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Thread: The Loyal Opposition, or IMO (comparing a 25W amp with a 50W one)

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    Default The Loyal Opposition, or IMO (comparing a 25W amp with a 50W one)

    I will take a position, that may be dangerous on this forum. Having just purchased a solid state amp (LFD Zero Mk. IV) after using a tubed amp (restored/modified H H Scott 222c) for the past 18 months with compact 7's, THERE IS A DIFFERENCE. I did double the power, but I don't think that alone accounts for all the difference. Perhaps it's differences in distortion levels, but I would describe the tubed amp as "warmer". In my opinion the bass is much "deeper and tighter" on the SS amp. Perhaps this would show on a frequency response graph, or maybe it's due to the increased power controlling the woofers, or both.

    I know comparing a 25 wpc amp with a 50 wpc amp is comparing apples to oranges in some respects, and I do not have an A/B switch. Both amps do provide a satisfying musical experience that might be somewhat dependent upon the program material. For example the tubed amp shines on most jazz recordings (warmer ?), and the SS amp seems to do best with symphonic recordings (bigger and detailed ?). Just my two cents. (a Yank expression !)

    Dennis Girard

    {Moderator's comment: so something with twice the gain sounds different from something with half the gain? And you are surprised???!!! Kind of logical wouldn't you say?!}

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    In the United Kingdom we don't have "two cents" but we do have "two penneth" (two penny's worth)!

    So my two penneth:

    Going up to 100w might see more of the differences - better bass control, greater clarity (assuming you have a good 100w amp) - more headroom before the amps starts to distort on the peaks. Such clipping distortion would not be noise in the harmonic series, and therefore not pleasant.

    Of course most of the time the system is trundling along under 1w, but when someone hits a cymbal or fires a cannon you need a bit of fast clout.

    http://en.wikipedia.org/wiki/Clipping_%28audio%29

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    Maybe at least some of what you're hearing is the difference between the harmonic distortion levels between the two amps, accounting for the tube amp's "warmer" sound (see the recent thread on harmonic distortion)?

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    And note should be taken of "soft clipping" as described in the wikipedia link above.

    It is much discussed. In general valve amps have more but more friendly distortion. As a generalisation valve amps "soft clip" and transistor amps "hard clip". The rounded corner of the soft clip as seen on an oscilloscope is a lot less audible and a lot more benign than the sharp corner of a "hard clip" that sends energetic harmonics shooting up into the ultrasonic and even radio frequencies.

    See also the "Valve Sound" Wikipedia referenced in the earlier link

    http://en.wikipedia.org/wiki/Valve_sound

    I wish I could still do the maths, but it's a long time ago . . .

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    I think the next steps in the Amplifier Harmonic Distortion thread here may cast some light on this nature of tube v. transistor amp distortion. I'm trying to make the time to scan some pages from my archives.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    Default The loyal opposition responds

    Could someone enlighten me on the role that current plays? I believe a high current 50 wpc amp may be (sound) better than a 100 wpc amp.

    Dennis Girard

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    Default Current is not pushed to the speakers, it is pulled from the amp by the speakers .....

    There is no correlation what so ever between current (capability) and sonic performance.

    Remember .... the current is drawn from (pulled out of) the amplifier. It is not 'offered to' the speaker. So, for a given speaker at a given replay loudness there is a fixed current that is being drawn from the amplifier regardless of the make of amp, the model, the specified power rating. tube or solid stated design of the amp etc. etc..

    Furthermore, for a given speaker at a given replay loudness there is no advantage whatever in having oodles of surplus power potentially available in the amp i.e. buying an amplifier that is capable of massive currents or wattage. If, for example, for a given loudspeaker playing at a given replay loudness, 5W is being pulled from the amp maybe a 25W amp would give you all the headroom you'd ever need for when you want to play the 1812 Overture loud. Beyond that 'safety margin' it doesn't matter how brutally massive the amp is and how back breakingly heavy, if 25W is all you need to have available the fact that the amp is capable of 150W, 500W, 1kW is a complete waste of money. Specmanship sells complicated, heavy (and possibly beautiful) massively over-engineered amplifiers to those who have no comprehension of how little power a speaker needs or can handle.

    If you don't drive at 180mph you don't need a highly strung engine that revs at 7000rpm and nor should you pay for one - and for the accentuated risk of premature failure.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

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    I have yet to see a decent article on the power and current delivery capacities of an amp. I have always supposed that the issue in question is "Wattless Current", or "Wattless Power" and its associated concept "Power Factor".

    If you can follow the maths, it's here

    http://www.cip.ukcentre.com/Power%20Factor.htm

    http://en.wikipedia.org/wiki/Power_factor

    If a generator (or an amplifier) is driving a pure resistance all is simple, but if the generator is not driving a pure resistance but a reactive load (that fights back) the current and the voltage can rise and fall at different times. They are said to be out of phase. In such circumstances the generator (or amplifier) is wasting effort - a current flows that does no useful work.

    Those who manage mains electricity supply are very keen to minimise this effect because it costs money and fuel. The electrical engineers want to keep the Power Factor as close to one as possible.

    An audio amplifier is not driving a simple resistance, but a complex reactive load which has resistance but also inductance and capacitance. In some circumstances and at certain frequencies the voltage and the current can get so far out of phase that the amplifier runs out of steam - it cannot deliver sufficient current to the loudspeaker even if that current when it gets there is destined to do no useful work.

    Alan says Harbeth speakers are designed to present an easy load to a amplifier, so he must have worked hard to achieve that - not all speaker manufactures set so high a priority on this.

    I say again, the notion of "Wattless Current" and "Power Factor" I have only come across in the physics mains power distribution, but I am guessing the same principles apply in audio. I have no idea how the design of an amp affects its capacity to deliver into difficult loads. It is simply a matter of upping the brute force, or are their other factors?

    Can someone point to a decent online article? I cannot find one.

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    Quote Originally Posted by A.S. View Post
    I think the next steps in the Amplifier Harmonic Distortion thread here may cast some light on this nature of tube v. transistor amp distortion. I'm trying to make the time to scan some pages from my archives.
    Hope measurements of this amplifier help the weave of that thread. It is a low powered tube amp,

    http://www.stereophile.com/content/m...r-measurements

    Imo, think tubes can indeed sound rich, weighty, comfortably nice, warm and maybe even give the impression of being “powerful”. A wall of sound. Cleaner amps can sound transparently crystalline. Imo low distortion amps are a slowly acquired taste. Its easy to like a tube amp but think they tend to bring music to a median point rather than showing the truthful poles.

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    Quote Originally Posted by Labarum View Post
    Can someone point to a decent online article? I cannot find one.
    try this...

    http://www.bcae1.com/hcvsnohc.htm

    in short... all things being equal, to make an amplifier more current oriented, reduce the supply rail voltages for the power amp section. The output power will be less as a result, but it won’t sag under low impedance circumstances. Its hard to have the cake and eat it too.

    There are very affordable amps out there eg. Some Yamaha integrated have a switch to choose either “voltage” or “current” preference for the type of speaker being used.

    In any case, high current is not required for Harbeths, and personally think High Current capability is either an amplifier marketing gimmick (because not all people need it), you plan on hooking up parallel pairs of speakers, or someone has really hungry pair of speakers.

    I can however see some Japanese amps which have very modest power ratings but well specified power supply stages which look like they can really deliver both voltage and current. The size of the power supply transformers and supply capacitors are a tell tale sign.

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