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 Post subject: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 12:32 am 
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Joined: Jul Tue 02, 2019 6:47 pm
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Location: Paducah, kentucky
I have built a couple of junction boxes with 3.5 mm adapter and toggle switch to go between iPod and the AM radio and for the most part they have worked very well.
It seems that the proper way to do this I should add an isolation transformer.
Does anyone have a simple drawing or a website with the instruction for doing this?
As always thanks for the help.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 6:28 am 
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Mike48 wrote:
I have built a couple of junction boxes with 3.5 mm adapter and toggle switch to go between iPod and the AM radio and for the most part they have worked very well.
It seems that the proper way to do this I should add an isolation transformer.
Does anyone have a simple drawing or a website with the instruction for doing this?
As always thanks for the help.

More info, please:

1. Are you connecting the iPod to the AM radio?
2. If so, what is the connecting point on the AM radio?
3. If not are you using an AM radio transmitter?
4. If so, what transmitter?
5. Or are you using the switch to connect headphones alternately to the iPod and the AM radio?


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 6:58 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Beautiful Downtown Burbank CA
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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 9:54 am 
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Joined: Jul Tue 02, 2019 6:47 pm
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Location: Paducah, kentucky
https://youtu.be/j8YeJ0T3DpI
I’m using this tube video as a guide.
One wire to and from volume pod with two 1k resistors and a 10k resistor on the ground.
It has worked fine but apparently there is some danger in doing this without the isolation transformer.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 12:09 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Arlington, VA USA
I've been using this device for adding bluetooth dongles. Works just fine.
https://www.amazon.com/BESIGN-Ground-Is ... CESAHVQCAP


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 2:54 pm 
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Joined: Jul Tue 02, 2019 6:47 pm
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Location: Paducah, kentucky
Thanks Erik, I’m not sure the noise filter would be the same protection as the isolation transformer that is hard wired in but I don’t really know.
I think from what I have read the danger is getting some kind of electrical feed back into your iPhone, Alexa or whatever device you are using to provide the music to the vintage radio.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 6:29 pm 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
Stereo isolation audio transformer...
http://dwarmstr.blogspot.com/2009/06/au ... ormer.html

see large photos (and text) at fickr...
"This last jack is not grounded to the can which breaks the ground and prevents ground loops".

Greg.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 8:44 pm 
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Location: Paducah, kentucky
Mike toon thanks for the drawing.
The transformers I currently have only has four prongs two on each side so I’ll have to look for these.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 9:39 pm 
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Those little Radio Shack transformers were readily available way back when. Ebay might have used ones.
I built mine over 10 yrs ago and until I bought Alexa it went unused. It has a little "application" but the dead quiet isolation makes it a winner.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sat 07, 2019 11:49 pm 
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Location: Paducah, kentucky
Mike, I have 3 different radios in 3 different rooms hooked to echo dots. I think that this has given the vintage radio a new life that will endure for years.
I absolutely love listening to the tube radios play 30’s 40’s and 50’s music with aid of the new technology.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sun 08, 2019 5:29 am 
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Location: Beautiful Downtown Burbank CA
Yea, faster than I can search my huge library, Alexa play Summer Wind by Sinatra and it transmits to AM radios anywhere on my property. I don't like it? Alexa next... It blasts from my old Zenith console and sounds amazing. Alexa play Moody Blues, Days of Future Past album and it plays instantly. Alexa louder. What's not to like?
Quality? It sounds like it did back then through those tube radios. Good enough for my ears. :lol:


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sun 08, 2019 11:48 am 
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Location: Arlington, VA USA
Mike48 wrote:
Thanks Erik, I’m not sure the noise filter would be the same protection as the isolation transformer that is hard wired in but I don’t really know.


These are isolation transformers. They eliminate noise by removing the ground loop using transformers.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sun 08, 2019 1:16 pm 
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Joined: Jul Tue 02, 2019 6:47 pm
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Location: Paducah, kentucky
Thanks Erik, that’s sure a simple fix plus some noise filtering.
I’ll definitely try one.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Sun 08, 2019 10:18 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3619
Location: Lexington, KY USA
The only schematic seen above does not do what the OP was asking about, isolating a low impedance stereo source from a mono tube type radio.

Usually you don't really need the isolation for a radio with a power transformer. It may still help with hum and noise, as well as with sets having funky volume control circuits.

Only one transformer is needed if the output is to be mono. You can mix the two channels ahead of the transformer.

The Radio Shack transformer is no longer in stock down at the corner store, and has no isolation voltage rating whatsoever.

If you are using both transformer windings, as you will if you are to have isolation, a transistor radio output transformer is not the best choice. The low impedance winding needs to have more inductance and low frequency level capability than the winding on an 8 ohm transistor radio output transistor will have. A winding rated for 125 or 500 ohms will be good for the input side, then you need a much higher impedance winding to feed the radio.

Ted


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Mon 09, 2019 12:06 am 
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Joined: Jul Tue 02, 2019 6:47 pm
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Location: Paducah, kentucky
Thanks Ted, I’m pretty confused at this point. Do you have a source for an isolation transformer that fits this application. Most of the radios I would be adding the input to do not have have a transformers, just 5 tube radios.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Mon 09, 2019 2:33 am 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3619
Location: Lexington, KY USA
A transformer that should usually work well is the Triad TY-142P, stocked by distributors such as Mouser.

Image

Mouser lists this at $5.60 ea.
It’s rated for 10k CT : 2k CT. The maximum voltage step up ratio is about 4.4:1.
When driven from a source with a low impedance relative to its ratings, it should have adequate frequency response and signal headroom.

Use a couple of resistors to mix the stereo signal into the lower impedance winding. Feed the higher impedance winding to the radio through a switch. Keep the radio side connections away from where they might be touched by someone.

At least one ARF member has reported good results with this transformer used in this application.

Ted


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Mon 09, 2019 4:43 pm 
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Joined: Jul Tue 02, 2019 6:47 pm
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Location: Paducah, kentucky
Thanks Ted


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Thu 12, 2019 2:28 am 
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Location: Phoenix, AZ
I use these.
https://www.ebay.com/itm/Vehicle-Audio- ... 2749.l2649

_________________
Everyone you meet is fighting a battle you know nothing about.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Thu 12, 2019 9:54 am 
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Joined: Jul Tue 02, 2019 6:47 pm
Posts: 101
Location: Paducah, kentucky
Thanks I sure had not seen those before. I assume that they have 3.5 mm plugs on each end.


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 Post subject: Re: 3.5 mm ADAPTER WITH ISOLATION TRANSFORMER
PostPosted: Sep Thu 12, 2019 4:28 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Beautiful Downtown Burbank CA
I found one for $2.62 shipped and ordered one to test.
https://www.ebay.com/itm/Xh-M372-Audio- ... 2749.l2649


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