Gain Setting Tutorial

[champaned_out 10+ year member]

would i be safe with using a -3db test tone @ 60hz?

my equipment is (1)12w2v3 in a sealed box with a Hifonics TXI7506 running 325rms x 1 @ 4ohms and a stock factory HU, 6.5, and 6x9

 

[sc197 10+ year member]

I read through this whole thread and I didn't see anyone having the same problem as me. (If so, my apologies for repeating the same question)

I have a JBL GTO1201.1, 787rms @ 4ohms. Therefore I should be getting 56.1V

I turned the DMM on to ~V 200v

My headunit is a cheap Pioneer so I have the loudness off, bass on 0, everything else set like it just came out of the box.

I unplug my negative speaker wire on the amp (leaving positive still hooked), I hook the positive wire on DMM to positive channel on amp, same with negative.

I then turn up my input sensitivity up like mentioned and when I have it maxed out, it only reads like 30-some volts. Do I need to turn anything else up since my headunit is weak?

Any help would be appreciated.

 

[DBfan187 5,000+ posts]

turn your volume to 61/62 then retry.

 

[sc197 10+ year member]

30 is the max on the headunit. I had it on 23.

Could it mean bad battery/alt? Poor headunit? I have the DMM hooked up wrong?

 

[DBfan187 5,000+ posts]

since when did Pioneer max @ 30? Everyone I've ever used went to 62.

 

[sc197 10+ year member]

Mine is the low end tho. It's the DEH-9 that Wal*Mart sells. //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

I'm going to upgrade to a P880PRS asap.

Any tips?

 

[DBfan187 5,000+ posts]

try volume 29/30

 

[89montero 10+ year member]

I recently bought two JL 12w3 subs in a sealed JL power-wedge box. The deal came with a fosgate power 360a2 amp to power them.

In the future I plan to upgrade to a better amp but for now is it safe to just turn the gain up all the way since the amp obviously isn't putting out close to what two of these subs can handle?

 

[Trey803 5,000+ posts]

NOOOOO....this is the point of this thread. Amp are only designed to put out a certain number of watts. If you push an amp past this you will clip the signal sending distoriton to your subs.

 

[thch 10+ year member]

So then I remembered the way Orion used to say to do it with the DMM (back before they were taken over by DEI this info was on their website). Instead of setting the gain to some calculated voltage they said to turn the gain up until you see the voltage stop increasing rapidly and sort of level off, then turn it back a bit. I did this and it "slowed down" at around 70V and maxed out at 72.x volts before I hit the stop on the gain knob. So I dialed it back to around 68 volts and left it there.

sure, this is a way to detect clipping. output increases by power-law as volume or gain knobs are adjusted. eg, e^x, as clipping starts, the percentage that each increase in HU volume (or gain) changes the RMS or average magnitude suddenly does not increase by power-law. (RMS and avg magnitude are different). you can plot HU volume settings vs output in a special way that will give an indication of what settings cause clipping.

But honestly I don't get how the root of the product of power output and impedance driven works out like that. Because say I had my sub wired for 4 ohms (instead of 1), then I would be looking at 450W from the amp and therefore it would be (1800W*ohms)^.5 = 42.42V . Why would I set the input stage gain such that the output voltage from the amp, with no load connected (as JL tells you to do), was at a higher speaker output voltage on the amp?

JL builds regulated amplifiers with high damping factors. Such amplifiers should have output voltage that are only marginally affected by the speakers. this method doesn't try to get the absolute max out of unregulated amps, as the orion method does.

How does that make any sense? Because the only difference with no load connected would be me making the amp's input stage more sensitive and nothing else. I.e. All I'd be doing would be making the amp more sensitive for the 4-ohm load (42V) as opposed to the 1-Ohm load (34V). But for what reason??? The RCA level from the HU did not change, so why would I look for a higher no-load voltage on the speaker terminals if I were driving a higher impedance? I don't get that. Because gain is supposed to match the amp's input stage with the RCA level it receives from the HU. How does that have anything to do with what load impedance I'm driving? Especially considering you measure the outputs of the amp with no load connected (other than the DMM itself).

I dunno but the Orion method seems a lot better to me. However I don't remember if you were supposed dial up the gain with the load connected to the amp or not, but I just did it without since I didn't want to deafen myself, lol...

the load shouldn't affect the amp's output voltage. the amp should be rated for 4x power @ 1ohm vs 4ohm, and the output voltage for both cases should be the same. many people ask about impedance rise, when its not really part of the formula. if impedance is higher, the amp isn't capable of the same power output, and the recalculation gives the same results.

the orion method works well with unregulated amplifiers, which are popular in SPL competition as they allow more power if you run higher power voltages. in such amplifiers, the point of clipping will be based on how much the load causes the supply to sag. the ideal setting will be affected by load and charging system, which do not appear on the amp manufacturer's specs.

 

[XTRProBoy 10+ year member]

^Chris I appreciate the explanations above, thanks //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

So from what I gather you essentially agree with me but you're saying that this method works only with JL slash/RIPS amps and no others? Because if that's the case why do we have 40 pages of people trying to set their (mainly non-JL) amps with this?

Shouldn't there be a warning "only use this method to set a JL Slash amp with RIPS"?

I dunno. Perhaps you could take a look at the other thread where I made some protest to the same method (starting on page 3) I'd be interested to see what you would say in regards to that:

http://www.caraudio.com/forum/showthread.php?p=2678394

The method mentioned here [if we choose to use it] seems to imply that gain is indeed a volume control--that's why going by this method you would want to set the input sensitivity differently for a different load (yet for the same amp and HU). Becuase you take into account the load you're driving not the voltage output of the HU and the input modifying by the amp; and you do so measuring with no load on the amp. If we disregard the load that is later going to be connected and set the gain the same at all times provided the source unit and amp are the same, then the saying "gain is not a volume control" does apply.

 

[thch 10+ year member]

it works suitably well with other amps, but having stiff supply regulation and a DF > 10 @ rated load conditions allows the amp to reject load and line variations to a large degree, thus making the testing of the amp based on rated specs @ 14.4V and unloaded give results that are very close to testing with 12V and a 1ohm load on the amp.

I beleive JL's site gives such a warning, though there are many amps out there that work fine.

unregulated amps will have variations based upon supply. if the DF is low, the load will give rise to variations as well. note that many guides suggest the gains be set to allow moderate clipping, conceeding that the penelty for clipping is not death, and for low levels of clipping can be a small penelty.

so DMM settings will cause a little more clipping if the user has a low battery, and a little less when the user has a high battery. or maybe the amp will have minor clipping when the battery is low and will be underutilized when it is high. either way, the method gets you close, and the penelty for being off by a bit isn't very high, so it still works.

the gain adjusts volume, but doesn't limit the user from excessive settings. fully turned is not 100% volume, so while the gain does adjust volume, it is not really a good volume control.

still, a user can set the gain to an arbitrary point, then use the HU to prevent clipping. this is why many people can get very loud at 10/30 on the HU, and then not be able to turn it past 20/30 without distortion. so long as the signal input to the amp is limited consciously by the user, the high gain settings won't cause clipping.

 

[phyphoestilic 5,000+ posts]

the test tones are down, is there any other place to get them?

 

[phyphoestilic 5,000+ posts]

nvm found a good page

*** Another tutorial with test tone downloads

http://www.resnet.trinity.edu/areynol1/gain.htm

 

[groggy23 10+ year member]

Ok here's my situation. I have a set of components that can handle 150w rms @ 4ohms. My Arc is putting out 50w rms x 2 @ 4ohms (NOT bridged). So should I calculate it like this:

sqrt(50x4) 14.1V

or like this:

sqrt(150x4) 24.5V