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Old 27th November 2014, 09:30 AM   #1
JordiMB is offline JordiMB  Spain
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Default 100V line transformer as output transformer?

Hi, I've got a 100V line transformer with these characteristics:

Power: 10 / 7,5 / 5 / 2,5 / 1,25 W
Impedance: 1000 / 1330 / 2000 / 4000 / 8000 ohms
Output: 4 / 8 ohms

Could it be suitable for using as output transformer in a SS poweramp, in some way?

Thank you

Last edited by JordiMB; 27th November 2014 at 11:48 AM.
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Old 27th November 2014, 10:34 AM   #2
JMFahey is offline JMFahey  Argentina
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You have an adapter for a distributed sound PA speaker (think Airports, Wal Mart, etc.), to connect a small ceiling type speaker (10W or less) to a 70V or 100V line distribution system.

4/8 ohms speakers will get the stated power (1.25 to 10W) and be "seen" as an impedance of 1k to 8k by the main amp.

Can't imagine how you could use that as you wish ; only practical application (if you had 2 of them) would be to send some music to a beach cabin, from a clubhouse 100 or 200 meters away, with minimal losses.
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Old 27th November 2014, 11:34 AM   #3
JordiMB is offline JordiMB  Spain
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Ok, that's what I was thinking. Thank you for your reply. Muchas gracias y un saludo.
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Old 27th November 2014, 11:39 AM   #4
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To get the specified powers out you'd need to swing a lot of volts from your SS poweramp. Most amps don't have sufficient swing - the ones that might would have specified output powers in the 1kW range. Upside of using the 100V transformer would be spectacular dynamics, the downside though would be fairly limited SPLs.
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Old 27th November 2014, 11:48 AM   #5
JordiMB is offline JordiMB  Spain
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Yes, Abraxalito, that was my fear. I'm no expert but I understand this transformers are designed for large voltages on the primary, so it's difficult to get something out of them from the output of a SS amp, isn't it?
Could I use one of the windings as an inductor, if possible? Just to give it some use... I don't know how much inductance it can have.

Thanks for your reply.
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Old 27th November 2014, 12:36 PM   #6
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If you're feeling a bit brave, you can always dismantle a transformer and rewind it. This would be too much of a pain if the secondary (which you'd like to keep) is wound over the top of the primary, but if they're on separate bobbins its quite possible. I've done that with several mains transformers to re-use them as audio output trafos. It works a treat.

Reusing a transformer as an inductor wouldn't be a good idea as the core's not gapped usually so you'll get a very large inductance but not be able to run much current through it at all before it saturates.
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Old 27th November 2014, 12:48 PM   #7
JordiMB is offline JordiMB  Spain
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Buff, I'm not this brave, I think. Not enough experience.
What you say about the use as inductor makes me think it could be an option for an inductor loaded guitar amp, where people look for current limiting in the output stage to get distortion. But don't know if the saturation of the core would lead to too low current to be useful.
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Old 27th November 2014, 01:10 PM   #8
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That's a kind of circular argument - if you don't dive in and have a play then you won't get enough experience. What do you have to lose? At worst you'll get a pile of stamped laminations and lots and lots of knotted enamelled copper wire.....

What I'd suggest you do is replace the primary with wire about twice as thick - so its 4X the area. That'll give you a 25V primary (a quarter of the turns) which can be driven successfully by a 50W power amp - like an LM3886 chipamp.
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Old 27th November 2014, 01:25 PM   #9
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I'm going to send you a box with all that mess of copper, and you can try to undo the knots, hehehe . I'll take a look at the bobbins, to see if they are separate. It's an idea.
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Old 27th November 2014, 02:14 PM   #10
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I'll swap you your box with knitted copper for mine, my junk copper bag's got the extracted and cut primary windings from maybe ten trafos of varying sizes, the wire's so thin its like the floor sweepings from the hairdressers' downstairs....
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