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New PCB for shoebox size NAC preamp part I

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Jiiim

bodger extraordinaire
EDIT:

Build manual here: http://www.sael.co.uk/pinkfish/starfish_build_manual_v06.pdf


/EDIT.



I've started a new thread to summarise my ramblings from the 'split rail pcb' thread (see http://pinkfishmedia.net/forum/showthread.php?p=264791#post264791 )


What does it do?
-Fits into a 'shoebox' Naim preamp case.
-Enables 'split-rail' or 'single-rail' power supply operation.
-Provides space for large film caps (smaller electrolytics are also caterd for)
-Implements a revised and updated version of Mr Tibbs's switch-mode psu.
-Uses multiple local regulators.
-Separate power and signal grounds.
-Attention to detail on star grounding.



(321) Gain stage:

gain.jpg
[/IMG]
Uses 2 positive regulators and one negative regulator.


(729) Filter stage:

filter.jpg
[/IMG]
Uses 2 positive regulators and 2 negative regulators.


Local regulators:

psu.jpg

One positive and one negative regulator shown.
Pretty standard 3 terminal regulators, with some LC filtering on the outputs.
Overall there are 8 positive and 6 negative regulators used.


Power supply:

input-psu.jpg

-1)Traco SMPS.
-2)Capacitive filter.
-3)Common mode transformer/choke.
-4)Capacitive filter.
-5)Differential mode chokes.
-6)Capacitive filter.


Output relay:

relay2.jpg

- Relay connections all taken to PCB pins to enable configuration of desired operation.
- Ground connections brought close via resistor.
- Configure operation with wire links.



....And finally, the PCB:

PCB7.jpg







This is 'just a design' at present. It contains lots of ideas that should work, but it has not been built yet.
Please feel free to check through my design, spot errors or ask questions (but preferably not point and laugh...)


Would anyone be interested in 'joining forces' and getting this made as a 'group buy' ?


Jiiim
 
Conratz Jiiim! Great job!

I am with this project.

The ground link between power zero and signal zero (I could do that easily in my 62 now when it's all separated), should they run separately to the PSU and not link in the pre at all??

Oz
 
Hi Linnik,

>>>should they run separately to the PSU and not link in the pre at all??


I've used a ground isolation scheme based around a Traco regulator.
This isolates the ground inside the preamp from ground in the PSU.
(refer back to Mr Tibbs's preamp nirvana thread for where this idea comes from)
The only connections from the signal ground to the outside world should be:
-Ground input from the source.
-Ground output to the power-amps.
There should be no connection between the power-ground and the outside world, other than via the signal-ground.
Where it says 'ground link' on the PCB, I plan to use an inductor/resistor parallel combination.
This should tie the two grounds together at DC, but help keep any power-supply rubbish out of the clean 'signal ground'.


In other words, linking these grounds back to the PSU would be a bad idea.
You could build the preamp without any of the 'power supply' components fitted, and use a 'traditional' power supply.
This would require you to link the grounds back to the PSU, and separate runs would be the way to do it.
I'm pretty sure this would be a step backwards...





Jiiim.
 
Yes yes, I got it. I was thinking as you mentioned Traco and regulated ground that it might be this way.

Looks fine to me.

Oz
 
Hi Jiiim

A very cool piece of work (and very colourful)

Looks a little more complex than the Air Guitar Jobbie that I just built ( which is still improving and sounds wonderful by the way) but count me in for at least on of these beasties. As I have the odd (8 pos and 2 neg) ALW regs would these be as good or better to provide power.

If I can help in any way with organisation (that will make SWMBO laugh) or any other stuff please let me know. nickatsvpsystemsdotcom

Keep up the good work.

Cheers

Nick
 
Hi Nick,

Thanks!


>>> ALW regs would these be as good or better to provide power.


Well, ALW superregs are certainly better than 3 terminal jobbies.
I went to great lengths to 'simplify' the load seen by each regulator on the board, so I think the gap between the 3 terminal reg and an ALW may not be as large in this case.

You could replace all the regs with super-regs - that's 14 of them :eek:
I'd be very interested in hearing how this would sound.
(My gut feel is that the setup with 3 terminal regs would give a fully super-regged version a good run for it's money - but dont let that put you off building one ;) )




As for organising stuff, again thanks!
I want to see if there is enough interest on PFM to organise a group buy of the PCBs.
I'm sure a group-buy of components could happen very shortly afterwards :)

I'm currently working on a component list and will publish it here soon.



Cheers,

Jiiim
 
I'm certainly keen if there is a group buy.
Are you planning a prototype first, as previously suggested in the original thread ?
 
Hi Napsac,

>>>Are you planning a prototype first?

There's nothing particularly original in the circuits I've implemented here, certainly nothing that hasnt been tested before.
The 'magic' that this board brings to the equation is the attention to detail in the grounding and the 'bringing together' of the various circuit elements.
...In other words, I've let others do all the prototyping work first, and I've just wrapped it all up into a PCB.

Cheers,

Jiiim.
 
Hi Jiiim

I was thinking in terms of proving the board layout wrt the desired schematic.
Still, with all the work you put in, that may be me being a bit pedantic.

Looking forward to the boards coming out, good work jiiim.
 
Hi Napsac,

Oh - I see.

That's not a problem - it's done automatically by the design software.
The schematics were entered into the software, and this controls what traces can and cannot be made on the PCB.
All I did was decide where to put the components and how to route the traces between them.

Jiiim.
 
I'm up for a board or two, as mentioned before I use www.zot.co.uk for my board builds at work so if you have Gerber files I can get a price.

The usual charge without Gerbers (or equivalent) is about £200 on top of the boards. :rolleyes:

J
 
Hi JimmyB,

I havent generated the gerbers yet, but it's not a problem.
I'll dump them out in the standard RS274X format.

Thanks,

Jiiim.
 
Here's the first go at a parts list:

(edit - well that didnt work at all well so I've removed it.)
(cut and paste from excell just...doesnt...work....well.... :( )

(I'll have another go tomorrow)
 
>>>can we paypal funds?


Erm, yes I think so.
I do have a paypal account, but I've only ever used it for 'outgoing' funds.
I think I may need to upgrade it and give it my bank account details in order to receive funds.

I'm going to start getting quotes on the PCB soon.
I believe the cost is largely governed by the number of boards I get to order, hence the group buy.
I think we are up to 5 so far.


Jiiim.
 
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