Car Radio in Van

Submitted: Monday, Aug 26, 2013 at 10:55
ThreadID: 104048 Views:1631 Replies:5 FollowUps:7
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Wonder if there is a forum member that could help me with this audio question?
I have recently purchased a car radio to install in my camper van. Supplied with the radio is an adapter that attaches to the rear of the unit and is labeled 2v line out - the adapter is fitted with a red and white RCA male jacks. I am able to buy a connector two female RCA to 3.5mm headphone jack. Using such a connector is it OK to use this setup to listen to the radio with headphones?
Thank you.
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Reply By: Allan B (Member, SunCoast) - Monday, Aug 26, 2013 at 12:29

Monday, Aug 26, 2013 at 12:29
Hi John,

'Line Out' connections are intended to drive recorders or supplementary amplifiers and have a constant loudness output independent of the volume control setting. This output typically has an impedance of 100 to 600 ohms and is unsuitable to drive loudspeakers or even headphones. Even if you were satisfied with the low volume, the sound quality would be adversely affected.

Your radio should have connections for loudspeakers and headphones could be connected there.
Cheers
Allan

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AnswerID: 517109

Follow Up By: Ross M - Monday, Aug 26, 2013 at 19:41

Monday, Aug 26, 2013 at 19:41
G'day Allan B

If the RCA's are line out and constant volume, how does and amp hooked up to them as the sound driver source vary the volume of the amp?


Cheers
Ross M
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Follow Up By: JohnKT - Monday, Aug 26, 2013 at 19:45

Monday, Aug 26, 2013 at 19:45
Thank you for your reply.
I have been reading about your comments. Am I correct in understanding that the mismatch between the impedance of the line out and a connected speaker or headphone (100 - 600 ohms vs 8 - 30 ohms) is too large for a workable connection? On the other hand, a connection between the speaker and headphones would be workable since their impedance values are closer together?
I am wanting to set up the option where the radio can be listened to through the speakers or through headphones. I have only the front speakers connected to the radio, so, if I were to set up a switch to disconnect these speakers from the radio, could a direct connection from the poles of one of the unused rear speaker to headphones be a possible solution?
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Follow Up By: Ross M - Monday, Aug 26, 2013 at 20:55

Monday, Aug 26, 2013 at 20:55
You could wire a 3.5mm std stereo socket to the rears and just alter the fore aft Fade setting when Headphones are used.
Best to check if the commons ie negative speaker wire is common to all channels or each negative is separate.

They can be one or the other.

For example, if you connected the two channels negs/earths together for the socket it may begin to overheat the output drivers of the radios amp section and may also sound a bit fuzzy.

If they are all common negs/earths then no problem.

Ross M
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Follow Up By: JohnKT - Monday, Aug 26, 2013 at 21:48

Monday, Aug 26, 2013 at 21:48
Thanks, Ross.
How does one check whether if negatives are common or separate?
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Follow Up By: Ross M - Monday, Aug 26, 2013 at 22:56

Monday, Aug 26, 2013 at 22:56
JohnKT
I only discovered it when finding why a friends radio got hot and mine didn't.
A knowledgeable person at a car radio installer might know which do and don't.
My experience with that was fitting a Fujitsu Ten unit, in a Toyota Lcruiser, it has two wires and the negs weren't common in the plug to the unit.

Some Mitsubisji units used common and therefore three wires, one common fed the front speakers and same for rears.

As far as I can tell it doesn't damage the unit, well not straight away, but it uses more power/amps to run the unit when it is happening.

If you have a multi meter and read the resistance between the earth/neg wires concerned it would show VERY LOW resistance f they are common whereas the separate negs may show a higher reading of ohms.

If required I can go and check that as I have Fujitsu Ten in the shed and it has the separate system. Also may have other radios which may be different so I would have to investigate, hoping to have confirmation one way or the other.

Some one else may know immediately though and be able to say if you tell us the name and product ID of the radio unit.

Cheers
Ross M
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Follow Up By: Member - PJR (NSW) - Tuesday, Aug 27, 2013 at 08:47

Tuesday, Aug 27, 2013 at 08:47
Ross M

I don't know about your amplifier but mine has a volume control on it that works separately to the actual audio source. Maybe you got yours from Aldi. Sorry mate but that is such a simple question to answer. Stop stirring him.

Phil
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Reply By: Allan B (Member, SunCoast) - Monday, Aug 26, 2013 at 23:37

Monday, Aug 26, 2013 at 23:37
John,

Connecting a "stereo socket to the rears and just alter the fore aft Fade setting" would work but getting into the 'Settings Menu' to make the changeover can be messy.
More convenient is to use a DPDT switch connected to the 'Speaker Positives' output to switch between the speakers and headphones. The negatives can remain connected to both at all times.
Alternatively, use a switching-type phono socket which disconnects the speakers when the headphones are plugged in.
Just be very careful with the speaker output wiring or you could blow the radio's output drivers. Take note also of Ross' comments re isolated negatives.

You are correct in your understanding of the impedance matching situation. However the problem is only significant when the source impedance is higher than the load impedance. Accordingly there is no problem connecting 30+ ohm headphones to a 4 or 8 ohm speaker output.

************************************************************************
Ross, line outputs are normally used to feed supplementary amplifiers which have their own volume controls.

Cheers
Allan

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AnswerID: 517139

Reply By: Member - PJR (NSW) - Tuesday, Aug 27, 2013 at 08:58

Tuesday, Aug 27, 2013 at 08:58
JohnK

Personally I would say don't bother. The quality will not be the best and you may do some damage.

However you could try a small amplifier with a headphone jack like this one.3-Source Audio Power Amplifier with DAC Digital Converter and Headphone Output. This one is way too expensive but it was the first that I found and also is driven by 12V DC. You will also need a suitable RCA to RCA cable to connect it to those RCA sockets on the radio you already have.

Phil
AnswerID: 517145

Reply By: JohnKT - Tuesday, Aug 27, 2013 at 10:35

Tuesday, Aug 27, 2013 at 10:35
Thanks all for your help - this forum is a great source. It seems, especially with my limited skills, the best solution would be to look for an inexpensive amp, with volume control and headphone jack, that could be connected to the rear line out.
John.
AnswerID: 517148

Follow Up By: JohnKT - Wednesday, Aug 28, 2013 at 12:51

Wednesday, Aug 28, 2013 at 12:51
From the discussion I had not expected the following to work but it does. Am I missing something? Any comment to put my mind at rest?
I bought a small earphone amplifier powered by a AAA battery which I connected to the rear line out RCA plugs from the radio via a RCA to 3.5mm headphone jack adapter (the input on the amp is a 3.5mm jack). The headphones were the connected to the 3.5mm jack output on the amplifier. The sound can be switched between the attached front radio speakers (I don't have rear speakers connected) and the rear out line using the fade control on the radio. The volume to the headphones is then adjustable by the volume control on the radio.
Thanks, John.
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Reply By: Member - PJR (NSW) - Wednesday, Aug 28, 2013 at 15:02

Wednesday, Aug 28, 2013 at 15:02
Excellent. That was what I was talking about. I did the same in our old Chesney pop top about 20+ years ago. Only thing is that I had to make the amplifier back then.

So when does the surround sound and big speaker system get installed!!!

Enjoy

Phil
AnswerID: 517218

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