Line out convertor

Hey,

I have a 2006 Pontiac Pursuit(Chev cobalt) with the base radio in it.  I need to keep the stock radio in the car, however I want to install a set of infinity 6.5's in the front, and my subwoofer in the trunk.  To power these I want to run my amps.  I have done stereo installations in previous cars, however have always had an aftermarket deck with RCA outputs.  

I know I need a LOC, and have heard good things about David Navone's LOC.  I'm looking at the N-7785V. 

The N-7785V is a four channel device that features two channels of full range output, plus two channels of low pass out with the same bass boost as the N-85 and N-85V. The signal level can be adjusted from a maximum of 9.5 volts rms down to zero volts. This is a great feature for optimizing the S/N of system and a must for competition or demo systems. Turning the knobs clockwise increases the signal level. At the amplifier/speaker we recommend a 1:3 gain structure for most systems. The N-7785V is a great device to connect an OEM deck into TWO aftermarket amplifiers. The front amps can be fed a full-range signal and the rear channels can be low-pass only.

I am wondering how to install this to work properly.  Any and all help is greatly appreciated.  Thank you..

Kyle

The Pontiac is a floating ground system, not common ground, so the brown (ground) wires on that LOC will not be used.  Just tie them up out of the way.  That leaves you with two wires per speaker output.  The striped is negative.  Two sets of wires are controlled with one gain adjuster, the other two sets with the other gain.  Use lengths of common 16 gauge speaker wire, the kind that is twisted pair cable, to connect the LOC to the individual speaker locations.  The LOC should be located within a short RCA cable's length from the four channel amp that it feeds.

I have used regular speaker wire that I've stripped apart at the seam, and twisted the two sides around each other to form twisted cable.  The twisting should be at about 1.5 to 2 twists per inch.  This twisting technique will eliminate unwanted interference into the signal path.

Locate the OEM wiring at each speaker and disconnect the factory terminals.  If the wiring shows bare terminal ends on these wires, tape them securely.  You don't want the original speaker wiring to come into contact with the car's sheet metal.  Strip a small portion of insulation from each wire, working methodically one speaker at a time.  Attach the length of twisted speaker wire to these bare spots and solder.  This is a proper "T-tap".  Secure each soldered joint with plenty of electrical tape, with the thought that some of the tape may unravel over time.  You still want to have plenty of tape over the bare soldered joint.

The twisted wires are secured to the LOC wires in the same manner.  Verify that all wiring is correct and test the system before closing up doors and putting things back in order.

LOC gain adjustment:  one gain controls the front, the other controls the rear.  Front is cabled to your amp with RCAs, and likewise the rear.  Set gains in the same manner as setting the amp gains;  by first finding the highest clean output level of the OEM deck.  Don't assume it's the 3/4 position on the dial that is often used with aftermarket decks.  The output through the speaker wires is not of the same quality as the output through the line level of an aftermarket deck.  It is higher voltage, lower signal current.  This lower signal is a "dirtier" signal than line level, and that attribute is shown in the OEM deck output.  You will find, if you use test tone sine waves, that the OEM deck will start to clip at about the halfway point.  Do a forum search for "gain" and read some of my posts for more info on test tones and gains.

You will be listening for deck output clipping through the amplifier and through the LOC.  The amp gains must be set to minimum (far left counter-clockwise).  The LOC gains are best set to maximum (far clockwise) at this point.  Once you have established highest clean output level of the deck, you can begin to match the amp and LOC to this output.  Begin with the amp, turning the gains of one channel at a time (or more commonly, front and then back channels) until you hear that familiar 'tick..tick' and slightly different tone that signifies the beginning of a clipped signal.  Adjust the gains until that sound is not heard.  You will then have the amp gains set.

Then the LOC:  this is purely by ear and your determination of what sounds clean and good compared to what sounds fuzzy or wrong.  With the deck set to fade to either front or back first, fiddle with the LOC gain (turning it downward) until the sound is as clean as it can be.  This can be done with the volume at any level you are comfortable listening to...and again, use the sine wave test tones for a pure response.  You can later test again using music sources for this LOC adjustment.  Fade the deck to the other way and do the same with the other gain. 

Once you've established where those LOC gains should be set, use a marker of some sort ( I use a dab of fingernail polish) to mark the location where each is set.  Leave it always on this mark.  Now, you must set the amp gains again, going through the process, so that you will end up with the best signal-to-noise ratio and highest amplitude possible.  This time, once those amp gains are set...mark the set points as you did with the LOC.  Then you can put everything back in order and enjoy your new system for a long time to come.

Translation for the common folk, tap the LOC into the speaker wires behind the deck and run RCA's, than set the gains properly

Stevdart,

Thank you for the complete explanation of how to install a LOC.  It will help ALOT when I go to install this next week.   Everything is clear as mud!! 

Cheers,

Kyle