How to use the OEM amp Wiring

[zdr93523]

I am going to do this using an Alpine KTP-445U which is a Class D mini amp. I'll post a review when it's complete. Thanks for the write up, I've been looking for a non-wire hacking solution.

[WiKKiD]

Awesome

[jadewbj]

So If I was planning on adding a single sub and amp in the trunk I could use that harness to power it all without needing to run any power, ground or remote?

I would run the RCA from the back the the head unit and that would be it, right? I guess if I wanted to I could also get a amp and give more power to the door speakers, right?

Any Idea on if it is possible to make the door speakers full range and not sub, since I would have a sub in the rear???

[WiKKiD]

Originally Posted by jadewbj

So If I was planning on adding a single sub and amp in the trunk I could use that harness to power it all without needing to run any power, ground or remote?

I would run the RCA from the back the the head unit and that would be it, right? I guess if I wanted to I could also get a amp and give more power to the door speakers, right?

Any Idea on if it is possible to make the door speakers full range and not sub, since I would have a sub in the rear???

Power wire is not big enough to power a subwoofer amp. Unless you get a very small wattage amp that's class D

[zdr93523]

BRZ Amp install without cutting, splicing, or otherwise hacking into any factory wires:

Today I installed an Alpine KTP-445U 45x4 RMS amplifier in place of the OEM amplifier. This amp is designed to go behind a factory or aftermarket stereo to provide more power to the speakers. The Alpine works on a 15A circuit which is (conveniently) identical to the OEM amplifier. The OEM amplifier runs only the 2 door speakers and I wanted to retain this setup to only power my Infinity Kappa 62.11s in the doors. The OEM HU provides plenty of power for the Reference 3.5s in the dash.

The OEM amplifier connectors are the same connectors used in 1987 and up Toyotas. (credit: RandomHero on FT86Club.com http://www.ft86club.com/forums/showthread.php?t=42239) So, in order to install this amplifier without cutting any wires, the only item needed is the Metra 70-1761 Radio Wiring Harness.

Here is the amp and Metra harness out of their packaging:

IMG_4169 by zdr93523, on Flickr

Then, following the advice of RandomHero on FT86Club.com http://www.ft86club.com/forums/showthread.php?t=42239 I removed the pins from the Metra harness and repinned the connectors to colors that match the amp connections. I used a very small jewelers screwdriver to unpin the connectors and had no issues.

Before:

IMG_4170 by zdr93523, on Flickr

After:

IMG_4171 by zdr93523, on Flickr

The next step was to remove the front input RCA connectors from the amp harness to accommodate the line level inputs and make all of the proper connections.

Note: Please do not post any wiring criticisms or "you should've soldered," etc... If you can splice wiring in an F-16 (you can, and we do), you can certainly do it in our cars.


IMG_4173 by zdr93523, on Flickr

Here is the harness with all necessary connections. Note that none of the rear output wires are used.

IMG_4176-4 by zdr93523, on Flickr

Once the harness was done, the amp was ready to be installed. I removed the factory amplifier (3 10mm nuts). Then, I connected the amp and performed a functional check and some tuning. I ended up setting the front gain to 1/2 power and the 80hz HPF on. The HPF does not defeat all frequencies below the cut off, it just filters 12dbs off of the frequencies below the cut off. Basically, it makes the bass coming out of my 6.5s sound clean.

OEM amp in top left corner of pic:

IMG_4178 by zdr93523, on Flickr

Harness connections with OEM amp removed:

IMG_4180 by zdr93523, on Flickr

HPF adjustments on the bottom of the Alpine amp (final settings with 80hz filter ON not shown):

IMG_4177 by zdr93523, on Flickr

To mount the amp, I used the OEM amp mounting points and the cable that runs through this area as mounting points for the supplied zip ties. Using this method, the Alpine amp is secure and has airflow all of the way around it, including underneath.

IMG_4182 by zdr93523, on Flickr

Here's the final pic. I left the wires long and unused wires intact in case I add speakers or remove the amp and want to use it in another car. I may clean up the wire bundle a bit, but for now, the wires are secure where they are. I will cut the zip ties after a day or two of driving once I am sure that they don't need to be tightened.

IMG_4183 by zdr93523, on Flickr

Review:
Wiring in the house and in car install took less than 2 hours. Then I sat in the garage for another hour or so listening to it. With the Kappa 62.11s and OEM amp, I could turn the volume up to 60 without distortion. Now, the this little Alpine beast set to a little less than 2/3 gain, I can turn the volume to 30 on some songs. It sounds really good at reasonable volume levels like 12 (used to be 30).

Alpine KTP-445U: Highly recommended!

[Fett4Real]

Nice Write up...if you wore ear defenders more you wouldnt have to turn the volume up so loud in the car to hear your music...will have to check it out when I return from Hell.

[f0rge]

Awesome write up, I'm doing the exact same thing except I was going to bridge the amp to get 90watts x2.

Still undecided on speakers (thinking JL C2) but the amp is in the mail. Can't wait!

Already have my wires re-pinned:

[zdr93523]

I would give it a try without bridging it. I have the 2ch input turned on and with my Kappa 62.11's (75W RMS) the amp is only turned up a little more than half way. I think this amp may be very underrated.

[f0rge]

Well I went ahead and installed the same Alpine KTP-445U following the instructions above and it worked! Sorry no pics I was too busy trying to keep the mess of wires organized.

I decided to go ahead and bridge the amp to 2 channel from the get go so I didn't have to go back and deal with all the crimp connectors if I got some higher wattage speakers.

The whole thing probably only took an hour and a half, most of that was figuring out how to connect the 2 harnesses together for the bridged output, in the car only about 10-15 mins to lay everything out and hook it up. It worked the first try.

Had the gain set to half and I scared myself to death it was so loud, reduced the gain to around 1/4 and it's better but will still need some fine tuning since I think it might be too quiet.

I understand the fruits of my labors (and money) won't truly be realized until I get some new speakers, but so far I'm very pleased, you can definitely tell the door speakers are running much cleaner and clearer than before.

[Leonardo]

Thanks for the information. It helped with my project. I used the oem speaker wire, and converted the oem amp input to rca for my 4 channel amp.

[mid_life_crisis]

This is going to be old news to some, new information to others, but there is a proper sequence for adjusting gains for cleanest sound. You first need to establish at what volume the head unit itself starts to distort. You do this by leaving the amp gain all the way down and listening to the sound on a high quality recording and slowly turning the head unit up until the sound starts to go bad. Turn the head unit down until it goes away. Make note of the volume. Never turn it up higher than this. Now slowly bring up the gain on the amp until the speakers it is driving blend properly with any other speakers in the car. With luck this will happen before the sound starts to distort. If the sound distorts first, you need a different amp because whatever you bought is over matched by whatever is driving the rest of the speakers.

Edit: This should be obvious but just in case.
Distortion may not be the H/U or the amp. It could also be caused by trying to make cheap speakers play too loud or too low for their design.

[mid_life_crisis]

Originally Posted by RandomHero

This wiring trick will only amplify the door speakers though. Not the dash or rears.

But it brings the signal and enough power for a small amplifier, which is nice and helpful.
A bit puzzled about one thing though. Does the head unit drive the rear speakers? They are small so it makes sense but too bad if that's the case because it would have been nice to have those signals here to tap into.

[f0rge]

The headunit drives the dash and rear speakers, the amp in the back is for the doors only. The HU should be able to power all those tiny speakers without a problem.

[RandomHero]

Glad to see this information is helping some people out!