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Car Forum / Driving, Maintenance, Tuning / Car Audio / July 2006How useful is having 3 pair pre-amps?
I'm sorry, I've been out of car audio for quite a few years so forgive me if I ask dumb questions :-) I have it in my head that I want front/rear/subwoofer pre-amp outputs on my receiver. How useful/important is this? I'm thinking once I get the levels correct, the balance between front/rear and subwoofer output, how often will it really need to be adjusted? More importantly, I want to have a multi-band eq and/or electronic crossover so should I just run front/rear pre-amps back to that, then just use the subwoofer pre-amp output that I assume it will have to adjust the subwoofer level, still giving me the front/rear fading capability? Keeping to only two pair pre-amps will give me more choice of head units as well. So what I want is head unit -> audio control type device -> 4 channel amp for front/rear and 2 channel amp to the sub. Simple enough. Thank you so much for your input. I have all my equipment sitting here, can't wait to install it :-) Joel | I have it in my head that I want front/rear/subwoofer pre-amp outputs | on my receiver. How useful/important is this? I'm thinking once I get | the levels correct, the balance between front/rear and subwoofer | output, how often will it really need to be adjusted? People buy systems with more pre-outs because they tend to adjust the fader and sub level from the HU frequently. If you intend not to change frequently then go ahead with 2 pair systems. I am having only 1 pair of pre-outs and this is fed to a 4 channel amp and the amp is also having pre-out. These go to the sub amp. Nowadays sub-amps also come with a remote bass knob which is heavily used by people at each change in song. Just that umph more | More importantly, I want to have a multi-band eq and/or electronic | crossover so should I just run front/rear pre-amps back to that, then | just use the subwoofer pre-amp output that I assume it will have to | adjust the subwoofer level, still giving me the front/rear fading | capability? I do not have experience with active crossovers. Hope I helped you. > I am having only 1 pair of pre-outs and > this is fed to a 4 channel amp and the amp is also having pre-out. These go > to the sub amp. So the voltage (signal?) coming from the amp's sub pre-out is adjusted by the head unit volume control? Thanks, Joel Yes the volume of pre-outs on the amplifier are in sync with the inputs. The detailed setup is as follows I pair of RCA pre-outs go to the one set of RCA inputs on the 4 channel amp. The amp can use the same pair for both the pairs and also outputs the same signal to outputs for second amp. I loose the fader control, but I have never felt the need to used the fader control. On my wife's car the fader control is used extensively. | > I am having only 1 pair of pre-outs and | > this is fed to a 4 channel amp and the amp is also having pre-out. These go [quoted text clipped - 6 lines] | | Joel > I have it in my head that I want front/rear/subwoofer pre-amp outputs > on my receiver. How useful/important is this? I'm thinking once I get > the levels correct, the balance between front/rear and subwoofer > output, how often will it really need to be adjusted? Once the level is adjusted between the fronts and rear speakers you will likely never need to adjust them again. I have three sets of outputs on my HU, but I never mess with my fader control. The subwoofer control is an entirely different matter. I am ALWAYS adjusting the subwoofer outputs level, practically from one song to the next (even in the middle of songs). I find that bass varies GREATLY from song to song and older recordings almost always, IMHO, seem to need a little help in the bass department. Most people I talk to feel the same way. The subwoofer control tends to be the most used control on any HU. Bass is a VERY personal thing and what is considered "enough bass" varies widely from person to person. Therefore, a HU with two sets of RCA outputs would be the minimum acceptable to me. That way, I could run one pair into a four channel amp (let's say) to drive the front and rear speakers. I could use the gains on the amp to adjust the "fader" settings (level to the fronts and level to the rear speakers) to my liking and then never touch it again. The other set of RCA outputs could then be run into my subwoofer amp, this way it would be adjustable from the HU (you would adjust the fader to increase the sub level). I had an old system configured this way for years (using an Alpine 7939) and it worked great. Of course, three sets of outputs makes this whole thing even easier, but IMHO, not necessary. MOSFET OK...I have a question here...... how do you feed one pair of RCA cables to a 4 channel amp?.. you have one pair (RCA) and 4 inputs on your amp. Or is it that you use a signal splitter?... MOSFET I have another question for you!!.... you have biamped your front channel?.. how did you do it?.... can you explain how you connected everything?... Like for eg... from HU --> passive cross over --> ... etc... thanks Antony. > Therefore, a HU with two sets of RCA outputs would be the minimum acceptable > to me. That way, I could run one pair into a four channel amp (let's say) [quoted text clipped - 7 lines] > > MOSFET > OK...I have a question here...... > how do you feed one pair of RCA cables to a 4 channel amp?.. you have > one pair (RCA) and 4 inputs on your amp. Or is it that you use a signal > splitter?... Almost ALL four channel amps have a switch that allows for either two or four channel input (and then output for all four channels). This feature is especially usfull when using a four channel amp to drive subwoofers. MOSFET > MOSFET I have another question for you!!.... > you have biamped your front channel?.. how did you do it?.... can you [quoted text clipped - 20 lines] >> >> MOSFET > MOSFET I have another question for you!!.... > you have biamped your front channel?.. how did you do it?.... can you > explain how you connected everything?... Like for eg... from HU --> > passive cross over --> ... etc... OK, first of all my HU has an adjustable high-pass filter so I employ this for the front channel. I have it set on a high-pass filter at 63 Hz with a slope of 24 dB per octave (the sharpest slope available on this unit, I can also choose 18, 12, and 6 dB per octave). My rear speakers are set with a high-pass filter at 120 Hz at 12 dB per octave. So that takes care of my high-pass filter for my midbass speakers in front. I do not use any low-pass filter for my midbass speakers. I just let them roll-off naturally. My midbass speakers are driven by an old school RF Punch 225.2 (112.5 x 2 RMS at .05% THD). OK, the tweeters. First, you should know that after my HU, I run the front signal through a Clarion 750 dash mounted EQ. This splits the signal into four channels (tweets and mids), this allows me to control the level of the tweeters and the midbass drivers from the dash. The Clarion has a built in line-driver that boosts the signal to 7 volts. I DO NOT employ any of the high/low pass filters available on the EQ. So the midbass signal runs to my RF amp and my tweeter signal runs to a Coustic XM-3 Electronic X-over. This is my high-pass filter for my tweeters. It is adjustable up to 8000 Hz with a 12 dB slope. I have it set to 3000 Hz. From there. the signal goes to my Jensen (YES, JENSEN!) XP45 amplifier. It has been a really great amp for my tweets and it is VERY powerful (60 watts X 2 RMS .5 % THD), I do not use any of the high/low pass filters incorporated into the Jensen amp to preserve sound quality. By the same token, I do not employ the high/low filters on the RF amp I use for the midbass drivers. Any time you employ filters you denigrate the sound so I try to use as few as possible. For that matter, I do not use ANY passive filters AT ALL in my system (capacitors and inductor coils). This is just my opinion (don't flame me, anyone), but I think passive filters tend to degrade the sound. Again, this is only my opinion. Anyway, that's how it's set up. I will soon be replacing my rear-fill speakers and front tweeters to an ALL JL set-up (except for the subwoofers, of course, they will stay MTX). And I may change some of those settings then if the need arises. Stay tuned. ;) MOSFET Something also to keep in mind, is that a lot of EQs/crossovers will take 1 imput and then give all the outputs itself. The Pioneer DEQ-P8000 I think did this. A case such as that, pretty much just runs from the front pre-out and doesn't use the rest. So it depends on what equipment you're planning on using as well. I've got a crossover that will accept 1, 2, or 3 inputs and any of them will do all three outputs. One of my favorite pieces of equipment, and made by Directed. Brandonb > I'm sorry, I've been out of car audio for quite a few years so forgive > me if I ask dumb questions :-) [quoted text clipped - 20 lines] > > Joel Three pair of pre outs are nice if u have a nice head unit with built in electronic crossover. It eliminates the need for an external x-over.. But if u want to have an outboard electronic x-over, go with using the front / rear pre outs to feed the fr-rr inputs on the xover. You will have total fade control and also level control and also different x-over points if needed for front and rear. Say u have big 6.5' seperates up front and wanna go down to 120hz but your rears are 4' seperates u can set at 200hz.. levels, freq, and other stuff can be fine tuned with a good x-over. But really, a good head unit now has all that built it and u don't need another external piece of hardware.. less rca patch cords and all.. check it out > I'm sorry, I've been out of car audio for quite a few years so forgive > me if I ask dumb questions :-) [quoted text clipped - 20 lines] > > Joel |
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