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    Icon32 Analyzed HU preamp outputs...they don't distort?

    Basically I set out to determine at what volume my head unit distorts, however what I found out is that it did not distort, not even to full volume. (However, at full volume, it ceased to give voltage to the amps due to the 'amp guard' feature...which I forgot what it meant exactly).

    I played a 50hz sine wave recorded at 0dBFS, burned that to a CD, made sure all EQ settings were flat, and hooked the o-scope up to the rcas coming from the head unit. The crests & troughs of the waves were always rounded, unexpectedly. is it supposed to be like that?

    Now the HU volume goes from 0 to 33 and the preamp output level is 1.8V; 75% of that would be at about volume 25, which is what I usually set it to in order to configure the gains on the amps. With the HU volume @ 25, and playing the sine wave @ 0dBFS, the voltage coming off the HU is .32V. even when I hooked the HU rcas into the 8 volt audiobahn line driver (yup...) and measured the output from that, the voltage was .42V. So at least I know the line driver doesn't do much other than serve as an EQ; however, that could be an install issue cause its source of power & ground is the HU's power & ground wires.

    and for some reason, now, 750 watts on the 2 subs in ported box doesn't seem that much louder than the old 300 watts on 1 sub in a sealed box. when I first made the transition, it seemed hella loud and I would only go up to 20 on the HU volume and would have the subwoofer level @ halfway. Now it seems I have to go to volume 22 & subwoofer level 3/4 to achieve that same level. gain settings have not changed (and hopefully my ears haven't either ) and just last night I noticed...dimming . I wish I had a termlab or something to actually measure sound pressure output cause something's just not right with my system.

    and 160 watts on components isn't loud to me either. I know you guys recommend 100 watts a lot; to me it seems like that would still only equate to HU volume.

    my brother's '01 malibu with the only equipment being an aftermarket pioneer HU and everything else stock (6x9s in back, and probably the same in the front - no amp) can match my system in terms of the loudness of the mids & highs at my volume of 20 out of 25_for_setting_amp_gains.

    my mind is all over the place but I hope you understand the issues & questions I've raised.



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    Re: Analyzed HU preamp outputs...they don't distort?

    Well, some amps don't produce full power at low voltages... I'm assuming your system is pushing your alternator and dropping voltage below 13 vols. Use a DMM to see your line voltage. I have a 100wrms x 4 channel amp that's clipping at under 25wrms per channel because I'm running it at 13.5 volts... It *****, get a new alternator Iraggi has a deal right now for forum member.




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    Re: Analyzed HU preamp outputs...they don't distort?

    well, voltage drops are only around .1 volts. On a good day the alt puts out about 14.3 and on others around 13.9. I have the gains set appropriately on the amps (in the millivolts-range). I was just wondering why the HU didn't distort its output signal at next-to-max volume.



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    Re: Analyzed HU preamp outputs...they don't distort?

    guess I found my answer at the one and only bcae

    Many CD players will be able to produce a 0dBfs signal with no clipping at full volume (or one step down from full volume) with their tone controls set to their 'flat' position (in the middle of their range - no boost or cut). Most of those players will produce a clipped output (when set at or very near maximum volume) if a 0dBfs track is played in a band of frequencies that are boosted by the tone controls (i.e. an 80hz 0dBfs track) and the tone controls (the bass control in this instance) are set for even 'minimal' boost (especially 2 volt preamp output models). Some decks will produce a clean signal no matter what the tone settings. Now, this doesn't necessarily make one deck better than another but you need to know how your deck performs. If you have access to an oscilloscope, you can check the output signal at the RCA jacks. Play a 0dBfs test tone between 40 and 100hz with the volume and bass at their maximum settings. Take note of the peak voltage (from the reference to the top of the waveform). You can multiply the peak voltage by 0.707 to get the RMS output voltage. Check to see where it clips (the volume control's position) with the tone controls set flat.



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