Gain Setting Tutorial

[SirClay 10+ year member]

Hey, I am trying to set my gains right now and I am to stupid to figure out the formula. I have a JBL 600.1 amp and 2 IDQ12 Dual 2 ohms subs. I have them hooked up to the amp in a 2 ohm load. Can you tell me the volts I am suppose to get? I know I already asked this, but I didn't write down the number. Thanks.

34.6 volts?

Is it AC or DC?

Click to read more...

 

[jellyfish420 10+ year member]

if you have access to an osilliscope would it be better to set the gains to the unclipped volume,or to use the voltage method?

 

[Acidburn 5,000+ posts]

if you have an o-scope, use it, great for making sure there's no clipping at all

 

[TooLowTooGo 10+ year member]

Hey, I am trying to set my gains right now and I am to stupid to figure out the formula. I have a JBL 600.1 amp and 2 IDQ12 Dual 2 ohms subs. I have them hooked up to the amp in a 2 ohm load. Can you tell me the volts I am suppose to get? I know I already asked this, but I didn't write down the number. Thanks.

34.6 volts?

Is it AC or DC?

Sqrt(600*2) = 34.641 volts ...

ok this is gonna sound stupid. LMFAO. but owell better to learn then to kill my subs at comps. i plan on givin my little 12's, lol about 350more watts then what they can handel. so i dont wanna clip em n then blow em right there at the comp.

they are rated 800PEAK so 1600PEAK for the 2 of them., im going to wire them @ 1 ohm, the amp is 2300RMS @ 1ohm. and i dont wanna clip my sub to blow em right there at comp.

n e way my amp is a pa a3000db amp. im going to run it at 1ohm for 2300RMS. so since it would be 2 subs would i times 2300x2=4600. then 65x65=4624. so that pretty close, lol. so would i tune the dial to about 65?

and another stupid question if that aint stupid enuiff lol. is that there are 4 dials.

1. Level (min - max)

2. Sub Sonic (15 - 40)

3. Low Pass (50 - 150)

4. Bass Boost (0 - +18db)

n e way wich one would be at 65? if 65 is even right.

pic below to sho u what i mean by the 4 dials.

also my headunit. should i tune the pass to about 60? or keep it at the restoerd 80?

 

[RemlapaN 10+ year member]

Another question for ya (not really as basic as the ones above):

It makes sense if you are bridging channels to do your calculations for 1/2 the impedance of the speaker, but what about running the channels in parallel mode?

So, if my sub is wired for 2 ohms, bridging I would use 1 ohm per channel for calculations...

But, if the amp is hooked up in parallel, would that mean i use 4 ohms per channel? (1/4 + 1/4 = 2ohms) ?

The wiring scheme for the amp to get parallel is this:

2ch:      + - + -

Bridge:   +     -

Parallel: +   - +
.         |_____|

(Yea its right, when you go to parallel mode, the 2nd positive connection is now negative, and the 2nd negative connection gets wired to the first positive connection)

There is a picture of each configuration here: http://manuals.harman.com/JBL/CAR/Owner%27s%20Manual/PowerSeriesPx%20BPxAmpOMFINALrev7_8_04.pdf

found on page 3 of that PDF document

EDIT:

So basically, if i am shooting for 1500w RMS, what voltage should i aim for, and where should i place the probes of the DMM? (DVC4 sub wired in parallel)

 

[JimJ 5,000+ posts]

so, if i was going to use this for a PG Tantrum 1200.1 (1450W) hooked up to two e12a.22's (2 ohm DVC's, wired to a 2 ohm load), the number I'd be shooting for is around 53.85V?

just making sure...

i'm off to make a test tone cd now.

 

[JimJ 5,000+ posts]

one more newbie-type question...i'm going to have a full range amp to set up also for my front coaxials, I assume this works the same way? What frequency should I use for a test tone for the front speakers?

 

[Moe Lester 10+ year member]

one more newbie-type question...i'm going to have a full range amp to set up also for my front coaxials, I assume this works the same way? What frequency should I use for a test tone for the front speakers?

1khz i believe

 

[sumone 10+ year member]

Maybe it's something I'm doing wrong or whatever, but I've tried this before on my sub amp: cl400...

- gain at MAX sensitivity

- test tone is 60hz @ 0dB (full message=Maybe it's something I'm doing wrong or whatever, but I've tried this before on my sub amp: cl400...

- gain at MAX sensitivity

- test tone is 60hz @ 0dB (full scale)

- HU volume is @ max volume (33/33)

- no dsp, eqs, or line driving going on anywhere

Since the amp is supposed to do 300x1 bridged @ 4ohm, I should get about 34.64 volts right, ...well I got about 18 volts...

Voltage at amp was 12.6 (car off)....

..seems like Jmac is our resident square rooter...lol

 

[RemlapaN 10+ year member]

Well, if you read the manual, parallel mode iallel mode is only for less than 2 ohms ... So with a 2 ohm load, you should be in bridged configuration, which basically means it's the same as a normal amp. You should be aiming for a voltage of 54.77 volts.

actually, Direct from JBL Manual: "NOTE: If the nominal impedance of your speaker is close to 2 ohms, be prepared to try noth bridged and parallel mode to determine which performs better"

For some reason, i seem to get better SQ and better power handling from parallel mode on my 2 ohm setup...

 

[sumone 10+ year member]

hmm...maybe I did do something wrong...

Tried again; this time, using a CD (the first time I was using my mp3 player, which has an RCA output)

And this time, no problem...

What I ended up setting it to:

For the sub:

- 60hz 0dBFS tone, 25/33 HU volume, for 300 watts, 35.07V (closest I could get to 34.64)

For the components:

- 1000hz 0dBFs tone, 25/33 HU volume, for 160 watts, 25.41V (closest I got to 25.298)

And based on these settings, I find myself listening to music on HU volume 24/33 (when the max setting I used for settting the gains was 25)....is this a sign I just need more powerful amps? I already know I need way more bass to match my 160 watt components...

Also, is there some elite/clever way using a multimeter to detect whether or not you have an under-rated or over-rated amp? Cause if I have an under-rated amp and I use this method of setting gains, I'm not getting would I COULD be getting....or is an oscilloscope the only way....

 

[sumone 10+ year member]

^ then that's what I need! //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[H4cK 10+ year member]

OK I dont know if I have this right, but anyway let me try to explain myself.

I have an Alpine MRP-350, which is supposed to give out 200RMS at 4ohms. My woofer is an infinity reference, which is 4ohms and 300RMS.

OK with that in place I do the calculations;

Sqrt(Power*Resistance) = Voltage

Sqrt(200*4)=28.28

I set all my settings as I would normally have them, ie bass = +1, SW = +1 @ 50 [bTW I have a 760MP Premier HU].

Now when I go to test the AC voltage coming out of the amp, its skyrocketing

So I then bring down the gain, and turn off any kind of EQ/Bass Boost, and bring my LP Filter down to its lowest setting, which is 50Hz I beleive. I get the voltage to what I beleive is 28. V, since I have an analog tester

Now I connect my woofers back, and try listening to it, and I dont find Im getting enough bass //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif I did set the HU volume to 30, which is just about the most I would listed to my stereo under normal circumstances. For some reason Im just not getting the bass I had before :s

Oh yeah I used a 30HZ tone to test the voltage. It did play decently, but not too nice when listening to actual music.

I was thinking, since the woofer is 300RMS, maybe its being underpowered. How would I work around this equation to get it the right power. This amp is supposed to produce 350RMS at 2 ohms, but then again, its a 4 ohm woofer, and I only have one

Any suggestions as to what I may be doing wrong will be sincerly appreciated //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

PS. Im using an audiocontrol epicentre in the setup.

 

[sumone 10+ year member]

^ lower the mids/highs...

I would set everything flat too. With this method you're trying to set the gain to the amp's theoretical limit. You may be safe to go past this point if the amp is underrated, but unless your ears are pristine or you have a scope, you should just turn down the other stuff to have the levels match better.

Also, don't know if it matters, but try using a 50hz or 60hz sine wave.

-------------------

on another note, if I wanted to buy a scope just for setting gains, any recommendations on what I should look for; cause these things are pretty expensive and I can't afford to blow 200 dollars on some scope where I only utilize 10 out of 100 features...

 

[H4cK 10+ year member]

Well I tried setting everything flat also, but then after I got the voltage to 28. volts, and went back to the HU to tune it, I ended up putting the base up a notch, and that ended up putting the voltage way past 28. I didnt get a chance to set the gain for my mids and highs amp, because I didnt have a 1khz sine wave.