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Discussion Starter · #1 ·
Considering the Alpine KTP-445U Power Pack, which is an amp that can be powered off your factory head unit's power wire as long as the fuse is 15A or higher. It seems the main fuse is only 7.5A, but my '89 also has the 20A Dome fuse in the engine bay's fuse box, and per the diagram below, apparently it is used with later MK3s that had a separate factory amp. My car does not have that external factory amp, but do I have what I need to power that Alpine amp? Or am I gonna need to run it directly from the battery like any other amp? If I do have what I need fuse-wise, would I then need to tap into a different wire, or just the usual power wire (blue/yellow, I believe) going to the head unit?



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If its 45w x 4 and its pulling it at 13.6-13.8v that means its pulling around 15 amps. Now that assumes its 100 efficient which and AB amp is more like 60-70% efficient. I would think 20 amps is probably more realistic. Either that or Alpine is fudging the numbers or they came up with a little trick to get a little more power out of it

If the "dome" is simply just powering the dome lights you should be fine to run the power wire through there.

Now if you really crank the radio up a lot you may want to run it straight off the battery or run the power wire directly off of the fuse box. That way you have a quality wire that isnt going to melt if you get on a road trip blasting the radio for a couple hours. Running it this way will also help keep down noise in the line.
 

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Discussion Starter · #3 ·
Seems to be a bit more going on with the Dome fuse. I'm not savvy enough to figure out if tapping an amp into it is safe though. It would be nice to avoid having to run a power cable through the firewall to the battery if I don't have to though. I also wouldn't want the amp to turn on just because the dome lights turn on though, either.


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Yeah I had a feeling it might be busy if it was 20 amps.

If you do decide to go straight to the battery there is a straight shot from the battery to the right of the brake booster. Someone just cut a slit in the plug on mine...? On the inside it has an over lap cover.

And those pictures are from when I got it. Its been cleaned up now.😉
 

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Discussion Starter · #5 ·
That looks like it would be a good option with minimal wiring. Thanks for the pics.
 

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Seems to be a bit more going on with the Dome fuse. I'm not savvy enough to figure out if tapping an amp into it is safe though. It would be nice to avoid having to run a power cable through the firewall to the battery if I don't have to though. I also wouldn't want the amp to turn on just because the dome lights turn on though, either.
You'll be fine connecting the new amp to the 20 amp dome fuse. I have been running with a 225 watt Acura/Bose amp for years on the 20 amp with no problems. My amp is 25w x 4 plus 12.5w x 2 for front door tweeters plus 100 watt for rear bass speakers.

Your amp gets its turn on signal from the radio off the 7.5 amp radio fuse. When I get back home, currently in Tampa airport awaiting flight home, I'll check the 89 Supra wiring manual for amp turn on wire color. I believe the amp power is a blue with white or yellow stripe wire at my 92 stock amp plug.
The 20 amp dome which is dome lights, door, vanity lights and the clock powered my stock 120 watt amp and it's now protecting a 225 watt amp.
 

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"Considering the Alpine KTP-445U Power Pack, which is an amp that can be powered off your factory head unit's power wire as long as the fuse is 15A or higher. It seems the main fuse is only 7.5A, but my '89 also has the 20A Dome fuse in the engine bay's fuse box, and per the diagram below, apparently it is used with later MK3s that had a separate factory amp. My car does not have that external factory amp, but do I have what I need to power that Alpine amp? Or am I gonna need to run it directly from the battery like any other amp? If I do have what I need fuse-wise, would I then need to tap into a different wire, or just the usual power wire (blue/yellow, I believe) going to the head unit?"

So on an '89 without factory CD player the P-L (pink w/ blue stripe) wire is the amp turn on from the radio power switch. It's from the 7.5 amp radio fuse and it's in the 10 space radio plug "A" at position 9 in pic below 3
Amp gets a turn on signal from the P-L wire once head unit is powered on.

The power for the amp is off the 20 amp dome fuse which is the L-Y (Blue w/ yellow stripe) wire which is also in the 10 space radio plug "A" It's Hot all the time. Top row below tab release on end at position 4 in pic.


 

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Discussion Starter · #10 ·
Nice -- that all looks very doable. In fact, I think my first choice will operate with that even better, since it only has a max draw of 8.5A:



I pretty impressed with its capability as demonstrated in some YouTube videos.


If that Kenwood powered sub will fit under the passenger seat, all I'll have left to do is get bass blockers wired in for the 6 standard speakers and I should be all set, with the bonus of everything looking stock (save for the non-USDM Toyota head units I'm messing around with).

Thanks for helping to confirm how this could work. (y)
 

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An Class AB Amplifier is progressive.. Meaning that at idle it will pull 2.5 AMPS with no signal and ramp up to the given power output at full volume. That is the nature of the Class AB amps.

Now the full amp draw happens if the amp is recieveing a continous 100hz or 1000hz sine wave. Music is dynamic and not a sustained wave.

With that said, i would not use 30 year old wiring for any car audio stuff.
 
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With that said, i would not use 30 year old wiring for any car audio stuff.
This is where I tend to find myself with audio installs. Fresh wire is cheap insurance, although it's a bit more work to tuck it away.
 
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Discussion Starter · #13 · (Edited)
I bought the Kenwood powered sub and started tearing into this project today. Since I'm replacing all the speakers (tossed the Polk DB501s), I had removed the rear interior panels on a previous day in preparation.

Speaking of old wiring, I agree it's a good idea but I don't think I'm up to the task of replacing it. However, after looking at the very thin blue-yellow wire going into the head unit for the 20a/amp+ power, I'm wondering if the red wire going from Junction Box #3 to the fuse block would be a better option to tap into if it's a thicker gauge. It appears JB #3 is somewhere behind the fog light and rear defroster switch panel. If that's not a great option I'm prepared to wire through the firewall.

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I also found a better weather strip for the rear speaker boxes. Last time I went through this, I used a white foam weather strip that was both too thick and too dense, so it wouldn't compress enough when it was time to replace the speaker covers. The new stuff is 3/4" x 5/16" which looks a lot like the OEM strip, so I expect it should work fine.

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I bought the Kenwood powered sub and started tearing into this project today. Since I'm replacing all the speakers (tossed the Polk DB501s), I had removed the rear interior panels on a previous day in preparation.

Speaking of old wiring, I agree it's a good idea but I don't think I'm up to the task of replacing it. However, after looking at the very thin blue-yellow wire going into the head unit for the 20a/amp+ power, I'm wondering if the red wire going from Junction Box #3 to the fuse block would be a better option to tap into if it's a thicker gauge. It appears JB #3 is somewhere behind the fog light and rear defroster switch panel. If that's not a great option I'm prepared to wire through the firewall.
On my 92 the L-Y wire is 14 gauge to the stock amp under pass seat and it was split to power in on 2 terminal pins, see pic:

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You could grab off the 30 amp pwr cb on R/B # 5 at drivers side. It's a heavy gauge 14 wire that feeds the power windows and seat. It's a L-W wire ( Blue w/ White stripe). Those 2 accessories are intermittent in use so it wouldn't be a problem taking amp power off the 30 amp CB.


MK3 TEWD On-Line Take power off at "5" in pic but Before the pwr main relay at either 5's
 

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I also found a better weather strip for the rear speaker boxes. Last time I went through this, I use a white foam weather strip that was both too thick and too dense, so it wouldn't compress enough when it was time to replace the speaker covers. The new stuff is 3/4" x 5/16" which looks a lot like the OEM strip, so I expect it should work fine.

View attachment 267594

View attachment 267595

I used that same open cell foam when I did my rear speaker upgrade on boxes. I added a 2nd OEM 4 ohm speaker next to the original for a 2 ohm load to match my 2 ohm amp.

On a side note: I bought 2 cans of Great Stuff minimal expanding spray foam for doors & windows and injected all the openings in the welded metal brace between rear shock towers. Let it cure and cut off flush after with a serrated knife and hack saw blade. What a big difference in rigidity especially when cornering. It stopped any flexing and made it quieter too. It was like I added a rear strut tower bar between the rear shock towers.
 

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Discussion Starter · #16 ·
I used that same open cell foam when I did my rear speaker upgrade on boxes. I added a 2nd OEM 4 ohm speaker next to the original for a 2 ohm load to match my 2 ohm amp.
Now I'm very curious as to exactly how you added a second speaker next to the original one in that spot. And since you have '92, you would have the 3.5" speakers in the middle that could be swapped out for 4 ohm to get your 2 ohm load.

The new speakers I have back there are Dayton Audio 4.5" midwoofers with a 150Hz bass blocker connected. Good frequency range so far, and as far as fitment, it does drop in, but mounting holes don't quite reach the ones in the box, so I had to orient it at an angle and drill new holes.

I will take a peek at the amp power wiring options again tomorrow when I have some daylight to resume this project. Gets dark fast outside at this point.
 

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Now I'm very curious as to exactly how you added a second speaker next to the original one in that spot. And since you have '92, you would have the 3.5" speakers in the middle that could be swapped out for 4 ohm to get your 2 ohm load.

The new speakers I have back there are Dayton Audio 4.5" midwoofers with a 150Hz bass blocker connected. Good frequency range so far, and as far as fitment, it does drop in, but mounting holes don't quite reach the ones in the box, so I had to orient it at an angle and drill new holes.

I will take a peek at the amp power wiring options again tomorrow when I have some daylight to resume this project. Gets dark fast outside at this point.
I did it to get more bass from rear after trying numerous new speakers in rear boxes. I'm now feeding the middle 3.5" separately with their own amp channel feed. I cut a second hole with a 4.25" hole cutter in both speaker boxes close to existing speaker hole and installed a second stock 4 ohm 15 watt speaker cause I needed all 2 ohm speaker loads for my replacement amp. I ran a separate pair of speaker wires to the mid 3.5 speakers from amp's location under the pass seat and replaced those stock 3.5" 8 ohm, 15 watt speakers with Bose 2 ohm 3.5" rated at 50 watts. The replacement 3.5" 2 ohm Bose's mounted right up in the stock brackets, all 4 holes too. I ran another pair of wires inside both doors thru the rubber bellows for the separate bigger 2.25" 2 ohm Bose tweeters (No Crossovers from the 6.5"s anymore) and I replaced my stock 6.5" 4 ohm 15 watt front door speakers with 6.5" 2 ohm 50 watt speakers all from a 96 Acura 3.5 RL except for the 3.5" 2 ohm Bose speakers which I got off eBay. So all my speakers are now 2 ohm to match the 2 ohm, 225 watt Acura Bose 4 channel amp. My stock 92 Fujitsu Ten amp was only 2 channel 120 watt which was probably the peak watts rating so I figure 60 watts rms since as all stock speakers were only rated 15 watts.
I now have a separate channel to the front 6.5", the 2.5 tweeters, the 3.5" rear middle speakers and the 4 rear speakers in the baffle boxes which are now house 2 4 ohm speakers connected in parallel.
Sounds Excellent with improved bass in rear. The lower 2 ohm speakers give you more sound volume over a 4 ohm speakers. Amp is rated 25 watts on each of the front door 6.5", 12.5 watts on each 2.25" front door tweeters with no more crossover, 25 watts on each of the middle by rear seat 3.5" and 100 watts total to the 2 rear speakers boxes which each contain 2 4 ohm speakers in parallel (50 watts each side). I have a 10 speaker system now.


New Acura/Bose amp under pass seat which just fit between seat tracks, Pic 2 is Bose speaker grill emblems and last pic shows the 2 W-L wires at Amp wiring pic on left top & bottom are both power in from 20 amp Dome to amp, the Y-L wire next to is amp turn on wire from radio, twisted pairs are to speakers, right top wires are inputs to amp from stock radio 4+ and 4- , Black wires are all grounds.

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Discussion Starter · #19 ·
Sinistar_xx, Here's what I did with your pic, it's a really good mod to do while you have it opened up.


View attachment 267601
I like the concept of that mod, but I'm gonna skip that one mostly because the benefit factor isn't enough for me and it's a mod you can't really undo. :)
 

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Discussion Starter · #20 ·
The crap we gotta go through just for a little bass.

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I think I found J/B No. 3 and of course it's in a horrible place with stiff bundles of wires, so not easy to confidently identify that red wire going to the 20A fuse. Pretty much the same for identifying the L-W wire from R/B No. 5. I think I'm just gonna go through the firewall and do an add-a-circuit on the 20A fuse. I did find a convenient grounding point on the inner door sill though.

 
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