multi-channel amp gain question

Kid Red · Post by **Kid Red** » Thu Jan 25, 2007 1:45 pm

I've read how to set the gain, so I'm cool on that. As I understand it, you want the amp to match the voltage (or something) from the HU. However, what about multichannel amps with 2 gains? I always adjusted each per listening and preference. But if you are trying to match the HU, would it not make sense to have both gains identical? Seems balanced to me that way.

I have channels 1&2 going to my mids/highs, and 3&4 bridged to my sub. So,do I want the gains to both match? Forgive my newbie ignorance.

solacedagony · Post by **solacedagony** » Thu Jan 25, 2007 2:15 pm

I don't think it would really matter.
If you think about it in terms of power, when you're running active on a 4 channel amp, you have your tweeters attenuated to meet the mid volume (sensitivity differences), so you'd effectively be putting out much less power to the tweeters and more to the mids.
In terms of the first stage of amplification, it must have two separate stages on 1+2/3+4 or it wouldn't have two different gain controls.
I very well could be wrong, but that's how I'm seeing it right now.

Kid Red · Post by **Kid Red** » Thu Jan 25, 2007 2:30 pm

My Alpine has two gains, one for channels 1 &2, (fronts) and then one for channels 3&4 which I have bridged to my sub. So, I figured if both gains were set to the same settings, wouldn't that mirror the sound better as opposed to going too light on the sub (3&4 channels) or going too high making it bassy.

solacedagony · Post by **solacedagony** » Thu Jan 25, 2007 2:35 pm

You should probably just set them either by ear or the DMM method. I don't think there will be any difference.
You should level match AFTER you set the gains, however, NOT level match WITH the gains.

Kid Red · Post by **Kid Red** » Thu Jan 25, 2007 2:42 pm

K, not sure what the DMM method is, can you clarify that? By level match what do you mean? Do you mean a line level adapter? I have the HU running speaker level into the Alpine (was told the Alpine is clean enough that i would be fine that way) Should I add a LOC? Or something else?

solacedagony · Post by **solacedagony** » Thu Jan 25, 2007 2:50 pm

Setting gain with a digital multi meter. cargodz did a tutorial on it in the FAQ section. Level matching = volume matching.
Running speaker level into your amp is basically the same as using a LOC, you just don't have to add the LOC. It'd be preferable to get a head unit that has pre-outs.

Kid Red · Post by **Kid Red** » Thu Jan 25, 2007 3:00 pm

Ah, yea, I've read the digital meter, didn't know the DMM acronym. SO I don't need a LOC. I running stock HU because it's a Mazda and you can't replace the radio, buttons everywhere, etc plus I want the stock look (especially for resale value)

So then, do the meter method the same for each gain, correct? Would that not make them the same setting since they are receiving the same signal from the same HU? Seems the gains would mirror each other. Unless because the 3&4 channels have a sub filter that may affect the gain somehow. I'll play with the meter if I can find mine and see if the 1&2 channels' gain ends up being the same setting as the 3&4 channels' gain on the amp.

I'm making sense right?

solacedagony · Post by **solacedagony** » Thu Jan 25, 2007 3:34 pm

The speaker level input on the amp basically IS your LOC.
Yes. Your first gain would affect the output on channels 1+2. Your second gain would affect output on channels 3+4. The gains won't be the same because you're bridging channels 3+4. I think the voltage on 3+4 should be double that of 1+2, assuming that each channel (1, 2, 3, 4) puts out the same amount of power. If you were running a speaker/channel instead of bridging 3+4, you would be aiming for the same output voltage.

Kid Red · Post by **Kid Red** » Thu Jan 25, 2007 3:35 pm

Ah, so the bridging does affect it, cool. Thanks, that's the answer I was looking for, thanks for explaining it :)