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Toroids as output transformers....
Toroids as output transformers....
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Old 23rd January 2019, 11:45 AM   #11
Schmitz77 is offline Schmitz77  Germany
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You should say that you're talking about guitar amps, thats what I hear in your video.

This is different field compared to exellent audio amps. With guitar amps, the standards are almost very poor in regards of sound quality. They should make some sort of sound, they should be capable to overdrive etc. With them, its not about the most purest signal transmission. You can see this when studying all the most famous brands schematics.

In general terms: NO toroid output transformer can be of the highest quality possible because for pure signal transmission there are techniques applied, that could not be done with a toroid core because of its dimensions and the shape. ALL exellent designs are non toroid transformers. That doesn't mean that it doesn't deliver some sound on the output, but its always of mediocre quality. And thats a fact because thats physics.
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Old 23rd January 2019, 11:53 AM   #12
abraxalito is online now abraxalito  United Kingdom
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Quote:
Originally Posted by SemperFi View Post
Btw, how do we best estimate power handling in OPT use? 160VA at 50Hz should indicate it can handle 160watts > 50Hz...? (Half that power at half the frequency etc). But that seams too optimistic when looking at typical OPT. ?
A transformer is thermally limited so you'll get short term power well above 160VA at freqs well above 50Hz. I use 30VA toroids for my audio but then I'm not pushing too many watts - the 30VA size is determined by my target for series resistance, not power handling. Given the typical crest factors for the majority of music you'll find 160VA rather overkill unless you're into kW territory or you're feeding a subwoofer.
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Old 23rd January 2019, 12:03 PM   #13
jazbo8 is offline jazbo8
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Toroids as output transformers....
Moved to Instruments & Amps.
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Old 23rd January 2019, 12:04 PM   #14
MagicBus is offline MagicBus  Greece
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Here's an extreme case that might be interesting.

I have used those Toroid Transformer for audio: Output ~12V/1A; In ~100/110/115/120/220/230/240V | eBay as OPTs in a small fun project. I had to remove some turns from the secondary to get the impedance ratio I needed so the final result was far from even spaced winding. On top of that, because the design is a push pull with self bias and separate cathode resistors for each tube, there is a DC imbalance of 3 mA.

I found that it could stand a moderate amount of NFB but no more than that. I can't tell if DC imbalance is causing any saturation but it's clear that it does not do any permanent damage and once signal is applied I think DC imbalance has no meaning anymore. Being new to measurements, I post a FFT delivering 2W@8ohm for you to evaluate.
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Old 23rd January 2019, 12:16 PM   #15
DF96 is offline DF96  England
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Quote:
Originally Posted by rifraf50
it may not be perfect but seldom are guitar amps made to be perfect
Sorry, I forgot that this is the Instruments and Amps forum. I was going to say that a cheap OPT may be OK for a guitar amp but not good for hi-fi.

"Pushing theory aside" is rarely a good idea, unless what is called theory is actually hopelessly simplified or approximated theory which happens to be inapplicable.

Oops: just noticed that this has just been moved to I&A forum, so I guess it was originally in Valves or Parts.

Last edited by DF96; 23rd January 2019 at 12:18 PM. Reason: just noticed
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Old 23rd January 2019, 12:38 PM   #16
Nrik is offline Nrik  Denmark
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There are already many tube amps with toridal OPTs.
It is not important if the transformer is toroid or EI or xxx (well yes it is but that is another discussion), the important part is the material in the core.
The material in a transformer for the full audio spectrum (20-20.000 Hz) must be of much higher quality, that a transformer only for 50/60 Hz mains current.

Transformers for mains may appearantly transfer all frequencies, but the distortion and loss will be higher than for a transformer built for audio.

...and then there is the missing DC-gap, which is never added in mains transformers but is needed if it carries DC.
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Old 23rd January 2019, 02:26 PM   #17
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by Nrik View Post
The material in a transformer for the full audio spectrum (20-20.000 Hz) must be of much higher quality, that a transformer only for 50/60 Hz mains current.

One should consider why toroids are much smaller and lighter than usual EI or whatsoever transformers. The answer is the core! All toroid cores are made from GOSS bands of about 0.1 to 0.2 mm thickness. In other words, you have very high core material even in standard power toroids!
The reasons why power toroids arent's that useful for HiFi audio are their rather small primary inductance and their simple winding scheme. One can improve that by increasing the number of turns and by interleaqing thje Primary and secondary parts.
Guitar amp OPT's completely are another world, though, as the OP has been showing to us.
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Old 23rd January 2019, 11:28 PM   #18
wg_ski is offline wg_ski  United States
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The biggest problem with using off the shelf toroids for output trafos is the limited voltage. You can have any turns ratio you want, but they are pretty much limited to a 170 volt (340 V p-p) swing on the 240 volt “primary”. More for frequencies higher than 50 Hz, but still there is a limit before magenrtization current eats your lunch. Fine for small amps where you can shove enough current into it to make 15 watts of power. But try to fully utilize a 160 VA, forget about it with standard audio tubes. Now if you had one with a 480VCT primary, you’d be getting somewhere. But that’s no longer in the realm of off the shelf cheap from Antek.

One possibility would be to start with a standard tube power trafo that’s more than 240V, and just ignore the 120/240 winding (perhaps use it for feedback) and add an 8 ohm secondary using the number of turns needed to make it work. It would probably have worse frequency response, but hey, at least you could make power.
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Old 24th January 2019, 02:10 AM   #19
PRR is offline PRR  United States
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Quote:
Originally Posted by rifraf50 View Post
...torriod transformers.... as a output audio transformer ..... how will it sound ?...
Vanderveen Home

Modern high-end valve amplifiers: Based on toroidal output transformers: Menno van der Veen: 9780905705637: Amazon.com: Books
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Old 24th January 2019, 05:58 AM   #20
rifraf50 is offline rifraf50
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Default torroids why not ?

I think we have gone off track here ....i have no intention of trying to re invent the wheel , or trying to convince you that this the way to go...etc

what this is about is utilising these seemingly useless trannys whether salvaged or surplus into something useful that those on very tight budgets can afford

I knew that i was gonna get a fair slapping for entertaining the thought that these can actually sound quite good in guitar amp service.....but it did !!!

What i did was a very quick and rude application to prove whether it was worth evaluating even further ......and my ears told me it was

As i stated , there was a mere 16 turns on this unit and it covered about one third of the diameter ......and needless to say it can definitely be improved upon ....perhaps more windings on the primary and in turn on the seconds....and as for interleaving why bother.... but it would seem one would try to go at least the full 360 degrees for the seconds but would it be needed if it performed quite well as it was ...another factor is i used a large tranny for this where a smaller may well saturate

but how would you know if you dont go there ?

I did run 360VDC into it and played at full volume for half an hour at around 18 watts as a guestimate and no saturation occured and temperature was mild... bass was punchy and highs were clear and bright ,18 watts into a quad box gets quite loud after a while ..... so it appears to be successful....

Another usefull thing is that with limited skills one can apply any combination of impedance to these things quite simply...to both primary and secondary to match whatever tubes one wishes to use....

This is the sort of info that i would like to see ......and i would encourage folk to give it a shot .....in previous threads i heard pretty well much the same comments that are appearing on this one and i guess thats why it took me so long to give it a go....i thought it was going to be piontless...

I think these are better than the M20 line transformers that have been mentioned in other budget amp threads and thats speaking as one who has used the m20 successfully in both SE and P/P aplications

Perhaps the trannies are like a box of chocolates .....you never know what your gonna get .... but worth the effort in my opinion...
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