Music Fidelity to make copies of BBC LS3/5A speakers

[mechanic]

That was the Sonus rep, not a John Lewis salesperson.

Also hard to see where any tones less that 500Hz or so, come from.

[Pamela]

[Trevor Wilson]

**Excellent. I have a couple of 33/303 units here, awaiting restoration. Should earn me a pretty penny.

Just because people want to pay big Bucks for them, doesn't mean they're good amps though.

[Animal]

+1. The II was excellent, the 22 tolerable. Their followup the 303 was a big fail. They should never have released it imho.

[Joe]

Quite robust, though. One university student union used them as disco amps in the early 70s, fitted with jacks instead of DINs.

[mechanic]

They have other interesting offers, like the Audiolab 8000A for 750 UKP. The refurb details are impressive.

[The Natural Philosopher]

Nope. Same with Marshall Valve amps

[Trevor Wilson]

**I'm pretty certain Phil will chime in with his opinion on Marshall valve amps. He experience with musical instrument amps is quite extensive.

[The Natural Philosopher]

I have one, its relative crap, its worth about £800. I have two sub £100 Fender solid state amps that are in almost every way infinitely better.

[Joe]

Valve amplifiers used to be favoured because of their distortion and greater difficulty of destruction, didn't they?

Then later, valve hifi amplifiers came into vogue because they were stupendously expensive and fashionable.

[Woody]

The main thing about valve amps is/was that their main distortion is second harmonic to which the human ear does not object. IMSMC whilst much above about 0.5% third harmonic sets your teeth on edge, north of

5% second harmonic is just not heard. Indeed a violin produces more second harmonic than fundamental and speakers equally have relatively high levels of 2nd and they don't sound too bad do they?

[Animal]

Another difference is hf distortion. Specs are at 1kHz, tranny amps rise a lot by 20kHz, decent valve amps not as much.

[Trevor Wilson]

**SOME humans accept even order harmonics as OK. I and many others, do not. Less distortion is always better.

IMSMC whilst

**Not so. It has been generally accepted that, under careful listening conditions, that humans can perceive around 0.1% THD.

Indeed a violin produces more

**Most musical instruments produce large amounts of harmonics. That does not suggest that adding extra harmonics is a good thing.

and speakers equally have relatively

**Nope. High quality speakers typically exhibit low levels of distortion. In fact, some speakers produce lower levels of distortion than many valve amps.

Distortion (100dB at 1m) Above 1000Hz 0.15% Above 100Hz 0.5% Above 50Hz 1.0%

Harmonic distortion

2nd and 3rd harmonics (90dB, 1m on axis) <1% 30Hz - 20kHz <0.3% 100Hz - 20kHz

[The Natural Philosopher]

The big problem with early transistors were that they were not fast and could not handle high queisecentt power: that led to under biasing in audio class B and crossover distortion which sounds horrible at low signal levels. Especially at higher audio frequencies. The Quad 303 was an example,. It tested out ok at moderate power at 1Khz, but look at

5hkz and a few hundred mW and it was awful. Once faster FETS came along and faster transistors this all became a thing of the past. A bog standard class D chip today will outperform a Quad 303 or a valve amp any day. For hifi and indeed for guitar *until you overdrive it*.

Then the valves inherent low feedback/soft clip is a bit more melodious than a hard clipping tranny amp, but modern guitar amps actually do signal shaping before clipping anyway, to simulate valve overload. My 'all digital' Fender can produce almost any sound you ask of it.

[The Natural Philosopher]

No, it isn't. Not where it counts on a symmetrical class B output stage.

to which the human ear does not object. IMSMC whilst

Mostly crap. The reason valve amps sound better is that the overload more gracefully so cloth eared hifi nuts get less high order ODD harmonics.

So 20W valve amplifier operating at 1% distortion will sound better than a 20W tranny at 1% distortion.

But a 100W tranny operating at 20W will sound better than either. In hi fi apps.

For guitar work the 20W valve will, all other things being equal, coupled to a suitable non linear response loudspeaker and cabinet, sound better than either, especially with negative feedback totally absent, Cf the VOX AC30.

[Fredxx]

Agreed, a typical push-pull valve stage into a transformer will have odd harmonics.

A singled ended class A valve output will have even harmonics. But these are rarely use as they are incredibly inefficient.

<snip>

Guitar amplifiers are all about distortion and harmonics!

[The Natural Philosopher]

The problem with loudspeakers in not distortion - at low sound levels they are excellent - its only when they are pushed to the limits of the cones travel that distortion increases. It is *resonance*. In practice you 'hear' the loudspeaker, not the music. This is perfect for electric guitars, as the loudspeaker is like the sound box of an acoustic guitar, but is its non ideal for hi fi. Hence the whole idea behind the KEF Bextrene cones. Stiff, and inherently 'dead' . And the idea behind multi element speakers, so that each speakers resonance was not where it was called to operate by the crossovers.

The adage 'Carbon fibre destroyed the point of Bextrene' has an element of truth., A good soft spider roll surround CF coned bass/mid range car speaker is actually better than a KEF unit and can be had for a few quid. Or Kevlar honeycomb. Tweeters haven't changed much and plastic or metal domes are almost universal with maybe silk cloth domes for mid ranges. I personally will always be a fan of compressions drivers into loaded horns, and some of the JBL style mid range and tweeter horns we used in disco and PA applications were way cleaner sounding than almost any HiFi setup except perhaps Quad ELS, but could still kick out 115dB on the dance floor. And at very high power - well above domestic listening levels - distortion does become an issue as cones and diaphragms get pushed to the limits of their travel - compression drivers operate at far higher pressures and lower movements and do not distort at very high power indeed.

But for domestic use a good selection of 3 ways bass/mid/tweeter is very adequate.,

[Trevor Wilson]

**Correct.

**Somewhat crap. The reason why SOME valve amps are preferred over SOME SS amps is due to their overload characteristics. There have been and still several schemes that very effectively allow for 'soft' Voltage limiting (aka: clipping) in SS amps. Some schemes include:

• A limiting circuit placed outside the feedback loop. (NAD et al)

• A system which ensures that output devices are never allowed to saturate, combined with zero global NFB. (ME et al)

• Some pro amps I've seen use a PTC element outside the feedback loop.

• Digital systems also can be used.

In fact, I've measured a few high(ish) global NFB, push pull valve amps that exhibit quite brutal clipping character.

**Again: That is a pretty broad claim, which is not necessarily true.

**Again: That is a pretty broad claim, which is not necessarily true.

[Trevor Wilson]

**That's correct. And it is (non-linear) distortion that we are discussing. Modern, high quality speakers can exhibit lower levels of distortion than many valve amps.

- its only when they are pushed to the limits of the

**Not relevant to the discussion. High quality speakers are built to address the issues surrounding enclosure problems.

**Of course. And irrelevant to the discussion.

[liang sek]

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