Reply to Thread

Post a reply to the thread: Lost in Amp Translation

Your Message

Click here to log in

Please correctly re-type the phrase f o o t d o c t o r in the form box. Re-type it without the extra spaces and put the one space where it should be. We apologize for having to do this but this silliness helps slow the spammers.


Additional Options


Topic Review (Newest First)

  • 03-11-2011, 04:09 PM

    At this point...

    I'd go for the line-levelers and keep the RCAs for the front channels. Using speaker-level inputs is considered less 'clean' as you are essentially double-amplifying the original signal; once at the head unit, and again at the amplifier. Convertibles are less-than-pristine listening environments anyway, so you'd probably never notice a difference, but since you've already run the RCAs and the Blaupunkts will benefit from the amp's power (vice the headunit), I'd go with the line-levelers... You could tuck them under the trunk cover on the right side, beneath were the CD changer goes - there's some space down there...
  • 03-10-2011, 10:28 PM

    Re: Well...

    Do I lose anything going from RCAs to speaker level inputs?
  • 03-10-2011, 09:43 PM


    You can disconnect the RCAs (leave 'em in place in case you decide to try a different head unit) and run all four speakers via the speaker level inputs, or, as you mentioned, get a couple of line-level converters and use them to power the rear speakers... The line levelers are ok, it's just something else you have to secure & hide away...
  • 03-10-2011, 09:23 PM


    The instructions with the amp said specifically to not to use the RCAs and the speaker level inputs at the same time.

    Are they being overcautious?
  • 03-10-2011, 08:59 PM

    No, you don't...

    You're not off that easy - the Alpine MRP F300 has a feature called speaker level inputs. There should be a 'plug' that came with the amp - you run the speaker wires in the trunk that came from the head unit (not the RCAs) on their way to the amp into that plug (you'll probably have to splice in wire) and then plug them into the speaker input section of the Alpine amp. Voila!
  • 03-10-2011, 08:36 PM

    The simple answer

    There are no rear RCA outs on the head unit. Duh!!!

    What a novice! I assumed one jack was for front and the other for rear but I never thought it through.

    If I want a front-rear setup I need 2-channel line level converter to take the signal from the original rear speaker wires (radio to amp) and end in a male RCA plug.

    I just drove top down and even the way it's set up with no discreet rear sound, it sounds great. So much better than stock..and what a learning experience.
  • 03-09-2011, 09:56 PM

    Regarding the fader/balance

    If your RCA cables from the head unit are hooked up correctly (front outputs on the JVC head unit to channels 1&2 on the amp, left and right hooked up correctly at both ends, etc.) the fader & balance should work as normal.
    Thanks for the call-out - whatever modest car audio knowledge I have is the result of people on this board helping me with all my questions, about 12 years ago... I learned a lot here - So I try to pay that back.
  • 03-09-2011, 09:12 PM

    Thanks - I'm there - Kinda Sorta

    Thanks again Mike

    I did the setup as you suggested and, while it took some tweaking with the amp settings, I have a sound I'm very happy with. The behind the seat speakers have really perked up and add a great fullness they never did before.

    At this point I don't think I'll miss the subs but I can always put in a second amp just for them. If I understand correctly I can just run RCAs from the new Alpine amp to a mono amp and run the subs from there. Sound reasonable? I think I can also pick up the sub output from the head unit but that would mean running more cables through the console.

    I'm still monkeying with the fader and balance controls which don't seem to be working as usual.

    Now it's time to settle everything in the trunk. Lot's of wires to organize! I mounted the amp on a piece of gray carpet-covered plywood and am planning on using the idea from here of industrial strength Velcro to hold it in place on the carpet. I'm not sure about the crossovers...options include: also mounted on a piece of wood and Velcro'd beside the amp?...Mounted to a board mounted to the bracket from the stock amp? Any other suggestions anyone?

    Thanks again to all who helped, especially to Mike for the early help and the suggested layout, Monolith for the early direction and info, and WB-MZ for the idea that helped me understand better what I was doing or trying to do.

    This board has been an amazing source of information and help over the 13 years I've had the M. I'm usually willing to try anything with the car knowing I can either find info in the archives or someone willing to give a hand.

  • 03-09-2011, 06:22 PM

    Yes to both Questions

    If you're running the stock subwoofer, I don't know if giving it the 150 watts from your Alpine amp would work or not - it may not be able to handle that much, and, I don't know the resistance of the OE sub - that Alpine isn't rated below 4 ohm in bridged mode, so you do that at the risk of frying the sub and/or amp (unless someone else has that info). I suspect the two-driver BMW unit is only 2 Ohm, but I'm not sure. And yes, you can still run the Blau's off the head unit, if you choose. IF you decide to try the sub off of the amp, bridge the channels and set the crossover for 3/4 to "LP" and set the dial somewhere between 80 hz -100 hz to start. And set the gain low, and bring it up slowly... Personally, I'd run the rear Blau's off the amp unless you know the resistance of the sub, but you're driving...
    P.S. several folks have commented that having good rear speakers, properly powered, made a significant improvement in the bass. I may add rear speakers myself someday).
    Regarding your earlier question, the amp does have crossovers, but they weren't intended to to separate the frequencies between the tweeter & woofer - the crossover provided with the speaker set is specifically designed by Alpine to separate the woofer & tweeter at the optimum frequency.
    You're almost there!
  • 03-08-2011, 10:38 PM

    Two More Questions

    Can I bridge only channels 3 and 4 and leave channels 1 and 2 unbridged?

    Can I run the rca's from the head unit to the amp and still run the two 4" directly from the head unit?
  • 03-08-2011, 09:00 PM

    Re: Learning lessons 'Long theWay

    I agree with Mike about going through the Alpine crossovers, but have you thought about bridging the amp channels 3 and 4 to drive your sub and either forget about the 4" rear speakers (they're almost worthless any way) or if you have to have them drive them from the head unit.
  • 03-07-2011, 11:18 PM

    Learning lessons 'Long theWay

    Thanks Mike

    I'm a little confused and you seem to be one who can clear things up for me.

    The Alpine amp has crossovers built in, right? Don't they split the signal the correct way?

    So you're saying that I should have a full range signal come from Channels 1&2 and let the crossovers split it between the tweeters in the door and the mid-ranges in the footwell?

    Then set channels 3 as you suggest, to get a full but not overpowering signal to the Blaus.

    It sounds simple but I thought the amp would split the signal adequately.

    Back to the trunk tomorrow.

    thanks again

  • 03-07-2011, 07:27 PM

    Unusual setup...

    Maybe I missed something, or I'm misreading your info. Did you install a new component speaker set (woofer, tweeter & crossover)? If so, your amplifier "front" channels (1+2) should be wired to the inputs on the crossovers. Then hook up the set of wires from your new tweeter to the 'tweeter' output on the crossover. Next, hookup the set of wires from the woofers in the footwells to the woofer output on the crossovers. All 4 of these speakers should be run from the 'front' amp outputs via the crossovers. Next, hookup the 4" Blaupunkts to the 'rear' amp outputs (3+4)... Make sure to keep all the speaker sets in phase ("+" on the amp goes to "+" on the crossover, which goes to "+" on the respective speaker). I think that'll work better for you! I'd also set the amp crossover on channel 3/4 to "HP" and at least 50hz, to avoid overworking the Blau speakers...
  • 03-07-2011, 01:47 AM


    I bought a new Alpine MRP F300 4-channel amp from Crutchfield. I'll live without the subs for a little while.

    I took out the 2 speakers in the door and put in the Alpine tweeters from the component set wired to the larger door speaker wiring.

    I ran RCA cables from the trunk into the soft-top well and under the console to my JVC KD AHD-59 radio.

    I'm going to try using the existing speaker wires and the connectors they attach to as well as the existing on/off wiring from the radio. To do that I took a section of speaker wire for each channel and soldered the pins stolen from the amp to the end of the speaker wire. I can then plug those pins into the existing connectors.

    I am using channels 1 and 2 to power the door speakers and channels 3 and 4 for the footwells and the 4" Blaupunkts behind the seats.

    I hope to actually power it up tomorrow and hold my breath when I turn the radio on.

    thanks to all for the help.

    I'll let you know what happens.
  • 02-23-2011, 09:29 PM

    Very helpful information

    Thanks a lot!

    I did as suggested using the placement of the door midranges for the new tweeters.

    I cut down the mounting brackets for the OEM midranges to hold the new tweeters and that worked fine.

    I have a Bentleys manual so I used the wiring diagrams and I think I have the new tweeters wired correctly.

    I can't test it though because I don't have a working amp yet.

    thanks again for all the advice!

  • 02-22-2011, 06:23 PM

    Here you go...

    First off - you have a schematic, right? Don't cut anything until you know what all the wires in the amp plugs are for and can identify them. There are six speaker wires on each side for the front speakers - one set (+/-) each for a tweeter, midrange & woofer. Your new tweeter will most likely fit where the OE midrange is - see the link to, the third picture down is what you'll have once you get the door panels off. Remove the midrange and secure your new tweeter in that mounting bracket (I did mine the same way DC did in this article, and it worked perfectly). Simply disconnect the OE tweeter at the amp & leave it in place - you don't need it. When you hook up the new speakers to your crossover, just use the respective wire set for the woofer & the midrange (which is now your tweeter).
    Word of advice - when you've taken a deep breath and decided to start cutting, leave some wire attached to the amp's plugs, in case you ever want to return the car to it's stock configuration - don't cut right next to the plug. If you ever go back to stock, for whatever reason, you can use butt connectors to re-attach the amp plugs. I saved all the pieces, just in case... Hope this helps...
  • 02-22-2011, 02:04 PM

    Roadfly prohibits my link


    Type in "erfest" in place of the asterisks above.
  • 02-22-2011, 02:03 PM

    Ron Stygar's Photos shows two separate pigtails

    One for the tweeter and one for the mid. You just want to make sure there is no filter going to the new tweeter. If the mid wiring goes although way to the rear amp, you'll just not use those wires.

    .com/forums/showpost.php?p=3845005&postcount=58]Ron Stygar's Door Removal Pics
  • 02-22-2011, 10:53 AM

    Mounting the Alpine Tweeters?

    I can't remember how the factory tweeters are mounted in the door - to the back of the door panel? Are they screwed in?

    If I pull the factory tweeters to put in the Alpine tweeter - can I use either set of speaker wires inside the door panel?
  • 02-22-2011, 09:27 AM

    Center console is fine for the RCA's

    The only thing to watch out for is the car's main power wire when running speaker wires (they run down the passenger side of the car). So, it's best to run the speaker wires down the driver's side. Since you're using the existing speaker wires, you don't need to worry about this.

    There are two rubber grommets in the rear deck - one on each side of the car. The passenger side has the car's main power wires running through it. I would route any additional wiring through the driver's side grommet (to keep them away from the vehicle's power wires).

    I believe there is a capacitor used as a filter in the door panel. I would bypass this if you're using the Alpine mid and tweeter combo with the Alpine crossover mounted in the trunk next to the amp.
This thread has more than 20 replies. Click here to review the whole thread.

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
1e2 Forum