Reuse stock amp with new headunit?

[sd_boxster]

Trying to get my crap straight so I don't make any awful mistakes. I'll be replacing the stock head unit in my '03 Boxster. I have the Bose subwoofer and the factory amp, which I _believe_ is a six-channel amp.

Can I use the factory amp? I've got the stupid fiber-optic lashup - is the amp a write-off?

If I cannot reuse it, should I run the dash and door speakers off the new headunit and just get a 2-channel amp to drive the Bose subwoofer?

Any guidance is greatly appreciated.

Thanks again,

DJ

[70Sixter]

Try a search on MOST + amplifier + head unit. MOST is the :censored: stupid glass fiber item. There is a JL Audio solution also, so try a search on that. Did you check DIY section?

This has been documented somewhere on this forum I'm certain.

[atmorris]

Trying to get my crap straight so I don't make any awful mistakes. I'll be replacing the stock head unit in my '03 Boxster. I have the Bose subwoofer and the factory amp, which I _believe_ is a six-channel amp.

Can I use the factory amp? I've got the stupid fiber-optic lashup - is the amp a write-off?

If I cannot reuse it, should I run the dash and door speakers off the new headunit and just get a 2-channel amp to drive the Bose subwoofer?

Any guidance is greatly appreciated.

Thanks again,

DJ

I have an '03. MY '03 used a MOST bus system. The HU and amp communicate over a fiber optic connection. You have to replace BOTH if you want to replace either one. I am not familiar with the BOSE system, but I have seen it referred to MANY times by those who have it as the BLOWS system FWIW. Not trying to be obnoxious, just communicating what I know....please don't take offense.

Amp power needed for decent sound with the top down at highway speed is around 70wpc rms minimum. The stock setup is underpowered anyway.

I replaced the HU with an Alpine 9886 and put a Swiss Audio SMX6600 100wpc x6ch amp in the front boot in the stock amp's location. I replace the drivers in the dash, doors, and rear storage compartment with same sized Polk Audio drivers (except the doors, I replace the 5.25" drivers with 6" drivers) and added a Kenwood KSC-SW10 subwoofer in the passenger side footwell. Sounds great, top up or down, at 20 or 120. Pricetag was just under $1000 complete, with me doing the install. Took a weekend taking my time, being ULTRA neat and hiding everything. Looks stock.

HU driving the dash and doors will work but will be severely under powered. Best luck on your project.

[juniinc]

with a new HU,MOST gotta go.

I would consider getting a mosfet 4CH amp with built in x-overs.

HU can drive the dash, 4Ch amp can power up the doors/subs,,,

[atmorris]

It's a little known fact that more drivers are damaged from a system being under powered than from it being over powered. The thing you have to remember about power is that, whatever listening level you normally use, strong passages and pulses can demand 10 times that much power from the amplifier to produce the music cleanly, without distortion. Distortion damages drivers.

So lets say that you have a 20wpc head unit powering your front speakers. You feed the sub outs and rear outs to an external amp - say a 4x75wpc unit. Your tooling along with the top down listening to the new Nickleback CD, The volume control goes from 0 to 30 and you have it set on 10 because you have the top down. For sake of simplicity, lets say that the volume control is linear, so since you are set at 10 of 30 that is 33%. Since your HU is rated at 20 watts that represents 6.6 watts. At this setting, a strong bass pulse or musical passage could easily demand 10 * 6.6 or 66 watts to produce cleanly. Your subs and rears are ok with that since your amp is rated at 75 wpc, but what happens to the dash speakers? The amp in the HU can only push 20 wpc. Thats 46 watts short ! What happens when this condition occurs is called clipping (see http://en.wikipedia.org/wiki/Clipping_(audio) ). It is harmfull to both the amplifier in the HU and the drivers over time, AND it introduces distortion from the clipping into the music reproduction....so it doesn't sound clean. This condition might only last a few seconds. You might not even notice. But the strain on the affected amp (the HU in this example) and the drivers is still there and will take it's toll over time.

I learned this the hard way years ago when I destroyed a brand new set of expensive speakers over a 10 month period due to underpowering the system. Pay careful attention to the wattage ratings on your equipment. Make sure they are properly matched up, and that you have enough power to support what you want to accomplish.

[Jay H]

It's a little known fact that more drivers are damaged from a system being under powered than from it being over powered.

Andy is 100% correct. I'm a musician and a sound tech and have been using pro-audio for 25 years. My rule of thumb was to take the RMS rating of the driver (speaker) and double it. Use that doubled rating and get a power amp that is able to deliver that amount of power at it's RMS rating. When I was running sound for bands, I would typically take 800 RMS watt JBL subs and run them with a 1600 watt power amp. With that amount of power, I'd never clip the amps and I'd never blow a driver. A 400 watt amp on that same 800 watt sub would most definitely blow the sub up if the amp clipped and it was easy to clip an amp when it didn't have enough power to do the job (400 watts on a sub in a small club isn't enough). This is similar to Andy's example of the head unit power not being enough power to drive the separates in the dash at a high level with the top down. The head unit amp simply isn't enough power to generate enough volume and amp clipping happens quickly. If an amp is clipping heavily, it doesn't take long to ruin the drivers. Plus, there are no such things as clip lights on internal amps in a head unit so that you can monitor output levels.

So, if you buy a 40 watt RMS set of separates for your dash, use a 60 or 80 watt RMS amp to drive those. Have a 200 watt RMS sub? Buy a 400 watt RMS rated amp to drive it. Kinda like engines, you can never have enough power...!

[grover]

How do you all feel about the "loudness" button, then, that intentionally clips the signal?

[Jay H]

How do you all feel about the "loudness" button, then, that intentionally clips the signal?

I have a 2002 986 with the 220 head unit and the 4 channel amp. No Bose. I currently have the loudness set to on and all the other tone controls set to 0 or flat. Nothing clips with that set up (even really pushed hard) and I believe the loudness contour reduces back to flat as one increases the volume on the head unit.

I'm not sure how much the 2003 and newer systems change, but you may wish to flatten all the tone controls to zero if you want to use the loudness setting too. If you feel you need more bass than what the loudness contour (or low end eq setting increased) can provide, then you need to add a sub.

Good sounding systems require very little additions of equalization.

Edited January 15, 2009 by Jay H

[JeTexas]

How do you all feel about the "loudness" button, then, that intentionally clips the signal?

There's a difference between limiting and clipping. Limiting keeps certain tones at a certain volume while clipping cuts the information of those tones out altogether. The loudness button limits the highs and lows while bringing up the mids to create a sound profile more appealing to your ear. It's like playing with an equalizer.

And I was always told to make sure the amp was double the wattage of the speakers as well - just remember to match ohms. I don't know if it's as much an issue with car speakers as it is with PA and stage speakers, but the double the wattage rules only works if it's an 8 ohm amp with 8 ohm speakers or with a 4 ohm amp with 4 ohm speakers, etc.

[atmorris]

How do you all feel about the "loudness" button, then, that intentionally clips the signal?

Thats not exactly how it works.....

The human ear does not function in a linear fashion, and perceives a greater loss of bass presence than it does mids and highs at lower volume settings. A "loudness" feature normally boosts selected bass frequencies, usually around 10 db or so, to compensate for this perception. It was designed to be a sort of a "low volume bass boost" if you will. It is one of the worst and most dangerously mis-useable features they have ever put on a piece of audio equipment. I never use it - ever. If it is used, it should only be used at low volume levels, and certainly NEVER should be used at higher volume levels. If you want to understand why I say this, just go back and read my earlier post about how bass pulses can demand up to 10x more power from your system amps than your average listening level. Using this feature can actually induce a clipping problem if used at too high a volume setting !!! (..and what is "too high" is VERY dependant on the music itself by the way...)

Listen to your music at a level that drives your speakers well and set the tone controls accordingly. Or take a more sphisticated approach and add a good parametric EQ like the Alpine KTX-100EQ , multi-band digital EQ like the Kicker 03KQ30, or a sound processor like the Alpine PXE-H650 to your system.

Edited January 15, 2009 by Andy_M

[sd_boxster]

Thanks for the replies, all.

After reading up here and elsewhere, I will wait to mess with the electronics until I have the budget to do so.

For now, I'll be adding an in-line FM modulator and a satellite tuner... myself, since I need to get my feet wet with modding the Boxster.

[grover]

I picked up a $35 FM modulator/mp3 player with a 1.5" color LCD display. It's a miserable mp3 player, but it actually looks rather good in the car, like it belongs there! And unlike the CD player on my CDR23, plays music.

All-in-all, not a bad stop-gap until I can get the radio repaired and buy a better mp3 player, I suppose.

Edited January 18, 2009 by grover