Valve power - feel the force!

[Ali Tait]

Perhaps so,but as I said earlier,if your speakers are sensitive enough,clipping will not occur.

[Marco]

Indeed, Ali. I know all too well what clipping sounds like and there was none at the levels I was listening to Tiesto at last night! The system just rocked in a very brutish and uncouth (but non-distorted) way, which is perfect for dance music, but maybe not so for those with more delicate sensibilities!

Marco.

[anthonyTD]

I (respectfully for anthony only, as a fellow engineer) disagree entirely. Feedback has nothing to do with it, that simply sets the gain. The reason is that the rise times are MUCH faster in a ss amp, therfore allowing it to emulate a square wave much more readily. This is what produces the prodigious harmonics.

Because a valve amp has it's output transformer in circuit, that has considerable inductance which modifies the wave form to approximate a sinusoidal one rather than a square wave.
This is the whole problem with output transformer design, to allow a small enough inductive effect to pass the higher frequencies accurately, rather than suffer HF fall-off, which incidentally, since it's on Chinese transformers, Marco's amp probably suffers from as well.
Therefore the output from a transformer coupled valve amp clips in a "sinusoidal" fashion and produces "musical" harmonics.
Whereas the ss amp clips in a much more flat topped fashion, more approximating to a square wave, with horrible sounding harmonics.

BUT, if you make the ss amp very powerful so that it doesn't clip then it sounds the best of all. (providing you haven't got to like the sound of valves clipping and confuse it with "musicality").

p.s. all this is very easy to see on a scope and that is the way you can "educate" your ears !

jc,
i use signal generators and scopes to test all the equipment that comes through my workshops, and i am quite aware of what an amplifier looks like when clipped, i also test them for frequency response at diffrent levels of power output. marco's amp tested well, it gave a true 60 watt RMS output into a constant 6.8 ohm load, at 1khz. its frequency response was flat from 7 hz to 100khz tested at half power!
the best solid state amplifiers i have heard are the simple ones, ie, using the minimum amount of devices, with the least amount of feedback, but sadly only producing around 10 watts. also, the first transistor amplifiers which by the way sounded pretty good when using gemanium [spellin] transistors were transformer coupled, like valves!
you hit the nail on the head when you said about using feedback sets the gain, feedback does various things when used in amplifier designs but the main three things it does are, reduce distortion,[ by linearising] increase damping factor, and de-crease gain!
anthony...

[Marco]

marco's amp tested well, it gave a true 60 watt RMS output into a constant 6.8 ohm load, at 1khz. its frequency response was flat from 7 hz to 100khz tested at half power!

As they say in Scotland, JC, GET IT RIGHT UP YE!

Read and weep, sweety, and stick yer "30W" bollocks up your ample-sized bottom, haha...

Marco.

[jcbrum]

Ali, Well ok ish, but it really depends how far you turn up the gain.

For those of a practical nature, it might amuse you to hear that the amps I use have no external gain controls, and are set to full volume without clipping all the time. therefore I know that they cannot clip till the drive voltage exceeds 2v peak.

[Marco]

Once was more than enough!

Marco.

[anthonyTD]

Well ok ish, but it really depends how far you turn up the gain.

For those of a practical nature, it might amuse you to hear that the amps I use have no external gain controls, and are set to full volume without clipping all the time. therefore I know that they cannot clip till the drive voltage exceeds 2v peak.

most valve amplifiers usually run their driver stages wide open, and are easily capable of receiving a 2v peak to peak signal without a hint of clipping!
some valve grounded grid pre-amplifiers i have made over the years will except many times that without clipping!
anthony...

[Mike]

(did you look it up ?)

Erm... Yes.

[jcbrum]

jc,
i use signal generators and scopes to test all the equipment that comes through my workshops, and i am quite aware of what an amplifier looks like when clipped, i also test them for frequency response at diffrent levels of power output. marco's amp tested well, it gave a true 60 watt RMS output into a constant 6.8 ohm load, at 1khz. its frequency response was flat from 7 hz to 100khz tested at half power!
the best solid state amplifiers i have heard are the simple ones, ie, using the minimum amount of devices, with the least amount of feedback, but sadly only producing around 10 watts. also, the first transistor amplifiers which by the way sounded pretty good when using gemanium [spellin] transistors were transformer coupled, like valves!
you hit the nail on the head when you said about using feedback sets the gain, feedback does various things when used in amplifier designs but the main three things it does are, reduce distortion,[ by linearising] increase damping factor, and de-crease gain!
anthony...

I have some early transformer coupled amps in my collection. I bought them new in 1967 I think.

So Marco's amp is only flat at 30w, that's what I expected. I wouldn't like to guarantee how long it would deliver 60w on a warm day !

Have I got this wrong or am I right in recalling Marco's amp has 2x KT88 per channel ?

[jcbrum]

most valve amplifiers usually run their driver stages wide open, and are easily capable of receiving a 2v peak to peak signal without a hint of clipping!
some valve grounded grid pre-amplifiers i have made over the years will except many times that without clipping!
anthony...

Yeah sure, but will they deliver 500w at that setting ?