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Discussion Starter · #1 ·
Ok Guys,

My current setup involves Mach amp with JBL GTO8628 speakers. According to my friends, its pretty damn loud. Doesn't cut it for me though.. The quality is good, but I wanna install an amp and sub to get more bass.

I am looking to buy a 4 channel amp that has built in crossovers, so I can amplify my front speakers on full range mode, and get a sub to bridge on the rear channels, which will be set on LPF.

What do you think?
 

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well this is what i did for my set up i have two amps one crossover. one amp is a 4 channel witch is used to power my front and rear speakers then i have my other amp witch is a 1500 watt used to power my two 1600 watt subs in the trunk. My crossover is used to block bass from the front and rear speakers. I don't why you would want to run a LPF on your rear spaekers that bound to cause more dilemmas, maybe i didn't understand you right.
a crossover bridged to the rear outputs with LPF with amp and a sub will get you what you want.
but like i said i don't think i understand what you were saying.
 

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I don't why you would want to run a LPF on your rear spaekers that bound to cause more dilemmas, maybe i didn't understand you right.
a crossover bridged to the rear outputs with LPF with amp and a sub will get you what you want.
but like i said i don't think i understand what you were saying.
He saying he will be bridging the rear amp channels for subwoofer.
 

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I am looking to buy a 4 channel amp that has built in crossovers, so I can amplify my front speakers on full range mode, and get a sub to bridge on the rear channels, which will be set on LPF.

What do you think?

This seems like a sensible budget setup. I prefer this to 5-channel amplifiers because they tend to have much weaker speaker wattage and much higher price tag than a nice 4-channel amplifier. Pretty much all amplifiers have built-in crossovers, so that's not an issue. However, I personally prefer to turn off the crossovers on the amplifier, and use the electronic crossovers on my stereo head unit, but it's not a big deal of difference. Check the new PPI Phantom Class D 4-channel amplifier. It almost as affordable as a comparable Class A/B, but the size is much smaller.
 

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Ok Guys,

My current setup involves Mach amp with JBL GTO8628 speakers. According to my friends, its pretty damn loud. Doesn't cut it for me though.. The quality is good, but I wanna install an amp and sub to get more bass.

I am looking to buy a 4 channel amp that has built in crossovers, so I can amplify my front speakers on full range mode, and get a sub to bridge on the rear channels, which will be set on LPF.

What do you think?
Check out madscientist's thread on modifying a base-model RCU with pre-amp outputs and a disabled "bass-nanny". Much better solution than any LOC-based system. Then go ahead with your amplifier setup.
 

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I've used 4-channel amplifiers several times in similar setups using the rear channel's bridged for a subwoofer. It's a great way to get a decent system on a budget and also saves you the hassle, expense and space of wiring multiple amplifiers. My advice would be to get a decent quality amplifier though. The cheaper ones tend to get really hot when you bridge them. Also, the crossovers on a better quality amplifier are going to be a lot better.

One interesting option out right now though is the Jensen Power 5500 5-channel amplifier. It can be had for around $130 and though not high-end by any means, for the price it is a solid little amp. I bought one for my Fusion and have been more than impressed for the price. I use it to power a set of components up front, a set of co-axial's in the rear and two 6-1/2" subs in the rear deck. The only down sides are that it is pretty big and gets fairly warm. It's doesn't hold a candle to my Infinity 5-channel amp, but it cost less than half as much. I do use external processing however, so I can't comment on the crossovers.

Whatever amp you use, I would switch to a stock RCU. Whether you use an LOC or modify the unit with pre-amp outputs, you're going to get a cleaner signal. The pre-amp gain in the Mach adds a lot of distortion, and that's in addition to the issues the stronger signal will cause with an LOC. It also has some EQ tweaks that don't play well with aftermarket equipment.
 

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Discussion Starter · #7 ·
I've used 4-channel amplifiers several times in similar setups using the rear channel's bridged for a subwoofer. It's a great way to get a decent system on a budget and also saves you the hassle, expense and space of wiring multiple amplifiers. My advice would be to get a decent quality amplifier though. The cheaper ones tend to get really hot when you bridge them. Also, the crossovers on a better quality amplifier are going to be a lot better.

One interesting option out right now though is the Jensen Power 5500 5-channel amplifier. It can be had for around $130 and though not high-end by any means, for the price it is a solid little amp. I bought one for my Fusion and have been more than impressed for the price. I use it to power a set of components up front, a set of co-axial's in the rear and two 6-1/2" subs in the rear deck. The only down sides are that it is pretty big and gets fairly warm. It's doesn't hold a candle to my Infinity 5-channel amp, but it cost less than half as much. I do use external processing however, so I can't comment on the crossovers.

Whatever amp you use, I would switch to a stock RCU. Whether you use an LOC or modify the unit with pre-amp outputs, you're going to get a cleaner signal. The pre-amp gain in the Mach adds a lot of distortion, and that's in addition to the issues the stronger signal will cause with an LOC. It also has some EQ tweaks that don't play well with aftermarket equipment.
I just finished reading your thread about adding pre-amp outputs. I have 2 stock rcu's laying around, (one that came out of my '99, and another that came from an '03.) So maybe you can assist me in modding them. All i need is 4 rca's, some wire, and .47uf capacitors correct?

Would you recommend removing the bass nanny if I am installing an aftermarket amp?

Thanks!
 

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I have the 5-channel Jensen too. The 60watt RMS channels are enough to drive Pioneer and Infinity speakers that I have had, but it's a little strained when powering my alpine Type R speakers. They still get loud, but you need to turn the gains so much that you can hear the noise floor on some tracks. So I bridged it for the front channels, sending something like 160watt rms on each channel. I am effectively using it as a 4-channel. I does get hot, I have seen it shut down twice on a hot Texas day. That's why I think it's a good idea to go with Class D amplifier, at least on the subwoofer section if living in hotter climates, if one can afford it. Another interesting option is MB Quart ONX4.125. It's Class A/B with plenty of power. 4x125watt RMS channels. 500watt RMS bridged. Only $30 more expensive than Jensen.
 

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I have the 5-channel Jensen too. The 60watt RMS channels are enough to drive Pioneer and Infinity speakers that I have had, but it's a little strained when powering my alpine Type R speakers. They still get loud, but you need to turn the gains so much that you can hear the noise floor on some tracks. So I bridged it for the front channels, sending something like 160watt rms on each channel. I am effectively using it as a 4-channel. I does get hot, I have seen it shut down twice on a hot Texas day. That's why I think it's a good idea to go with Class D amplifier, at least on the subwoofer section if living in hotter climates, if one can afford it. Another interesting option is MB Quart ONX4.125. It's Class A/B with plenty of power. 4x125watt RMS channels. 500watt RMS bridged. Only $30 more expensive than Jensen.
Needing to crank the gains is soley due to low voltage preouts on the head unit. With proper preout voltage, amp gains rarely exceed 2/3. If yours is shutting down it is most likey because your cranked gains are causing the amp to clip, which likes to make things hot. Or you have it mounted where it isnt getting adequate cooling. Perhaps install some fans?
 

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Needing to crank the gains is soley due to low voltage preouts on the head unit.
That's not entirely true. It's the function of the sensitivity of your speaker. Plug a speaker with 3dB less sensitivity than before and now you need to increase gains or your average sound level will not be as before, requiring to turn up the head unit volume, if amp gains are unchanged. Some amplifiers, specially cheaper ones increase the sound of the noise floor when their gains go up. And my head unit has "4V" preouts (in reality, it's probably 3V pre-out on 0dB tone, because I calibrate amp gains to make the stereo volume knob to be roughly at 3/4 level).

With proper preout voltage, amp gains rarely exceed 2/3. If yours is shutting down it is most likey because your cranked gains are causing the amp to clip, which likes to make things hot. Or you have it mounted where it isnt getting adequate cooling. Perhaps install some fans?
The amp gain has little to do with how hard amplifier works. Even with minimal amplifier gain level, it can still run stupid hot and shut down with appropriate input voltage and music content on an appropriately hot day. It won't happen every summer day, but can happen like I have seen on that specially hot week in August. Then there is the issue of subwoofer sensitivity again. Plug in a less sensitive sub, and your gain has to go up. My sub channel is indeed at approximately 2/3 amp gain level. The amplifier runs stupid hot when I flog it, even when driving in freezing temperatures. So, it's not wonder it can shut down on a truly hot Texas day. It's a feature of most class A/B amplifiers. They're just not that good for driving subwoofers, specially at 2ohms. Also the front and rear channel sections are bridged on my amplifier for front components, which means that the front 4 channels are _also_ running at 2ohms. So I have all 5-channels driving 2 ohm load. Class A/B amplifiers have terrible efficiency running at 2ohms, converting something like 40% of electric current into heat. That's why I recommend Class D amps, at very least to drive the subwoofer..
 

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That's not entirely true. It's the function of the sensitivity of your speaker. Plug a speaker with 3dB less sensitivity than before and now you need to increase gains or your average sound level will not be as before, requiring to turn up the head unit volume, if amp gains are unchanged. Some amplifiers, specially cheaper ones increase the sound of the noise floor when their gains go up. And my head unit has "4V" preouts (in reality, it's probably 3V pre-out on 0dB tone, because I calibrate amp gains to make the stereo volume knob to be roughly at 3/4 level).



The amp gain has little to do with how hard amplifier works. Even with minimal amplifier gain level, it can still run stupid hot and shut down with appropriate input voltage and music content on an appropriately hot day. It won't happen every summer day, but can happen like I have seen on that specially hot week in August. Then there is the issue of subwoofer sensitivity again. Plug in a less sensitive sub, and your gain has to go up. My sub channel is indeed at approximately 2/3 amp gain level. The amplifier runs stupid hot when I flog it, even when driving in freezing temperatures. So, it's not wonder it can shut down on a truly hot Texas day. It's a feature of most class A/B amplifiers. They're just not that good for driving subwoofers, specially at 2ohms. Also the front and rear channel sections are bridged on my amplifier for front components, which means that the front 4 channels are _also_ running at 2ohms. So I have all 5-channels driving 2 ohm load. Class A/B amplifiers have terrible efficiency running at 2ohms, converting something like 40% of electric current into heat. That's why I recommend Class D amps, at very least to drive the subwoofer..
Ooook. First the sensitivity of the speaker being lower, and causing you to turn up the gain is exactly how people distort the crap out of signals. Second, if the gain level didnt matter. Then why didnt you buy a head unit with a 2v preout? People run line drivers for a reason. A stronger input signal and lower gain setting is more efficient, and makes for cleaner power.
 
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