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Thread: Need a Little Help on Setting My System Gain Levels

  1. #1
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    Need a Little Help on Setting My System Gain Levels

    Hey all, Well I'll keep this as short as I can, hopefully without missing anything.

    System:

    - Car PC with Creative Audigy NX USB sound
    - Stereo O/P from this into Vibe deltabox 3-way line amp
    - First O/P goes to 2 channel amp for front components
    - Second is split to a 4 channel amp for two sets of 6x9's
    - Third is split to two one channel amps for two 12" subs (stereo input, mono output)

    So overall 2 x 12" subs, 4 x 6x9's and 2 x components. Everything is up and running and works together really well and now I've come to setting up the gains throughout the system and need a little advice to make sure I'm clear on it.

    After a bit of googling, here's what i've done so far:

    - Set all amp gains to their minimum, all bass boosts/enhancements off or minimum
    - Set vibe deltabox gain to 0 (dial can be set from 0 to 20db) and set all output attenuation dials to 0 (can be set from -20db to 0)

    So I figure everything after the carpc was at a base level with a minimum of gain throughout the system. Then setup a 1khz sinewave on the carpc and increased the carpc volume right up to 0db, no distortion, sounded perfect. Was certainly not quiet but I know that the amps/speakers are capable of much more.

    Next step was to playing a track on the carpc and adjust the low pass cutoff frequency on one of the sub amps to just about drop out the vocals from the track. Then played a 100hz sinewave and measured the voltage output from that sub amp and took a note of it. Then moved the voltmeter over to the second sub amp and adjusted its LPF to match the output of the first. Finally I attenuated the deltabox outputs to the component and 6x9 amps to balance the system (only roughly for now).

    So thats about where I am, all gains set to 0db (or as low as possible) the LPFs set to my liking for the subs and the overall balance pretty much right. Now I need to introduce some gain, just not exactly sure where!

    I know I have a few db's to play with at the CarPC. I have 20db's from the deltabox and then there's the various gain dials on the amps. What I've read tells me that if I need gain then I should start from the beginning, i.e. carPC and if thats not enough then move onto the deltabox and then onto the amps if I have to.

    Would readers agree with this? I was thinking of starting by increasing the carpc gain and litenning for distortion (distortion from the soundcard I mean, I know there won't be enough gain to trouble the amps/speakers at that stage). If this gets up to its max then moving onto the deltabox.

    The deltabox has a little LED gauge that shows the output from its internal gain amp (1v up to 5v then overload). Now with the current output level from the carpc, I know that the delta box can give enough gain to overload its own output so I know that I wont be setting that gain to max. If i get to the point where I have maxed the gain from the carpc without distortion and maxed the gain from the deltabox without overload then its time to move onto the amps (very unlikely given the quick bit of playing around that I did this evening before packing it in for the night).

    hhmmmm, not as short as I was trying to make it, lol. Anyway, thats pretty much all the info. Would really appreciate any thoughts or suggestions from the guys out there who know their stuff when it comes to audio.

    Thanks, Jon.

  2. #2
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    i would recomend setting the gain on the line amp to about 3 volts, and then using the gains on the amps to adjust for that(i think most amps have a marking for 2 volts-- so just above that). if it does not seem loud enough, re-adjust that amp gains. or, if you seem to have noise issues with the amp that need a louder source level, than up the gain on the lineamp, and lower the amp gains.

  3. #3
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    Thanks for the reply,

    Thats pretty much what I ended up doing, I maxed out the CarPC output (about +10db) without any distortion then increased the line amp to just under 4 volts, was the highest level without any risk of overloading the output in future.

    Then adjusted amp gains to get the level I was after. I'm sure they're nowhere near what the amps are capable of but they're more than enough for my needs.

    Thanks

    Jon

  4. #4
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    no problem.

    one of the things i forgot to mention is that you will want to try to balance the sub amps as good as possible-- use a 60hz test tone, and disconnect the speakers, and use the multimeter set to a/c and adjust the gains until they are the same... this is really only for multi amp sub setups though(and the reason i forgot to mention it-- i have a single sub amp setup.)

  5. #5
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    would you be able to get some pics of how you have everything wired up? i am at the stage myself where i need to figure out how i am going to get sound from the 3.5mm jack on my carpc and into a 4ch and two sub amps. it sounds like you have figured it all out.

  6. #6
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    I wouldnt say all figure out, lol, but i've got it wired in a way that im very satisfied with. I dont have pics that would help, wires are everywhere in my car, lol. But i'll draw a little diagram up showing how its wired. Might be tomorrow now tho, it's getting later over here.

    J

  7. #7
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    deffinatly, when ever you get a chance. I am still just planning my setup so im working on one stage at a time.

  8. #8
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    Thinking about it, there's no point with a diagram, its pretty simple.

    Im using a 3.5mm stereo to twin RCA phono cable to connect the output from my audigy 2 NX to the input of my vibe deltabox:



    This has an overall gain control for the input and attenuation dials for each of the three outputs.

    The first output feeds my front component amp. The second feeds my 4 channel (with the inputs from the first two channels looped to the second two. The thrid feeds my first sub amp which has a line out which i pass onto the second sub amp.

    Thats it.

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