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 Post subject: Drive a horn speaker from a IPhone?
PostPosted: Jul Wed 08, 2020 7:36 pm 
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Location: North Providence, Rhode Island
Does anyone have a circuit to drive a horn speaker or 20s headphones from an iPhone?

Thanks
Len

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 Post subject: Re: Drive a horn speaker from a IPhone?
PostPosted: Jul Wed 08, 2020 8:12 pm 
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Joined: Jun Wed 08, 2011 2:33 am
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Location: Ohio 45177
You need a small stepup transformer. Something small would be like an output transformer reversed, so that the phone goes into the low impedance winding and the speaker across the primary or hi impedance winding. You could use one of the small transistor radio/amp output transformers that match say, 8 ohms to 1000, or the output transformer of an old parts radio like an AA5 that would step up to an even higher output impedance. Not super critical to need an exact transformer but we need to step up the impedance a great deal to match the solid state outputs. Those small transformers used to be easy to get at Radio Shack and not expensive. Don't know where else they sell them now. Probably ebay or one of the electronics hobbyist parts sites. Here is a generic example: https://www.ebay.com/itm/1-x-NOS-Submin ... SwPihd4HZ2 I would not bother to spend money on a 8 to 500 ohm. You might have something already that would work if you have radio parts and stuff.

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 Post subject: Re: Drive a horn speaker from a IPhone?
PostPosted: Jul Thu 09, 2020 10:10 pm 
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Joined: Jan Tue 16, 2007 7:02 am
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Location: Lexington, KY USA
It would be best to use two transformers, one for each stereo channel from the iPhone. The high impedance windings on the speaker side can be put in series to mix the signals down to mono. The resistor network used for mixing the stereo output driving a single transformer to feed mono to an old radio is lossy, so you don't want that.

Unfortunately, I think that the sort of impedances you are trying to match call for a transformer that may be hard to find.

Ted


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 Post subject: Re: Drive a horn speaker from a IPhone?
PostPosted: Jul Tue 14, 2020 6:11 am 
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Joined: Jan Thu 16, 2020 12:29 am
Posts: 768
arzoo623 wrote:
Does anyone have a circuit to drive a horn speaker or 20s headphones from an iPhone?

Thanks
Len


Len,

The attached amplifier in this link takes a signal from an iPhone or iPod and amplifies it up to drive a high impedance speaker (6k Ohm in this case, and generate 2W of power). The only difference being I made the high Z speaker myself by fitting an impedance matching transformer to the rear of a modern speaker. It will happily drive any vintage high Z speaker too:

http://worldphaco.com/uploads/UX-171-A_ ... ifier..pdf.

For vintage high Z headphones though you wouldn't need an amplifier at all, just an impedance matching transformer, and probably also not for a horn speaker either, if you didn't require much output power.


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 Post subject: Re: Drive a horn speaker from a IPhone?
PostPosted: Jul Tue 21, 2020 2:47 am 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 10874
Location: Ohio 45177
What I have done, is plug a stepup transformer into the headphone jack of a transistor radio and a transistor radio has enough to drive a horn to listenable levels as the horns were designed to work with milliwatts, not watts, of audio power from the old radios. Maybe not really loud but normal listening level nearby. I have no idea what amount of audio your device provides but I suspect modern headphones may not be quite as efficient as antique types or the drivers of horn speakers, which were equivalent to the old headphone drivers coupled to a horn instead of your ear.

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 Post subject: Re: Drive a horn speaker from a IPhone?
PostPosted: Jul Fri 24, 2020 3:40 am 
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Joined: Sep Thu 14, 2006 3:27 pm
Posts: 13072
Location: Carmel, Indiana
Try this setup.

Image

Image

Just use a small 8 ohm to 1k ohm transformer.

https://antiqueradio.org/iPodAdaptor.htm

Years ago there used to be a ready made adapter that you could hook up the output of a transistor radio or smartphone and drive a horn speaker. I forget who made them and if their still available. It looked very much like this device but it was more compact and professionally made.

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