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Is the Cambridge Audio 640p worth upgrading?

Mine will be posted on Friday.
As the MC I have bought is a low output one (0.15mV) can you do something about increasing the gain of the MC stage when you mod it? I believe it is something like 55dB as standard.
Mike
 
The gain will indeed be increased as part of my standard mods.
The noise will be higher than the original.. partly due to the higher gain and partly due to the fact that the guy who designed it in the first place has gone for low noise and bollocks to everything else..... In fact he has made some basic mistakes when it comes to the MM section...;)
What Doug Self thought of the original design in personal correspondence can not be published on a public site!
 
Oh, and for the record, the transistor stage gives 43.25dB of gain and the op-amps an additional 12db, so pretty far from the op-amp providing most of the gain.
 
I've not looked at this circuit schematic, but in these cases it is usual for the input stage to provide most of the gain while the RIAA correction is configured around a unity gain stable op amp. Thats quite a common way of doing things particularly for a low cost stage.

Might also be worth looking at the new 641P for ideas since CA have just done a refresh of the design.
Their comment on retaining the high pass filter option made me chuckle though. It was provided "as a nod towards audiophiles" ;)
 
sq225917 said:
Oh, and for the record, the transistor stage gives 43.25dB of gain and the op-amps an additional 12db, so pretty far from the op-amp providing most of the gain.
Click to expand...

Wrong. There is no transistor stage as such. They are merely a low noise differential input stage for the op amps.
You obviously don't understand it so I won't waste my time arguing with you over it.
 
Now this is probably a bit mischievous, but I am curious:

I hear all sorts of accusations about hifi reviewers in magazines getting free stuff in return for good reviews, and how it's all appalling and reprehensible.

Which it is. If it's true.

And then I read about a chap on here who is promising to upgrade somebody's kit, essentially doubling its value and probably trebling its performance per pound, and he's doing all that for free, in return for a write up on this forum.

Just saying... ;)
 
Sue Pertwee-Tyr said:
Now this is probably a bit mischievous, but I am curious:

I hear all sorts of accusations about hifi reviewers in magazines getting free stuff in return for good reviews, and how it's all appalling and reprehensible.

Which it is. If it's true.

And then I read about a chap on here who is promising to upgrade somebody's kit, essentially doubling its value and probably trebling its performance per pound, and he's doing all that for free, in return for a write up on this forum.

Just saying... ;)
Click to expand...

and what if i don't like it?
 
darrylfunk said:
and what if i don't like it?
Click to expand...

More to the point, how are you supposed to know that it's better than the unmodded one?

After all, you don't have the original to compare with, and musical memory lasts only seconds. And A/B tests are so unreliable anyway.

All in all, a bit of a can of worms, if you ask me.
 
sq225917 said:
Oh, and for the record, the transistor stage gives 43.25dB of gain and the op-amps an additional 12db, so pretty far from the op-amp providing most of the gain.
Click to expand...

The "transistor" stage includes an opamp inside the f/b loop, with the gain set by the 2k6 and 18R resistors. Most of the O/L gain is provided by the opamp.

Assuming the RIAA stage has 12dB of gain, this is normally specced at 1KHz. At 20Hz this stage will have ~32dB of gain.
 
S-Man said:
The "transistor" stage includes an opamp inside the f/b loop, with the gain set by the 2k6 and 18R resistors. Most of the O/L gain is provided by the opamp.

Assuming the RIAA stage has 12dB of gain, this is normally specced at 1KHz. At 20Hz this stage will have ~32dB of gain.
Click to expand...

Spot on. At least someone on here knows what they are talking about ;)
 
Still watching with much interest, I must admit I prefer the sound of the in built MM stage in the Rotel RA-04 (actually an EAR834P is miles ahead of both but I guess it should be, MM type input only though:-( ) i'm using to the 640P MM, but with MC i've no choice at present but to use the 640P.
 
Sue Pertwee-Tyr said:
Now this is probably a bit mischievous, but I am curious:

I hear all sorts of accusations about hifi reviewers in magazines getting free stuff in return for good reviews, and how it's all appalling and reprehensible.

Which it is. If it's true.

And then I read about a chap on here who is promising to upgrade somebody's kit, essentially doubling its value and probably trebling its performance per pound, and he's doing all that for free, in return for a write up on this forum.

Just saying... ;)
Click to expand...


I don't think this is for commercial gain or is it is it? Maybe it should be in the DIY room where there are many people doing many things to lots of kit. Some to make a better product that may be perceived to be sonically superior and some just because they like tinkering with things one thing is for sure it all costs something. I think the 540p/640p is good for the price but i soon moved on from mine and now find i cannot bear listening to it. Good on someone to want to take something and change it, hopefully for the better.
 
nirvanah said:
I don't think this is for commercial gain or is it is it? Maybe it should be in the DIY room where there are many people doing many things to lots of kit. Some to make a better product that may be perceived to be sonically superior and some just because they like tinkering with things one thing is for sure it all costs something. I think the 540p/640p is good for the price but i soon moved on from mine and now find i cannot bear listening to it. Good on someone to want to take something and change it, hopefully for the better.
Click to expand...

Yes it is for commercial gain. Several people said things along the lines of "we would do business with you but haven't heard of you before" and suggested that I do a couple of jobs for free to get my name better known and to get some feedback to other members on the forum.... Eventually I succumbed to this idea and hence this offer..... It's allowing a couple of people to get theirs done at no cost to them in order to get some feedback both for myself and to create interest from other potential customers. The two lucky people who are getting theirs done gratis may of course not like the result! time will tell...
 
schematic here

< http://akdatabase.org/AKview/albums/userpics/10004/Cambridge%20Azur%20540P-640P%20Service%20Manual.pdf>
 
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