The grounding of these 2 Zerozone kits and the hum problem was discussed in this thread only a few months ago. I don't recall the full solution, but the preamp PCB allows for other grounding grounding arrangements than Naim's system and if you confuse them, you will almost certainly get hum. The grounding is by 1 only connection at the preamp PCB and 1 only ground return to the 24V DC power supply in the power amp.
The cable Naim uses has a single shield enclosing all 3 leads (power, L channel+, R channel+) which is why there can only be 1 ground lead which is the braided shield wire. The amplifier chassis is not connected to the signal ground.
Note that in the above pic, there is no 24V power supply and the input is via 2 x RCA sockets which is probably intended for a different type of preamp.
a few details here: Modifying and building audio power supplies
The cable Naim uses has a single shield enclosing all 3 leads (power, L channel+, R channel+) which is why there can only be 1 ground lead which is the braided shield wire. The amplifier chassis is not connected to the signal ground.
Note that in the above pic, there is no 24V power supply and the input is via 2 x RCA sockets which is probably intended for a different type of preamp.
a few details here: Modifying and building audio power supplies
How is everything connected groundwise? A diagram or photo may help.
The ground pin of the 4-pin DIN sockets need to connect to the NAP200 signal ground and the signal ground of the NAC42. The inputs to the NAC42 (RCAs?) grounds should also connect to signal ground but not chassis ground.
Is the DIN cable shielded? So if the shield connects to NAP200 chassis (mains earth) then this will make the NAC42 chassis mains earth too. If so you probably don't want the NAC42 signal ground connected to the NAC42 chassis.
What is the source you are using?
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A few words about ground related hum. The problem arises because wires don't have zero resistance. If a rogue current shares a signal ground wire then it will induce a small voltage on that wire which will add to the signal voltage. So the idea is to stop these rogue currents.
It gets tricky with sources with unknown internal grounding. If your source has a current to mains ground from its signal ground then if you attach it to an amp that also connects signal gnd to mains gnd, a parallel path to mains gnd is created through the signal gnd between the two (through the cable). Or if the two boxes are plugged in to different parts of your mains system it is possible for the earth potentials to be different and this will induce a current through the signal gnd linking the boxes.
Obviously, you could just never connect signal gnd to mains gnd in your pre-amp and power amp. I don't like this idea in a power amp because I don't like the signal ground floating around untethered when the amp inputs are disconnected. This can result in loud cracks and hums when connecting and disconnecting the inputs. Hence a 10 ohm resistor that ties them together in the amp but has enough resistance to hugely reduce any rogue currents (they much prefer to take the direct route in the source).
Ideally, you need a single connection between signal ground and mains gnd in your entire system. To this end some frustrated folks resort to removing the earth wires in equipment plugs but this is dangerous and should never be done. Luckily you can take the precaution of avoiding a direct connection between signal gnd and mains gnd in your NAC and NAP builds.
Eg: connect NAP chassis to mains gnd. Connect NAC chassis to NAP chassis via DIN cable shield. Have no connection between sig gnd and chassis in the NAC. Have a 10-ohm resistor between sig gnd and chassis in the NAP.
That ought to stop your hum. Otherwise it's a different cause and we'll figure that out too.
It gets tricky with sources with unknown internal grounding. If your source has a current to mains ground from its signal ground then if you attach it to an amp that also connects signal gnd to mains gnd, a parallel path to mains gnd is created through the signal gnd between the two (through the cable). Or if the two boxes are plugged in to different parts of your mains system it is possible for the earth potentials to be different and this will induce a current through the signal gnd linking the boxes.
Obviously, you could just never connect signal gnd to mains gnd in your pre-amp and power amp. I don't like this idea in a power amp because I don't like the signal ground floating around untethered when the amp inputs are disconnected. This can result in loud cracks and hums when connecting and disconnecting the inputs. Hence a 10 ohm resistor that ties them together in the amp but has enough resistance to hugely reduce any rogue currents (they much prefer to take the direct route in the source).
Ideally, you need a single connection between signal ground and mains gnd in your entire system. To this end some frustrated folks resort to removing the earth wires in equipment plugs but this is dangerous and should never be done. Luckily you can take the precaution of avoiding a direct connection between signal gnd and mains gnd in your NAC and NAP builds.
Eg: connect NAP chassis to mains gnd. Connect NAC chassis to NAP chassis via DIN cable shield. Have no connection between sig gnd and chassis in the NAC. Have a 10-ohm resistor between sig gnd and chassis in the NAP.
That ought to stop your hum. Otherwise it's a different cause and we'll figure that out too.
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Some time ago I watched a Nelson Pass lecture on youtube. I think from some audio show. He was talking about 2nd and 3rd harmonic only and was explaining that the relation between and the phase of these harmonics relative to the fundamental has distinctive sound character. I don't remember the details, but it was interesting approach to amplifiers' sound. I think his examples were the most basic ones - 2nd and 3rd in phase with the fundamental, both 180 degrees out of phase, and one in phase the other 180 out of phase.
My point is that maybe old Naim amps just hit the right harmonics phase/balance that people seem to like. Unfortunately not many of us in DIY have the equipment to compare and listen to different distortion profiles and harmonics phase relationship.
IMO, if two amps have the same distortion profile, at same power, in the same speaker, and both have reasonable bandwidth and reasonably low noise, they will sound identical to the listener. But what's the chance?...
I don't follow your project very closely, but are your input and output RCA jacks, or whatever you use (DIN?), isolated from chassis? In my early DIY years I had lots of problems with ground loops because of that
I learned my lesson to use only isolated ones, since they give more flexibility in grounding.
So here you can see Naim have provided a handy switch on the back of this pre-amp to select whether signal gnd and mains gnd are connected or not.
I think this may be a new feature of modern Naim gear. I think the assumption in olden days was that you should only use Naim kit in your system so you would never have to make this decision. It is essential now that electrical connections are being made to computers, etc.
I think this may be a new feature of modern Naim gear. I think the assumption in olden days was that you should only use Naim kit in your system so you would never have to make this decision. It is essential now that electrical connections are being made to computers, etc.
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Imo, whatever the amp, the phase has to be correct, i.e. in phase. I believe that in many ways we can have a direct target which is not phase, but the indirect target is the phase itself.
Do you mean the new NAP200 as big Zero Zone PCB (I'm not naim expert)?
Black Box の Clone Naim NAP200 Amplifier PCB AMP PCB | eBay
This one?
Yes...this one.It sounds exactly like you want.The only thing bothering me is a little harsh treble.Of course i i have used 2x250 VA trafo and genuine BHC Aerovox caps accompanied by 100nf mkp each.Low frequencies are quite inflated and also HF.3D is very open and deep enough.And all at a low sound level.if you don't use the small capacitors I think the HF soften a lot.
Thanks! This is how it is connected at the moment.
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Good diagram.
The 4-core shielded cable that connects between the two chassis: does its shield connect to both chassis?
Is the NAP-200 chassis connected to mains ground?
I also think it's fine. When you hear the hum, do you have a source connected to any of the inputs? The source is one possible loop.
With more than one source is even worse, because you don't switch the returns. E.g disk player and TV connected to the inputs. One will be selected, but both will affect the grounding in the current configuration. I usually use 3-pole make-before-break switching, so the returns also are switched.
If you use several sources at least try to connect their power to the same power bar where your preamp is.
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The shield of the 4-core shielded cable doesn’t connect directly to neither of the chassis. Both the 4-pin jacks and the 4-pin sockets have solder lugs for connecting one or more pins to the chassis, but I didn’t use them.
Yes, the NAP-200 chassis is connected to mains ground.
Yes, the hum is always there, no matter if a source is connected or not.
But when I disconnect and bypass the preamp PCBs, but leave the rest of the configuration exactly as it is (with exactly the same switch wiring and RCA socket wiring) then there is no hum at all.
Only with this preamp (which is powered directly from the NAP-200) there is hum. No hum at all when I connect the source (no matter which, e.g. phono preamp) directly to the NAP-200.
I only have a 19V switching mode supply left. Would this be sufficient just to try it out?