output transformer sizing - is there such a thing as to big?

[danFrank]

One concern I have with respect to core size is:

It takes a finite amount of energy to reverse the magnetic domains. Part of the energy is lost and can be considered part of core loss and does not contribute to the output driving a speaker.

The larger the core, the larger this loss is.

At what point does this loss make a noticeable loss of detail?

This is what I'm trying to get across; Thank you.... Better explanation than mine.

400Hz or thereabouts is where the core doesn't play much of a role any longer in transferring signal from primary to the secondary. Above 400Hz, most signal is transferred directly between windings.
Daniel

 

[45]

I think this is your best "rule of thumb" answer.

Well it is not only my rule of thumb. If you have a look at top SE and PP OT's they are more or less there.

Also remember, it takes energy (current) to magnetize the core, so if I have a transformer that is built for 100ma optimal to go through it's primary but am using a 45 triode at 30ma, it's probably not going to sound so good because the 45 isn't pulling enough current to put the transformer in it's sweet spot.

Don't get this point. If you use it with a 45 will work at that power level. It is supposed to work in a linear way. If you refer to inductance then it could be that transformer has been designed so that there is quite some difference between minimum and maximum inductance but this not necessarily related to the size and the fact that it can handle 100 mA DC.
The core plays a role less and less important as you go up in frequency. So the transformer size, geometry, materials will have more and more influence on the sound. As the number of combinations are endless (while they would measure the same or very similar) an influence on the sound can be expected. Always one should not forget that a transformer alone doesn't sound. The amplifier sounds....

I like permalloy cores because they magnetize much easier than standard silicon steel cores.

For output transformers I don't. They are the best at signal level. This is one case where the core plays a role way above 400 Hz....

 

[danFrank]

Permalloy Cores....
For output transformers I don't. They are the best at signal level. This is one case where the core plays a role way above 400 Hz....

My point exactly! To each his own. Everybody has different tastes as to what sounds good to their ears....
Daniel

 

[esltransformer]

So you saying EI is a less good choice then a c-core concerning THD and a the low frequencies.

That was referred to E+I, this way transformer distortion will be very low. For HI-B core you can go higher.



Depends on the actual hysteresis loop (with or without gap). Linearity dictates how far you can go. Depends on your expectations as well. I prefer to minimize THD as much as possible. On top of this I always prefer to stay far away from saturation down to 30 Hz for SE and 20 Hz for PP at full rated power.

 

[45]

So you saying EI is a less good choice then a c-core concerning THD and a the low frequencies.

No if you use it properly. The real disadvantage can be the size. You posted a link where a French guy made some measurements and you can see that among 25-30 OT's both commercial and DIY, OT n.16 is used a comparison for benchmark performance for FR and THD in most cases. That n.16 is DIY E+I transformer....

 

[esltransformer]

This "no 16" wil have lower THD and better low frequency response IF it had a good c-core. So after all a YES

btw you mean this link:
http://www.triodefestival.net/index.php?page=etf2009-shootout
and these results: http://forums.melaudia.net/attachment.php?aid=1228

This shootout on the Triodefestival wasn't very good and i don't think the results are reliable enough.

No if you use it properly. The real disadvantage can be the size. You posted a link where a French guy made some measurements and you can see that among 25-30 OT's both commercial and DIY, OT n.16 is used a comparison for benchmark performance for FR and THD in most cases. That n.16 is DIY E+I transformer....

 

[45]

This "no 16" wil have lower THD and better low frequency response IF it had a good c-core. So after all a YES

btw you mean this link:
European Triode Festival - ETF2009 Shootout
and these results: http://forums.melaudia.net/attachment.php?aid=1228

This shootout on the Triodefestival wasn't very good and i don't think the results are reliable enough.

There are other important things at this level that make a good sound other than the C-core. FR is already very good and THD is low (and could also be a little bit better). In fact at 0.5W it is 0.1% at 20Hz, less than 0.04% at 100Hz and lees than 0.01% from 300 Hz. This is quite better than any zero feedback amp can hope for. This figures will not increase as quickly as THD generated by active devices if designed to withstand full power.

 

[esltransformer]

My point is not that you get a good transformer by using a c-core. My point is that you get a better transformer if you replace the EI core for a c-core and that for just a very very little bit more money.

There are other important things at this level that make a good sound other than the C-core. FR is already very good and THD is low (and could also be a little bit better). In fact at 0.5W it is 0.1% at 20Hz, less than 0.04% at 100Hz and lees than 0.01% from 300 Hz. This is quite better than any zero feedback amp can hope for. This figures will not increase as quickly as THD generated by active devices if designed to withstand full power.

 

[45]

My point is not that you get a good transformer by using a c-core. My point is that you get a better transformer if you replace the EI core for a c-core and that for just a very very little bit more money.

Again, I disagree. I also disagree about the cost, I have not been able to find best grade C-Cores at comparable prices. I am not a manufacturer so 100 pounds/Kg are already too much for me unless I need big transformers...not really my first requirement in most cases. I am "only" interested in the final result (i.e. musical performance) and the core is only one of several variables. I have found I can make a transformer where the core importance for the final is very small.....negligible....nisba!
This doesn't mean I don't use OT's made with Hi-B C-Cores.

 

[esltransformer]

I was talking about a fact, it's not a matter of agree or disagree.

An externally hosted image should be here but it was not working when we last tested it.

Again, I disagree. I also disagree about the cost, I have not been able to find best grade C-Cores at comparable prices. I am not a manufacturer so 100 pounds/Kg are already too much for me unless I need big transformers...not really my first requirement in most cases. I am "only" interested in the final result (i.e. musical performance) and the core is only one of several variables. I have found I can make a transformer where the core importance for the final is very small.....negligible....nisba!
This doesn't mean I don't use OT's made with Hi-B C-Cores.

 

[45]

I was talking about a fact, it's not a matter of agree or disagree.

An externally hosted image should be here but it was not working when we last tested it.

This is just an unspecified list. I see no facts. Where did you get that list???
I already asked you where to buy C-cores in small quantity at convenient prices but I dindn't get anything but generic indications that do not translate in anything convenient for me.

 

[LinuksGuru]

where to buy C-cores in small quantity at convenient prices

There are several companies (large to medium distributors) which sell ferromagnetic materials, like BFI Optilas and Sekels GmbH.
Welcome | Acal BFi
Home : Sekels GmbH

As an option you may try INDEL in Poland, but I'm not sure they will sell anything but finished transformer built upon your specification.
.:: INDEL Sp. z o.o. ::. - transformatory, d?awiki, cewki, zasilacze.

Insulation and wire you can buy at Brocott UK.
Brocott UK

Please note that some companies may not sell to private persons, they may ask for valid EU VAT # (ask someone of your friends for a favor to cut his profit tax).

 

[LinuksGuru]

Quick search "transformer lamination site:uk" results for example this company:
ASCO Components - Transformer Laminations, Bobbins, Angles, Frames, Terminals and Enclosures.

They even sell other components like bobbins, terminals, etc.

You may try this search by *.it domain to get shopping places closer to your region.

 

[esltransformer]

I just wanted to give an impression what prices could be. Every (audio)transformer manufacture can buy for these prices or even less if they buy more cores then I did.
Developing a high quality audiotransformer and use budget materials is a waste of money in my opinion or not taking the customer serious.

If you can't find a good supplier then you didn't look good enough. Enough postings here on diyaudio where you can read where to buy.
The problem with small quantities is for EI laminated materials almost the same as for c-cores, specially when you want to buy the best EI laminations

some other helpfull links:
Weichmagnetische Kerne mit Entwicklungs-Support | MB Electronic
Electrical Insulation Materials, Cables, Cable Processing, Components, Varnishes, Casting resins, trasnsparent,Coil Winding Tools and Equipments, Clearpur
MES Manz Electronic Systeme OHG | Softmagnetic products | Semiconductors | Busbars | Military and Space | Heat sinks
C core (C-core) manufacture and supply

This is just an unspecified list. I see no facts. Where did you get that list???
I already asked you where to buy C-cores in small quantity at convenient prices but I dindn't get anything but generic indications that do not translate in anything convenient for me.

 

[45]

There are several companies (large to medium distributors) which sell ferromagnetic materials, like BFI Optilas and Sekels GmbH.
Welcome | Acal BFi
Home*: Sekels GmbH

As an option you may try INDEL in Poland, but I'm not sure they will sell anything but finished transformer built upon your specification.
.:: INDEL Sp. z o.o. ::. - transformatory, d?awiki, cewki, zasilacze.

Insulation and wire you can buy at Brocott UK.
Brocott UK

Please note that some companies may not sell to private persons, they may ask for valid EU VAT # (ask someone of your friends for a favor to cut his profit tax).

Again! Do you buy from them? Could I know how much do you pay? My experience is not good at all price wise and unfortunately I do not have friends that can cut their profit tax.....
3 years ago I contacted BFI Optilas in Milan because I saw they had the AMS Ireland Ener-GTM amorphous cores. They were asking for 32 euros for 2C's 16x45 cross-section! If I wanted to use 4C's with one bobbin for each transformer the price for the cores only would have been 128 euros. For Hi-B cores of similar size they charged around 20-25 euros for 2C's depending on the lamination and other properties. Not convenient at all.
With these companies lower prices are just for those who have a business (with VAT) and buy quite some quantity.
Instead I can find best quality M6 "at the market around the corner" for about 4 euros per Kg just buying 10 Kg.....

 

[LinuksGuru]

2 my colleagues bought from INDEL finished custom transformers, and were very pleased with the quality and price. As far as I remember, they paid about 50 Euros/pc

I'm was thinking to buy amorphous toroidal cores from Sekels or BFI Optilas, but the price was outrageous - 550 Euro (550, not 55) for 4 stacked cores just for a pair of transformers.
I had to drop an effort to build toroidal output transformer with the amorphous core for the time being.

BTW, 20 - 25 Euro for D2C HiB lamination seem to be very reasonable. I can't understand why you looking to save few coins. If you buy it for a couple of your home-brew units, this is not an issue at all, and you'd better to buy locally because shipping boxes weighting several kg across Europe costs around 30 Euro.

I don't think any of these companies will cheat you so you are free to ask.

 

[esltransformer]

I am very curious on how many "markets around the corner" sell the best M6 .......... (besides M6 is still not very good)
Most transformer manufactures don't even have this quality standard at home

I bought directly in China, nice people there

Again! Do you buy from them? Could I know how much do you pay? My experience is not good at all price wise and unfortunately I do not have friends that can cut their profit tax.....
3 years ago I contacted BFI Optilas in Milan because I saw they had the AMS Ireland Ener-GTM amorphous cores. They were asking for 32 euros for 2C's 16x45 cross-section! If I wanted to use 4C's with one bobbin for each transformer the price for the cores only would have been 128 euros. For Hi-B cores of similar size they charged around 20-25 euros for 2C's depending on the lamination and other properties. Not convenient at all.
With these companies lower prices are just for those who have a business (with VAT) and buy quite some quantity.
Instead I can find best quality M6 "at the market around the corner" for about 4 euros per Kg just buying 10 Kg.....