Saves money to use the same transistors. Then again, someone has to manually solder those big fins to them. Fins, heatsinks whatever. The heat in this area might be a reason to use a solid tantalum; wet electrolytics tend to dry out when hot. Just speculatin'.
The soldered fins look rather amateurish. If a DIY posted a pic of their amp which happened to incorporate a similar approach to cooling SMDs, it would be criticised or at least draw comment from the engineering fraternity and probably the artistically inclined among us.
Still, I like innovative touches. I've been tempted a few times to do similarly with copper or brass sheet for SOT223 and TO251/252-3 package devices. It also echoes JV's early work which was characteristically maverick, at times unprofessional and left you in doubt about the rest of the design. Somehow though, the amplifiers did hang together and were reliable for many years in careful hands.
Still, I like innovative touches. I've been tempted a few times to do similarly with copper or brass sheet for SOT223 and TO251/252-3 package devices. It also echoes JV's early work which was characteristically maverick, at times unprofessional and left you in doubt about the rest of the design. Somehow though, the amplifiers did hang together and were reliable for many years in careful hands.
Of course the Darlington deals with positive current and the pseudo-Darlington with negative current. So your characterisations may apply half the time.
The two configurations are quite different in their function. I can see why JV used a mixture of the two (he wanted only npn power transistors) but I’m not sure why SS chose two CFPs instead of two Darlingtons for fully complementary, aside from potentially slightly better bias current stability.
It’s hard to untangle the possible motives; sound quality is not the primary aim of the Nait series.
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Hey Brian - I wonder.....An oft ignored side benefit of the CFP output is thermal control - you only have to control the drivers not the power devices and so the thermal inertia is low and the cost of mounting a sensing element on the heatsink is avoided. It's known that bias control is more critical with the CFP but it's really not that hard.
I think for those who listen a lot, it should be sufficient to choose the topology merely based on available examples, which should tell (me at least) that the CFP is the better sounding one. It is hard to think that sound quality is not the primary aim. From business POV, it is necessary to cover more market segments: cheaper amps for the poor, different sounds for different tastes.
CFP designs allow a little more output swing which means slightly better power ratings, if that matters but the reasons traditionally given for preferring EF designs here are mostly arguments and anecdotes about stability and driving difficult loads - a problem with some early designs that is now better understood and dealt with to the point where it's no longer any great concern.
Randy Slone made some interesting comments and showed graphs of the differences in performance between CFP and EF output stages in his book "High power audio amplifier construction manual". One of his main points was that the type and amount of distortion depends on the width of the crossover region and the CFP is quite narrow by comparison to EF and quasi designs. It thus measures rather better though the harmonic components tend to be higher order and maybe unpleasant because of the more abrupt transition. Where the second harmonic content can be increased somehow (as in unbalancing the LTP or by tweaking the VAS design) I think the final sound of a CFP design can actually be quite satisfying whilst maintaining lower distortion.
In an EF design amp. playing at low level (and that's most of the time for suburban folk) the crossover region can be wider than the audio signal and thus you have more scope for harmonic distortion than CFP. The harmonic profile may be mostly low order but how much distortion can you tolerate, even though it sounds great with just a brief listen?
Randy Slone made some interesting comments and showed graphs of the differences in performance between CFP and EF output stages in his book "High power audio amplifier construction manual". One of his main points was that the type and amount of distortion depends on the width of the crossover region and the CFP is quite narrow by comparison to EF and quasi designs. It thus measures rather better though the harmonic components tend to be higher order and maybe unpleasant because of the more abrupt transition. Where the second harmonic content can be increased somehow (as in unbalancing the LTP or by tweaking the VAS design) I think the final sound of a CFP design can actually be quite satisfying whilst maintaining lower distortion.
In an EF design amp. playing at low level (and that's most of the time for suburban folk) the crossover region can be wider than the audio signal and thus you have more scope for harmonic distortion than CFP. The harmonic profile may be mostly low order but how much distortion can you tolerate, even though it sounds great with just a brief listen?
Good thinking. The photo is none too clear but it looks like T211 (vbe multi) is located snuggly between the drivers. So you may be right that CFP was chosen to avoid the complexity of mounting it on a heat sink.
A pseudo-Darlington is less stable than a Darlington and so is more sensitive to load.
The bigger issue is that there does not exist a npn and pnp power transistor pair that have identical characteristics. It’s a law of nature.
So JV chose a compromise with a Darlington and a pseudo-Darlington. There are other compromises possible.
If you choose the compromise of having power devices of opposite gender then you can use either Darlingtons or CFPs. It is better to use the former (like Krell did). Sells may have had several reasons for using CFPs but as this is Naim’s budget
rofl integrated, the thermal tracking benefit that Bigun suggests would swing it.
Excuse me, but with the acronyms, I'm lost!
What exactly do you mean by CFP and EF designs?
This forum could do with a glossary!
Let me try to translate...
EF = emitter follower (Ian used as shorthand for a Darlington as opposed to a CFP)
CFP = complementary feedback pair, or Sziklai pair or pseudo-Darlington
Darlington = two same-polarity transistors in emitter to base cascade
Pseudo-Darlington = two opposite polarity transistors in collector to base cascade.
VAS = voltage amplification stage, or Miller cap stage
LTP = long-tailed pair, or differential amplifier
Quasi complementary = one Darlington and one CFP in push-pull
Fully complementary = usually two Darlingtons or two CFPs in push-pull
HP = haut parleur or loudspeaker
Let me try to translate...
EF = emitter follower (Ian used as shorthand for a Darlington as opposed to a CFP)
CFP = complementary feedback pair, or Sziklai pair or pseudo-Darlington
Darlington = two same-polarity transistors in emitter to base cascade
Pseudo-Darlington = two opposite polarity transistors in collector to base cascade.
VAS = voltage amplification stage, or Miller cap stage
LTP = long-tailed pair, or differential amplifier
Quasi complementary = one Darlington and one CFP in push-pull
Fully complementary = usually two Darlingtons or two CFPs in push-pull
HP = haut parleur or loudspeaker
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Guys, sorry to mystify you if that's how you read the post. The abbreviations have been used here on the forum for longer than I have been a member and I seem to have absorbed them as part of the jargon of DIY electronics. I guess if you only read threads that have familiar amplifier titles, you'll be missing the educational content in some of the serious design discussions which may come in handy some day.
You could skim some of the engineering threads occasionally where these terms often appear, because like it or not, we really do need to use short acronyms that can be considered universal on the forum. It's just unfortunate that the terms themselves may be from a different language which limits their ease of use and means they they can still be confused or misused.
Thanks traderbam, for posting some translations
You could skim some of the engineering threads occasionally where these terms often appear, because like it or not, we really do need to use short acronyms that can be considered universal on the forum. It's just unfortunate that the terms themselves may be from a different language which limits their ease of use and means they they can still be confused or misused.
Thanks traderbam, for posting some translations
@Ian Finch
No problem, writing in Forums and with some small problem of understanding the language, in fact it is always quite complicated to deal with technical issues.
I also thank Traderbam for the useful translation.
So, if you want to include the circuit typology of a NAIM 140, in which category would it be more correct to include it in your opinion?
No problem, writing in Forums and with some small problem of understanding the language, in fact it is always quite complicated to deal with technical issues.
I also thank Traderbam for the useful translation.
So, if you want to include the circuit typology of a NAIM 140, in which category would it be more correct to include it in your opinion?
The category of the original NAP and Nait power output stages is known formally as Quasi-complementary. It has been so since at least 1980 when I studied them and worked on a few NAP models. "quasi" suggests that the design mimics a complementary design though it actually uses the same power transistors in both upper and lower or positive and negative power rail locations as shown on conventional circuit diagrams. The schematic diagram of NAP250 amplifiers that you see posted many times in this thread and appears almost everywhere on the internet, is conventional and you can refer to it .
Traderbam mentioned other commonly used terms too. Some, I think are contrived ones as I've almost never seen them in print. There is further discussion here: How to identify a quasi-complementary amplifier?
Conventionally, the term "Darlington" now refers to an emitter-follower cascaded pair of transistors fabricated on a single die and packaged as one device. It probably should not be used to confuse it with the arrangement of two discrete transistors in a similar emitter-follower diagrammatic arrangement nor with Sziklai pairs because the thermal and electrical behaviour is quite different under stress and we may not know what the internal circuits really are.
Traderbam mentioned other commonly used terms too. Some, I think are contrived ones as I've almost never seen them in print. There is further discussion here: How to identify a quasi-complementary amplifier?
Conventionally, the term "Darlington" now refers to an emitter-follower cascaded pair of transistors fabricated on a single die and packaged as one device. It probably should not be used to confuse it with the arrangement of two discrete transistors in a similar emitter-follower diagrammatic arrangement nor with Sziklai pairs because the thermal and electrical behaviour is quite different under stress and we may not know what the internal circuits really are.
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Rod had a name for the Nait XS or P3A CFP topology: Compound Complementary.
Compound vs Darlington
Compound vs Darlington
Attachments
you need mixed PNP and NPN devices for CFP designs - that would not be possible on a single chip.
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Though I respect Rod's historical use of it, the problem with using a term like "compound pair" or even "compound complementary" pair is confusion. Example from Wikipedia: "the Darlington configuration (commonly called a Darlington pair) is a compound structure of a particular design made by two bipolar transistors....."
In other words, both EF and CFP discrete forms can described as compound and also complementary transistors. Which do we mean??
In other words, both EF and CFP discrete forms can described as compound and also complementary transistors. Which do we mean??
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