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screen vs 0V - confusion here

H

hakan

Happy member again
Hi!
I have just finished the avondale mono amp build. Great amp this. I have sed naim before so I am a bit confused now about the difference in signal carrying.

I will probably help a friend out with building an avondale power amp, but he is using a naim pre amp + supercap, so he want to do a more naim like amp equipped with a din-socket for input.

So how do I do the wiring? The snaic will carry left and right channel of course, and a 0V. The power amp boards have signal input, but a screen socket to.

Where do I take the 0V from the input?

Where do I attach the SCR from the amp boards?

Help needed, and this will help me when modding my 110 into a normal phono input kind of amp.
/
Håkan
 
Hi Hakan - I've just completed the wiring of my 260z too!

I think the Naim preamp is supposed to hold the main 0v point, so I guess you could connect both SCRs to the 0v that comes from the preamp snaic and leave it at that.
If you look at the NCC boards, the 0v connector on the input side is linked to SCR - the idea being that the 0v ties back to the 0v position on the capacitors - whether you do that or not in this scheme I'm not sure, but Les really emphasised the need to tie the input 0v back to a "proper" 0v, or it would float all over the place. The SCR and 0v are separate, I assume, so that it's easier to connect everything up.

For what it's worth, here's a pic of my 260z so far...

 
Hi Richard!
thank's for the answer! Nice build there, I am just so glad I got my ncc pre made ;)

Ah so the scr and the 0V is essentially the same then. Makes it easy if I'll go for active drive using avondale amps
and naim filters. And it seems very easy to plonk a new set of ncc200 boards inside the old 110 of mine then. :)

So the scr goes to 0V to input DIN. Easy
But we need to find out where to attach the 0V on the ncc-board then, either to the cap module or to the
same 0V on the DIN-socket.

cheers
Håkan
 
You're right re getting the amps pre-built - though I've saved some money, it has taken a long time. Mind you, a lot of the time is in drilling the case, getting it all in the right position etc, so it's not just the module build.

I think you'd better wait for Les to call in here - he's obviously the right guy for this!

Looking at a pic of the insides of my 250 though, it looks like the 0v from the snaic input doesn't actually get connected, but the 0v reference for the input side of the amp board is supplied by a central 0v point which is set up at the -ve speaker terminal - see attached image.
 
but the 0v reference for the input side of the amp board is supplied by a central 0v point which is set up at the -ve speaker terminal
Click to expand...

and that green bundle seems to end up at the capacitors 0V.

confusion remains, but on a higher level

thank's for the 250 pic BTW.

What's the functions of the two boards per channel in the 250?
 
but the 0v reference for the input side of the amp board is supplied by a central 0v point which is set up at the -ve speaker terminal
Click to expand...

A quite barmy idea in my opinion - it makes not the slightest sense for the following reasons:

All the zero volts are hung on the end of a few centimeters of cable, a strategy used only by Naim and not a good idea in my experience. There are some very high currents flowing along these connections which means the zero volt reference point is not stable but will 'float' according to how much current is flowing and at what polarity.
The effect is to introduce a 'rip' into the sound which may be interpreted to be 'dynamics' by the affionados.

With the NCC200 modules, DO NOT adopt this configuration as it will degrade the performance quite noticeably.

Hakan, build the amps as per the map you have and then common the two signal screens at the input socket.

It's no more complicated than that................
 
Hakan, build the amps as per the map you have and then common the two signal screens at the input socket.
Click to expand...

Hi Les!
I'll build the amp for my friend and he wishes to have a din socket instead of two RCA-inputs. Guess you have had him on the phone.

Just to be perfectly clear about it I'll put the 0V at the input side of the NCCboard as done with the RCA-version, ie on the cap module. Clear to me and makes sense indeed :)

But I still don't get where to attach the two screens? :confused:

At the 0V pin of the DIN-socket or the outer pin? This is pretty crucial!

cheers
Håkan
 
Not the outer pin of the DIN - this is connected to case earth. Connect to the 0v pin that goes back to the preamp.

R
 
Hi Richard and Les!
Thank's both for your help, I feel a lot more comfortable now.
:)

And it opens up for replacing the amp boards in the 110 of mine.
 
You've got me thinking now, Hakan - maybe I'll add an XLR socket on the back of my amp so I can drop it into a "standard" Naim setup if need be.
 
My friend and I are planning the same, well a 4 pin DIN plus normal RCA, so if he replace his pre to a more 'normal' one than naim, he is prepared. No need for drilling. Just some soldering and new wires.

Guess that is just what Les have made on his amp he showed on the web pages on the old forum.

Just wish I plonked the dins in myself :(
 
As I happened to have my 250s disconnected, I checked the 0V connection with a multimeter.

The -ve (0V) input socket does connect through to the -ve speaker sockets.
 
Looking at a pic of the insides of my 250 though, it looks like the 0v from the snaic input doesn't actually get connected, but the 0v reference for the input side of the amp board is supplied by a central 0v point which is set up at the -ve speaker terminal
Click to expand...
Looking at the pic of your 250 there are three connections to the bottom edge of the power amp board, that's signal and 0v from the input and 0v from the common internal 0v. So no mystery.

The upper boards in the 250 are the power supply regulators.

I wouldn't rush to dismiss the Naim wiring layout, I think they probably know/knew what they were doing. The high current pulses are between the smoothing capacitors and the transformer centre tap, I think these are routed interestingly.

Paul
 
I wouldn't rush to dismiss the Naim wiring layout, I think they probably know/knew what they were doing. The high current pulses are between the smoothing capacitors and the transformer centre tap, I think these are routed interestingly.
Click to expand...
I haven't rushed in the slightest Paul. In point of fact, I've been looking at this strange arrangement for many a year and made a good few measurements as well. I think that the arrangement was initially a remedy for some oscillation or somesuch as has stuck along with the attendant veil of mystique built up by the faithful. Colleagues in the industry are of the opinion that the configuration is nonsense and flies in the face of all accepted practice and theory. Even Naim's newest offerings don't use it.

Routed "interestingly" - never seen that term in engineering.
 
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