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Toroids as output transformers....
Toroids as output transformers....
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Old 23rd January 2019, 07:38 AM   #1
rifraf50 is offline rifraf50
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Wink Toroids as output transformers....

Hi folks .....i was experimenting with torriod transformers as i had bought a box of 6 for 50 bucks

i was wondering how they could be utillised for tube service ..... output and power , there are two 115v primaries which can be connected for 230/240 vac service and the seconds are 2 x 14.5vac and 2 x 36.5vac

So by using voltage multipliers one can get a number of different voltages ....which was great as they are rated at 160 va

None of which were useful for filament though .....i know some folk break into them and simply unwind some of the windings to get the voltages they desire as the seconds are generally wound over the primaries...

But i didnt do that , i just wound on some varnished copper , nice and thick, about 1.2mm i beleive so as to accomodate high loads and "presto" it worked a treat exactly 6.3vac supplied

and yes i realise it will add extra load to the primaries .....but at 160va i hade room to move ......

so that was good .....so moving onto the same transformer as a output audio transformer ..... how will it sound ? ....well i done the maths and wound on 16 turns by hand of course (nothing complicated here )

it worked out at 7.9k into 4 ohms and the demo amp was a el84 push pull

I was stunned !!!! It sounded as good as the proper one already fitted into the unit

well there seemed to be no loss of gain when i A/B 'ed the two transformers and the toroid seemed to exhibit a fraction more bass

I attached some short vids so you can see that there is indeed limitless possibillities for these things ...cheap too !!!

I thought it might be usefull to put this thread in as i recently couldnt find much useful stuff in regards to this ... but this encourages me to go further
Attached Files
File Type: mp4 dirty_Trim_Trim.mp4 (1.93 MB, 26 views)
File Type: mp4 clean_Trim_Trim.mp4 (1.97 MB, 15 views)
File Type: mp4 the toroid.mp4 (1.60 MB, 18 views)
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Old 23rd January 2019, 08:15 AM   #2
jazbo8 is offline jazbo8
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Toroids as output transformers....
Surprised that you could not find much "useful stuff", since there're quite a few threads on the topic going back a decade at least.
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Old 23rd January 2019, 08:20 AM   #3
abraxalito is offline abraxalito  United Kingdom
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I've been using toroids as OPTs on my classD amps for a couple of years now, What's not to like?
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Old 23rd January 2019, 08:37 AM   #4
SemperFi is offline SemperFi  Wake Island
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The biggest worry is DC imbalance in the two primary halves. Toroid cores saturate much quicker than equivalent EI cores.
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. ?
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Old 23rd January 2019, 08:40 AM   #5
gholl is offline gholl  United Kingdom
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I spoke to a chap called Stan Kelly (Decca Kelly Ribbon) several decades ago and he told me that he had experimented with toroids as output transformers, but his designs had segmented winding around the toroid to reduce capacitive effects, etc. This made them quite expensive. I've used Farnell mains toroids but have had difficulty getting any significant open loop bandwidth (~7kHz). Good luck.
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Old 23rd January 2019, 08:47 AM   #6
rifraf50 is offline rifraf50
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Arrow toroids ....

Quote:
Originally Posted by jazbo8 View Post
Surprised that you could not find much "useful stuff", since there're quite a few threads on the topic going back a decade at least.
It really depends on how tech savy you are and how much time you have to sift through all the speculation that appears on some threads and the amount of deviation that occurs on threads

As a simple minded enthusiast most things are trial and error and i guess what i was looking for was simple practical examples of how to utilise stuff that could be considered as junk and with good results

The toroids i used were not built for audio or for tube amps and yet so simply utillised through simple means , and any who see this thread will see this

I dont have workshop gadgets and benches and arrays of test equipment ....just ears ,some knowledge , a soldering iron and a respect for high voltage

I do love tinkering with tubes though .....

this was my objective....
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Old 23rd January 2019, 08:55 AM   #7
rifraf50 is offline rifraf50
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Default toroids

Quote:
Originally Posted by SemperFi View Post
The biggest worry is DC imbalance in the two primary halves. Toroid cores saturate much quicker than equivalent EI cores.
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. ?
This is what i mean by "speculation" ......

all i did was try it ....and it sounded GOOD!!!!

if it saturated then so be it .....but it didnt

perhaps a smaller unit might , but this impressed me enough to seriously consider using them totally .....no more buying expensive EI's !!!
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Old 23rd January 2019, 09:39 AM   #8
fb2017 is offline fb2017
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Do you have the means to measure is response at 1kHz square signal input?
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Old 23rd January 2019, 10:40 AM   #9
DF96 is offline DF96  England
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If toroid OPTs were so simple and so wonderful then everyone would use them.

DC balance is an issue. Get that wrong (or simply ignore it, as you may have done) and you lose inductance and so lose low frequencies.

A power transformer will not have been wound for good HF performance, so you will get HF problems especially if feedback is used.

I am sure this has already been pointed out in other threads by other people. Power transformers are OK for OPT use provided you are not too fussy about audio.
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Old 23rd January 2019, 11:19 AM   #10
rifraf50 is offline rifraf50
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Default toroids...

its plain that there will always be an element of doubt when one weighs up if it should be attemped or discouraged for whatever purpose .....all the technical information will tell us its a bad idea or marginal at best .....

The thing is , what i did took a mere 5 mins of application to prove beyond doubt that something can be utilised effectively.....it may not be perfect but seldom are guitar amps made to be perfect

As for loss of output over conventional tube transformer ....this seemed negligible to my ears , when A/B'd there really wasnt much in it ....certianly enough to make me consider using it again

would you be temped for just $10 a shot ?

listen to the samples supplied , they were recorded by a phone

i can understand that when we build we try to build it as best we can ,and i have made a dozen amps now including 2 hifi amps ......just because i enjoy making them always using conventional transformers for the task ...this whole thread is about pushing theory aside and just giving it a go, and being pleasantly surprised by it

I know the purist will not agree with me ......but sometimes what does not look great on an oscilloscope may sound great to your ears !!!!

And it works....
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