Gain setting: PPI 900.4 with a Stock HU voltage output I don't know

[kiteman]

I have a 2012 Camaro with the upgraded Boston Acoustics system. My system includes:

Stock head unit

PPI 900.4 powering Polk db6501 front components (145w @ 4ohms) and 1 Infinity Kappa 100.9w (450w @ 4ohms) in a ported box.

I don't know the voltage output on my HU, and therefore don't really know how/where to set the gains on the amp. My HU goes to a vol max of 45, so I've decided not to exceed 25 and am guessing anything above that will clip on the HU. Just a guess though. On the amp I have both gains set to around 65%, but I think I want to bring the fronts down a bit because they seem to overpower the bass a little and also get a little muffled sounding in the 22-23 volume range. I don't know if that means they are clipping or just can't handle high volumes.

Do you guys know what my stock HU output voltage might be, or think that I'm safe at these gain levels? I tried the test tone and DMM ways of setting gains, but honestly the subwoofer was barely audible at the level my DMM suggested. I turned it up and the bass still sounds clean, although I suspect light clipping I wouldn't actually hear. Everything I've read about gain setting hints that you are trying to match the amp's voltage with your HU voltage, but without knowing my HU voltage, I don't know if I'm in a *safe* range.

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[n2audio 5,000+ posts]

Those don't have high level inputs do they?

Are you using an LOC?

 

[kiteman]

I am using a LOC. I can't exactly explain how it works, but someone built a series of adapters that allows the plug and play from the factory boston acoustics amp to an aftermarket amp (in my case the PPI 900.4). Here is more on it, thought not incredibly detailed:

Our connectors simply snap onto your car's audio harness sections. The (5G-X3RCA) Input Harness has RCA's to plug directly into your amp via RCA cables for audio input. Our (X2) Cable is the output harness. Snap this harness onto the car's X2 connector and hardwire the 8 wires to your amp's speaker out terminals.

Subthump Exclusive 2010 & Up Camaro Plug & Play Factory Amp Replacement Kit V3.0

 

[n2audio 5,000+ posts]

If it plugs in before the amp it's probably not much voltage at all. If it plugs into the outputs it could be 10v+.

The best way to find out for sure is get a DMM and play a 0db test tone at fairly high volume and measure the voltage on the harnesses rca's.

 

[kiteman]

as long as i unplug both the front and rear channel rcas from the amplifier (and then use my DMM to read off of them), is there any harm in leaving my speaker terminals plugged into the amp while i do this? i assume no RCA in the amp will mean speakers won't play anything, but just want to make sure there isn't some weird ground loop that could happen when i hook my DMM up.

 

[n2audio 5,000+ posts]

No, that shouldn't cause any problems.

 

[kiteman]

No, that shouldn't cause any problems.

OK, so did this and both RCA cables showed a grand total of 0.00 volts lol. I did a search and someone else had a similar problem with a completely different car trying this. Any other thoughts? I emailed the people who made the harness I linked to and they said 3v is the output of the HU. Don't know if that's right, but let's just say it is. Does that help in determining where approximately my gains should be set?

A strange thing I've noticed is that after volume 17 or so (and I don't go past 23), I notice that the subwoofer doesn't seem to be getting as incrementally loud as the front stage. Could just be that the front stage is getting so loud that the audibility (is that a word?) of the subwoofer is diminished because your ears/mind are distracted by the front stage. I'm not sure, it could be all in my head. Otherwise, I think everything sounds pretty good aside from the darn rattles in my trunk and some of the rock music I like not having enough bass in their recordings (apparently).

 

[joom 10+ year member]

Did you have our dvm set to ac volts?

 

[n2audio 5,000+ posts]

Must be an issue with your measurement. Playing a 0db tone at high volume and getting 0v would mean no output at all from the subs. Is the tone in the subwoofer frequency range (typ 50-60hz)?

Amps sensitivity is up to 6v so @ 3v you'd be in the ~50% range.

 

[kiteman]

i did have the dmm on ac volts, tried again at max volume and the reading was still 0.00. i also checked and apparently the gain is also at 50% on the sub and probably 40% on the mids. anything else i can really do aside from getting an o-scope here? like i said i don't think i'm hearing any clipping, but i know that doesn't necessarily mean anything.

 

[n2audio 5,000+ posts]

specifically what tone are you using?

Negative probe on the rca outer ring? Positive on the center pin?