Absolutely
Naim = bright?
- Thread starter zarniwoop
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Absolutely
Paul R
pfm Member
I disagree, although this is a matter of opinion. This is one end of Class C and is inappropriate for any 'hifi' audio application.
For the definitions to be useful they have to be distinct, so, assuming 'push pull' conventionality,
Class B, minimum bias for minimum crossover distortion. The output halves are never both fully on except for an instant during crossover or at idle.
Class AB, designed to run in Class A for some part of output, more crossover distortion once Class A output exceeded, but this is at a higher signal level and therefore probably less significant.
Class A, no crossover distortion by design. Gimmicks to achieve this by topological subterfuge need qualifying.
Paul
i_should_coco
I am weasel
Hmmm... I've always understood class-B to be zero bias. As soon as you start adding any, it becomes AB.
Barrymagrec
pfm Member
It was a long time ago but I seem to remember the definition we were taught was :-
Class A Device conducts for the whole of the input waveform (360 degrees)
Class B Device conducts for more than 180 degrees but less than 360 degrees
Class C Device conducts for less than 180 degrees (RF Amps only)
Class AB is obviously a mixture of A and B where class A prevails for small signals, AB1 and AB2 was to do with whether or not grid current flowed - can`t remember which was which.
i_should_coco
I am weasel
Yes, A2 or AB2 is positive grid operation (in tubes).
With tubes it's a bit easier, I guess as there's no switch on threshold. Maybe the definition of "B" was revised for transistors. I honestly don't know, but it does seem like one of those grey areas....
With tubes it's a bit easier, I guess as there's no switch on threshold. Maybe the definition of "B" was revised for transistors. I honestly don't know, but it does seem like one of those grey areas....
Barrymagrec
pfm Member
Yes, It can be looked on as a convention, not a 'law'
James
Lord of the Erg\o/s
This is a proper class A amplifier.
No gimmicks, just lots of wasted BTUs wafting from the massive heat-sinks for a measly 30W per side. But what glorious watts they are.
James
sergeauckland
pfm Member
As there has neven been a British Standard or IEC standard for what the different classes are (as far as I know) there is only convention to fall back on.
My understanding is as follows:-
Class A. Both output devices are conducting for the whole 360 degrees of the audio cycle.
Class B. Each output device conducts for 180 degrees of the audio cycle
Class C. Each output device conducts for less than 180 degrees of the cycle (used only for RF)
Class D. Each output device switches between full on and full off.
Class AB allows for both output devices to conduct in the region of crossover due to a suitable bias current. The amount of output that is provide under Class A conditions depends on the amount of bias.
Special case of Class B operation, such as Peter Blomley's circuit need special treatment as each output device only carries half the audio signal with no overlap, but the output devices are both biased on, like an AB amplifier.
In valve circuits, there is Class A, Class AB1 and AB2 depending on whether and grid current is allowed to flow. AB1 is the usual operation of tetrodes and pentodes where the bias voltage is sufficient such that grid current cannot flow, whilst AB2 is allows grid current to flow and as far as I'm aware isn't used in HiFi applications. Pure Class B also exists for valves, but again isn;t used for HiFi applications although instrument amplifiers and PA amplifiers have used it.
As I said above, none of this is written in standards as far as I'm aware, so other interpretations are perfectly possible and may account for some of the discussions here.
S.
If we agree that no loud speaker is transparent and that a high fidelity system is only as good as it's weakest link can we also agree that the potential transparency of a high fidelity system is only as good as it's weakest link?
BTW - What does this have to do with whether Naim = bright or not anyway?
BTW - What does this have to do with whether Naim = bright or not anyway?
sergeauckland
pfm Member
Indeed. If both output transistors are biased at cutoff, then get turned on by the audio, there's no need for any standing current. However, the linearity of the transistors will be very poor under those circumstances, and so a large amount of distortion will be generated, which is why it's not used for audio amplification where there's any regard for quality.
This is why just about every SS audio amplifier of any quality is Class AB if not pure Class A.
Looking at the circuit diagram of some early transistor radios they look like they are in pure Class B because of the desire to minimise current drain from batteries, and this was presumably deemed more important than the poor audio quality that resulted.
S.
sergeauckland
pfm Member
Yes, that's a reasonable view to take. No loudspeaker is transparent, but that doesn't mean that the electronics driving it shouldn't be if the aim is to achieve the least distortion.
As to the Naim = bright issue, that was disposed of very early on when graphs were posted showing that Naim amplifiers are not bright, if anything very slightly dull at the top end, but that hasn't stopped those who say they don't care what the graphs show, what matters is what they (think they) hear.
S.
I agree that Naim can sound slightly dull (aka "shut in"..or lacking "air")
My guess is that some folks confuse "bright" with "harsh"....and Naim amps can certainly be made to sound this way quite easily
My own take on this is that the view is somewhat historical: many systems evolved during the 70`s and 80`s which included a Linn LP12, Naim amps and Linn Speakers
The original LP12 was known to produce a bass "hump".......most of the (earlier) Linn speakers I am familiar with balanced this with a rather "dry" (sealed box) bass and a rather forward balance (ie a prominent upper - mid)..whatever else Linn speakers of that era were...neutral they were not!.....said owners of such systems then went out and purchased CD players which were essentially flat in response, but were certainly not flattered by the upper-mid prominence of Linn speakers. Naim amps, having a sight top-end rolloff, also tended to exaggerate this feature somewhat
Hence, I believe, this led to the myth that Naim amps sound harsh (ie bright)
Feel free to disagree...
Mark
russel
./_dazed_and_confused
They might not show any HF boost into an eight ohm resistor but they will not be driving an eight ohm resistor, they will be driving a cable with an inductance and a capacitance and a reactive loudspeaker. Given that early Naims were cable sensitive due to needing a the speaker connecting wire to form part of the zobel network and people not following Naims advice its hardly surprising that it could sound "bright" as it would be ringing into the reactive load placed on its output.
James
Lord of the Erg\o/s
Yes, it is now thank you. It had a dodgy 2SA798 on the left channel. Just as a precaution, all the small-signal transistors were replaced too.
You may be right about 4-ohm loads. I've used the M-22 so far only on the E-IX (nominal 8-ohms) but am considering MF/HF duty on the E-X in due course.
James
Paul R
pfm Member
It's better to come out of Class A than to clip. The Pioneer is a very appealing amp, both visually and technically.
ATC use a 16 Ohm mid driver in their actives. This allows them to use a Class A amp at higher volts but less current, so less idle heat but still quite a lot of Watts.
Paul
ATC use a 16 Ohm mid driver in their actives. This allows them to use a Class A amp at higher volts but less current, so less idle heat but still quite a lot of Watts.
Paul
Yank
Bulbous Also Tapered
It's odd then that even some fairly modest speakers can reveal the lack of transparency upstream.
sergeauckland
pfm Member
Not odd at all, as a lack of transparency in one area, like a flat frequency response, can still show a lack of transparency in the driving electronics, like high distortion.
S.
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