noobie question about gain staging with new amp........or is my amp bad?

[TTBlues]

I did my first install today. It was pretty straight-forward.

But here's the thing:

In the middle of the install I decided to test it with the amp only driving the left door speaker. I let the head unit drive the right so I could compare. I turned the gain on the amp all the way down.

The side driven by the HU had a much hotter signal than the one driven by the amp. Is that how it should be? I had the impression that with the gain on the amp all the way down, I would still be getting power from the head unit un-attenuated, but maybe that's not the case?

Is that because I'm using the RCA outs on the HU for the amp? Do they have a much lower signal? Or with the gain all the way down on the amp, have I actually turned things down?

When I hooked up the right side to the amp as well, it was also much less hot than what it was by bypassing the amp.

I just want to make sure my amp is okay. I feel like I have to crank the gain all the way to get it to beat what the HU was doing without it.

My HU is a Kenwood KDC-355U

My amp is a Alpine MRV-F300

The Kenwood has about 21 Watts RMS

The Alpine has 50 watts RMS

Stock door speakers.

Thanks.

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[UGHH]

You should never have to crank the gain all the way up. The gain isn't a volume knob, it's to match the voltage level coming from the head unit.

You'll just clip the speakers to death cranking the gain all the way.

 

[TTBlues]

OK. Is there a ballpark max that you can crank it? Right now its at one notch past NOM (2 O'clock). There are 2 more notches before it's at Max. Given my set-up, at what amount of gain should I reach the amp's RMS rating which is more than double that of the HU?

 

[UGHH]

You have to use a DMM to figure that out. Google "setting amp gains with dmm." Or YouTube has several videos on how to do it

 

[TTBlues]

I see. Thanks for the tip. I'll have to pick up a DMM tomorrow.

 

[TTBlues]

Can you answer another quick question so I don't have to start another thread? Something I thought of while doing this.

I hooked up the amp to the blue power wire so its shuts on and off with the HU. That's fine.

But what if I want to listen to the stereo while the car is not running? It'll drain my battery quick. Is there a switch that can be installed to manually turn the amp off for this situation? Or another solution?

 

[bradl79 10+ year member]

u may be able to install a switch inline with the remote wire to the amp, ,i don't see y u couldn't but never heard or tried it

 

[TTBlues]

Back to my original question. To you or anyone else, does it sound normal that with the gain all the way down, the amp's speaker output would be putting out less power than the head unit's speaker outputs?