The core -sonic reasons

[felixx]

There's a few possiblities to choose the right output transformer when you want to make a good sounding amp.
I find the ideea based on some "old fashion" or "old school" manufactures and said the amorphous and permalloy core isn't that good in sonic terms.Same story with the silver windings on the transformer. Also they look impressive on paper but sonicaly don't have a very good mark.
That thing reminds me about the tone test-mark- of different speakers.Ex:
-look very good on paper but sound flat,without soul,cold,direct (check SEAS) and other (check Altec) with a very good tonal balance and amaizing resolution-details....personally speaking.

What is your subjective oppinion about these "new" output cores?

[analog_sa]

Originally posted by felixx
I find the ideea based on some "old fashion" or "old school" manufactures and said the amorphous and permalloy core isn't that good in sonic terms.Same story with the silver windings on the transformer.

Interesting. Have you got any links to these opinions?

I enjoy both amorphous and nickel transformers very much. And also silver windings. Obviously the old fashioned tone is missing, but so what?

[smoking-amp]

I haven't listened to any of these exotic material output xfmrs. But a few technical issues that would raise some questions do arise:

The permalloy cores solve an important factor of increased permeability, but sacrifice max. flux level. This would mean less power or bass from a comparable size core versus M6 material (but greatly reduced hysteresis distortion). Increasing the core size to compensate power-wise will increase cost substantially. The increased permeability also leads to DC stauration problems like encountered in toroids, so DC servo's would be a big help. (putting in an air gap cancels out the permeability advantage)

The striped permalloy/M6 core idea appears interesting, raising the permeability for small signal fidelity. But it has an issue of sudden drop off in permeability at some flux level when the permalloy saturates and the M6 takes over. This would be akin to a class AB output stage when one tube cuts off (losing transconducance). So you get class AB like effects even with a class A output stage here. This should be fixable with a low output Z tube stage (see below, but note that the same fix works for M6 alone). DC servo-ing to avoid saturation at idle would be important here too.

The amorphous alloy and micro-crystalline materials cover a large range of characteristics and depend on final heat/magnetic treatments as well. But the most affordable (and most likely used) ones are the type used for utility power transformers to reduce hysteresis losses. Since losses in output transformers aren't really an issue, the main advantage here would be reduced hysteresis distortion. Hysteresis distortion in M6 can be dealt with very successfully by just using a low output Z tube stage (plate feedback schemes or partial CFB or even UL to some extent), so this issue can be overcome by design at lower cost.

So I don't see any compelling reason to pay for exotic materials.

The Berning type (and related switching type) switched ferrite or switched capacitor OTs also can reduce hysteresis effects nicely, but at considerable complexity and risk of HF noise. It has a very steep technical learning curve to successfully apply however, but once overcome, enables easier, low-turn, OT winding and reduced cost (if self implemented with that in mind). For the DIYer making his/her own OTs, these are nice advantages.

Don

[MQracing]

Don wrote:

The striped permalloy/M6 core idea appears interesting, raising the permeability for small signal fidelity. But it has an issue of sudden drop off in permeability at some flux level when the permalloy saturates and the M6 takes over.


Don

The nickel cannot saturate if you design the transformer to operate within the flux capacity of the nickel material by itself.

MSL

[felixx]

Interesting. Have you got any links to these opinions?

I read a discussion based on Hashimoto transformers (japanese forum) some time ago,but I can't remember where.

I enjoy both amorphous and nickel transformers very much. And also silver windings. Obviously the old fashioned tone is missing, but so what?

This mean you are be able to share some of your thoughts (based on your subjective perception) in this issue?THX.

#smoking-amp
Well explained.

After PP,consider to build a SE class A -no feedback based on this schematics.

The nickel cannot saturate if you design the transformer to operate within the flux capacity of the nickel material by itself.

And...how to do that?

[smoking-amp]

MSL: "The nickel cannot saturate if you design the transformer to operate within the flux capacity of the nickel material by itself. "

Well, yes, but the high permeability of the permalloy will cause most of the flux to build up in the permalloy first, rather than the M6. Could just as well put plastic in instead of the M6. Waisting space in the core (unless the permalloy has special air gapping to equalize its effective permeability with the M6).

Don

[MQracing]

Originally posted by smoking-amp
MSL: "The nickel cannot saturate if you design the transformer to operate within the flux capacity of the nickel material by itself. "

Well, yes, but the high permeability of the permalloy will cause most of the flux to build up in the permalloy first, rather than the M6. Could just as well put plastic in instead of the M6. Waisting space in the core (unless the permalloy has special air gapping to equalize its effective permeability with the M6).

Don

If you have a EI-100 by 1" stack---- the flux density at any given drive level and frequency will be uniform if the number of primary turns is kept constant (this to a first approx--- i.e., ingoring for example the magnetic skin effect)----

your imagining that there are two separate cores at work--- but this is not the case. There is only one core--- and the flux density of that core structure will be the same whether we use nickel, M6, or bumper steel or any combination of these three materials. In-other-words the magnitude of the flux density is independent
of the materials which make up that core.


what we have to be careful about is to make sure that the core does not operate at a flux density greater than the material which has the least amount of flux density capacity--- if we do that the core cannot saturate. I.E., different grades of core materials have different maximum flux densities that they can support. Some will saturate easier than others. So we design around the core material which is most easily saturated and make sure that the flux density is less than than maximum that can be supported by that material.

What will vary is the permeability--- the nickel for instance will have greater permeability than the M6. So that given at any given drive level across the coil's primary--- the perm of the nickel will be greater than the perm of the M6. But at any given drive level ALL of the core will be "energized" (i.e., will have the same flux density).

"Pinstriping" cores in audio transformers has been done for more than five decades. The earliest examples that I have seen were made by Peerless. Even some of their small signal input transformers used a combination of both high and low nickel at the same time.

what the pinstriping does for you--- is that at very low drive levels---
especially in the case of M6 (which has a reverse knee in it's bh loop)--- is that at very low flux density levels--- the nickel exhibits greater permeability---- so that it "jump starts" easier than M6.


So that given that nickel has greater perm--- think of perm as an
"inductance multiplier"---- air has a multiplication effect of 1--- magnetic core materials might have a perm of say 5,000 to 50,000 or even higher---- meaning that you will get (as a first approximation) 5,000 to 50,000 (or even more) times the inductance (given a specific set of operating conditions) than if you had no magnetic core at all.

And that is why you might use a few slivers of high perm core materials--- to simply enhance the perm at very low drive levels--- so that the inductive reactance produced by the larger amount of effective L is greater than it would be if you did not use the high perm material as an enhancement.

MSL

[MQracing]

Don wrote:


::::The permalloy cores solve an important factor of increased permeability, but sacrifice max. flux level.:::

True.


:::This would mean less power or bass from a comparable size core versus M6 material.... :::

Only partially true. Your mixing two different factors and treating them the same.

For a given size core with a fixed number of turns and at a specific frequency---- M6 can handle a greater amount of voltage across it's primary and stay below it's saturation point--- so from this perspective, yes, M6 can handle greater power than the nickels.

But--- bass response depends also on the amount of inductive reactance that you have--- when you say "less bass" I presume you mean less bass extension as in low frequency response.

For a given level of bass response at a specific power level--- what we need is a core that has enough flux capacity to handle the power at the lowest frequency of interest AND we also need that coil\core combination to be able to develop enough inductance to support that lowest frequency of interest.

But these are two different considerations or factors---- it's possible that we could have enough flux capacity to support X amount of power at frequency Y without saturating the core--- but yet still be lacking the necessary amount of inductance to support that same lowest frequency of interest.

The same core and coil combination made with say all nickel lams--- and operated within it's permissible flux capacity---- i.e., at power levels which will not saturate the nickel---- may very likely still produce a much greater amount of inductance--- which (within it's power range) would permit or extend the low frequency response (i.e., what you call the bass response) much lower than the same core and coil combination built with M6.

Any given low frequency power response capability depends on both flux density (i.e., keeping the core from saturating) as well as the properties of the core\coil combination that results in the production of inductance. You need a sufficient amount of inductance AND you need to keep the core from saturating to deliver a given amount of power at some stated low frequency of interest.

But simply having enough flux capacity--- is not in-and-of-itself sufficient to produce a specific low frequency extension.



::::Increasing the core size to compensate power-wise will increase cost substantially.::::


yes... from a power only point of view--- a nickel core will require a greater core area and\or a greater number of primary turns or some combination of these two---- this is due to the fact that you cannot run nickel nearly as high flux density wise as you can M6.


::::The increased permeability also leads to DC stauration problems like encountered in toroids, so DC servo's would be a big help.::::

this is perhaps awkwardly stated. It is not the perm which limits or provokes dc saturation----


Saturation is produced by demanding of the core more flux capacity than it has.

Since nickel has a smaller magnitude of permissable flux density--- then obviously it can saturate easier than M6.

when a core material saturates--- by definition---- a wholly saturated core would have a permeability of zero.

But the zero permeablity is the effect not the cause. It is not because the material has a high perm that it might be more easily saturable---

for a good example of this--- cobalt has significantly higher permeability than M6 and also has greater flux capacity.


:::putting in an air gap cancels out the permeability advantage)::::

I want to agree with you on this point---- perhaps "cancels out" if meant entirely is worded too strongly---- but if your point is that an airgap rapidly diminishes the effective permeability of the coil\core combination--- your on pretty safe grounds in making this moreso qualified statement.


MSL

[jlsem]

I find the ideea based on some "old fashion" or "old school" manufactures and said the amorphous and permalloy core isn't that good in sonic terms.

If I recall correctly, Permalloy has been around longer than grain oriented silicon steel. As far as amorphous cores go, there are many different alloys available with at least three heat treating methods each but so far it is unclear who is using what in which transformers. Does anyone know, for example, what kind of cores are being used by Tamura, Lundahl, or Intact Audio?

John

[smoking-amp]

MSL: "There is only one core--- and the flux density of that core structure will be the same whether we use nickel, M6, or bumper steel or any combination of these three materials. In-other-words the magnitude of the flux density is independent
of the materials which make up that core. "

The total core flux IS proportional to the voltage drive level, but not the flux distribution in the material. For that, one has to consider the ampere turns around the materials. At any given moment, some level of current will be in the windings, and the amount of flux thru each material type will be proportional to the lamination permeability times the current (divided by path lengths, which I will assume are equal for same size laminations).
[this is a very standard, elementary magnetics calculation]

This means that 100X higher permiability material will develop 99% of the flux, up until it saturates, then the lower perm. material will pick up the flux increase required for the voltage increase.

This, in turn, means that driving a mixed/pinstriped core only up to the permalloy sat. level will have only about a few% of the flux developed in the M6 before the permalloy saturates. (hence my comment about just putting plastic in for the M6)

This discontinuity does not put a kink in the voltage transfer curve if driven from a hard voltage source (since that can handle the suddenly increased magnetizing current at sat. crossover seamlessly). But if driven from a resistive source, a voltage drop will develop (in the source itself) in the transfer as the discontinuity is crossed, due to the increased magnetizing current thru the source resistance.

Because of this phenomena, only using the core up to the permalloy sat. level would be silly and waistful. Using the core fully up to the M6 sat. level will work fine if driven from a low Z source, but so will just plain vanilla M6 alone with low Z drive. The pinstiping idea is another example of a marketing driven poor design. (UL transformer taps at B+ DC are another.)

Don