When you get a 70.7 Volt Public Address Transformer, you see that it has connections \u00a0for different speakers, such as 4, 8, and 16 ohms. \u00a0On the other winding are various taps for different power outputs such as .625, 1.25, 2.5, 5 and 10 Watts. \u00a0But there is nothing to tell what the impedance is of the winding taps. \u00a0I was curious what these impedances were, so I did some simple calculations \u00a0and found the impedance of each winding.<\/p>\n
In a DC circuit, the power is equal to the voltage E squared divided by the resistance. \u00a0We will assume that \u00a0the reactance is zero so the answers are the same for DC and AC circuits. Algebraically \u00a0rearranging the formula, we have the resistance is equal to the voltage squared, divided by the power.<\/p>\n
We take the 70.7 voltage and square it and we get 5000. \u00a0We divide this by the power, .625 watts. \u00a0We get 8000 ohms, which is the impedance of this winding tap. For the 1.25 way tap we get 4000 ohms. \u00a0For the 2.5 watt tap we get 2000 ohms for the answer. \u00a0For the 5 watt tap we get 1000 ohms for the answer. \u00a0And for the 10 watt tap we get 500 ohms.<\/p>\n
So if you need an audio transformer that is 1000 ohms to 4, 8, or 16 ohms, you can use one of these and choose the 5 watt tap, for example. \u00a0You can also use one for a 5000 to 500 ohm autoformer, but since both taps are on the same winding, they are not isolated from each other. \u00a0To get isolation, you could put two transformers back-to-back, and contact the 16 ohm windings together. \u00a0You could also connect \u00a0two of them together in various series sand\/or parallel combinations to get various impedance combinations.<\/p>\n
These transformers seem to be much cheaper and more easily obtainable than an audio output transformer. \u00a0I used a 10 watt transformer in the above examples, but they come in various wattages, both higher and lower.\u00a0\u00a0So next time you visit an electronics store, check these out to see what they cost. \u00a0Sometimes when buildings are demolished there are ceiling speakers left in the rubble, and even if the speaker is damaged, the transformer may have survived. \u00a0More here: \u00a0http:\/\/en.m.wikipedia.org\/wiki\/70_volt<\/p>\n","protected":false},"excerpt":{"rendered":"
When you get a 70.7 Volt Public Address Transformer, you see that it has connections \u00a0for different speakers, such as 4, 8, and 16 ohms. \u00a0On the other winding are various taps for different power outputs such as .625, 1.25, 2.5, 5 and 10 Watts. \u00a0But there is nothing to tell what the impedance is <\/p>\n (Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-9217","post","type-post","status-publish","format-standard","hentry","category-audio"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/9217","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=9217"}],"version-history":[{"count":9,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/9217\/revisions"}],"predecessor-version":[{"id":9227,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/9217\/revisions\/9227"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=9217"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=9217"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=9217"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}