Some of those parametric changes are measurable although I have not usually bothered.
I have compared brand new LL1941 amorphous SUTS with ones that had been in use for hundreds of hours and can very comfortably dismiss the psycho-acoustic possibilities from the equation. The differences between them were not at all subtle.
I was able to measure significant differences in LF response (more than 1dB) and wide band distortion using a low distortion osc driving an attenuator simulating a 5 ohm 200uV source into the primary of those transformers and the differences were significant; 12 hours with a couple of mV at a few hundred Hz to 10kHz resulted in a small but measurable reduction in distortion and flatter LF response. Clearly nothing in the coils changed but would guess something occurred magnetically in the core, although I am hard pressed to come up with anything - don't know enough about materials science..
My 3 LOMC cartridges have either 2 or 6 ohms of source impedance and max out at between 200uV - 300uV @ 5cm/sec so the test was reasonably representative of actual use conditions.
More recently I've swapped the transformers between the two TT set ups I use and they sound identical to me which is what you'd expect. Same transformers, boxes, wiring, internal layouts and connections and only minor differences in RCA jacks which doesn't seem to matter.
The funny thing is I listen to enough other systems and live music so that I have extreme difficulty getting used to anything that doesn't sound right by comparison. This usually results in some fairly significant re-engineering using scopes and meters or more specialized measurement tools amongst other things.
I have compared brand new LL1941 amorphous SUTS with ones that had been in use for hundreds of hours and can very comfortably dismiss the psycho-acoustic possibilities from the equation. The differences between them were not at all subtle.
I was able to measure significant differences in LF response (more than 1dB) and wide band distortion using a low distortion osc driving an attenuator simulating a 5 ohm 200uV source into the primary of those transformers and the differences were significant; 12 hours with a couple of mV at a few hundred Hz to 10kHz resulted in a small but measurable reduction in distortion and flatter LF response. Clearly nothing in the coils changed but would guess something occurred magnetically in the core, although I am hard pressed to come up with anything - don't know enough about materials science..
My 3 LOMC cartridges have either 2 or 6 ohms of source impedance and max out at between 200uV - 300uV @ 5cm/sec so the test was reasonably representative of actual use conditions.
More recently I've swapped the transformers between the two TT set ups I use and they sound identical to me which is what you'd expect. Same transformers, boxes, wiring, internal layouts and connections and only minor differences in RCA jacks which doesn't seem to matter.
The funny thing is I listen to enough other systems and live music so that I have extreme difficulty getting used to anything that doesn't sound right by comparison. This usually results in some fairly significant re-engineering using scopes and meters or more specialized measurement tools amongst other things.
20h of listening on my LL1664AM and no change or psycho adaptation . i wouldn't say it"s an upgrade at this moment just a change in presentation, . more details and micro dynamics for sure but a sort of unbalance between low medium and high frequency and less impact on bass. see you for the next report 
I don't know how long they take, but it is definitely a while. They sound weird and kind of bad out of the box. Once ready, they are fantastic.
From my experience Amorphous transformer needs 200h of burn in minimum. After this time it will become smooth and extended, however overall sound signature will not change. IMO - amorphous cores are very airy, detailed, precise, subtle etc, but its not my cup of tea. If you want colour, musicality and magic - look for permalloy transformer.
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Audionote dos use permalloy ( but just 50%)
Monolith Magnetics uses finemet and i saw that Thomas Mayer uses in one of his 211 project finemet too.
If i look at the size of those 211 transformers then i think they are very small for a finemet 211 transformer. Probably not full range.
You will loose at least 60% low frequency response if you use a finemet core instead of a silicon core.
Moste of the time it means poor bass or poor copperlosses or a combination of both.
Monolith Magnetics uses finemet and i saw that Thomas Mayer uses in one of his 211 project finemet too.
If i look at the size of those 211 transformers then i think they are very small for a finemet 211 transformer. Probably not full range.
You will loose at least 60% low frequency response if you use a finemet core instead of a silicon core.
Moste of the time it means poor bass or poor copperlosses or a combination of both.
the only permalloy transformer i know is the TAMURA but they are not available anymore . other brands ?
and what is the deal with Finemets , they seems the more exotic and expensive and hard to find ( tribute do not make output transformer too..)
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No, permalloy has the same problem.
Permalloy, finemet are made for small signal transformers and finemet and amorphous alloys are specially designed for high frequency transformers.
They are also used in very sensitive current transformers and microphone transformers.
Permalloy, finemet are made for small signal transformers and finemet and amorphous alloys are specially designed for high frequency transformers.
They are also used in very sensitive current transformers and microphone transformers.
We seem to have some transformer specialists on the thread right now, and I wonder if it's possible to answer the question "How would you design for a normal full bass frequency response from some of these more exotic compounds". Is the answer winding techniques, smaller percentages, just plain size or what?
I have Tribute finemet MC cart step up wound on toroid core (MKII model according to Pieter, I guess something that is pretty new and nothing I have heard sounds like them. I have had Cinemag 3440a, 1131, Lundahl 1931 and 1941 and Peerless 4722.
Real shame Pieter is not winding for DIY'ers. I would buy S/E OPT from him in heartbeat after hearing these MC transformers.
Real shame Pieter is not winding for DIY'ers. I would buy S/E OPT from him in heartbeat after hearing these MC transformers.
Finemet is indeed excellent for mc transformers. They are easy to make and cost are not so high.
Given the same output power, low frequency limit (e.g. 20 Hz), and primary number of turns, one have to considerably increase core cross-section in case of amorphous, nanocrystalline or 45-50% nickel-iron alloys (compared to conventional grain oriented steel).
BTW, Finemet and Metglass are trademarks of Hitachi, not engineering terms.
Metglass = amorphous
Finemet = nanocrystalline
Permalloy = nickel-iron alloy
Building SET transformers with nanocrystalline doesn't make much sense (it will be enormously big), amorphous or permalloy - may be.
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Message from Tribute: In other words, we have to take into account the maximum core excitation of these materials, which is 1.56T for amorphous, 1.25T for nanocrystalline and about the same for nickel-iron (depends on nickel content). 80% nickel-iron cores have 0.8T. High quality silicon steel can have over 2T.
A quality OPT will stay under 1T with maximum voltage swing at 20 Herz.
It makes sense to apply Finemet. Over the last 15 years I have gone through the process of winding OPT's with high quality silicon steel, amorphous and nanocrystalline (Finemet).
The good properties of high quality silicon steel (HiB) and nickel-iron in terms of permeability, and the low loss properties of amorphous, are combined in nanocrystalline.
Nanocrystalline is made as an amorphous alloy (same tape thickness of about 22 mu); nanocrystallization gives the material a high permeability, so with nanocrystalline we have a low loss high perm core.
Applying airgaps in single ended OPT's will cost part of permeabilty, but there is enough "left" to make it worthwile. This is confirmed by comparitive inductance measurements of amorphous and Finemet.
Feedback from customers confirm Finemet to be top grade material.
Already some three years ago I replaced amorphous by Finemet; the cores are marginally more expensive but total cost of transformers is dominated by labour anyway so it was a logical move.
Finemet c-cores come in the same dimensions as amorphous c-cores, so with the same coils good comparisons could be made by just exchanging the cores.
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I am not an engineer so I am unable to provide any technical explanation but from my personal experience I believe that it is good to oversize all iron in a tube amplifier, that is also relevant for output transformer.
For example:
in a 45 tube SET [1.5W-2W, ~35ma] - output transformer should have at least 8W, 80ma and high inductance [+20H]. My friend in same application uses custom amorphous output transformer (15W, 150ma, 35H at 30hz] and you would not believe how much power and drive that amplifier can provide! Same with chokes and PSU transformer.
I had Tamura F475, F2004, F7003, Lundahl LL1663 and few others.
To make long story short: F475 had the weakest bass response, like it was ending on 80hz or so. Serious issue with dynamics, power and proper sound weight. Most good psu chokes are heavier in weight and size than F475. Overal sound signature was very good with a lot of "tamura magic", but there were to many compromises to settle on this transformer. In theory F475 are more than enough for 45 tube SET, but in my case it didnt worked out, and IMO that OPT is good for headphone amplifier, but not standalone speakers.
F7003 is the most sweet, magical, musial, engaging transformer I heard. I believe it is because of the nickel core inside, just like good AlNiCo speakers [Aluminium, Nickel, Cobalt].
F7003 Sound signature is like a dream for me, and my primary object is to find musicality.
F2004 had slightly better bass response than F7003, it was also slightly more dynamic, but there was no magic, no sweetness and realism that F7003 can provide.
All comparison were done in a 45 type tube SET amplifier and 102dB 3-way horn with JBL alnico speakers.
small transformer = small sound
big transformer = big sound! ;-)
if you love details and want to hear everything that is recorded - go for amorphous core
if you are music lover and want to have eargasm during listening sessions - save for permalloy
if you look for good price/performance ratio OPT - go for copper Lundahl [not amorphous or silver!].
This is only my experience, please treat as "IMO".
For example:
in a 45 tube SET [1.5W-2W, ~35ma] - output transformer should have at least 8W, 80ma and high inductance [+20H]. My friend in same application uses custom amorphous output transformer (15W, 150ma, 35H at 30hz] and you would not believe how much power and drive that amplifier can provide! Same with chokes and PSU transformer.
I had Tamura F475, F2004, F7003, Lundahl LL1663 and few others.
To make long story short: F475 had the weakest bass response, like it was ending on 80hz or so. Serious issue with dynamics, power and proper sound weight. Most good psu chokes are heavier in weight and size than F475. Overal sound signature was very good with a lot of "tamura magic", but there were to many compromises to settle on this transformer. In theory F475 are more than enough for 45 tube SET, but in my case it didnt worked out, and IMO that OPT is good for headphone amplifier, but not standalone speakers.
F7003 is the most sweet, magical, musial, engaging transformer I heard. I believe it is because of the nickel core inside, just like good AlNiCo speakers [Aluminium, Nickel, Cobalt].
F7003 Sound signature is like a dream for me, and my primary object is to find musicality.
F2004 had slightly better bass response than F7003, it was also slightly more dynamic, but there was no magic, no sweetness and realism that F7003 can provide.
All comparison were done in a 45 type tube SET amplifier and 102dB 3-way horn with JBL alnico speakers.
small transformer = small sound
big transformer = big sound! ;-)
if you love details and want to hear everything that is recorded - go for amorphous core
if you are music lover and want to have eargasm during listening sessions - save for permalloy
if you look for good price/performance ratio OPT - go for copper Lundahl [not amorphous or silver!].
This is only my experience, please treat as "IMO".