Passive pre

[David Mccallum]

Hi all, i've got my eyes on a Naim nap140 for my second system (main system is valve based) and i would like to use my pc as a source.
My plan is to make a passive pre-amp to control it, does anyone think this would be a bad idea? also can anyone help with choice of a volume pot, im thinking alps blue but im not sure which value pot to buy, 50 or 100k?
Also does any one know where i can buy a decent well made selector switch, one which can handle WD's heavy knobs without it's shaft wobbling, i dont want a wobbly shaft.
No viagra wont help in this case

Cheers

[pre65]

If you are interested in a NAP140 how about these ?

http://cgi.ebay.co.uk/HI-END-POWER-A...d=p3286.c0.m14


Philip

[David Mccallum]

Hi Philip, i've been looking at these recently and wondering if they are the full monty so to speak.
I however came across a post on pinkfish media which basically advised against trying them, their own Naim Guru aparently had problems with the boards. I forget the technoblurb but basically their not Naim clones as advertised but someones attempt at a copy.
Enough said, i could do without the hassle, so a basic passive pre with a known decent NAP140 for what seems like a dam good price should do the trick.
Have you any ideas about which volume pot i should use? could save me money and hassle if someone can suggest a suitable candidate.

Cheers

[Chopsaw]

50K for solid state, 100K for tubes. That's what I use and it works fine for me.

Si.

[David Mccallum]

Thanks, it seem's everyone i've talked to has different opinions- some say as low as 10 or even 5k.
Others say a naim poweramp needs to be driven by an active pre, a soundcard wont drive it properly. Think i'll hunt ebay for an old naim pre, may be worth having anyway - grumble grumble moan etc.

[Richard]

Hi Davy,

The unknowns are the soundcard output impedance/recommended load and the Naim input impedance.

You may be able to check the recommended load for the soundcard and use a pot value to suit (=/>).

Whether that value pot would then allow the soundcard to drive the Naim will depend on the load the Naim presents. (The pot will raise the source impedance from the soundcard.)

An example with known items would be a typical CD player and power amp. A CD player is usually happy into a 20K load/pot. A 20K pot will keep the source impedance fairly low and will work well into a 100K input impedance of a power amp.

If the power amp however has only 20K input impedance (as some ss are) then that arrangement would not work well. Hence perhaps the suggestion of a 5K pot - but - the soundcard may not drive the 5K pot.... This is where an active pre comes into it's own; as a buffer, offering a high load for the source and a low impedance source for the power amp load.

Rich

[Bill Petrie]

Why not use the volume control in your software, if all your music sources are coming from the PC? At least you could give it an initial try - feed your soundcard output directly into the amp with software vol at minimum, then gradually increase it. You could then decide if you actually needed a hardware preamp.

[David Mccallum]

Hi Richard, thanks for that, it's nice to hear from you again.
The Naim poweramp appears to have an input impedance of 18K, so it's probably a wee bit ambitious to try driving that load with a soundcard.
As for the soundcard, a friend fitted it for me, it's second hand and i dont have any info but it's supposably decent.

Cheers Bill, yes you have a good point, i have a second system though which has a pc and a cd player/recorder as source's hence the switchable passive pre i had a mind to build. I would have tried the direct route out of interest though anyway but i did have reservations about the soundcards ability to drive this poweramp.