Not that I want a Mercury Magnets tranny Moose, it is just that you know your trannies. Do you know if those guys at MM ever cloned an original Pacific? They advertise to send your vintage in and they will clone it.
Mark
I played an Express clone that utilized the MM "Wreck" transformers. It was bright, way too bright for me.
I totally missed Mark's original question. I apologize for that.
I don't know anything about the MM wreck tranny. Don't know where they got the design, what they based it on, or anything.
Thanks for chiming in with your experience.
I'm really sorry for this thread derailment. The discussion seems to have confused some people even more! Especially folks who weren't here back when folks were actually feeding misinformation to the people trying to dissect these circuits, or during the years before a few of the local heavies got their hands on the real deal and revealed all. It has been a long, interesting learning experience for a lot of us.
I was reading Mercury Magnetic website and ran into this FAQ. I was a bit surprised. I always thought that the saturation aspect of the transfomer offered the dynamic non-linearity that not only shifted frequencies around, but also provided some "give" to the amps response. I thought this was a "good thing".
Am I off base?
Thanks,
Robbie
core saturation:
The condition where the core material (usually iron) is completely magnetized. Any further increase in input energy will not produce an appreciable increase of magnetic flux. When this happens, the inductance of the coil is greatly reduced because no counter EMF is produced when the flux is unable to increase.
Myth: "Transformer saturation is a part of my amp’s distortion; it is an important part of my tone." -- Knucklehead Smith
Wrong! Don’t you believe it—nothing could be further from the reality! Audible symptoms of this type of saturation are the absence of bass and the fuzzing out of your mids along with dark and dull treble frequencies. Does that sound like something you find desirable? Core saturation also greatly increases running temperatures of the transformers and tubes. Your amp at this point is crying out in pain! Sorry, not the best working environment for your amp and for your tone. Think of core saturation as playing with a virtual noose around your neck (and your amp's tone). It's a bad thing
I believe MM's take on core saturation is a true statement and I have been saying the same thing for years. IMHO, if you are saturating your OT then you have an undersized OT for that particular amp and it is going to fail sooner or later. There are a lot of types of distortion. Most people, Guitarists and ampbuilders, think of clipping when talking about distortion. Distortion is actually defined as any change in the signal between input and output. If what you are getting out isn't exactly the same as what you are putting in (only louder) then you are adding distortion to your signal. An OT can cause distortion without saturating by adding or reducing harmonics or just changing the freq response of the signal applied to it. If part of your tone is coming from an OT that is running with it's core saturated for long periods of time, then you better be stocked up on OTs because you will be changing a few of them along with a few other parts in your amp from time to time. Not only that but I would guess Mr Murphy would also have something to say about when he would like to see the OT fail. (Like right in the middle of a performance).
I wouldn't call that a very reliable design.
The core saturation that MM is talking about is the bad saturation. But there's more to it than that. If the technical babble is confusing, skip it and read the bottom conclusion.
Realize, I don't design these trannies. I read a white paper or two, I'm NOT a transformer expert, so I try to keep it all in terms of "flux" and "Saturation", but that might be too simple. I don't understand it well enough to teach it, but let me try and break it all out, simply, here.
First, flux is the term regarding the magnetic field around a wire that is conducting current. Those invisible lines of magnetic force, if you will.
Obviously this is the fundamental force that excites the secondary.
Second, Flux Density is, roughly, the combined strength of the flux -- that field of magnetic force radiating out. More power on the primary, greater flux density, more induced on the secondary, etc...
In MMs explanation, complete core saturation occurs when you cannot get any greater flux density. This is at the very edge of the usable range of a transformer, far beyond what we use with stancor or dynaco trannies that are more than adequately rated for our purposes.
They're talking about using an early 50s tweed tranny with 6L6, or something along those lines, as a lot of folks thought those trannies were small for the sake of tone when, in fact, they were small for the sake of frugal engineering. They were just large enough to handle the nominal load, clean signal only, and no bigger because bigger was wasteful and more expensive.
Anyway, let's talk about the "more" in the "there's more to it."
When in the normal operating range, there are other factors involved in a transformer. Transformers are not ideal, and steel transformers are REALLY not ideal.
Magnetic flux always takes a closed path from one magentic pole to another. And it always takes the easiest path, just like current in an applied voltage context. In fact, there are lots of parallels, but this is Magentism, not strictly electricity.
In this context, we're talking about Magnetic Circuits -- not electrical or voltage circuits. The equivalent of applied voltage in electrical circuits would be Magnetizing Force in magnetic circuits. The equivalent of a current flow is Flux Density.
The relationship between flux density and magnetizing force is the measure of the effective conductivity of a magnetic circuit. That is called "Permeabiility'.
Using a high permeability core gives a coil of wire significantly more inductance. That makes the coil significantly more efficient, allowing far greater flux density for the number of turns of the coil.
To give a rough idea, assume that air has a Permeability of 1.0. Most non-magnetic materials, are also around 1. Ferro-magnetic materials will be higher. Normal steel will be 300 or so. High Si transformer steels start around 5000, and exotic nickle/molybdenum/iron alloys can range all the way up to 100,000.
So, by choosing a higher permeability core material, we can make a more efficient coil, but there's a price to be paid. The core material, when magnetizing force is applied, retains some of the magnetism. Virtually ALL core materials experience some magnetic memory, and the strength of this is measured in magnetic hysteresis.
If you drew a graph of magnetic force compared to flux density, it would be a perfectly straight line in a perfect transformer. In a real-world transformer, there are two lines, making a sort of loop. The positive side and negative side of an AC signal will follow opposite legs of this loop.
How far apart these lines are is the hysteresis, or a measure of how much residual magnetic memory affects the characteristics of the transformer.
Now, let's get back to the MM explanation of saturation. In their explanation, it's when you hit the definition of saturation, you're putting so much current in that the core material becomes COMPLETELY magnetized. This is bad, m-kay, you don't want to completely saturate anything.
However, the core material itself causes hysteresis even in the normal operating range. This is why there's distortion in every transformer that can be measured. And that measurable distortion might be so mild that it only adds the slightest of texture -- but it also might be significant for other reasons.
For example, we are driving a speaker, which is not exactly 8 ohms at all frequencies. In fact, the impedance of a speaker varies significantly with frequency (see aikenamps.com for a really good chart of this). Impedance is reflected across the transformer, and varying impedance will give all sorts of artifacts including magentic hysteresis, phase shift, and the like. Remember, this is the load for the power tubes as well, so if we're pounding the poweramp it's seeing differences in its loading, as well.
Simply, there are a lot more things going on between the EL34s and the greenback than I can even get a mental handle on.
So, while it's not the textbook explanation of "saturation" -- which is when the core cannot take any more -- the core material imparts significant character on the signal that can be increasingly heard with greater signal even without getting to the point of true saturation.
I hope that made some sense instead of being more confusing.
