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  1. #1
    FEP Power Member fgross2006's Avatar
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    Default Aftermarket amp question

    In my 84 vert I have a retrosound head unit and a Alpine KTP-445U 45 watts RMS x4

    I have 4 six in round JBL speakers in the front doors and rear interior quarters. Those are jacked into the front and rear channels of the Alpine.
    I have 2 three and a half inch JBL's and a pair of JBL 3/4 tweeters in the dash. Those four are all jacked into the head unit direct.

    I just rewired all new speaker wire to all speakers bypassing the stock wiring. My set up prior was done by a stereo guy but i hated the sound. He had the front door speakers tied off the three and half's and I felt it was siphoning wattage and making the door speakers useless. There was also engine noise coming into one of the rear speakers. I didn't have the tweeters before. i just added them myself to thew space where the stock amp used to be. I made a mount plate to hold them.

    The thing is now the dash speakers are considerably lower, which I expected since they are going to the head unit. I could have lived with that. But now when I crank it up the amp cuts out until i lower the volume.

    Is it not possible to run 4 speakers off the amp and 4 to the head unit at the same time? if I jack them all together it will just waste wattage and sound like crap. As a last resort I will add a second Alpine amp but I'd rather not if I can tweak this to function as is. Theres settings on the amp I dont know how to tweak. Any suggestions?

  2. #2
    FEP Super Member gr79's Avatar
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    With those componants, will sound real good once all is correct.
    Amps can cut out if not enough power is available or is too hot.
    My Sony radio did that all the time. Then i got a Sony 222 amp. No change
    Then i connected that amp to a factory radio. Same deal as you. Rears ok, fronts too quiet. 4 ch time. Solved.
    Even if the radio has high power, rear channels are getting reamped higher again, while fronts are not.
    The radio output is the same f +r, but the rears are being Alpined. Fronts are 1x boosted, rears 2x.
    The best balance is to connect all 4 channels from radio to one 4 ch amp. Then the F/R input levels will match again.
    Worth the many hours one will spend wiring and adjusting.

    Subject: Amping all eight speakers. Radio fader, balance, volume controls will be operational,
    Task: Rewiring 4 front speakers (dash), 4 rear (door and 1/4 panel), 4 channel amp to radio.
    Assuming: Amp and radio power/ground connections are correct and need no further attention.

    Notes:
    Prep ahead to minimize confusion and time. Notes and hand diagrams a plus to save for later reference.
    Lots of wiring. I have long wires and connections stuffed behind console (radio to amp) and under seat (speaker connections).
    Helps greatly to mark wires with tape and label LF, RF, etc at the amp connections. And have easy access to them.
    Black Sharpie on clear tape ok.
    Label either the plus wire or negative (ground) the same way on all wires.

    All front channel speakers to be wired in series to protect amp.
    Series wiring each pair of speakers (one 3.5, one tweet) gives 3 ohm + 3 ohm= amp 'sees' a safe 6 ohms.
    Plenty of power will be available. Amping all speaker will make everything come alive.
    Make sure + and + connections do not get mixed up or will have weak sound or unclear stereo separation.
    Front speakers to rear speakers level will be matched using the amp f/r gain (volume) controls.
    Overall volume, balance, fade will be adjusted at the radio.

    Radio head unit wiring (output) to amp (input).
    Disconnect radio F output from FT speakers and connect hose radio wires to amp F input.
    1- Radio LF +/- speaker output to amp L front speaker level input.
    2- Radio RF +/- speaker output to amp R front speaker level input.
    3- Radio to rear speakers is already connected. Amp may be in 2ch mode. Switch to 4 ch mode.
    4- One set of rear speakers may be connected to amp front speaker out. Rewire.

    Front LF speaker wiring:
    Parallel wiring two 3 ohm speakers together results in 1.5 ohms, too low for amp.
    Series wiring mixes + and - but will sound fine in this case.
    1- LF wire from amp LF (-) speaker terminal to LF 3.5 speaker (+) terminal.
    2- Wire LF 3.5 speaker (-) terminal to LF tweet (+) terminal. Cross wiring here makes a series connection.
    3- Wire LF tweet (-) terminal to amp LF (-) speaker terminal.
    Repeat for RF.

    Rear speaker connections.
    With two 4 ohm speakers , can wire series or parallel. Parallel is simpler. Positive to positive, neg to neg.
    Connecting two 4 ohm speakers together in parallel is safe for amp (4 ohm + 4 ohm= amp 'sees' 2 ohms).
    1- LR wire from amp LR + speaker terminal to door and rear speaker +.
    2- LR wire from amp LR - speaker terminal to door and rear speaker -.
    Repeat for RR.

    Speaker summery JBL:
    1- LF dash 3.5" + 3/4" tweet, 3 ohms each.
    2- RF dash 3.5" + 3/4" tweet, 3 ohms each.
    3- LR 6" door and 6" rear, 4 ohms each.
    4- RR 6" door and 6" rear, 4 ohms each.

    Wire each front channel together in series. Total 6 ohms each channel.
    Wire each rear channel in parallel. Series is 8 ohms, parallel is 4 ohms each channel.

    Notes:
    Before turning on system, turn down Alpine's front and rear gain adjustments (loudness) to minimal for now.
    Double check Alpine amp switches per document.
    1- Input config switch up to 4 channel config.
    2- Hi pass filter switches F/R up for now, input signal switch down for speaker level input or up if using RCA from radio.
    3- Set radio to about 1/2 volume. Adjust Alpine F/R gains (F/R volume levels) clockwise (louder) for best sound.


    http://support.alpine-usa.com/produc...M_KTP-445U.pdf
    http://www.regiscoyne.com/tech/spk_cab_wiring/
    Last edited by gr79; 05-12-2019 at 11:11 PM.

  3. #3
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by gr79 View Post
    With those componants, will sound real good once all is correct.
    Amps can cut out if not enough power is available or is too hot.
    My Sony radio did that all the time. Then i got a Sony 222 amp. No change
    Then i connected that amp to a factory radio. Same deal as you. Rears ok, fronts too quiet. 4 ch time. Solved.
    Even if the radio has high power, rear channels are getting reamped higher again, while fronts are not.
    The radio output is the same f +r, but the rears are being Alpined. Fronts are 1x boosted, rears 2x.
    The best balance is to connect all 4 channels from radio to one 4 ch amp. Then the F/R input levels will match again.
    Worth the many hours one will spend wiring and adjusting.

    Subject: Amping all eight speakers. Radio fader, balance, volume controls will be operational,
    Task: Rewiring 4 front speakers (dash), 4 rear (door and 1/4 panel), 4 channel amp to radio.
    Assuming: Amp and radio power/ground connections are correct and need no further attention.

    Notes:
    Prep ahead to minimize confusion and time. Notes and hand diagrams a plus to save for later reference.
    Lots of wiring. I have long wires and connections stuffed behind console (radio to amp) and under seat (speaker connections).
    Helps greatly to mark wires with tape and label LF, RF, etc at the amp connections. And have easy access to them.
    Black Sharpie on clear tape ok.
    Label either the plus wire or negative (ground) the same way on all wires.

    All front channel speakers to be wired in series to protect amp.
    Series wiring each pair of speakers (one 3.5, one tweet) gives 3 ohm + 3 ohm= amp 'sees' a safe 6 ohms.
    Plenty of power will be available. Amping all speaker will make everything come alive.
    Make sure + and + connections do not get mixed up or will have weak sound or unclear stereo separation.
    Front speakers to rear speakers level will be matched using the amp f/r gain (volume) controls.
    Overall volume, balance, fade will be adjusted at the radio.

    Radio head unit wiring (output) to amp (input).
    Disconnect radio F output from FT speakers and connect hose radio wires to amp F input.
    1- Radio LF +/- speaker output to amp L front speaker level input.
    2- Radio RF +/- speaker output to amp R front speaker level input.
    3- Radio to rear speakers is already connected. Amp may be in 2ch mode. Switch to 4 ch mode.
    4- One set of rear speakers may be connected to amp front speaker out. Rewire.

    Front LF speaker wiring:
    Parallel wiring two 3 ohm speakers together results in 1.5 ohms, too low for amp.
    Series wiring mixes + and - but will sound fine in this case.
    1- LF wire from amp LF (-) speaker terminal to LF 3.5 speaker (+) terminal.
    2- Wire LF 3.5 speaker (-) terminal to LF tweet (+) terminal. Cross wiring here makes a series connection.
    3- Wire LF tweet (-) terminal to amp LF (-) speaker terminal.
    Repeat for RF.

    Rear speaker connections.
    With two 4 ohm speakers , can wire series or parallel. Parallel is simpler. Positive to positive, neg to neg.
    Connecting two 4 ohm speakers together in parallel is safe for amp (4 ohm + 4 ohm= amp 'sees' 2 ohms).
    1- LR wire from amp LR + speaker terminal to door and rear speaker +.
    2- LR wire from amp LR - speaker terminal to door and rear speaker -.
    Repeat for RR.

    Speaker summery JBL:
    1- LF dash 3.5" + 3/4" tweet, 3 ohms each.
    2- RF dash 3.5" + 3/4" tweet, 3 ohms each.
    3- LR 6" door and 6" rear, 4 ohms each.
    4- RR 6" door and 6" rear, 4 ohms each.

    Wire each front channel together in series. Total 6 ohms each channel.
    Wire each rear channel in parallel. Series is 8 ohms, parallel is 4 ohms each channel.

    Notes:
    Before turning on system, turn down Alpine's front and rear gain adjustments (loudness) to minimal for now.
    Double check Alpine amp switches per document.
    1- Input config switch up to 4 channel config.
    2- Hi pass filter switches F/R up for now, input signal switch down for speaker level input or up if using RCA from radio.
    3- Set radio to about 1/2 volume. Adjust Alpine F/R gains (F/R volume levels) clockwise (louder) for best sound.


    http://support.alpine-usa.com/produc...M_KTP-445U.pdf
    http://www.regiscoyne.com/tech/spk_cab_wiring/

    Thanks for the reply. Theres a lot of info there. I may be better off going back to the stereo guy. This is not my strong point.

  4. #4
    FEP Power Member fgross2006's Avatar
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    Default

    Then again maybe its in my best interest to just get another Alpine power brick. They are pretty good and not expensive. Would probably make everything easier.

  5. #5
    FEP Power Member fgross2006's Avatar
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    I had the gain all the way up and that was probably the reason it was cutting out. I lowered gain to 3/4 and dove around for a few hours yesterday only cut out briefly once. Maybe if I lower gain just a hair more it will be set in the sweet spot.

    I just want it functional for now. I plan to get a new head unit later in the summer. Still debating if I should get a second Alpine power brick for the dash speakers. Maybe if I just keep the three and a half inch speakers hardwired to the head unit but connect the tweeters to the amp wired together with the front door speakers? Less wattage for the 3-1/2's is a good thing. They tend to blow frequently. I've been through at least 4 pairs in 5 years.

  6. #6
    FEP Super Member gr79's Avatar
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    Too high of gain will definitely affect amp. Like running a car wide open or 3/4 throttle all the time.
    The amp heats up putting out high power then protection circuit cuts off amp if low volts or overheating.

    Gain is adjusted to match radio input to amp so the speakers will not get overloaded.
    Gain boosts the input signal to the amplifier section of amp circuit.
    Gain tunes the amp to correctly amplify either type of input signal to any type speaker.
    Like a carb, timing, etc adjustment. Not too much, not to little. Dials to find the overall sweet spot.

    Amp gains have wide settings to accommodate types of radio connection and speaker loads.
    They usually are not found in house systems, which use RCA inputs to connect to other items.
    High amp gain levels are for RCA plug in connections, which have a low level signal and need more gain.
    Low amp gain levels are for direct connection to radio speaker wires, a high level signal, need less gain.
    Gain does not adjust the power of the amp. That is fixed in the amp's amplifier circuit section.

    RCA input connection is like low water flow. Needs to be pumped (gain added before amping).
    Speaker level needs much less pumping.
    Roughly, gain controls the pressure the amp (pump) puts out to the speakers.

    A connection to radio speaker wires can be pretty much passed thru the amp with out much gain needed.
    The amp will still amp the signal.

    Just like an engine, smaller amps have limits. Big amps cann be costly and overkill. And kill speakers.
    Most small-mid size speakers can't take high gain, power, nor need it. That is for huge subwoofers.
    45 watts is a good step up. Not the loudest, not quiet factory.
    Another amp would be great if more wires and taking up space is no issue.
    Virtually the same can be accomplished with one amp and wiring as above.

    We both have similar JBL 3.5's, and almost same amp wattage. The have a capacitor to limit bass and protect them.
    This can also be done using the amp crossover settings in combination with gain settings.
    1/3 amp gain is about all they can take. To high of gain will only heat speakers up and eventually fry them.
    Like full gain.
    Even at 1/3 setting, the amp will crank out all its wattage when needed, say for bass notes.
    Connecting more speakers may need a little more gain dialed in, but still under 1/2 in this case.

    Gain is like a gas pedal. Sort of the amp's volume control. Has to be matched to radio output.
    Pretend speakers are tires. Max loudness (speed), with no distortion (spin), is peak performance with combo.
    When setting amp gain, have dash radio volume at 1/2-2/3, amp gains at zero.
    Then slowly bring up each amp gain until distortion, then back down a bit.

    i have a JBL 50w four channel running 8 speakers.
    Split 2 speakers front, 6 rear.
    Factory 90's Ford DIN radio. I like reliable push button stations and electronic tuning.
    Amp front gain and rear gain are set to about 1/3 setting. Plenty loud and clear.
    Loudest radio volume setting without distorting is about 2/3.
    Anything more distorts the speakers.
    When parked engine off and radio turned up, the amp power LED flashes red on bass notes.
    Will cut out if power LED stays in red for very long. Green or yellow LED color is ok and normal.

    Learned enough about car stereo long ago to change config at will. Wiring usually is confusing.
    More mental than physically hard like body work or engine work.
    Plus wanted results as quick as possible. Too hard to translate exactly what i need to hear to someone.
    Right or wrong about tech notes, system works fine.

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