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Diabolical Artificer · 15th Jul 2019, 4:26 pm

I've several transformers labelled "matching tfmr" and another labelled "speaker isolation tfmr"; your bog standard output tfmr is essentially an impedance matching tfmr, these are the same so why the designation and traditionally why were they used in the past but not now?

There is a little booklet in the box that says this - paraphrased - This auto tfmr is designed to match any combo of load and OP Z's in the range 2-16 ohms..." Most of the ones I have are auto tfmr's but I do have a "isolation matching tfmr", in the booklet it says a matching/iso tfmr can be used to connect an ext lodspeaker to a TV set.

I'm guessing in the 50's most speakers were 16 ohm and the "new" transistor amplifiers of the 60's early 70's were designed for a nominal 8r speaker Z so maybe these were sold then to save loss of power Op or similar.

One last thing, I had a trannie PA amp that has an OPT between OP stage and spkr terminals, one sec for 100v line but also for 4 and 8 ohm spkr's, it sounded superb.

Any thoughts welcome, Andy.

15th Jul 2019, 4:26 pm	#1
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,667	"Matching" transformer. I've several transformers labelled "matching tfmr" and another labelled "speaker isolation tfmr"; your bog standard output tfmr is essentially an impedance matching tfmr, these are the same so why the designation and traditionally why were they used in the past but not now? There is a little booklet in the box that says this - paraphrased - This auto tfmr is designed to match any combo of load and OP Z's in the range 2-16 ohms..." Most of the ones I have are auto tfmr's but I do have a "isolation matching tfmr", in the booklet it says a matching/iso tfmr can be used to connect an ext lodspeaker to a TV set. I'm guessing in the 50's most speakers were 16 ohm and the "new" transistor amplifiers of the 60's early 70's were designed for a nominal 8r speaker Z so maybe these were sold then to save loss of power Op or similar. One last thing, I had a trannie PA amp that has an OPT between OP stage and spkr terminals, one sec for 100v line but also for 4 and 8 ohm spkr's, it sounded superb. Any thoughts welcome, Andy. Attached Thumbnails __________________ Curiosity hasn't killed this cat...so far.