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Old 2nd May 2011, 11:43 AM   #1
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Default power transformer as output transformer

Hi all,

i have a transformer that is 110 volts to 50 v ac of course and i would to try and use it as a output transformer on a compressor circuit. From what i have read materials and the way they are made and different winding ratios are what give output transformers there particular sound. What i would like to know is is it possible to use power transformers as this providing you work out the turns ratio and impedance and try and match it up. If anyone has done this or knows anything about it could you please let me know as obviously it could be a cheaper alternative. I have been trying to work out how to modify other transformers i have. I got to admit iam not overly keen on the whole wind yourself method. Of what i can see you need some sort of jig roller with a counter to hold the tention and count the turns to do a good job. but trying to work out best method. Anyone can go and buy the correct part and install. But having not huge funds to play with i try and find alternative methods to make things a bit cheaper. Who doesn't love a bargain. So sometimes its worth the effort. I think in output transformers this may be one possible one. I would love to hear from anyone who has done some output transformers with standard power transformers thanks
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Old 2nd May 2011, 11:59 AM   #2
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You'd have to derate the transformer and make sure there's no DC on it.
You might (for example) be able to use a 100VA mains transformer with split primaries, ie. 120 + 120V, as a pushpull output transformer at maybe 20 Watts, but for guitar use only, it'll be hopeless for HiFi. You could try a quad of EL86's with (really guessing here) a 150V supply?
I'll probably get shot down in flames for the heresy....
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Old 2nd May 2011, 12:19 PM   #3
DF96 is offline DF96  England
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Yes, no DC as there will be no air gap. You might not have to derate, as higher frequencies will help. However, I assume we are talking about instruments rather than hi-fi. It was common in the past for radio amateurs to use power transformers as AM modulation transformers, although only a limited frequency range (up to about 3kHz) was needed.
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Old 2nd May 2011, 02:37 PM   #4
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High quality audio transformers use thinner laminations in the core. Thinner metal reduces eddy current losses in the iron at higher frequencies. Disadvantage is that it costs more and is somewhat more difficult to make when using thinner laminations (thinner means more of them, and assembly time is increased as a result). This will become evident as higher losses and a degrading linearity at higher frequencies.

paul
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Old 2nd May 2011, 06:07 PM   #5
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Quote:
Originally Posted by seedseed View Post
Hi all,

i have a transformer that is 110 volts to 50 v ac of course and i would to try and use it as a output transformer on a compressor circuit. From what i have read materials and the way they are made and different winding ratios are what give output transformers there particular sound. What i would like to know is is it possible to use power transformers as this providing you work out the turns ratio and impedance and try and match it up. If anyone has done this or knows anything about it could you please let me know as obviously it could be a cheaper alternative. I have been trying to work out how to modify other transformers i have. I got to admit iam not overly keen on the whole wind yourself method. Of what i can see you need some sort of jig roller with a counter to hold the tention and count the turns to do a good job. but trying to work out best method. Anyone can go and buy the correct part and install. But having not huge funds to play with i try and find alternative methods to make things a bit cheaper. Who doesn't love a bargain. So sometimes its worth the effort. I think in output transformers this may be one possible one. I would love to hear from anyone who has done some output transformers with standard power transformers thanks
I tried it out before and didn't go well
That's right , You would have to ensure there's no DC , and it would be good enough for guitar use , maybe a practice amp .
And you need to make sure there's 4ohms or 8 ohms or so if you desire coming out of the secondaries .
How much power do you need ?
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Old 3rd May 2011, 07:48 AM   #6
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Ok, so general consensus is it'll work, but probably not the spare transformer you already have as it probably has a single primary (implying single ended and therefore DC use) and the 50V secondary will be far too high impedance for speakers (you'll probably want something in the 6/9/12 Volt range).
I also tried it out some time ago with a 6080 driving a 120/120 primary toroid with low voltage secondary and it too wasn't too promising.
Anybody else fancy a go and reporting back?
Regards
Henry
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Old 4th May 2011, 02:55 AM   #7
singa is offline singa  Singapore
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Hi, If you want to diy output trans then I would suggest reading up
the theory and winding techniques.I have not tried it myself but after
reading all the theory it is a formidable task and you need the hardware as well.Of course you can sort of wing it.Like if you want to account for the
DC saturation then you would have to strip the transformer E and Is
and stack them separately and use a suitable isolator of a certain thickness
of paper to get the desired DC current provided the core dimensions are
comensurate with the current or power output.

You can as an emergency use power transformer of equivalent
turns ratio as a stop gap measure but the disadvantages apply.
It's not a matter of the secondary voltages but the turn ratio that
matches the original output transformer.The important thing to know
is ... turn ratio equals voltage ratio.So...for instance the output
requires 3000 ohm/ 8 ohm speaker.Then the ratio is... just for illustration
1500 primary turns divide by 100 turns secondary =15 :1

Say you have a shorted left channel. Just pump a little AC voltage into the good one and measure how much is at the secondary and do the math.
You need to take it out of the circuit or amp.

So you would select a power transformer with 120V primary divide by
8V secondary or somewhere close = 15:1

In this case use a much larger capacity transformer maybe 2 or 3 times
to account for the DC but don't get excited about the frequency response.

The above description is for single ended use.For pushpull you need a center tap
so calculate accordingly or maybe use two tranformers in series.Remember this is
for temporary use only.Don't forget the winding direction for series connection
because if wired in opposite or opposing direction it will cancel out the other transformer
and your meter will measure zero volts.

Last edited by singa; 4th May 2011 at 03:14 AM.
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Old 4th May 2011, 08:21 AM   #8
Tajzmaj is offline Tajzmaj  Slovenia
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Hi check this out...
Building The DIY Gyraf 1176 Clone
Audio | element14 Australia
If you want to experiment with mains transformers use small one some 2-5W for this line out application. And be careful because if you pick one with 220v primary and 6v secondary and reverse it you will get very high voltage at output. High enough to burn the unit which follows.....on the other hand if you connect it normal than the output voltage will be to low. So you need transformer with low ,,gear,, something like 220v to 110v...and you will get 2:1 ratio. But because of high number of turns and separate pri-sec.....high parasitic inductance and capacity......don't expect batter results than cc35Hz to some 5Khz of response....which means no highs,,,,
Regards
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Old 4th May 2011, 08:36 AM   #9
singa is offline singa  Singapore
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seedseed said
Quote:
different winding ratios are what give output transformers there particular sound
Strickly speaking or in theory ,winding ratios are for matching output
tubes resistance with the speaker load so to achieve maximum power
transfer.It has nothing to do with how it sounds.

Of course the method of winding affects the frequency response because
the capacitance between each turn will affect high frequency and the
inductance of the winding will affect the low frequency.So if you want good
low frequency response or bass then a bigger core is necessary and for
high frequencies ,reducing the interwinding capacitance is important.If you can do this then most probably you will have a good sounding output transformer.
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Old 4th May 2011, 11:43 AM   #10
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Default wow great response

Wow great response. Thanks guys for all responding. I learn't a lot from that. I love this forum. I guess i have collected transformers here there and everywhere overtime. and you sit back and look at them in your junkbox and think to yourself surely there is a way i can utilise these things so obviously i try and work out different ways to do it. I was figuring that as taj said a 2:1 ratio would be the go but hard essentially to find in general most transformers drop down to a lower level such as 12 v or 15 or whatever. but obviously if you want a 2:1 ratio you need more winding on the secondary. I was not aware that you lose the high frequencies so much but as i play bass guitar this is not such an issue it actually might sound ok. Just a matter of finding a actual 2:1 ratio transformer only one way to find out.
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