Of course, 0dB is very loud, but the point is, do you hear anything at all with open input like noise, hiss or hum.
If not, your preamp seems to be ok.
The next step is to go to -20dB with 10K/1k and listen to some input source.
Is everything still O.K. then ?
Hans
I appreciate that, thanks. However, for me personally, excitement and motivation only come from the sound and therefore someone portraying that to me so I can imagine it. Whereas measurement helps me choose the best path to take but provides me, ultimately, no motivation to get there.Which Neutrik sockets?
So... finally I'm getting around to ordering my parts!
But I am left wondering, after reading Bruno's white paper again and his section on correct shielding practice, why he then lists the cheapest, plastic Neutrik sockets on his BOM?
His white paper talks about connecting the shield to the chassis as soon as possible, i.e. at the socket itself.
Therefore I'm about to pick out Neutrik's B-series sockets at twice/three times the price of the cheapest plastic A series. B-series have a metal mounting flange featuring continuous circumferential ground contact to chassis for best EMC practice.
NC3MBH - Neutrik
Is this over the top? Does the BPPBP's differential stage mean that this is unneccesary? Why does he mention it in the white paper but then not talk about it in the actual " Let’s put a few things in practice." section of the demo pre-amp?
So... finally I'm getting around to ordering my parts!
But I am left wondering, after reading Bruno's white paper again and his section on correct shielding practice, why he then lists the cheapest, plastic Neutrik sockets on his BOM?
His white paper talks about connecting the shield to the chassis as soon as possible, i.e. at the socket itself.
Therefore I'm about to pick out Neutrik's B-series sockets at twice/three times the price of the cheapest plastic A series. B-series have a metal mounting flange featuring continuous circumferential ground contact to chassis for best EMC practice.
NC3MBH - Neutrik
Is this over the top? Does the BPPBP's differential stage mean that this is unneccesary? Why does he mention it in the white paper but then not talk about it in the actual " Let’s put a few things in practice." section of the demo pre-amp?
Further more, Bruno selects sockets where pin one and connector housing are separated and the PCB holes reflect this (these sockets having 4 connectors, the 3 usual ones plus an extra for the separate ground). Yet both pin 1 and the connector for ground go nowhere on the PCB.. so there is no possible connection between chassis and shield at all ???
Confused? You will be..
So... I have decided to choose B-series sockets which have pin 1 connected to the chassis housing and the connector housing.
i.e. NC3FBH1 - Neutrik
and
NC3MBH-1 - Neutrik
This leaves the separate ground through-hole connections on the PCB redundant (but they're not connected to anything anyway).
Confused? You will be..
So... I have decided to choose B-series sockets which have pin 1 connected to the chassis housing and the connector housing.
i.e. NC3FBH1 - Neutrik
and
NC3MBH-1 - Neutrik
This leaves the separate ground through-hole connections on the PCB redundant (but they're not connected to anything anyway).
I would just like to add that Enrico's 6 input board does use B-series sockets and those with connected ground/chassis/pin 1 . This seems to be the way that actually adheres to AES48.
(p.s. before anyone says anything, I'm buying sockets just for the BPPBP at the moment - I realise that Enrico's board uses the V, vertical mounting versions).
(p.s. before anyone says anything, I'm buying sockets just for the BPPBP at the moment - I realise that Enrico's board uses the V, vertical mounting versions).
The B series is a nice choice but there is nothing wrong with the A series as long as you pick the version that has a contact in the mounting hole, connected to pin1.
This is exactly the purpose of the BPBP. The B series does not differ in this respect, it should also have this contact internally connected to pin 1.
Take care that you use blank parkers for mounting, to be sure making a solid connection to the chassis. The mounting hole in the chassis should also be blank for the same reason.
Countersunk parkers are therefore the best option not to damage the area around the countersunk mounting hole in the chassis.
Hans
I think this conversation is along the lines of whether the XLR are connected to the metal chassis/case or not.
Maybe why Bruno chose the plastic XLR so not to tie to the chassis/case ground.
The plastic XLR do include a metal spring which ties the XLR plug body to ground, and within the plug the body can be connected to pin 1, so all is good.
Also the plastic XLR are also the only practical way of attaching the PCB to the case.
Personally I favour the metal body connectors, and will use them with a plastic rear panel and short leads to the PCB.
I'm currently listening to Si's build.> N-Core Monos>Quad 989 ESL and this is a seriously good Pre better than the MDAC pre, though as it allows the MDAC to run at 0dB as opposed to the -25dB on the MDAC digital Vol. control
The comparison is slightly skewed.
Maybe why Bruno chose the plastic XLR so not to tie to the chassis/case ground.
The plastic XLR do include a metal spring which ties the XLR plug body to ground, and within the plug the body can be connected to pin 1, so all is good.
Also the plastic XLR are also the only practical way of attaching the PCB to the case.
Personally I favour the metal body connectors, and will use them with a plastic rear panel and short leads to the PCB.
I'm currently listening to Si's build.> N-Core Monos>Quad 989 ESL and this is a seriously good Pre better than the MDAC pre, though as it allows the MDAC to run at 0dB as opposed to the -25dB on the MDAC digital Vol. control
The comparison is slightly skewed.
Sorry for the confusion.
A blank Parker is not covered by paint or any sort of electro-plating.
So it is naked Stainless steel, that's what I meant with blank.
And a countersunk stainless steel parker is here.
Hans
Ah, I see that the plastic ones do indeed have the option for "connection to the front panel" , presumably via a mounting screw.
The connected pin 1 though is not what Bruno's BOM has listed, nor what the PCB is made for.. I think it would be better to have this connected than to rely on correctly made cables?
Or will forcing the pin 1 to be connected within the socket possibly going to cause incorrect shielding in cables that have been made incorrectly (or at least not adhering to AES48) and therefore hum?
A little confusing in that the male output sockets DO have pin 1 connected whilst female inputs do not. I guess that once you've made the choice of socket (whether intentional or not) and then you drag and drop the PCB template in the gerber making software, you end up making it look more intentional than it might otherwise be!
Do you mean because of the use of self-tapping screws rather than requiring bolts/machine screws?
Bruno repeats what AES specifies, ty pin1 as soon as possible to the chassis ground.
That is exactly what the right XLR with a contact to pin1 in the mounting hole does
A bit confusing might be that Bruno has also connected pin 1 to the ground plane of the PCB, but this ground plane has to be regarded as chassis ground also, so the XLR connectors connect one to the other.
Just to repeat, Pin 1 is there to connect the chassis ground from all pieces of equipment together. The connection from signal ground to chassis ground has to be made with great care, and that is exactly what the BPBP does.
Hans
I was referring to my possible choice of panel mounting the XLR's rather than using PCB mount connectors.
If I follow my choice, physically mounting the PCB will be a PITA.
Here is Simons build which I have volunteered to 'burn in' for him
I built a breadboard which just traps the PCB between 2 foam pads.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Given the quality of this baby, I think it worth spending some extra on components when I build mine.
Has anyone tried exotic Caps ? which and any improvement ?
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Looking at the PCB in my hand I can now see the very subtle difference between the through hole mountings of pin 2 & 3 and pin1 and separate ground.. Pin 1 and separate ground ARE connected to the groundplane by very small lines at the four compass points whereas pins 2 & 3 do not have this, are isolated.
I hadn't looked at the PCB this closely - the differences really are very small - hence my confusion! It looked to me as though the separate ground and pin 1 were not connected to anything at all, so were doing nothing.
OK - I've worked out what is causing my main confusion, there are two things:
1) The main one: Bruno's choice of male socket on the BOM does not match up with the PCB AND it would appear that the one stated on the BOM is discontinued anyway.
He chooses NC3MAH 1 - this version ties the pin1 to chassis and connector housing. There is no ground pin on this version yet there IS a ground pin hole on the PCB. It is no longer listed on Neutrik's website and is not available on Mouser but it is listed in Neutrik's brochure.. however that version IS available in the B series (and A series by Amphenol) . It is also a different grounding scheme to the female sockets.
There are two others; NC3MAH (no number) and NC3MAH 0 . Only NC3MAH (no number) has a chassis connection and it also matches the female versions used.
So there is a mistake on the original BOM I think: NC3MAH1 should instead be NC3MAH (no number).
2) His choice of socket with their separate grounds and the associated holes on the PCB do not tie pin 1 to the chassis as soon as possible.. Pin 1 is only connected to the chassis via the groundplane and not connected directly. The plug housing IS directly connected to the chassis when inserted into the socket and so best practice is only achieved if the cable is wired in a particular way (pin 1 connected to plug housing). It doesn't seem right to me to rely on the cable wiring to achieve best practice.
Wouldn't sockets that do tie pin 1 to chassis and plug housing internally be better? The ground plane can still be connected via pin 1. Those don't match up with the PCB though.
Perhaps this doesn't matter? Doesn't the white paper seems to suggest that it does? Or maybe there is another reason regarding connecting of the ground plane between pin 1 and chassis ground that is more important?
I'd guess none of this will have much of a sonic effect so it's more an academic discussion I suppose.
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Yes, definitely, unless you want to use OEO (One End Only). See Linear Audio Vol 10.
What's wrong with the design of the pcb layout? Everything is perfectly alright.
No
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They don't bite into the panel. There a kind of spring in one of the mounting holes and the self-tapping screw bites into that and thus establishes the contact to the panel. Thus Hans' insistence on 'blank' screws ;-)
And make sure the countersunk hole in the panel is also scraped clean of anodizing and such.
The drawings on the Neutrik website show all.
Jan