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QUDOS - the brilliant new amplifier boards from Avondale

misterc6 said:
The NCC220 does not retain the same musicality as the NCC200, it improves on it as several contributors to this thread have noted.

The two designs are very similar but it's the fully complementary output stage of the NCC220 that puts it in a different, higher, league than the NCC200 with its quasi-complementary output stage.
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There are two main changes from NCC200 to 220:
1) Quasi > fully complementary o/p stage
2) Change of R2 from 22K to 1K

The effect of #2 is not that subtle, it cleans up the sound and makes it sound less "dense" i.e. less of the Naim sound.

I would hazard a guess that this makes more difference to the sound than the changes to the o/p stages.

@Joppe - you could try linking/shorting R2 on your NCC200 boards and have a listen.
 
S-Man said:
There are two main changes from NCC200 to 220:
1) Quasi > fully complementary o/p stage
2) Change of R2 from 22K to 1K

The effect of #2 is not that subtle, it cleans up the sound and makes it sound less "dense" i.e. less of the Naim sound.

I would hazard a guess that this makes more difference to the sound than the changes to the o/p stages.
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Agreed.
 
@S-Man - No, definitely not; I've long said look at the effect of the large R2, model it, and realise what it contributes to 'naimness' by imposing a definite, shall we say, harmonic profile on the output? If that's what you want, that's mostly how it is done! Move away from that and logically you are into finessing a classic 3-stage, LTP/VAS/OPS, Class aB amplifier much like any other.

(To me - like most things audio - beyond a certain competent minimum, it's mostly about personal aesthetic choice more than much else: and that is what DIY is for)


ETA: do I have to point-out that in such a DIY context, unfortunately the choice of what is 'competent' also tends to become somewhat subjective? That's likely a separate debate, entirely!
 
Totally agree Martin.

I have listened to the R2 effect, back and forth, quite a few times. It's an interesting subjective effect.
Setting R2 to to 22K (or 7.5K in a NAP200) gives a more dense sound which can be quite appealing. I have found I can listen to new music at modest levels all day (e.g. Radio Paradise) on these type of amps, due to some sort of tune-enhancement (or simplication?). On a more neutral amp there is more variation to the sound from one track to another, with some stuff sounding worse, but most sounding better. The really telling test is when you wind the wick up a bit and the denseness of the sound becomes tiresome.
Maybe this is why owned and sold NCC200s twice. I should have tried the R2 mod on them!
 
S-Man said:
Totally agree Martin.

I have listened to the R2 effect, back and forth, quite a few times. It's an interesting subjective effect.
Setting R2 to to 22K (or 7.5K in a NAP200) gives a more dense sound which can be quite appealing. I have found I can listen to new music at modest levels all day (e.g. Radio Paradise) on these type of amps, due to some sort of tune-enhancement (or simplication?). On a more neutral amp there is more variation to the sound from one track to another, with some stuff sounding worse, but most sounding better. The really telling test is when you wind the wick up a bit and the denseness of the sound becomes tiresome.
Maybe this is why owned and sold NCC200s twice. I should have tried the R2 mod on them!
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I found this interesting. Since I have simulation models of both the ncc200 and qudos I thought I would see what the sims showed using 1k input (0.05v) for an output of 100mw (0db)

The FFT distortion profile showed no difference between R2 as 1k or 22k for either amplifier.

Further the FFT distortion profile showed that the qudos is inherently a much better design (in terms of distortion) than the ncc200.
For the qudos, 1k input for an output of 100mw 2nd harmonic distortion was -90db, 3rd -100db and all the rest at -130db

For the ncc200 2nd -90db, 3rd -90, 4th -92, 5th -110,6th -100,, 7th -110, 8th -110, 9th -115
 
Many thanks S-Man, That's really interesting!

I'd have to get a hold of some 1k resistors and try the effect on my ncc200. Naim amps (especially of olde) do indeed have a denseness to the sound that is also present in the ncc200. Wonderful if I can wind this effect back and find my subjective preference.

Can it be the difference between R1 and R2 that loads TR1 and TR2 differently and thereby generate an even-order harmonic distortion profile that gives the subjective perception of 'denseness' to the sound?
 
Couldn't find 1k, but dug up a 3k3 and squeezed in in parallel to the 22k -and yes, the difference is not subtle at all!
Have to do some listening to see where this is going, but direction is clearly less dense and more 'correct' with more sense of air and extension -even though this is still about a factor of three above the 1k target value.
Just need to figure out whether the musicality is retained in the ncc200.
 
Joppe said:
Can it be the difference between R1 and R2 that loads TR1 and TR2 differently and thereby generate an even-order harmonic distortion profile that gives the subjective perception of 'denseness' to the sound?
Click to expand...

Martin and I think so, but pattox's sims seem to show something different.
Of course sims depend entirely on the accuracy of the models.

Looks like Harold Leak was wrong when he said <0.01% distortion is not audible!
 
Been reading bits of this thread as it goes along so interesting to see that changing the feed resistor on the 2nd transistor in the LTP changes the sound as described above. Can anyone explain the "NAIM rip" and how does this affects the sound? Is this a slight de-emphasis in the upper mid coupled with a slight emphasis in the low treble and is this purely due to the quasi output stage? I am asking because I have been playing around with an OD speaker driven by NCC200s and want to remove all other effects as much as possible. I may consider going to NCC220 but want to get the best out of what I have first.
Cheers,
AP
As a further note, could this be 'tested' using the differential amp idea on the ESP website (Sound Impairment Monitor) where the inv. / non-inv. inputs to a differential amp are connected to the input and feedback points on the LTP?
 
If I'm reading this page of the thread correctly, both Martin Clark and Pattox have done simulations,
and found different things. This is ... disconcerting. I'm long used to people
listening to systems and forming different opinions, but differing on the numbers out of a simulation is new to me.

Presuming that both sims were on Spice (or a variant) can they be compared for substantial differences?

BugBear
 
Thanks S-Man,
Read the thread which is quite interesting. Reminds me of when I first built a clone of the ESP pre-amp. I mistakenly routed the output of one op-amp to a sub-board (to allow switchable gain) directly under the 100R input resistor. Took about 3 weeks to work out why it sounded a bit shut-in - was behaving as a circa 2MHz oscillator at about +/- 5V so I had to snub the feed-back with 100pF COG to get it down to circa 1mV.
 
bugbear said:
I'm long used to people
listening to systems and forming different opinions, but differing on the numbers out of a simulation is new to me.
Click to expand...

Well, when you think about what a simulation actually is, it isn't that weird. It comes down to what the underlying model describes, choices of parameterizations and tuning -if the target system is complicated (when isn't it?). Models build form what is known (and in many cases believed) and are blind to factors external to the parameterizations. So good tool when useful, but inherently never truthful ;)
 
My sims were done long ago and probably not well! it may also depend a bit on whether you use a default 'perfect' current source in the LTP or a more-realistic/less 'stiff' model element
I also messed about with a model amp for a while, but again, only long enough to test my curiosity, and not a precise measurement.
 
OK ... i'm just a minute (maybe) away from firing up my first pair of Qudos ... but there's one thing perplexing me - i cannot seem to find ANY information for whatever reason on whether wet tantalums are polar or non polar! The case markings sure make them look like they are polar - and if THAT'S the case then I guess it's always a bit tricky replacing a polar with a non polar cap ... any advice?
 
OOPS! never mind ... just assumed it wasn't marked on the diagram .. all should be well then. that's what i get for making an assumption without first checking
 
hmmmm ... okay ... well for the life of me i'm not seeing anything in the build notes on how much to feed this thing from my power supply - nor anything on current limiting guidelines etc? can anyone help? 15-18V? current limited to 0.5A?
 
Joppe said:
+/- 30-50 Volts is what it needs. Many report best performance on 50 V supplies
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GAHHHHHHH ... i only have two bench power supplies ... both max out at 20-25V ... who has supplies like that?? hmmm - maybe i should hook them up to the minicap 6 boards? is that what people are doing here? thanks
 
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