RichardH
Bodging pleb
Thanks to Andy Weekes for this one:
here's the lazy mans way of building a NAPSC.
It's not the cheapest, but it is good quality and easy to build, since the PCB / PSU is purchased pre-built and tested.
Firstly you'll need one of these: -
This is a Lawtronics SLA1500 sealed lead-acid, current limited charger. It's basically a PCB containing toroid / rec / smoothng + an LM317K with heatsink.
They are available from Farnell, in a couple of flavours (Data Sheet ) the 12/24V being the one to go for. The farnell p.no. for the charger unit is 4271040, and they are £42.65 in 1-off's.
Note that there's also a diode in series with the o/p that should be removed, since it worsens regulation - it's there to prevent damage from incorrectly connected batteries.
In addition you'll need a case, and if you fancy something nice, it can be squeezed into one of these: -
Sexy Enclosures
The largest sizes are the ones you want. The board slides into slots in the case - so no drilling to fix it in!
There's little room for an IEC inlet so a couple of cable glands to take the mains cable in and the DC out + an internal fuse holder (which you can attach to the PSU board) will save space. If you're careful you may be able to fit a single panel-mounted fuseholder, but things are tight and you'll need to plan carefully.
Finally you'll need a connector for the NAPSC supply, again Maplin come to the rescue, with a two-pin microphone connector that is exactly what Naim use: -
Cheap Connectors
Don't forget to earth the metal enclosure, you'll have a unit that looks the business for a fraction of the new price and a piece of piss to build.
I doubt it would be much cheaper if you built the raw PSU bit yourself.
The charger boards have an on-board current limit (designed for charging sealed lead-acid chargers) but this can be disabled easily if you want to. YOu can also upgrade caps etc as you see fit, and the output voltage is set with a pot - I'd remove it and fit fixed R's to give the correct output, to save future unreliability and additional noise.
I'd also permanently link the 12/24 V selection jumpers too, for the same reasons.
You can obviously add an LED (a useful reminder of the presence of power in there, I use one of these for the purpose of keeping preamps warm, whilst swaaping and evaluating.
--------------------------------------
There was also a question re earthing/grounding:
"If I only want to feed the external PSU to the analogue stages of a CD player, will I need to isolate the analogue stage ground from the rest of the player, or is it OK to feed both O volts to the same ground."
ALW replied:
"You should not need to isolate the 0V's - in fact you'll need them connected.
The only thing to watch is connections to mains earth - just ground the case of any enclosure you use, but keep the mains earth seperate from the 0V."
Added 23 / 03/ 2005: -
NAPSC Pinout: Pin 1 = +V, Pin 2 = 0V
here's the lazy mans way of building a NAPSC.
It's not the cheapest, but it is good quality and easy to build, since the PCB / PSU is purchased pre-built and tested.
Firstly you'll need one of these: -
This is a Lawtronics SLA1500 sealed lead-acid, current limited charger. It's basically a PCB containing toroid / rec / smoothng + an LM317K with heatsink.
They are available from Farnell, in a couple of flavours (Data Sheet ) the 12/24V being the one to go for. The farnell p.no. for the charger unit is 4271040, and they are £42.65 in 1-off's.
Note that there's also a diode in series with the o/p that should be removed, since it worsens regulation - it's there to prevent damage from incorrectly connected batteries.
In addition you'll need a case, and if you fancy something nice, it can be squeezed into one of these: -
Sexy Enclosures
The largest sizes are the ones you want. The board slides into slots in the case - so no drilling to fix it in!
There's little room for an IEC inlet so a couple of cable glands to take the mains cable in and the DC out + an internal fuse holder (which you can attach to the PSU board) will save space. If you're careful you may be able to fit a single panel-mounted fuseholder, but things are tight and you'll need to plan carefully.
Finally you'll need a connector for the NAPSC supply, again Maplin come to the rescue, with a two-pin microphone connector that is exactly what Naim use: -
Cheap Connectors
Don't forget to earth the metal enclosure, you'll have a unit that looks the business for a fraction of the new price and a piece of piss to build.
I doubt it would be much cheaper if you built the raw PSU bit yourself.
The charger boards have an on-board current limit (designed for charging sealed lead-acid chargers) but this can be disabled easily if you want to. YOu can also upgrade caps etc as you see fit, and the output voltage is set with a pot - I'd remove it and fit fixed R's to give the correct output, to save future unreliability and additional noise.
I'd also permanently link the 12/24 V selection jumpers too, for the same reasons.
You can obviously add an LED (a useful reminder of the presence of power in there, I use one of these for the purpose of keeping preamps warm, whilst swaaping and evaluating.
--------------------------------------
There was also a question re earthing/grounding:
"If I only want to feed the external PSU to the analogue stages of a CD player, will I need to isolate the analogue stage ground from the rest of the player, or is it OK to feed both O volts to the same ground."
ALW replied:
"You should not need to isolate the 0V's - in fact you'll need them connected.
The only thing to watch is connections to mains earth - just ground the case of any enclosure you use, but keep the mains earth seperate from the 0V."
Added 23 / 03/ 2005: -
NAPSC Pinout: Pin 1 = +V, Pin 2 = 0V