[JN] magik ???

Christian Rintelen christian at rintelen.ch
Mon Feb 1 16:58:25 CST 2021


AFAIK peerless used the pinstripe design only for large signal i.e. output transformers (i’m not even sure whether they only used it for SE OPTs). if you have an airgap to avoid saturating the core, the inductance drops like a rock. to make up for some of that loss, the pinstripe makes perfectly sense — the airgap prevents saturating the permalloy (aka mu-metal) too fast, and the SiFe gets a jump start so to say. but applying the same principle to a microphone or phono cartridge transformer doesn’t make sense. first, because there is no DC to saturate the core. second, the signal voltage is so small that it will never saturate even a pure nickel core. third, these types of transformers were the first toroids as soon as these became available. and why would anybody roll SiFe and permalloy into a toroid?? 

core material tecchnology has advanced quickly and with big leaps fueled by (among others) the demand for «faster» core material in switching power supplies and regulators. i think the peerless engineers would be pinstriped with envy if they saw what materials are available today. and i’m equally convinced they would have switched to toroids instead of taking the scenic detour with pinstriped EI or M cores.

(btw i remember reading a paper by sowter senior (brian sowter’s father) advocating airgapped cores even for PP-OPTs (and we’re talking post-war cheap english steel, not peremalloy or that kind of stuff). his reasoning was that the airgap flattened the inductance and this the impedance jumps of the transformer; he’d rather use a bigger core and put more wire on it than dispose of the airgap. which of course makes perfect sense as there is (or was at the time) no PP-amp that had perfectly symmetrical current draw through both windings at all levels and frequencies. even small AC or DC imbalancies can drive an ungapped PP OPT into saturation so you needed either an oversized core (expensive after WWII!) or a smaller core with an airgap. so why not take the big core and apply a small airgap? it will give you headroom re: DC saturation *and* a flatter inductance curve)

on the other hand, there is absolutely no reason to use any of these high tech materials for a mains transformer. quite the contrary — you want to keep the bandwith of a 50/60 Hz core as limited as possible so it acts as a filter.

((hold the press: i just localized sowter’s AES paper. enjoy.))

©
_ _ _
aka christian rintelen

> Am 01.02.2021 um 22:41 schrieb Philip Yates via Sound <sound at soundlist.org>:
> 
> Well, I've long thought that the key point in the old Peerless Pinstripe trannys was not to "add a little Permalloy" to the silicon iron, similar to bypassing a medium quality cap with a small high-quality cap, but to provide a crossover from one material to the other, with the Permalloy handling the tiny changes in the signal. The trick is to have the permalloy begin to saturate just as the silicon-iron is beginning to overcome its hysteresis, i.e., as the Si-Fe's mu is beginning to rise, which is the "crossover." To do this (1) the two permeabilities much match -- i.e., the permalloy's air-core must reduce its mu (permeability) to that of the Si-Fe (which may also have an air-core), (2) the ratio of the Permalloy's mass to the Si-Fe's mass must be such that the Permalloy saturates just as the Si-Fe kicks in (overwise you get a boost in the overall mu), and (3) the shape of the Permalloy saturation curve and the Si-Fe's initial mu curve must be compatible, i.e., they must combine to form a reasonably good  crossover (I think a 1st-order crossover).
> 
> In other words, the Supermagic boxes may use two core materials that meet the above 3 requirements, although really, you should add a 4th requirement, namely, the core materials must have zero magnetostriction (zero core expansion/contraction with the signal, causing it to vibrate). The trick is to find various combinations of materials that are compatible, and then sort by price and theoretical quality. One that I've long been interested in, especially for output trannys, is a Sendust main core combined with a permalloy. Sendust is very similar to permalloy, being only very slightly inferior, has quite a few variants, and is much less expensive! It is brittle, but when combined with its zero magnetostriction, that makes it very stable. Another potentially very good main core is Vitroperm, which has an incredibly linear B-H curve, which I think means that the low-freq pole remains constant. I'm not sure whether that's actually all that great of an advantage, but it might be. However, it's initial mu could definitely be helped by crossing over to one of the permalloys. Unlike Sendust, however, it is very expensive.
> 
> Or, maybe they just used a powdered molypermalloy core, which might be the best core of all, although I've never heard of it actually being used in audio (mainly radio), so I'm not sure.
> 
> Phil
> 
> On Mon, Feb 1, 2021 at 8:14 AM Marc Wauters via Sound <sound at soundlist.org <mailto:sound at soundlist.org>> wrote:
> https://sophiaelectric.com/products/pages-tube-preamp-magik-box <https://sophiaelectric.com/products/pages-tube-preamp-magik-box>
> 
> Anyone want to take a stab on just what is in those cans. If it really does anything I have to ask just why transformer would do it. I'd generally be rather skeptical that noiseless gain of 6 dB at line level can do much of anything to improve sound. Their claims are quite ambitious. They even claim it improves (or have in the past) the sound from MM cartridges when placed between it and the phono input. Seems the impedances there might be an issue.
> Thing is that similar claims and reports were given on the Expressive Technology SUT 1 ( I think that was the model name) moving coil step up, that improved the sound beyond any other step up available, but of course in that position it's hard to compare.
> Tell me this is just something like a Jensen J11 wired as an autoformer for 6 dB gain and I'll go buy a bunch!!!
> Regards
> Marc
> 
> 
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