Naim NAC 552 Preamp

[Melon Head]

I have a couple of questions about this preamp.

1) I noticed they use a 800VA transformer which is larger than what they use in most of their power amps. What benefit would their be in using such a large transformer for a preamp?

2) The output of this preamp says 0.775v. This is less than unity gain what benefit would their be in using less than unity gain in a preamp?

I hope you guys can enlighten me a bit on this

Thanks
anyway

[Melon Head]

Here is the link.

http://www.naim-audio.com/products/nac552.html

[analog_sa]

Originally posted by thanh1973

2) The output of this preamp says 0.775v. This is less than unity gain

Actually the gain seems to be x10 which is above unity


Many designers like the audible effects of an oversized PS. As this adds disproportionately to the cost of a commercial product it is not very commonly seen.

[Melon Head]

How did you come up with a gain of 10, a CD player puts out 2V?

I understand about going with a bigger transformer I was a little confused though why they would go with something larger than what is actually in their poweramps which draw significantly more current

[traderbam]

Originally posted by thanh1973
I understand about going with a bigger transformer I was a little confused though why they would go with something larger than what is actually in their poweramps which draw significantly more current

Good question.

Naim are in the business of selling idiosyncratic hifi products for a profit.

Of course the preamp doesn't need 800W.
I'd think about what Naim Co. are trying to achieve (beyond sound quality) to understand why they made this decision.

There are many ways to skin a cat. A pre-amp certainly doesn't need an 800W psu to function. But it does need a very clean supply of energy. There are many ways to achieve this with a fraction of that transformer size and some additional components.

[martin clark]

This is less than unity gain what benefit would their be in using less than unity gain in a preamp?

All Naim preamps actually have a gain of 13x and can swing over 7.5Vrms at the output.

Stating '775mv output' is essentially a marketing speak way of saying 'it's a line-level preamp'

[Melon Head]

I don't have a turntable or tape decks, I only have a cd player.
So I am only interested what this preamp does while using cd as source.
If the preamp uses 13x gain regardless of source then you would be looking at 26V output while using a CD player.
From memory the Poweramp has an input sensitivity of about 1V.
So surely 13x gain can't be right while using cd as a source, that would definitely be asking for trouble.

[martin clark]

Remember that most recordings the average level is 20-40dB down from 'full scale', and you'll see why most preamps actually have some gain. And when did you last use a preamp 'wide open'? that's what the volume control knob is for! It feds the preamp with an attenuated input...

One might criticise Naim for having a touch too much gain at the preamp end, which can lead to a slightly cramped useful range on the volume knob, but that's actually entirely another discussion.

[Melon Head]

I am not doubting you, but to me any company that would purposely add that much gain to a CD signal is either to lazy to develop something a bit more appropriate or has no idea.
Are you sure this is correct?

[Melon Head]

I just did a spice simulation of the NAP 250.

To get 12W RMS into an 8 Ohm load the amp needs to see approximately 0.35V RMS at its input.
Divide this by 13 and you get 0.027V (seen by the preamp) divide this by 2V and you get 1.35% of the original CD signal.
Now that is a massive amount of attenuation.