Hi everyone, I want to keep the factory look of my GS radio but the amp stinks. I want to wire in a KTP-445U Alpine Power Pack to the factory head unit.

Below is a link to a video about the power pack. They state that it typically isn’t compatible with cars that come with factory amps but I’m questioning whether this is true as I’ve seen YouTube videos of this power pack being installed in a GS with an aftermarket head unit.

Any advice or thoughts as to whether this is even possible? Thanks so much!

https://m.youtube.com/watch?v=GeP0l-dwYvA

https://www.alpine-usa.com/product/ktp-445u

 

Yeah, people install aftermarket amplifiers in the 2GS all the time.
Check the FAQ or run a search to find the many threads discussing and explaining how.

 

Thanks @firelizard ! I will do another search but I am having trouble on finding info on wiring an amp to the factory head unit. Most everyone seems to swap out the factory radio for an aftermarket headunit.

 

My '00 GS400 came with the Nakamichi radio/navigation/hvac touchscreen control unit, which was ugly and ancient:

Stock Nav/Radio/HVAC Touchscreen

Opposite of what you are trying to do, I pulled it all out: Navigation unit, front/rear speakers, CD changer, navigation computer (in the trunk), and installed a fully custom, modern multimedia system. This gives me HD bluetooth music, internet, modern navigation, back up camera, front parking camera (keeps the lowered front end off of curbs!), Torque app gauges, and 2,000 watts of high def music through 12 speakers. Why in the world would I want to keep my GS400 limited to music/multimedia tech from 2 decades ago?! Of course, installing this system took some effort, and about $3k. Here are some pictures of the upgrades:


Custom real burled walnut trim over ATOTO S8 Pro android multimedia unit and factory HVAC controller. Can also see a switch for electric exhaust cutouts, an alternator charge controller, and a Tein EDFC controller below.


The system at night.


At night with engine running (HVAC LCD lights up). Replaced old and burn out button lights with LEDs.


Custom carbon fiber 3+1-way front door speaker pods. Each speaker gets 75 watts from a VX800/8i (with DSP), or 225 watts per speaker pod up front.

Anyway, I'm sure you have your reasons. I took a quick look at the KTP-445U amp, and I believe you will need to intercept and re-route the factory speaker wire harness through the amplifier. You will connect the factory speaker outputs to the line-level inputs of the amplifier, and then insert the cut factory speaker wires (that run to your speakers) into the amplifier outputs. The convenient RCA connectors you see on the amplifier have no application here.

You should first take inventory of your factory sound system. My 2GS came with four speakers up front (a door speaker pod with a midrange speaker, and a tweeter mounted higher, in each door), two speakers in the rear doors (a speaker pod with a midrange speaker in each door), and an 8" subwoofer in the rear deck (under the rear window). There were different audio system options though, and you need to understand what system you have.

If there is only one wire running to each front door speaker (I can't remember), then you can use this 4 channel amplifier.
However, this amplifier is rated at 45W x 4, which does not seem like much more than what the factory puts out (not sure about this though).

Can you tell us more about what your audio goals and budget are? Will you be doing the work, or subbing it out?

 

Thanks, @CurlyG for your detailed post. Your setup looks awesome! I'm doing a budget build. Originally I was going to go your route and do a touch screen but wanted to keep the 90s look of the old radio. Why? I have no idea lol I just like the nostalgia of the tape deck look.

My current setup is the non-Nakamichi stock system. Radio, 4 door speakers, two tweeters in the front, and a sub in the back. My plan is to add a Bluetooth module to the existing radio with a kit I found online. I installed Rockford Fosgate speakers and wired the tweeters inline to the front door speakers . They all are all top end at the moment and there is hardly any bass/midrange even with the tweeters adjusted down and midrange/bass adjusted all the way up.

From what I saw on youtube a couple of people were installing the Alpine power pack as a solution to get more bass. I saw a video of a guy installing it to a similar setup - decent door speakers and stock tweeter/sub and got great results. However, he wired it to an aftermarket head unit like the one you have (video here - ). I'm going to be doing the work myself and have a good idea as to how to run the speakers like you mentioned above. Where I am hung up is how I wire the power/ground to the amp. What would the connection to the amp from the head unit look like? I can't seem to figure this out. I have also never wired up an amp so excuse my ignorance if what I am saying doesn't make sense.

I basically want to do exactly what that guy did with the power pack but wire it to the factory radio rather than an aftermarket headunit. He shows some of the wiring, but I am lost on how to wire the amp to the factory radio. The video is very detailed but I get a bit lost and confused when trying to make sense of it in the context of the factory radio.

 

Hi Vincent, OK, I got it. I can help you with the install. First, could you tell me what you plan is for the amplifier? From the KTP-445U manual, you can do 4 x 75W, or bridge the outputs and get 2 x 90W. Which speakers do you want to power?

 

Awesome! thank you so much in advance. I'm planning on powering the 4 Rockford Fosgate speakers (two of which have the tweeters wired inline) and possibly the sub. According to Rockford my door speakers are rated at 45w each. I have no idea what the sub is rated at in the GS stock system. I'm wondering if you are right in pointing out that this power pack may not be powerful enough now that I am doing the math. If I bridge the outputs would I be able to run the 4 speakers to the amp? I'm assuming the answer is no because I would only be left with 2 outputs after bridging. If the answer is yes but without wiring the sub to the power pack then I would be okay with that. I'm not convinced the sub will be great anyways once wired to the power pack. It seems like my only option here to get adequate wattage for the door speakers is to bridge the amp and sacrifice power to the sub OR go with a bigger amp.

 

Hi Vincent, to power the 4 door speakers, you will need either a 4 or 6 channel amp. The KTP-445U Alpine Power Pack is rated at 45W x 4 @ 4 ohms. The front speaker channels (Left and Right) each have 2 speakers (a midrange and a tweeter), for a total of four speakers up front. Also, by speaker wire, I mean 2 co-molded insulated wires that run together as 1 wire.
I'm not sure if the speaker set in each door is powered by 2 separate speaker wires (crossed over at the radio; active), or 1 speaker wire (crossed over at the speaker; passive), or if that even matters. There may be an impedance difference with 1 versus 2 wires, but the amplifier probably won't care, unless is drops below 2 ohms.
Anyway, 1 wire is ideal, because you can run that to, say, your front left output of the amplifier (run both the midrange and tweeter with one channel). The front right then consumes the 2nd channel, and each of the rear speakers consume 1 channel each. So, if your tweeter and midrange in each door speaker can be driven with 1 wire, your amp has all four channels going to all four (six) door speakers. This should be the same configuration as the Rockford speakers you installed. Also, there are no channels left to power the subwoofer.
Again, you can bridge the channels to get 90 x 2, but now you only have to channels. You cannot further bridge those 2 bridged channels to get 180 x 1.
Looking at the tiny gauge 12VDC input wire on the amp, that is an indicator that it doesn't produce enough wattage to drive the subwoofer any harder than what the factory amp is sending it. Truthfully, the amp looks like a Mickey Mouse solution.
What I recommend is you design your system to be powered by a 5 way amplifier, mounted in the trunk, powered by a real 4-gauge power cable, run directly from a fuse at the battery. Such a system can send solid power to your Rockford speakers, and can also power a subwoofer.
On both systems, you will still have to find and splice into your factory speaker wire harnesses. With the 5 way amp system, you'll also have to run the power wire from battery to trunk, a remote wire from the dash to the trunk, run 5 speaker wires (FL, FR, RL, RR, Sub Control) from the radio harness to the trunk, and run 4 speaker wires from the trunk to each speaker input wire (found at the B-pillar for the rear speakers, and behind the fuse blocks at each kick panel in the front). I can post diagrams and pin-outs of these wires and harnesses.
While you're at it, I would replace the factory sub with a free air sub that can be driven with more wattage.

 

I've given it some thought @CurlyG and I am going to go the route you took. Double din, backup camera, and 5 channel amp in the trunk. I'm still a little vague on how to wire this due to a basic understanding of car stereos. From my understanding, I wire in the double din (having trouble finding how-to's step by step on how to wire this in) and then wire the amp as you mentioned. A line with a fuse directly to the battery and then wire in the speakers from the new head unit to the amp and then run wires from the amp to the speakers. I would say figuring out how to go from the amp to the speakers is still a big question mark for me.

 

Hi VV, here are some aftermarket solutions that may work for your stereo system:

• Scosche LS02B Compatible with 2005 - 2011 Lexus GS Amp Bypass
  • Check Scosche online for installation help, or post a question here
  • I did not use this b/c I installed a full custom system with all new power and comm wiring
  • Your install might use the harness a bit different, as you will be driving the speakers from your 5 channel amp
• Scosche LS2083B Compatible with 1998-03 Lexus GS ISO Double DIN & DIN+Pocket Dash Kit Black
  • I used this to mount my double din radio

I ran my 2 gauge +12DV wire from the battery (fused), through a new hole in the firewall just behind the battery, along the passenger side door well, and back up into the trunk.

• You may only need 8 gauge if you're pulling less than 600 watts (43A at 13.8V); I'd run 4 gauge if you ever plan on going big.
• I ran 2 gauge b/c I'm pulling about 150 A (2000 watts at 13.8V)
• I also ran a 2 gauge ground from the battery, but that is not required (I wanted to make sure I had a solid ground with no noise)
• I drilled a hole through the firewall behind the battery, and installed a rubber grommet in the sheetmetal hole. I'll post a photo of it ASAP.
• Search for photos of un-snapping the door bottom trim and carpet edge lines.
• To remove the back seat (trunk access)
  • First remove the bottom seat cushion by pulling up on the front edge. There is a plastic snap on each side (left and right) which take a sharp upward pull to break free of.
  • There are four bolts securing the seat back at the bottom, and 2 nuts behind the cover of the left and right headrests. All bolts/nuts require a 12mm wrench/socket.
  • Once the bolts and nuts are removed, carefully pull the left and right seat belts toward their door opening, and loop them behind the seat back. You may have to remove the bottom bolt that holds the center seat belt to the chassis. I removed this seat belt, so I don't recall how it's done.
  • Once the seat belts are managed, the rear seat back can be removed.
  • Lift the black plastic curtain up, and carefully roll it backwards while sliding it up and onto the rear deck.
  • You should now have access to the trunk from the inside (important for running your power, signal, and speaker lines, and mounting your amplifier)
  • Pop the trunk lid, and remove the large back trunk trim panel piece. You may have to remove the side trim panels first. Use an automotive trim fastener removal tool (if you don't already have one, get it if you plan on doing this kind of work) to remove the plastic trim fasteners.
  • Plan a place to mount your amplifier. Ideally, you will surface mount it over the factory trim panels. Avoid burying it underneath or any mounting where it cannot breath (or it may overheat).
  • Find a ground to ground the amplifier.

This is all the info I have time for, but let me know if you have any questions. I'll try and post photos, and support your project as you go.