Modified Naim NAP140 Schematic

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I cannot vouch for the authenticity of this, but if it's correct, it's what I would call the old Naim front end:

Exposure-XX-Super.jpg
 
I don't know where I go the schematic from and the Super XX has 6 output devices from what I can see... so tread with caution.

The 6 output device are labelled N P N on one channel and P N P on the other. They do appear to be FETs but I've no idea what the extra 2 are doing, unless to regulate the supply?
 
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In the later Exposure 2000 series models, the power transistors are TO220 hexfet types and given the tiny PCB, very thin chassis for heat dissipation and modest transformer, they are not powerhouses and the sound is nothing to get excited about. In the pair I used for bi-amp experimenting, there was something of a sheen on the sound, to my way of thinking.

I understand these were Malaysian products as production had moved there after a change of ownership. The later 2000S series reverted to BJTs (Sankens actually) and these models were better received. It wouldn't be the first time that Sanken's BJTs, particularly the LAPT types, have trashed mosfets, perhaps in this case, due to design and quality control issues. A bit more verbage here: Exposure 2010S integrated amplifier | Stereophile.com
 
What I find interesting is the supplementary review by Jim Austin on the link above.
The subjective effect he mentions is IMO mostly/partly due to the 22K collector resistor. But Expo chooses to "defeat" this effect at HF by adding a 39pF cap in parallel.

I must give this a try sometimes... to try to get the warmth of the 22K effect without too much of the the wall-of-sound effect.
 
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That's a good question but I can't answer it as I've not had an opportunity to look inside. I would think that these are powered with STD series Darlingtons going by manufacturing dates, available power ratings and usual cost constraints. Apart from Naim style quasi-complementary designs, I don't think I've ever seen Sanken transistors used commercially in a CFP output stage but that may have changed.
 
They do appear to be FETs but I've no idea what the extra 2 are doing, unless to regulate the supply?

The current through the 100 ohm of driver transistor won't be close to 10 mA i presume, giving little voltage for Vgs. Latfet is suitable there. The Naim circuit will give good distortion spectrum (monotonic), good bass and the nature of the latfet itself will give HF better than Naim.
 
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You don't consider it as CFP?
The preface was, "Apart from Naim style quasi-complementary designs...."
However, even if the topology suggests that quasi output stages should have something in common with fully CFP types, since it is a hybrid, I don't think it does because the sound is strongly influenced at low levels by the very different crossover behaviour. We can't predict the distortion products exactly but generally, asymmetric topologies will have a higher proportion of even order harmonics than either CFP or EF type.
 
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We can't predict the distortion products exactly but generally, asymmetric topologies will have a higher proportion of even order harmonics than either CFP or EF type.


I think if we like to play around with harmonics, we can always do that 'whatever' the topology. I think I'm about to give up (again) of the CFP topology. There is a design dilemma, trilemma or worse there. I'm not going to build the Exposure. I will try to put the Nait XS into Spice and examine it. May be it is not my cup of tea either. After working with P3A and listening to it, I'm more aware of how the dilemma affected my perception. And I'm not mainly looking for impressive/musical sound, which is what we usually get with (lowly biased) CFP amps.
 
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I think if we like to play around with harmonics, we can always do that 'whatever' the topology.
Not really. Some topologies, particularly those of the output stage, are fundamentally going to generate much more odd/even, low/high order distortion products than others. Some well-known designers exploit this in their audiophile products too.

The art of turning this raw distortion into a pleasing array of harmonics is in applying what you learn from the designers. You won't learn anything useful from conventional, best practice but we sometimes find odd examples among consumer products (look at NAD310) that sound a lot better than their price might suggest. It isn't magic but this shows what can be done by using standard parts in unusual arrangements. Have a listen using a proper layout, decent quality power supply and all good caps :)
 
The art of turning this raw distortion into a pleasing array of harmonics is in applying what you learn from the designers.

I'm pretty sure that electronics is simple but psycho-acoustics is probably harder and having good ears is another thing. Who will tell the designer how 0.0001% THD will sound different from 0.001% if the designer doesn't have good ears? There is very few designers with good ears, so there are more secrets there, more important than thd profiles.
 
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....Who will tell the designer how 0.0001% THD will sound different from 0.001% if the designer doesn't have good ears? There is very few designers with good ears, so there are more secrets there, more important than thd profiles.
johnego, you are going round in circles and trying to make arguments from surmise. You aren't serious so I'll leave you to it.
 
The art of turning this raw distortion into a pleasing array of harmonics is in applying what you learn from the designers. You won't learn anything useful from conventional, best practice but we sometimes find odd examples among consumer products (look at NAD310) that sound a lot better than their price might suggest. It isn't magic but this shows what can be done by using standard parts in unusual arrangements. Have a listen using a proper layout, decent quality power supply and all good caps :)

I was so impressed with the sound of the 310. But that's 25 years ago. I had no better or more expensive amp in my hands. But the trick to impress listeners with something stand out is rather silly imo. There are two things that i learned from such designs. First, it is important to understand that what we think is impressive, is often not good at all. Second, technically, I can see good things in such design/topology but its not the distortion profile as many have thought.
 
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