View Full Version : unique question for audio guys
hyunelan2
10-12-2005, 11:39 PM
A friend of mine bought a fairly good condition 1972 240Z that he is restoring. It is missing the original stereo. He is going to put in an original 1972 Datsan stereo, and wants to wire it up so at shows he can show that it works. However, he wants to drop a modern deck in the glovebox for all the modern features of CD, lol.
Anyway, I've got a pretty good idea on how to do the power wiring for it, but what about the speaker wiring. If he has Headunit A and Headunit B connected to the same speaker, will the one stereo backfeed into the other? Some advice or suggestions would be appreciated.
A friend of mine bought a fairly good condition 1972 240Z that he is restoring. It is missing the original stereo. He is going to put in an original 1972 Datsan stereo, and wants to wire it up so at shows he can show that it works. However, he wants to drop a modern deck in the glovebox for all the modern features of CD, lol.
Anyway, I've got a pretty good idea on how to do the power wiring for it, but what about the speaker wiring. If he has Headunit A and Headunit B connected to the same speaker, will the one stereo backfeed into the other? Some advice or suggestions would be appreciated.
wow well I thought I was going to be able to answer that but after reading it not really no... but seriously..
wire the speaker wires to both and just turn the power off to one then there should be no backfeed since its off.. but I'd wait for 2loud or southwest to come in here
hyunelan2
10-12-2005, 11:47 PM
Well, I don't think it'll be a problem with the one being off... but if you've got it wired like
A-----> [speaker] <------B
What is to keep the current from going
A-----> [Speaker] -----> B ???
chaos GT
10-12-2005, 11:51 PM
Well, I don't think it'll be a problem with the one being off... but if you've got it wired like
A-----> [speaker] <------B
What is to keep the current from going
A-----> [Speaker] -----> B ???
the fact that current takes the path of least resistance
hyunelan2
10-12-2005, 11:53 PM
So the speaker will 'eat up the signal,' and it won't make it down to the second headunit then?
jfreak921
10-13-2005, 12:01 AM
So the speaker will 'eat up the signal,' and it won't make it down to the second headunit then?
Yep. Just don't turn both on at the same time.
Yep. Just don't turn both on at the same time.
should work, we will see though.. what I would do is hook it up outside real quick and see if it works
hyunelan2
10-13-2005, 12:47 AM
Yea... it's just rare to find a working 1972 Datsan radio, so I wouldn't want to blow it up. Thanks for the input guys.
try it with an aftermarket one first or your stock hyundai deck before you try the 1972 datsun one.. walmart's a good place.. you **** it up you return it! lol
Yellow_Elantra
10-13-2005, 04:07 AM
A more safer way to do it would be to use relays on the speaker wires
and use the remote output(amp output) on one of the h/u's to swich
the relays on.
Im sure you can but a special relay for this, but ordinary relays will
do the job, you'll just have to make a network of 8 relays.
kylemorg
10-13-2005, 09:05 AM
A more safer way to do it would be to use relays on the speaker wires
and use the remote output(amp output) on one of the h/u's to swich
the relays on.
Im sure you can but a special relay for this, but ordinary relays will
do the job, you'll just have to make a network of 8 relays.
Good idea. Actually, you'd probably only need a network of four relays for the positive (+) wires to the speakers. Ideally, you'd want DPDT (dual pole dual terminal) relays.
You could also do it with switches, but you'd need two DPDT switches. I don't know if they make a quad terminal switch...
As people have said, for a basic hookup you could just make sure only one unit is powered at any given time. To use Yellow's relay idea in a slightly different way, you could always hook up just one NC (normally closed) 12VDC relay to the amp power up lead on the new HU to cut the power to the Datsun radio when you turn it on.
hyunelan2
10-13-2005, 10:54 AM
^^^ Yea, I planned on something similar like that for the 'on' feature of the headunits... just need to figure out the speaker wires. Nothing has been purchased yet. He's on the planning phases of the audio setup now, so I'm trying to help him get his 'shoping list' together.
kylemorg
10-13-2005, 12:10 PM
I'd say just get one normally closed 12V relay and install it on the power line for the Datsun HU, with the trigger hooked to the remote am turn on lead from the new HU. I don't think you'll have to worry about the feedback on the speaker wires to the old Datsun HU at all -- there's only about 1V going through the wires to the factory speakers anyway.
Leviathant
10-13-2005, 12:52 PM
If you don't mind having a switch, you could very easily rig up an A/B switch, but it'd be another button to push.
I did something similar on my computer. See, I needed to be able to quickly switch between output to my speakers, my GuitarPort, and my headphones. I had this radioshack RCA switcher thingie my dad used with his old stereo for additional auxiliary inputs. The signal path worked in such a way that I could run it backwards - one source input into three outputs, and select any of the three from the switchbox.
So if you wanna be lazy about it, you could pick up that box from Radio Shack, and just connect your speaker wires to the appropriate + and - bits, and use that to switch.
ryan s-b
10-13-2005, 02:11 PM
i agree with leviathant, wire it up a/b switch style. best course of action.
kylemorg
10-13-2005, 02:21 PM
Two problems with the A/B switch:
1. the A/B switch is for RCA line level outputs, not speaker level.
2. an A/B switch only has a pair of left-right inputs / outputs -- if the car has front and rear speakers, you're SOL.
An A/B switch would work if you were using a line level converter from the Datsun HU and the RCA outputs from the aftermarket HU and running them both into a multichannel amp, but that's the only way.
ryan s-b
10-13-2005, 02:29 PM
that's the way i would do it. but relays would also work... most peeps aren't familiar with how relays work tho
southpawboston
10-13-2005, 04:09 PM
i think an obvious solution has been neglected here...
most likely, the original radio is monaural, and powers up a single speaker in the dash. why would you want to listen to a single tinny speaker with a modern deck? it will sound awful.
if it were my car, i would keep the stock radio hooked up to the stock speaker, but then wire my modern deck to two self-contained speakers (i'm thinking a/d/s L200's-- 4" woofers, 1" dome tweeters, and a small cast-aluminum sealed enclosure with bracket mounts) bracket-mounted somewhere under the dash where they can be heard in stereo, but don't alter the car by cutting speaker holes in the doors.
this is how most high-end audio shops deal with classic cars-- self-contained systems that don't integrated into the car's metalwork.
note the a/d/s L210 tucked away in the passenger foot well in this 1971 alpha:
http://cartunes.com/installs/alfa_romeo/1971alfa/dashboard1.jpg
2loud2k2xd
10-13-2005, 04:22 PM
Yep. Just don't turn both on at the same time.
^^^^^
exactly
dont have both powered up at the same time, or FRIED decks, speakers, and who knows what else
Kenshin
10-14-2005, 05:44 PM
Oooo... Southpaw is right. I hadn't thought of that, but yeah, a deck from 1972 I can almost guarantee is mono. Do like he said and wire up the aftermarket deck separately to a diff. set of speakers than the 1 speaker the stocker is hooked to.
hyunelan2
10-14-2005, 06:17 PM
Yea, I never thought about that either - but that would undoubtedly be the best way. I don't think I've ever even seen a 1972 headunit, especially since that's 7 years older than me. It would make sense that it's mono. The car, as he bought it, had some mid-80s tape deck in it... so there is no telling how the OEM stuff was/is supposed to be.
Yellow_Elantra
10-14-2005, 09:09 PM
Technically you're not suposed to have it wired together so you
dont turn them at the same time,
If you do this then voltage will still reach the H/U that is powered off
and *can* (sometimes youll be lucky) blow the output ic of that unit
Sending voltage up a turned off output ic could blow it up and possibly
strain the output ic of the unit turned on, and do the same thing.
I agree with southpaw, leave the origional H/U and wire in the new 1
seperate.
southpawboston
10-15-2005, 11:42 AM
what yellow says is absolutely correct, and even if sending voltage to a closed output IC doesn't blow it, it may distort the signal going to the speakers.
and if it doesn't have the original radio (they weren't called head units back then, lol), then there's no reason to leave the mid-80s deck in there and throw a new one in the glove box.
this is a pic of the 240z dash-- it looks like it will accomodate a modern HU very easily:
http://i22.ebayimg.com/04/i/05/2b/97/61_1.JPG
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