.
So should I just try it out and maybe add a switch to connect the PCB ground to the chassis and see what works better?
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Safety earth connects to chassis always and be careful, some project chassis are anodized and just because you connect to one part of the chassis doesn't guarantee the other parts are also safely connected.
Signal ground is best connected to the chassis through a 'disconnecting network' of parallel pair of opposite direction diodes. Quite a common approach - see Nelson Pass, Hugh Dean and others.
Signal ground is best connected to the chassis through a 'disconnecting network' of parallel pair of opposite direction diodes. Quite a common approach - see Nelson Pass, Hugh Dean and others.
What I wrote before was valid in my system and also valid by the Naim user manual that I read very carefully. You can try what gives the least hum. Just keep the chassis always grounded! Floating or grounded alsewhere (in another component) is not a problem from operating point of view. The return signal does not necessarily need to return to ground.
So, whatever works.
The inverters that we design at work have grounded and floating option. It's not in violation of any code.
sorry, this would be option C then:
An externally hosted image should be here but it was not working when we last tested it.
Option A appears to be floating but this is only true for DC. There is inter-winding capacitance in the transformer which effectively connects the mains live to the output windings at AC. This can be mitigated by using a transformer with an electrostatic shield winding that is connected to earth.
Option C tethers the amp gnd to earth through a 10 ohm resistor. I like this as it breaks a potential ground loop and provides some damping. But the 100nF cap shorts the gnd and earth at AC inviting an AC ground loop. Just use a resistor.
Option C tethers the amp gnd to earth through a 10 ohm resistor. I like this as it breaks a potential ground loop and provides some damping. But the 100nF cap shorts the gnd and earth at AC inviting an AC ground loop. Just use a resistor.
