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 Connecting a stereo output to mono radio pick up
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 Return to top of page · Post #: 1 · Written at 10:01:07 AM on 11 December 2019.
Oldtvmelb's Gravatar
 Location: Lakes Entrance, VIC
 Member since 28 July 2013
 Member #: 1384
 Postcount: 26

Hi all,
Wondering if it is possible to connect a stereo output from say a cd player to a pick up connection on old radio. I have been told there are problems changing the stereo output to mono and you risk blowing the stereo source. Will I get a combined output of both channels or just one channel? Any help will be appreciated.. Thanks

 Return to top of page · Post #: 2 · Written at 12:27:37 PM on 11 December 2019.
Irext's avatar
 Location: Werribee South, VIC
 Member since 30 September 2016
 Member #: 1981
 Postcount: 399

The o/p of the CD player will be around 0dB with high impedance (around 10K) so no problem combining left and right channels to form a mono source.
The old radio p/u input have been for a xtal or ceramic cartridge which is a similar level so it should work fine.

 Return to top of page · Post #: 3 · Written at 12:29:20 PM on 11 December 2019.
Irext's avatar
 Location: Werribee South, VIC
 Member since 30 September 2016
 Member #: 1981
 Postcount: 399

I'm assuming you mean the RCA o/p of the CD player not the speaker o/p of a combination unit.

 Return to top of page · Post #: 4 · Written at 1:52:53 PM on 11 December 2019.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 881

The only "danger" is if the terminals on the radio have a large DC or AC voltage on them!
That voltage may then overcome some part in the CD output.
There may also be a AC mains voltage difference with reference to earth if the radio is NOT properly earthed.

So the logic is no one can say connecting two pieces of unknown equipment together may not have some risk.

Meanwhile back on earth, taking the audio channels from a device and just paralleling them together tp go into a mono device is done so often. I just use a RCA two into one adaptor and then feed one channel into the terminals /jack socket/RCA whatever on the radio.
The audio voltage level out should be in the same ball park as what a crystal/ceramic cartridge was as Irext notes.

The experts will be crapping on about tone correction and level controls and pointing out 100 things that technically may be not quite right.
Just ignore all that go with a 2 to one adaptor try it and see.
Remember that most "stereo" tapes and records and most radio transmissions are MONO anyway so the music wont be affected.
You may lose the "sound stage" width that a very few tracks have had crafted into them in the studio, check out Beatles "Rubber Soul" album original record pressing, for one off the top of my head, but that's about all.

In my AM band micro transmitter , for a sound sources I just use the 2 into 1 RCA from CD/Tape/FM source to modulate the carrier.
I cannot hear any difference to the music from the "stereo" original, but then again i'm supposed to be musically tone deaf anyway.


 Return to top of page · Post #: 5 · Written at 10:22:44 AM on 12 December 2019.
Tallar Carl's avatar
 Location: Latham, ACT
 Member since 21 February 2015
 Member #: 1705
 Postcount: 1574

There are very good instructions on eBay for this. Each channel has a 1k resistor combined to the input with a 10k going to ground. Take a look at the YouTube video. I do this all the time . To prevent DC destroying your CD player you connect the two 1k resistors via a .01 capacitor.


That's the link. It's easy as.

 Return to top of page · Post #: 6 · Written at 9:20:25 PM on 12 December 2019.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4339

There are also links (which I probably downloaded) where two transistor radio OP transformers are used. That allows remixing, and voltage gain, whilst also providing a degree of isolation between the two items.

Refer Antique Radio Forums (USA)

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