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]

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]

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.

 

[jacco vermeulen]

One day, Mr Vereker will surely receive a Le-Gaulle medal of honor PM for being such a loyal Sic-Safco Felsic (+ Promisic) user.

Felsic CO39

Naim 555 powersupply, a steal at $8600 or 4750 Pounds =>

 

[analog_sa]

One day, Mr Vereker will surely receive a Le-Gaulle medal of honor PM for being such a loyal Sic-Safco Felsic (+ Promisic) user.

I remember these as the best caps i could lay my hands on in the eighties. Still like the sound.

 

[analog_sa]

I just did a spice simulation of the NAP 250.

You needed a simulation to find out how much is the gain????


Excessive line stage gain is pretty much the norm among preamps. There may be some justification as phono stages often produce much lower outputs.

The worst offenders are probably tube preamps designed for zero global NFB. One way or another you have to burn the extra gain.


What's the purpose of this thread anyway? You start off complaining the gain is too little and now it's suddenly too much?

 

[Melon Head]

The purpose of this thread is to gain a better understanding of the operation of this preamp as they claim it is the best.

I was not complaining about too little gain, I just had never heard of using less than unity gain in a preamp so I wanted to be sure this was right.
I was then corrected about this.

I just find it hard to believe that the "best" preamp design in the world would intentionaly apply such a large amount of gain to a cd signal which is fed into a poweramp that also has a fair amount of gain.
Considering the cost of this preamp I suppose I would have expected a dedicated gain circuit for phono connection (hi gain) and dedicated gain circuit for CD connection (Low gain or Unity gain).

I am not making attacks on anyone personally.
I am just not sure whether what has been said about this preamp is fact or just peoples opinions.

 

[Melon Head]

You make a good point about the balancing act between negative feedback and attenuation.

Although there is an alternative to this and that is not to have a gain stage at all but have a buffering stage instead (with zero negative feedback).

 

[analog_sa]

I am just not sure whether what has been said about this preamp is fact or just peoples opinions.

Regarding the gain it is certainly a fact. It's even written on the page you linked.

Although there is an alternative to this and that is not to have a gain stage at all but have a buffering stage instead (with zero negative feedback).

A unity gain preamp is not a particularly marketable item. You can always find a source and a power amp that need some gain in between. Check out the Mc Cormack SMC VRE1 for a cool variation of your idea.

I don't think that a Naim preamp can be a particularly interesting topic for discussion. The topologies of the older ones are completely uninspiring, the part quality dubious and the sonic results very questionable. I kind of liked the older power amps but the preamps just don't meet my minimal requirements for sound. The pricing is just hilarious - check out Jacco's post above.

Naim are not alone at offering poor value and certainly not the worst offenders. As a minor consolation i see a lot of these "hi-end" audio companies not making it through the credit crunch

 

[Melon Head]

The way you reply to my posts comes across as a personal attack I am not sure if this is intentional or not.
I am here to learn not to make enemies.
I appreciate the time you take to give your opinion on this matter, hope to learn all I can from you and anyone else that takes part in this thread.
I was sought of hoping for a bit more detailed discussion on why they would use such a large transformer in a preamp.

I wouldn't be too quick to write off Naim pre and power amps, while their designs may be a bit dated they obviously know how to implement them to produce a pleasing sound, otherwise no person in their right mind would pay the sought of money they ask for their products.
The fact the company still exists given the prices they charge and number of positive reviews they receive, they are obviously doing something right.

 

[analog_sa]

The way you reply to my posts comes across as a personal attack I am not sure if this is intentional or not.

You are definitely imagining things. Unless you work for Naim's marketing department (this is a joke)

 

[Bonsai]

One reason for using an over sized transformer core is so that you can run the core at (very) low flux density. This makes for a quieter transformer and also helps to avoid any core saturation. Additionally, you can also avoid mains DC problems that would cause problems in cores that are run close to their maximum allowable flux density. In a high quality power amp, using a this approach can be justified.

However, I cannot se e how an 800VA trasformer can help on a pre-amp, since the overkill is so great as to completey kill any potential gains.


If there is someone from Naim out there, please help us understand this design choice.

 

[Melon Head]

Thanks for your input Bonsai.

Thanks Analog_SA for your reference to Mc Cormack SMC VRE1. I found a review of it at 6moons. This definitely looks impressive.
http://6moons.com/audioreviews/smcaudio/vre1.html