Need some help with setting up my LOC and amp gains

bando81 Newbie
Here’s my setup to help with some of my questions.

My amp is 5 channel rated at 60W x 4 + 400W at 4 ohms.

My speakers are diamond 652 the website says they’re at 50W RMS and don’t list the impedance but another site says 4ohms

The sub is RF p3 12” d2 dual voice coil at 2ohms. The specs say it’ll take 300-600W RMS. (The amp is rated for 4ohm & 2ohm loads, this sub should be able to be wired for this amp, right?).

I have a factory head unit running to the LC7i line output converter.

So my amp is rated for a max input sensitivity of 5V. The LC7i is capable of putting out 8.5V. My plan was to get 5V running from my LC7i to my amp. Here’s where I’ve had some issues.

I ran a 50hz -5db test tone with my HU at 75%. I used a multimeter to get the voltage coming from the RCA outputs. I raised the output level for the sub channel until I got a 5V reading. When I went to check the voltage the amp was putting out for the subwoofer, it was in the high 50s. If my thinking and math are correct, I want to send 400W to the sub at a 4 ohm load so the target voltage would be the sq root of (400x4) which comes to be 40V.

What should I do here? Should I ignore my preamp voltage and just set it so the speaker outputs on the amp match my target voltages?

What I ended up doing was playing test tones for the front rear and subwoofer (50hz and 1khz at -5db) with my HU at 75% and then turning up the output level on the LC7i until the Maximized light turned on and backed it down a little. After that I went and checked the voltage at the amps speaker outputs and adjusted the gain on my amp to get to the target voltage.

Lastly, I know a lot of people don’t like the multimeter method and honestly I don’t either. Also my multimeter is very cheap. Going to try to get the ddm1 or an o scope but until then I need to do something. If you read all this thank you.

nauc Veteran
10+ year member
turn the deck up 3/4, turn your LC7i up (just under clipping) set your amp gain voltage


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