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Posted: 31 Jan 2009 13:36
by bauzace50
@ Andyr,
you are spot-on, of course! :P Personal preference is the key. Didn't Shakespeare write "As You Like It"? :lol:
Regards, b50

Posted: 31 Jan 2009 15:58
by Guest
Tonal accuracy is the easiest thing to get right--the designer just has to take the trouble to do it (and the buyer be willing to pay for the effort). The hard part is transparency, the illusion that one is listening to the performers and not to a recording. Timing ("PRaT") seems inherent in transparency, in that improving accuracy in the time domain always improves transparency. Detail, hall ambiance, imaging, and spaciousness then fall into place as side effects. At least, that's my experience in evaluating ongoing circuit development for a manufacturer.

Posted: 31 Jan 2009 23:57
by andyr
lanny wrote:
Timing ("PRaT") seems inherent in transparency, in that improving accuracy in the time domain always improves transparency. Detail, hall ambiance, imaging, and spaciousness then fall into place as side effects. At least, that's my experience in evaluating ongoing circuit development for a manufacturer.
Even though I'm just an amateur DIYer, I'd have to agree with you, lanny. A year ago, I upgraded my 6 monoblocs (I run 3-way active Maggies) to the latest version of their amp module ... the result was significantly improved resolution that made everything better - transient attack, soundstage, emotional involvement ...! :D

The interesting thing about this (well, to me, anyway! :D ) is that the new amps have an upper roll-off point of around 80Khz ... compared to the 35Khz of the 6-year old circuit. IE. the tweaks which the designer had been doing over the years increased the bandwidth (which wasn't the primary aim!) and made the amp faster and gave it more resolution.

BTW, love your sign-off quote! :lol:

Regards,

Andy

Posted: 01 Feb 2009 23:13
by michaelevans60
vincula2008 wrote:To PRaT or not to PRat? I knew this thread will come after a certain message, michalevans... :twisted:
Sorry vincula2008, didn't mean to irritate! I just wanted to explore it in its own thread rather than hi-jack the other! Please don't get me wrong, I just wanted to explore the term and understand it a bit. I really, really appreciate your responses, all of you, thanks.

So to sum up, I think (and if you look at one of my earlier posts I put "vive la difference"!) that it is a term that many struggle with. I'm much clearer now; but for me I struggle with the term as I think many of us look for many aspects of it, but just have different preferences. The world would be a boring place if we didn't. But I've nothing against those who can interpret it themselves and apply it.

Sorry if this is a well trodden debate and I really didn't mean to antagonise anyone. Apologies, and thanks to all for your contributions.

Mike

Posted: 09 Feb 2009 21:37
by andyr

which Maggies are you running?

Marc
MG-IIIas.

Regards,

Andy

Posted: 11 Feb 2009 19:26
by edd9000-us
Merriam-Webster:
P.S. So why is it that Rega's are touted as PRaT decks if suspended LP 12's are what you need for PRaT? That is a question BTW, not a dig at someone's post. I really don't know what you need to get it as I've never really sought it out. I just like it.
As i understood it, PRaT was tied to the flat earth hifi movement. Linn, naim, rega come to mind as the main manufacturers.

My first hifi fell right in this catagory, rega planar 3, nytech amps (poor mans naim) and kef 103.2 speakers.

I used to frequent a dealer who was very into this kind of thing, his ultimate system was an lp12, naim aro arm, naim amps, and probably lin isobariks.

edd

Posted: 17 Feb 2009 12:02
by bastlnut
hallo,

i must have some PRAT in me too.
i now have a Naim Nait....yes the original one tho with the green LED.
i am using Rega speaker cable, the silver coated copper flat one.
hooked up my Monitor Audio Studio 7's and wow, this is fun.

i got this from a recycling depot where they cut off the power cable.
so, replaced that, and tested it, firstly on my work bench speakers.
then i did some research, and took the MA's from my home cinema set up.
very nice.
the volume control is noisy on start up, this baby likes to get warm to give its best.
it thumps a little when you turn it on, and less when turning it off.
guess i need to recap the thing. are there volume pots still available?
what is it i have heard about setting the pcb bias for a less warm sound or less roll off?

may just be a keeper for a Büro or small room system
now where did i put my DIN connectors ? :lol:
who has my ProAc Tabletts that i loaned them..... :mrgreen:

i just may be a PRAT too.
regards,
bastlnut

Posted: 17 Feb 2009 14:30
by Guest
bastlnut wrote:
what is it i have heard about setting the pcb bias for a less warm sound or less roll off?

bastlnut
Hi,

AFAIK Naim kept the circuit secret to avoid comparisons with their
other power amplifiers, the circuits of which are very straightforward.

Assuming similarity implies a quasi complementary emitter follower
NPN output stage with the additional baxandall diode modification.

There is an optimum bias. Too low = lots of high frequency distortion.
Too high slightly = more distortion due to "gm gain doubling". The
latter applies to the operating region of a class A amplifier, to have
a reasonable region of class A operation requires heatsinking that
is inappropriate (read a lot more expensive) for a class AB design.

It will blow up if bias is set too high. By careful monitoring of the
heatsink temperature you could increase bias somewhat, but this
increase in bias will cause more distortion than it is allegedly worth.

A better approach for more "class A" is the same optimum bias
voltage (this voltage matters, not the current) and reducing the
value of the emitter resistors by ~ half = more class A region
with no increase in distortion, i.e. optimum bias is maintained.
(It will run warmer at idle).


Posted: 17 Feb 2009 14:50
by bastlnut
hallo,

without a schematic, i dont have a chance of looking at possibilities.
i have read that there are more possibilities because they didn't couple the output,
this is the reason for the specific LS cable requirements.
it also allows more variables for sound tuning.
this is also the reason for my hesitancy in recapping the amp myself.
i need to know what values i need to check or keep constant.

regards,
bastlnut

Posted: 17 Feb 2009 15:13
by Guest
Hi,

The omission of the normal output inductor does not affect the biasing.
It does affect stability and the cabling requirements and is related
to the stability margins, phase and gain, set by the VAS stage Ccomp.

http://www.diyaudio.com/forums/showthre ... adid=69199

Shows some schematics.


Posted: 17 Feb 2009 16:30
by bastlnut
ha,

thank you, gr8 info

regards,
bastlnut