audio transformer, about 30W size, easily available?

Google "70 volt line transformer". Scads of good hits.

John

ad?

Good luck finding anything with high frequency response, 4K to 17K That almost has to be ferrite

It won't be small. I still have a 25 - 30 W ultralinear output transformer that I used with a pair of 7034? tubes. It is about 4"square and 5 - 6 inches tall. Must weigh about 5 pounds.

Tam

How about some more details on what you want. What primary and secondary impedance? what taps, if any? how much unbalanced DC in the primary, etc.etc.

The standard 70 volt stuff is probably OK for 100 - 5000 Hz, with no DC > > Google "70 volt line transformer". Scads of good hits.

Hi,

Know of any easily available (inexpensive and stocked) 30W audio transformer to couple to an 8 ohm speaker?

I am experimenting with a custom audio amplifier design that uses tranformer coupling rather than the usual capacitors. I took a gamble and tried to use a power transformer, but that's not working well because they are designed to work well at 60 Hz and the ones I've tried roll off very fast at higher frequencies. This isn't an audiophile project, but I want something a little better.

I want something I can get at a place like DigiKey or Newark or Mouser, not from a custom house or scrounging at hamfests or one of those "classic tube audio transformers" that go for $100. I can't use the little audio transformers sold in Digikey because their power handling is too small.

Would one of those 70V PA distribution transformers work for this? Is there a PA transformer vendor with real spec sheets, not just a catalog ad?

Thanks for any ideas, mw

you might try

might be what you want.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

That's the problem... too many hits. This seems to be a simple issue where today's manufacturers don't bother to give any detailed info. Just advertisements and surface level details.

I'd like to find a spec sheet showing some details before spending more money... something with freq response, dB losses, watts, weight.

The closest I've seen to what I am looking for is the PA transformers on the Hammond page mentioned by Michael A. Terrell (thanks, Michael). I'll probably spring for the 117F32. Not perfect, but close. Or maybe the 119Y30... wish Hammond had more details on the web site.

mw

Could you clarify this for me? Exactly what impedance should they be loaded with?

Thinner laminations than power transformers and interleaved windings.

Even top-quality laminations loose interest in the proceedings at higher frequencies and the transformer effectively becomes air-coupled. The tighter the windings are interleaved, the better the HF coupling.

With valve O/P transformers you have high primary impedances and lots of turns, which gives lots of stray capacitance and the possibility of self-resonance all over the place. That is another reason for splitting up the windings.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Yes, but you are calculating the impedance that the transformer places across the 70 volt line. You specifically state that

What do your calculations do to support your point? You haven't mentioned a single word about the transformer load (secondary winding) other than to say that it must be other than 8 ohms. What does the reflected primary impedance have to do with the optimum secondary load, and why are 70 volt transformers no good for 8 ohm loads?

I'm still confused. Why can't a transformer with a 167 ohm primary be designed to match an 8 ohm speaker?

???????????????

You don't say what the primary side drive is - i.e. tube or transistor.

If it's transistor and you want and you want something like a 1:1 transformer you can pretty much forget it unless you want to pay for a custom wound job. There's simply no market for such things.

70V transformers are designed to be loaded with quite a high impedance - no good for 8 ohms. Their audio performance is typically pretty lacklustre too.

What on earth do you *want* a transfomer for anyway with all the limitations it entails ?

Graham

It's calculated from first principles.

If it's 30W you want and the voltage is 70V then I = W/V = 30/70 = ~ 0.43

Zl = V / I = 70 / 0.43 = ~ 163 ohms

70 V line sytems are commonly used for distributed audio with multiple loads. Each transformer is designed for a given wattage. If you have a 30W amplifer you can load it with up to 30W worth of loads.

Graham

--
ciao Ban
Bordighera, Italy

That's exactly what I was looking for... amazing... I was hoping such a thing would exist.

EM4045 30W audio transformer input: 70 V output: 8 ohms freq response: 50 to 15kHz, +/- 1 dB (how do they do it?!) insertion loss 0.5 dB $21.88 (no minimum order!) (that's very competitive with the "no spec and non-in stock" parts I've seen listed on the distributor's web sites)

Thanks!

mw

ad?

I've used some mains toroids from Farnell in a push-pull pentode circuit and achieved

That sounds like exactly what "mw" is looking for. Offer to sell it to him or her. :-)

Cheers! Rich

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Oh, you are talking about the transformer that DRIVES the 70 volt line. Everybody else is talking about the transformers that connect the 70 volt line to the speaker.