70 volt transformer...can I use this?

B

BJ James

Junior
Jan 11, 2011
260
0
0
I have a couple 100 watt 70 volt transformers. There are no wires coming off it, just 5 tabs marked COM / INPUT4R / INPUT8R / OUTPUT100 watts / OUTPUT50 watts.
My hope is to use these and grab a few more to temporarily convert some fullrange passive boxes to 70 volt operation. A PL340 is of a suitable voltage to drive a 70v system without a stepup transformer (confirmed with QSC). Just not sure how I would wire up these transformers as the ones I usually come across have clearly marked wires but are a lower wattage.
Would this be right (although looks backwards according to the labelling)? (-) from the amp to the transformer COM then COM to the (-) speaker terminal. (+) from the amp to the OUTPUT100 watts tab(assuming I want 100 watts to the speaker) then from the INPUT8R to the (+) speaker terminal (assuming the speaker is an 8R box).
Like I say, this seems to me to be correct, except for the labelling on the transformer.
Thanks,
BJ
 
Re: 70 volt transformer...can I use this?

It should be as simple as it looks. If there are only those 5 tabs, it may be an auto-former instead of a fully isolated transformer, but that will work too.

The only unknown is the low frequency response of the x-former. Generally you need lots of copper and iron to go very low frequency so as long as you HPF your system output at some reasonable cut off, you should be fine.

Note: an auto-former will be physically smaller than the same power transformer, because part of the primary current is shared with the secondary, so its more efficient.

JR
 
Re: 70 volt transformer...can I use this?

Thanks for the reply JR.
This little thing weighs close to 4 pounds if that means anything with regards to the low end response. I'll hook 'em up and give'em a try anyways.
Thanks again.
BJ
 
Re: 70 volt transformer...can I use this?

Sounds like it is an output transformer meant to allow a lower output amp to drive a 70V system, you'd essentially be using it in reverse fashion from it's 'normal' use and that may be why the labeling reversed from what you expect.
 
Re: 70 volt transformer...can I use this?

Ya, that's what I am thinking. But it can be used in reverse too right?
 
Top Bottom