Short signal paths? What short signal paths?

[petercom]

In reply to Ianm2 and others in the crossover debate, I thought it might be pertinent to continue this discussion in a dedicated thread.

I doubt that you should consider the length of wire in a transformer as strictly being 'in the signal path'. The trouble with electromagnetism is that we are working with things we really don't fully understand. We work with amplification by visualising what is going on as current and waves and 'potential' or voltage. None of these really exist as what we are actually working with are changes in charge fields in, and around, structures that channel the movement of charge and energy. Once you get into quantum theory you begin to realise that our concept of 'electricity' is ridiculously simplistic and doesn't at all describe what is really happening. But it is, obviously, a useful paradigm as the electromagnetic theory is built on practical examples and allows us to use it to design.

So, to my mind, the signal doesn't travel 'through' the winding of a transformer to get out the other side! Instead the signal develops in the primary of the transformer a field which creates a potential in the secondary. It does this near instantaneously and this practical application of magnetic field transfer makes transformers very useful things indeed. Having grown up with transistors I tended to regard transformers as bad things to put in the signal path. However once I had heard a few good transformer designs I realised how good they can be. For example there is common consensus that a good MC transformer is better than an amplifying stage 'head amp'. And interstage transformers offer a good alternative, though the design is hairy, to valve driver stages.

Now from that we can start to look at inductors. You would imagine, using the simplistic view of electricity, that the signal has to travel 'through' the wire in a series inductor in order to get to the drive unit. I would like to promote another way of looking at this. When the signal is present in the inductor coil it creates a field which affects every part of the conducting parts of the inductor at once. The creation and collapse of this field is restricted by the core such that the strength of the field is reduced as the frequency increases. The signal at the output end of the core is therefore a result of the field within the core. We can experiment with this idea by putting, say, a shorted coil in the inductor which dramatically alters the field behaviour. The coil also has a resistance to the transfer of charge potential, but this is a DC effect and is, invariably, mixed up with the AC field effects. Whatever, it is probable that the signal is present at the input and output ends of the coil but doesn't have to travel 'through' the metres of cable in the inductor in the way we like to think it does based on the concept of 'current'.

Of course you can also think of the same thing happening within a moving coil speaker drive unit. If it was really the case that loudspeaker cables have a different sound because of the 'goodness' of the materials used for the transfer of 'electrons' then their sound should, of course, be negated by the rubbish wire we use for crossover inductors and speaker voice coils. But the fact is that many of us can hear the difference speaker cables make and, therefore, there is something else going on. So, for example, if we reduce the speaker cable to an impedance and see how this acts as an interface between the speaker/crossover and amplifier then we can start to see that the interface effects are more important than the quality, or 'goodness', of the materials used.

It makes me smile to look at the BS promoted by some cable companies as to the 'goodness' of the materials in their products to enhance the 'flow of electrons' when inside the equipment these cables are connected to all the signals have to travel through all sorts of 'not good' materials, PCBs being a prime example. In my view it is far more instructive to consider all the components and methods of signal routing as impedance transfer devices which, to my mind, fits theory and practice together in a more practical way.

(continued)

[James D]

Interesting idea but I'm not sure I entirely agree. For instance the wire and hence the dcr component of the transformer is definitly in the signal path and its effect can be quantified in theory and measured in practice as existing with the inductance that the coil produces. Energy considerations show that not all of the energy goes into the field and that some does indeed go into moving the current through the wire that comprises the coil... so we can't just ignore the wire. At the same time I completely agree that we don't understand how the E/M field is generated by the current varying through the coil. At a phenomenological level we can describe what happens and quantify it 'exactly' - Maxwell did a very good job, but the fundamental generation mechanisim escapes us... At least with a transformer we know where the field energy goes as it is captured by the secondary and collapsed back to current in the wire (ignoring losses) but how does an inductor work? The field gets generated by the varying current in the coil and then collapses back into itself??? WHat does that mean? Ina psu you can sort of work it out in terms of stored energy but for a signal coil its doesn't work the same way at all...

Still coils and iron in an amplifier are very helpful things - and I ended up using them in my sand designs before going back to tubes

James

[Dave the bass]

Originally Posted by petercom

Having grown up with transistors I tended to regard transformers as bad things to put in the signal path. However once I had heard a few good transformer designs I realised how good they can be. For example there is common consensus that a good MC transformer is better than an amplifying stage 'head amp'. And interstage transformers offer a good alternative, though the design is hairy, to valve driver stages.

Thats intresting Peter. I too have 'grown up' with transistors and my first experience (aged 18 ish) with transformers actually IN an audio cct not a PSU was my first ever home built bass guitar amp.

It was a 'Tuac' transistor power amp that had a transformer in the signal path, I think the phase splitting was done with the Xfmr, can't remember TBH. I remember it had terrible cross over distortion that really showed up on long sustained notes. Sounded like a a crisp packet type rustling under my playing but because I was strapped for cash at the time I made do with it.

At that time I thought the Xfmrs were the cause (maybe I was wrong) so I used to associate them in Audio ccts with poor quality/**** sound. Fast forward to 2006 and HFW, there's a review of the Eastern electric Valve Phono pre-amp stage that uses 2 Xfmrs in the first stage of MC amplification. It was awarded 5 Globes, funny how my early experiences can lead predujices that are later proven wrong later innit!!!

DTB

[petercom]

So where do valves, transistors and ICs fit into all this. Well the one thing we are able to do is look at the signal transfer through a device in its simple state. The valve is ideal for this as we can literally see the space charge in the valve and how the various charge modifiers (grid etc) in the valve work. Most valves are highly linear devices because of the eons of work that has been done on them. When we consider transistors, however, things are not so clear as we are trying to look at the device at a quantum level (transfer of 'holes' across semiconductor boundaries for example). What we do know is that transistor characteristics are very non-linear and we wouldn't be able to make amplifiers with them if it wasn't for considerable levels of feedback. Translating that to ICs we are just packing more transistors into a small space and using greater amounts of gain to compensate for greater amounts of feedback. It might look fine and dandy when we compare input signal to output signal from a good IC, but there seems to be a valid argument that high levels of feedback do not compensate for non-linearity in the amplifying devices in a way that is satisfying to the amplification of music signals. Unfortunately what is going on inside an IC is at the mercy of the designer and to us they are just black boxes with input and output terminals.

To my mind the main thrust of the acceptance of semiconductors in the hi-fi market has been through higher and higher levels of feedback compensated for by even higher levels of gain. I'm not sure this is getting us anywhere. As a result I would rather stick with the valve as a superior amplifying device.

[Ianm2]

Originally Posted by petercom

What we do know is that transistor characteristics are very non-linear and we wouldn't be able to make amplifiers with them if it wasn't for considerable levels of feedback.

To my mind the main thrust of the acceptance of semiconductors in the hi-fi market has been through higher and higher levels of feedback compensated for by even higher levels of gain. I'm not sure this is getting us anywhere. As a result I would rather stick with the valve as a superior amplifying device.

hmmm, I can't entirely be comfortable with point 1, as a student of solid state amplifier history, there have been class A output stage designs with no loop feedback.

With regards to distortion, unquestionably, the transistor (don't misinterpret that ) as much as can be is a far more perfect device when implemented as a whole, ie. a transistor amplifier is far more perfect w.r.t. measured performance.

Tubes measure appalling, but as we know, its obvioiusly no indicator of aural pleasure.

And the goal of hifi engineers, is to correlate aural perceptions with measured parameters.

Engineering will go on, and on to try to get that perfect device, that is its aim, its goal, almost its predestined fate.
that's the only way it can work. That's how it works, by maths.

But of course it needs feedback, from an engineering point of view, feedback is excellent if used correct.

This is what the old boys, langford-smith calls fidelity-statistics being better.

Indeed he goes on to say about the worrying aspect that people underwent tests and was troubled by the fact they preferred some (2nd H?) distortion to it not being there.

That's an engineer through and through, obviously, one designs to the parameters that one can see and are known. ANd that's why I say you can't engineer in a sound, by sound I mean, what circuit configuration will give excellent imagining and space....I don't believe that can be designed in.

Its very hard to get across what I mean there. ( perhaps a good way of saying what I mean, is, if you listen to a system, and hear something in it, a certain sonic character, I bet no designer in the world could reproduce that on demand in an electronic design, or in other words, design an amp., say with glassy midrange, how do you do it? imo not possible)

Finally, it is true to my knowledge, that its not the components one uses, I have heard some incredible sounding units with opamps decried....5534s, tlo72s. By none other than my keywood.

and I have heard some very poor implementations, I put it down to whether the designer is good bad, or doing something to a cost, or just doen'st know at all.

Its not what you use, but how you implement it.


Some transistor amps can very nearly approach valve amps for that 'sound' the presence, ambience, space, and sheer presence you get.

however, as I have always maintained, I am a valve person at heart myself, ad am only using tranny amps for convenience.

I still will be having a go at a small single ended amp.

It is an extremely moot point to question if the signal goes via 1/2 a mile of wire in an output tx, or just sees the magnetic core, or not even that, just sees the secondary.

I have no idea, but its a useful argument to sceptics, about a big core of iron and half a mile of wire.

shuts them up stone dead

Is this a digression to the thread?

[Darren D]

I always thought the comparative to water flowing through pipes gave an easy way to comprehend electrical flow.

We all know that electrons flow from negative to positive, quite the opposite to current.

In reality, I'd been led to believe than nothing flows at all, rather an excited electron simply excites the one next to it and so on down the chain. Rather like sound waves.

Then we have the flow of electrons across the "valve" space, called the space charge.

Are they flowing or not?
It's all very confusing......

[Richard]

Originally Posted by Darren D

I always thought the comparative to water flowing through pipes gave an easy way to comprehend electrical flow.

We all know that electrons flow from negative to positive, quite the opposite to current.

In reality, I'd been led to believe than nothing flows at all, rather an excited electron simply excites the one next to it and so on down the chain. Rather like sound waves.

Then we have the flow of electrons across the "valve" space, called the space charge.

Are they flowing or not?
It's all very confusing......

Yes it took me a while to relax about having long speaker leads until I considered the op TXs, wirewound resistors, inductors, and voice coils.

The water analogy is fine but in a contained way as in hydraulics - push your car brake pedal and the caliper piston moves instantly. There's no time delay - if the pedal moves so does the piston - and the end applying the pressure isn't the same as the end doing the work. A bit like prodding something with a stick

There will be losses as heat due to LCR and perhaps things we don't understand. There may be material issues such as crystal boundaries within conductors and chemicals within caps which cause small disturbances in the transfer of energy.

Rich

[Darren D]

Yes Richard, Hydraulics gives a better picture than water flowing through pipes.

[petercom]

Now this is getting interesting (as I knew it would).

Darren, you are quite right, electrons don't flow but the charge is transferred through the conductor at the speed of light. The water analogy is close, as Richard points out, but it is still too simplistic.

Ianm2, I'll take it step by step.

Simple Class A transistor amps can be created with no loop feedback by using substantial local feedback. They sound OK, but a valve in the same circuit sounds much better.

Feedback has only been considered a 'good' thing once everybody started getting hooked into steady state distortion measurements and the stability problems were 'solved' for steady state signals. Implementing feedback that copes with transient signals is far more difficult and such circuits can easily be tripped up.

The human ear has difficulty hearing levels of harmonic distortion below 2%. Why, then, are we so intent on making transistor amps that have 0.001% if a valve amplifier with harmonic distortion hovering around 1% or less is preferable to our ears? The answer is, of course, a commercial one dictated by designers and manufacturers who are looking for a measure of 'goodness' and steady state distortion is easy to measure. But transistor amps are very convenient devices to use compared to valves, so they have their place in the scheme of things. It's just easier to demonstrate how valves are superior for the amplification of music.

[Primalsea]

Peter from what you say it would be easy to think that you could snip the wire in an inductor, half way through its coil and it would still work.

Surley something has to come out of the other end for the field to be generated.

Cyrus say their amps are zero feedback and have very low distortion levels. In a review once it said distortion increased from somethig like 0.000018 to 0.0001 as frequency increased.

Oh my god, how can we be happy with that sort of increase in distortion!

The Cyrus amp one the group super test in the mag. I heard some cyrus gear once and felt like someone had sand papered by brain for 15 minutes.

In many ways the phrase "let your ears be the judge" carries a lot of weight. I try my best just to comment on what I think, based on my experience. Its very easy to have your perspective bent by the media.

The problem is many of these hi-end manufactures also use this phrase but along with marketing designed to make you feel you like their sound.

I always thought that the idea of a signal traveling from source to reciever is just a convention as it's easy to understand. I thought that the signal is really a force that travels from an area of high electron density to an area of low electron density.

This would mean that stuff flies backwards and forwards all other the place. If this is so how can cables be directional? Well, Just let your ears be the judge my friend.


posted by befuddled of forgotten location