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In Reply to: PP vs SE posted by Giuseppe Gualandi on November 12, 1999 at 13:55:58:
Hi there,>>>Who is so sure that Push-Pull (PP) ampli sound worse than Single-Ended (SE) ? <<<
Anyone who has done extensive testing under equitable conditions. So that means using speakers that allow the SE Amplifier to work well within it's powerlimits.
>>>- SE add a lot of 2° harmonic (euphonia not Hi-FI). <<<
Does it now? What do you define as "a lot"? It is easy to make SE Amplifiers that cancel the 2nd harmonic almost to zero. I have done so. The sound of this technique is however debatable. It makes the SE Amplifer sound more like PP Amp, taking away some of the good sides without giving any audible advantage.
However, even without using Distortion cancellation techniques it is possible to make an SE Amplifer that produces < 0.2% 2nd Harmonics at 1W Output.
If we then consider the MECHANICAL distortion charateristics of the Ear, we will find that several percent of 2nd harmonic distortion are of little consequence. Please consider the following:
(I know it is a bad habit to quote oneself, however the piece of work this sniplett is taken from has not yet been officially published)
"Experiments by Patterson in 1969 revealed that if a PURE tone of 200Hz is presented to the ear with a SPL of 94db harmonics are produced within the ear at 400Hz, 600Hz, 800Hz, 1kHz, and 1.2 kHz with magnitudes of 84dB, 76dB, 70dB, 66dB and 60dB. This represents a roll-off of around 12dB per octave. The distortion levels are thus extremely high, corresponding to 32, 12.6, 6.3, 4 and two per cent respectively.
So the Ear itself produces over 30% Harmonic Distortion at 94db. Yet we ourselves perceive this kind of tone as ABSOLUTELY PURE. Our Brain indeed will effectively "filter out" the Distortion and let us hear the pure tone."
With that considered, it seems that the IDEAL distortion of a classic Triode operated from a signal essentially free of distortion is masked by the ears onw non-linearities for levels of around 5 to 10% THD, assuming that SPL at the listening position for the Output power producing this kind of distortion significantly exceeds 94db.
>>>- a lot of 2° harmonic means a lot of Intermodulation Distortion (IMD)<<<
Correct. However, as noted above, a similar distortion is already inherent to the Ear. Experiments in (I believe) the 1960's done by D.E.L. Shorter of the BBC showed that the IMD produced by non-linearities are the less audible, the lower the order of the HD produced by the same Nonlinearities is.
So the relatively high distortion of an SE Amplifier near it's powerlimits is irrelevant in terms of AUDIBILITY (rather than measurability), especially if care is taken to use suitable Loudspeakers.
>>>- IMD is far far detrimental for sound that a bit of prevalence of 3° harmonic in a context of lower THD and IMD of PP. <<<
Correct. And hence, based on D.E.L Shorters observations, the usally pretty high numbers Harmonics (high order and hence high audibity of both HD and IMD) as well as their unnatural character (odd order harmonics are dominant) tend to be much MORE audible that the more (sonically) begnign distortion Products of a SE Amplifer of competent execution.
>>>- Class-A PP are very less sensitive to output and bandwidht of power supply.<<<
Yes. PP Class A Amplifers allow the Manufacturer to skimp in the Powersupply. This is one of their chief reasons of entry into the market, combined with 9obviously) more than double the output of a equivalent SE Amplifier having only one triode of the same type.
>>>In my opinion SE don't stand comparison with well designed direct heated triodes Push-pull amplis ( see NAGRA or latest MARANTZ).<<<
Having done similar comparisons (arguably all with DIY Amplifiers - yet many of these are technically more advances than ANY commercial Design known to me) I cannot agree. My experience (and this is with listening pannels) place so far the 2-Stage SE Amplifer ahead of all other options.
Tests where conducted primarily with a System based around 103db sensitive Horns (plus active Sub below 50Hz) and also with antique "Goodmans of England" Axiom 201 12" Full-Range Speakers (101db/W, 15 Ohm).
Amplifiers included in tests are my own 300B SE "Fugue" Design, a 300B PSE Design, similar in circuit to the Audio-Note P4, a 300B PP Amplifer based around the same components as the PSE Unit (indeed the unit was switchable PP and SE for a while), 2A3 SE and PP amplifiers, an 845 PP Amplifer, a 813 (triode wired) PP Amplifer as well as a commercial 211 SE Amplifer. Also tested where some Croft OTL Amplifers, Quad II, Leaks and so on...
I dare say that so far my own little 300B SE Amplifer has stood tall and managed to comprehensively outperform ANY commers by a good margin. It offers a putity of tone and a degree of transparency and delicacy matched by little else.... However, when needed it has serious BALLS, enough to kick a pair of Watt/Puppies to serious levels....
Ciao Thorsten
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- Re: PP vs SE - Thorsetn 04:04:39 11/15/99 (0)
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