John Curl's Blowtorch preamplifier part II

[SY]

You haven't shown any results whatever, much less a method. Nothing. Nada. Zip. Bupkis. Rien. Nichts.

[john curl]

Now, what do I think about circuit construction? I think that WHEN you use the 'best' parts, the best circuit board material, best soldering quality, etc, etc, then this 'estimate' that I make for the reduction in higher order distortion will drop to ridiculously low levels in normal operation, and 'third order' effects will not dominate. That is what I try to convey here, and one of the 'secrets' of successful audio product design.

[john curl]

Do the math, SY.

[wahab]

Originally Posted by john curl

Now what about my 'estimate' of the Blowtorch's harmonic distortion?

So what is your estimation , actually ?...

Even a number with one or two order of magnitude error would
be infinitly more accurate that what followed this sentence of yours...

[SY]

Originally Posted by simon7000

That's the -40

OK, then let's do the math without the need for a codex. If I have a bare bones supply (cheap 10,000uF/25V cap, no fancy choke or extra RC) and a whole pile of circuitry (let's say 100mA of draw), raw supply ripple is 120mV. At your chosen 3kHz, harmonics are -40dB wrt 120mV. A 7815 will knock that down another 55dB (and a 317 with cap bypass will be about a hundred times better, but let's stick with a 7815). 797 knocks that down another 95dB. So there's our line stage. The power amp is likely to have 26dB of gain. Overall, then, we deliver a signal -164dB down from 120mV at the speaker terminals (something less than a nanovolt). I haven't taken the math further, but I bet that's pushing the thermal noise of the voice coil.

[SY]

Originally Posted by john curl

Do the math, SY.

Show data to support your claim, John. Or man up and admit that you simply don't have any.

[john curl]

I would like clarification on your criticism, wahab. Did you not understand what I put forth as the METHOD of estimating harmonic distortion with level?
I realize that many of you are probably suspicious of such an easy mathematical process, but I was exposed to it for many years with analog tape recording, in which the 3'rd harmonic (totally dominant because of the tape itself) could be reliably predicted, over and over, with different recording levels, once a single distortion with level was measured.

[Chris Hornbeck]

One strong conclusion leaps out though: class A operation gets a lot of the work done. We may already know it, but doesn't hurt to be reminded.

Thanks,
Chris

[fas42]

Originally Posted by Chris Hornbeck

One strong conclusion leaps out though: class A operation gets a lot of the work done. We may already know it, but doesn't hurt to be reminded.

Thanks,
Chris

Because, the power supply is nice and relaxed doing its job: that's a major part of the story. Stress, nasty current spikes in that area equals crappy sound ...

Frank

[RNMarsh]

Originally Posted by gpapag

Leg pulling.
With waveguides the second conductor has no meaning.
EM waves have already been generated (e.g. by an antenna, a klystron tube) just before the entrance of the wave guide.
We tap the wave’s EM energy after (or just at) the end of the guide through an EM sensor (e.g. antenna)

The wave guide just confines the wave to propagation. Waves are confined inside the wave guide due to total (should) reflection from the wave guide walls.
Cross sectional shape of the guide has to match polarisation mode of the already generated wave. Cross sectional dimensions have to match wavelength.
Electric field is (should be) perpendicular to the wall.
Magnetic field is (should be) parallel to the wall.

These last two could and do happen within a coaxial cable as well.

The similarities stop when we think of the way we feed energy to and tap energy from in the case of the cable .

We apply an electrical potential difference between the inner and outer conductor.
We tap another potential difference between the inner and outer conductor at the far end of the cable.

What happens in between –how to explain the energy propagation- is the puzzle of my late life. The chicken and egg problem.



That’s why I refered to it.




Charge diffusion (ha, ha we can't get away with that so easy), eddy currents generation, counter magnetic action, finally leading to skin effect. All dynamically influenced by time. I agree.
The (many) nonlinearities observed all these years are due to materials variables.
Our recent problem as it seems is not the skin effect’s effects but how the proximity effect’s effects indicate an inherent (theoretical derived) frequency distortion.

Does Fred. W. Grover's book says anything about this distortion?

George

Comments -- skin affect and proximity have the same affect... but are caused by different means. The lowering of inductance is what causes the currents at higher freqs to flow in that region of the 'skin'. But what causes that to happen? The wire(s) geometry causes electromagnetic fields to be concentrated more and less across the conductor. In a round conducting wire the field is concentrated -denser- at the center... thus the center has the higher inductance. Where ever the fields get concentrated, the inductance is increased. Proximity can reduce inductance but it is not evenly distributed or symetrical anymore.. as skin affect is in a single conductor or a coaxial arrangement. does this asymetry result in harmonics generated ... I dont know. Maybe. Or would it present itself as group delay? But would be geometry dependant.

Without further adoooo.... In a coax configuration --> the dc resistance and the high freq 'resistance' from skin affect can be such that the ratios of the two 'resistances' become >>1. If one wanted to maintain a ratio of 1:1, then you could use a twin-axial cable design without using the center conductor at all. the two closely spaced shields or 'tubes' with a thin dielectric between them will do the trick. And, if the two tubes or 'shields' were made of a single layer of spiral wrapped individual insulated wires (small gauge) at 90 degrees to each other, the inductance will be very low and the dispersion will be very low. But the C will be high... no problem if the driving stage has ample current drive capability -- such as a power amp and wire cable interconnect.

Thx- RNMarsh