In addition to JL Audio's tutorial at http://mobile.jlaudio.com/support_pages.php?page_id=143 , I also found a message forum discussing a similar method to tuning the gains on an amplifier so I attempted to do this tonight.

My Phoenix Gold Xenon 100.4 amplifier is rated at 100 watts a channel (4) -- I don't have the birth certificate, but I wouldn't be surprised if actual output was close to 120 wrms per channel at 4 ohms.

I'm driving some Polk Audio Momo 6.5" components (can handle 125 watt RMS) straight wired (no biamping). As a result, I'm aiming to set the amp's gains to see 20.0 V -- square root of 4 * 100 (4 ohms x channel output).

Using a 1 KHz sine wave test tone at 0 db, I had my stock unit's volume set to 30 out of 40 and adjusted the gains for the front channels that drive the speakers to read close to 20.0V. I'm actually around 19.7x V. My end result was the gain ended up around the 2 o'clock position.

Now does that sound like it's too much??? Does it make sense?

Or is the fact that I'm using a line output converter (PAC OEM-2: http://www.pac-audio.com/products/oem1.htm) causing some sort of complications? For what it's worth, the gains on the LOC are set at halfway, which is the default.

Oh, I'm using a $90 multimeter that is true RMS digital multimeter.

 

I think you're getting too technical for your own good. Try using your ears for setting the amp gains.

I'm just saying that it will never sound better (to you) if you're the one who set it using your own subjectiveness.

 

Valid reply. Perhaps it is too technical for my own good. However, the tutorial and process seem rather straightfoward to me.

 

Although your math is correct, your "tuning" methods are wrong. The way you are doing it, will probably result in clipping.

Do it the right way.

1)Set gains to 0.
2)Put headunit loudest you will ever put it...on alpine, I like 25.
3)Turn up gains, slowly until you hear distortion (clipping)
4)Back the gains off a bit.
5)Pop open a beer.
6)Repeat step 5 as necessary.

 

are all your crossovers off and all your settings set to flat?

if you do not have access to an o-scope then just do it by ear like eevryone else suggested.

 

Amp's crossovers are off. The components have their own passive crossovers but they aren't factor since I disconnect a speaker wire at the amp.

And yes, Tremble and Bass are set to 0 on my factory HU.

I guess I'll have to do it by ear...

 

actually -- as best i can tell your technical technique is just fine. nicely done.

and yes, 2 o'clock sounds about right, and the PAC set at 1/2 IS going to affect your final result, but all in all, it really looks good. how does it sound? any clipping at high volumes?

of course, setting the gain by ear isn't bad either...

 

I'll tell you what. I set the gain with the OEM HU at 30 and there is no way I can see myself approaching that volume level with the way the amp's gain is set!

In fact, I will have to minimize the Bass and Treble to it's minimum of -6 to get the HU's volume level in the 15-20 range.

Does the fact that I feel I should drop both Bass and Treble (especially Bass) to between -4 and -6 with the amp's gain set the way it is an indicator of anything?

I had somewhat of a lengthy discussion with a JL Audio tech earlier today regarding this and he said that this method is definitely the proper way of doing it and that everything I did was correct. However, I'm not sure I'm 100% totally at ease with the settings.

The thing is damn loud and tons of bass!

 

why would you lower the bass? (and/or treble) is it distorting? if so, the gains may be set too high. or is it just too loud for comfort? given the sensitivity of the Polk's and the amount of power you're working with -- you could easily get into the too loud range.

still -- all the numbers look right to me. *shrug*

 

That's what worries me. I think it is indeed distorting, but to tell you the truth, I simply don't have the ear for this stuff anymore so I'd rather play it safe by lowering the Treble and Bass, and that's why I set the input senstivity this way.

Again, I'm not totally at ease with the way I have things setup, despite the fact that the numbers and methods seem solid to me.

I guess I can try a local audio shop to see if they're willing to do a quick "tune" and listen. Not sure if that's better however