Anonymous | i have a jbl bp600.1 i am running it at 1ohm w/ a 180A alt. i calculated that this amp should put out ~24.45V of unclipped power. if you put a 60hz sinewave in my HU and set all EQ setting to flat, and put teh volume at 3/4...i should be able to turn my gain up on the amp to reach 24.45V output. but if i set up my HU like i discribed and set my crossover on the amp around 80-90hz (bass boost @ 0dB), i can only get to an output voltage of 19.2V...and that is w/ the gain maxxed out!!! (if my calculations are correct then the amp is only putting out ~370wrms!) does this mean my amps not putting out the 600wrms that it should??? could it be that my HU isnt pushing enough voltage through the RCA's??? WHATS UP W/ THIS??? ITS MESSING W/ MY HEAD!!! |
Anonymous | can anyone help me out here??? should i try to set the gain w/ the bass boost on??? if so then how high should i set the boosts??? the bass boost on the amp goes from 0dB-6dB, and the boost on the HU goes from -6 to +6...i have the amps boost to 0dB and the HU's to 0 (flat). HELP!!! |
Gold Member Username: Jonathan_fGA USA Post Number: 1658 Registered: May-04 | Do you have a load connected while you're checking this? Is the car on? Try cranking it up and getting the alternator turning. You'll need a dummy load (resistor) to perform this test, be it 1, 2 or 4 ohm, you'll need it. Remember that JL amps are regulated, your 600.1 is not, so you need to run a certain load to get this voltage. |
Anonymous | so i should put a 1 ohm resistor in ths circuit when i test it w/ my volt-ohm meter, right??? i was just putting the volt-ohm meter leads in the speaker terminals on the amp. should i put the 1 ohm resistor on the pos. or the neg. terminal? Or could i just run the sub while i use the volt-ohm meter to check the voltage??? |
Bronze Member Username: FishyTamarac, FL USA Post Number: 58 Registered: Sep-04 | I don't understand why you would need a dummy resistor. Aren't amplifiers modeled as voltage sources? so the voltage at the outputs should be independent of load(assuming the amp can deliver the power) and just dependent on input level and gain. I mean in JL's tutorial the voltage is measured in a no-load situation. http://www.jlaudio.com/tutorials/index.html# -Fishy |
Bronze Member Username: FishyTamarac, FL USA Post Number: 59 Registered: Sep-04 | Nevermind, I missed the regulated power supply part. Is there a simple explanation on how a load would "regulate" the voltage on that JBL amp? -Fishy |
Anonymous | i got a 1 ohm resistor and put it on the speaker output on the amp. i then increased the gain until my Volt-ohm meter read 24.5V. I then removed the resistor and just hooked the volt-ohm meter up directly to the speaker outputs....the voltage was the same as it was w/ the resistor, but my gain is set really high (a little over 3/4). the sub sounds better now than when i just set the gain "by ear". everything in the vehicle moves. is this method of setting gains OK??? by the way...if you sound like your talking into a fan w/ a 60hz wave and the steering-wheel rattles, bout how many dB would it be? |
Bronze Member Username: FishyTamarac, FL USA Post Number: 68 Registered: Sep-04 | lol, remember that Chris Farley movie "Black Sheep"? "Luke, I am your father." Sry, that talkin into a fan quip just tickled me a bit. ![]() -Fishy |
Bronze Member Username: FishyTamarac, FL USA Post Number: 69 Registered: Sep-04 | Oh, how hot did that resistor get at 24.5V? hehe -Fishy |
Gold Member Username: Jonathan_fGA USA Post Number: 1690 Registered: May-04 | Probably pretty hot. Resistance will cut voltage down, the load determines the power (volts & amps) that the amp puts out. 4 ohms will have less voltage than 2 ohms because the amp can't produce as much power with that load, and you will need more voltage to produce the same power at 4 ohms. That JL Audio amp determines the load before it produces power, via different voltage rails, so if the load is 2 ohms (opposed to 4) it will drop to a lower voltage rail because less voltage is needed to produce the same power, and it produces the same power at any load from 1.5-4 ohms. That's why the JL amp shows it needs less voltage to produce it's power at 1.5 ohms than 3. That's also why you can run a JL amp without a dummy load, because the amp determines that the multimeter (whatever load it may put on the amp, it will put a little) is the load and adjusts the amp accordingly. The reason that the voltage was the same when you took the resistor off is probably because that JBL amp is regulated at 1 or 2 ohms, meaning you probably kicked the regulator in and the amp had determined the impedance, thus adjusted to the voltage rail needed for 600W at 1 ohm. As far as a your gain being a little over 3/4, some head unit preouts are inherently weak, even though they say they put out 4V, 2V, etc., a lot of them are peak (not RMS) ratings. Some Alpines are especially weak on the subwoofer preout, and some Pioneer 2V preouts are pretty weak as well. If you have an Alpine, and your subwoofer level is all the way to 0, that's actually -15(it cuts the sub level), 15 is supposed to be flat. 0 is not flat on those head units. You'd need to turn the sub level to about 3/4 to max if you have an Alpine, then reset the gain and it'll be right. |
Silver Member Username: InsearchofbassPost Number: 580 Registered: Jun-04 | jon how would a line driver (8v phoenix gold) effect output on a alpine 9805 back to an mtx 81000d would this help? |
Gold Member Username: Jonathan_fGA USA Post Number: 1693 Registered: May-04 | It would step up the output, but you better check the input sensitivity of that MTX as I don't think it can accept 8 volts. |
Silver Member Username: InsearchofbassPost Number: 582 Registered: Jun-04 | they accept 8 volts |
Gold Member Username: Jonathan_fGA USA Post Number: 1695 Registered: May-04 | Then you'll be good with it, it'll provide a lower noise floor (means that the amp won't have to be turned up so high, so the amp doesn't introduce noise into the system). Remember to install that line driver as close to the head unit as you can possibly get it, that way you'll have less chance of the Alpines lower signal picking up noise. |
Silver Member Username: FishyTamarac, FL USA Post Number: 104 Registered: Sep-04 | Ok, I'm really confused now. I always thought that a car amp was just a simple A/C voltage source. You dial in the voltage with input and gain and it tries to provide that voltage across a lumped impedance(your speaker(s)) or "load" with the power produced governed by the Ohm's law stuff: 1) V = IR => I = V/R 2) P = IV = I^2R = V^2/R Theoretically the voltage remains constant and the power is inversely proportional to the resistance or impedance in this case. For example twice the resistance yields half the power and this is the way it works, at least for "good" amps within normal operating conditions. When the impedance drops too far, for whatever reason the amp no longer can produce this power. The JL's switch voltage rails at this point, effectively reducing the voltage that was "dialed in" with input/gain so the amp can continue at a more acceptable power level. This I think I understand. What I don't get is what this has to do with a dummy resistor. I mean we're talkin about running the amp at a huge impedance(the internal resistance of a multimeter is LARGE) where the power produced when measuring is rediculously small. How does JL's 3 voltage rails(think it was 3 they had) have anything to do with this? They only come into play at lower impedances. Its seems at super high impedances(like measuring with a multimeter) the JL's should behave like any other amp with a regulated power supply. If anything it seems it should be a more difficult task to setting the gains on a JL amp, not easier. Now regulated power supplies I don't get. All I know is that they keep the voltage constant or rather "independent" of supply voltage(to a point of course). I dunno I guess I'm mainly confused by the "Resistance will cut voltage down" statement. The load does "determine the power(volts and amps)", but in the case of voltage amplifiers voltage remains independent of load in normal operation and what changes is the current. The higher the impedance the less the current and visa versa. Thats why "cheater" amps were called high current amps. They operated at lower impedances with the same voltage but higher current. This is all stuff I picked up at Ga Tech(Aerospace Engineering) and FAU(Ocean Engineering) while tryin to get a degreee years ago. All theory. What is it about the way these amps ACTUALLY work in real life that makes a dummy resistor necessary. I mean I can see using one on a tube amp(open circuits not a good thing), but thats a "current" amplifier is it not? -Fishy |
Gold Member Username: Jonathan_fGA USA Post Number: 1707 Registered: May-04 | Voltage amps amplify via means of a transformer to step up the voltage, and the transistors get this power and amplify beyond that. Meaning voltage is what changes, and current is the constant. If current was what fluctuated, A) We wouldn't be measuring voltage at the amp terminals because the voltage would remain the same at all impedances, we'd be measuring amperes. B) The amp wouldn't use potentiometers to set level, it would use rheometers. This is why, regardless of what load you're running the amp, the current draw is about the same. As far as the multimeter, remember that when hooking a meter up to measure voltage, you hook it in parallel, and since you're running the meter in parallel to the dummy resistor, you're not adding to the resistance, you're actually cutting it down since it's a parallel connection, and then the meter compensates. The amp will still see the impedance of the multimeter, but how a voltmeter measures voltage is by the voltage drop across the load that it's presenting, so basically it tells you what the voltage would be had the meter not been placed there. If you were measuring amps, then the resistance would add to the dummy resistor because when hooking a meter up to measure amps, you wire it in series(but the meter still compensates). This site explains how to measure amp power, aka voltage. http://www.bcae1.com/measpwr.htm |
Silver Member Username: FishyTamarac, FL USA Post Number: 113 Registered: Sep-04 | Of course the voltage at the outputs changes(as well as curent). Music is produced by alternating current through a transducer induced by an alternating voltage. However, multimeters measure the AMPLITUDE of alternating voltages and since we're measuring the voltage of a test tone which has a constant amplitude the amplified output will be constant as well just at a higher level. I think I'm right, but there's an easy way to test this. Just run your 50 Hz, 0 dB tone and place a number of different loads(all higher than what the amp is stable at, like 4, 8, and 16 ohms) and measure the voltage across those guys, w/o changing the gain of course. The voltage should remain pretty much the same especially at higher impedances where the amp isn't "working so hard". I'm not denying that a dummy resistor may be needed for non regulated amps. I mean I have ZERO practical experience in the matter. I was just curious as why that would be the case. What would really be cool would be to do that dummy load test on a SLASH amp, but step it down the other way. Use like an 8 then a 4 then a 3.5 then a 3 etc. all the way down to 1.5 ohms. It'd be neat to see where the amp decides to switch down to a lower voltage rail. Seems to me that I wouldn't want to be presenting a load to one of those amps that was right at the borderline of one of those voltage switches. JL probably designed those amps to stay in "low(er) impedance mode" in these areas and I would think you'd be running less power than at other loads as a result. Of course my take on how that voltage rail thingy works may be messed up. I really don't understand how the voltage rail controls the transistor output, but it generally makes sense to me. If you reduce the voltage across a load you reduce the power being dissipated which gives your amp a break. It would be real interesting to do that experiment with a JL amp with real fine load increments just to see how "smooth" its output is across its load range. I heard someone say that the 500/1 can actually put out 600 watts. Given a "bumpy" power/impedance curve that makes a lot of sense to me. I just want to know if there's a load between 4 amd 1.5 ohms where it produces LESS than 500 watts. It would also be neat to see if these "decisions" are made based only on load or if power output is a factor. It would be a simple task to repeat this experiment with different input levels. Oh btw, thats an awesome site. I think I could spend days going through some of the stuff he has there. I'm even thinking about gettin that amplifier repair course CD and maybe try and repair a couple "old school" amps I have laying around. I just need to find some money for the necessary equipment. -Fishy |
Bronze Member Username: WrestlertreecePost Number: 37 Registered: Sep-04 | You guyz got alot of time on your hands to write so much dang..... |
Silver Member Username: FishyTamarac, FL USA Post Number: 114 Registered: Sep-04 | ![]() |
Anonymous | sorry i havnt been back to my thread in a while. i hooked up to dummy load to the amp (1 ohm), only had the resistor on it for bout 30sec at a time so it didnt heat up all that much. i got the amp gain set to 24.5V, but in order to do this the subwoofer level on the HU has to bee @ +2...on a -6 to +6 scale. and the gain is over 3/4 the way up! i wanna know if adding a crossover to the system will help me out? by the way is this method of setting the gain an acceptable one??? |
Silver Member Username: FishyTamarac, FL USA Post Number: 118 Registered: Sep-04 | It sure makes sense to me on paper anyways, but Jonathan's the installer. I don't think its really gona hurt anything unless you accidentally short your outputs or something. Does it sound bad? If you don't have any noticeable noise or distortion then I'd say things were fine. Try measuring the output voltage off the head unit just like you did with the amp MINUS THE DUMMY RESISTOR(don't wanna fry your h/u) at one of the RCA's and see how it compares to what the specs say. I've seen Jonathan say a couple times that these output voltages can be overated especially off the sub preout. A good crossover can "help" too. A lot are considered line drivers. I knoticed better imaging after I installed my PPI FRX456. -Fishy |
Gold Member Username: Jonathan_fGA USA Post Number: 1726 Registered: May-04 | "I think I'm right, but there's an easy way to test this. Just run your 50 Hz, 0 dB tone and place a number of different loads(all higher than what the amp is stable at, like 4, 8, and 16 ohms) and measure the voltage across those guys, w/o changing the gain of course. The voltage should remain pretty much the same especially at higher impedances where the amp isn't "working so hard"." I see what you're talking about now, I was on a different page. I thought you were talking about voltage changing at different power levels for the same load, for example a 4 ohm load at 1/2 power compared to full power. I also think I confused you on this statement of mine above: "Resistance will cut voltage down, the load determines the power (volts & amps) that the amp puts out. 4 ohms will have less voltage than 2 ohms because the amp can't produce as much power with that load, and you will need more voltage to produce the same power at 4 ohms." I typed that up wrong, I meant to put that 2 ohms will show less voltage than 4 (got it backwards) at the same power level, just caught that and wanted to correct my mistake. I was basically saying it takes more voltage+amps to produce the same power into a higher impedance. You are right about the voltage and current remaining (of course in optimal conditions with a properly designed amplifier) the same at all resistive loads(as long as the amp isn't regulated), I misunderstood you and I apologize for that. In the case of the JBLs, though, a dummy resistor is required for a 1 ohm load b/c the amp only operates on that voltage rail with a 1 ohm load. I will also say that a dummy resistor ISN'T required on most amps, it's optional, but remember that not all amplifiers are perfect (the amp may not double the power at half the impedance, for example 150x2 at 4 ohms and 200x2 at 2 ohms) so it may benefit to use one to present the load that you plan on using, it's more of a better safe than sorry deal. What I thought you were trying to say was that voltage remained the same at different power levels for the same load, and this was what I was about to say: Voltage is what changes with level because the transistors are connected to both the power supply and the input signal, and the gain controls set the how sensitive the amplifier is to the input signal via a potentiometer(the ratio of amplification basically). Since the input signal varies via voltage, voltage is what increases with power level in an amplifier. This is why gain controls and volume from the head unit are all potentiometers, when you want it louder, the voltage increases. It's also why preouts are measured with voltage. The amplifier can amplify via high voltage or high current, but in the end it's the input that determines the level of power that the amplifier is producing, and it's the voltage coming into the amp which determines power output. |
Gold Member Username: Jonathan_fGA USA Post Number: 1727 Registered: May-04 | And anon, from what you've described from the head unit, it sounds like you have a Pioneer, and if you have the Pioneer with the 2V preout, those are very, very weak and I wouldn't doubt that you would need to turn the gain up that high. You could also try hooking up a 2 or 4 ohm resistor to try to get the gain set that way, but I honestly don't think it'll change anything. I think that the only thing that has changed has been the fact that your head unit is not set flat and the sub level has been altered. What I don't get is why the voltage didn't actually drop after presenting the 1 ohm load. How did you hook up the resistor to the amp? Also, what volume did you have the head unit turned to? 3/4 volume is very general and a lot of head units can go all the way to 90% volume w/o clipping, and with your weak preout, you'll need to turn it up as high as you can go as you don't have a lot of room to work with. That may be your problem, try turning the volume of the head unit above 3/4 and see what happens. If you hear distortion being introduced, the turn the head unit down until it stops. |
Silver Member Username: FishyTamarac, FL USA Post Number: 120 Registered: Sep-04 | "In the case of the JBLs, though, a dummy resistor is required for a 1 ohm load b/c the amp only operates on that voltage rail with a 1 ohm load." THATS what I wanted to know! I thought there was somethin crazy about that amp. They were talkin about "bridging" the thing(a mono amp?) into 1 ohm at the JBL site. So its switching rails too then or are there different outputs for 1 ohm operation that you physically have to change? I just wonder why you don't have to do the same with the JL's. Maybe its just a smarter amp. Good thread. ![]() -Fishy |
Gold Member Username: Jonathan_fGA USA Post Number: 1729 Registered: May-04 | It's a switching rail on the JBL, and the rail is solely for a 1 ohm load. As far as the JL amp, it a constantly monitors supply voltage and determines impedance when the amp is turned on, and stays on the same rail as far as impedance goes. Meaning as long as you leave the amplifier on, the amp stays on the same impedance rail regardless of if the sub is disconnected, so you'll get the correct voltage according to the impedance you run when setting the gain as the above method describes. It would be a BAD idea to switch impedance rails constantly, as the sub's resonance etc. come into play, and since speakers are a reactive load, just different frequencies in themselves would throw the amp out of whack. While operating, the JL amp monitors supply voltage and switches voltage rails if needed. The JBL is only regulated for impedance. It performs the same as an unregulated amp as far as supply voltage goes. |
Silver Member Username: FishyTamarac, FL USA Post Number: 126 Registered: Sep-04 | Yeah thats right "4 ohms" is a nominal rating being the average of that speaker's impedance over its frequency range. Thats part of what makes a good driver huh, smooth impedance curve so it ain't drivin the amp crazy with big impedance swings. So I guess with a JL you need to disconnect the speaker while the amps on so the correct rail is set(unclear in tutorial)? That sounds strangely similar to applying a dummy load if you ask me. ![]() -Fishy |
Silver Member Username: FishyTamarac, FL USA Post Number: 127 Registered: Sep-04 | Are regulated power supply amps like my Xtant generally less efficient? My 4180c is only 360 watts but has a 60 amp fuse! Was wondering why JL didn't use one. Oh and btw, your replies have gotten incredibly specific tonite...errr this morning. You haven't been switchin voltage rails have you? *scratches chin* hmmmm........ ;P -Fishy |
Anonymous | jonathan, this is how i hooked to 1ohm resistor to the amp. i put one end on the resistor in the (+) speaker terminal on the amp, i then put the (-) lead on the voltohm meter in the (-) terminal. i touched the (+) lead on the meter to the other end of the resistor. i then ran a 60hz tone to the amp a turned the gain up until the meter read 24.5V....does it sound like i did this right??? my HU begins to clip a little ofer 3/4 volume, so i only turned it up to 3/4. in order to get the voltage to read 24.5V i had to put the sub level on the HU to +2, if i had not put it to +2 the gain would run out of adjustment before the voltage reached 24.5V....w/o puttin the HU's sub level to +2 the max voltage the amp would put out was ~18V. also, the bass boost on the amp is set to 0db. do you think i should i get a cross over? i can get a kicker xover cheap, not sure of the model, its about 3 years old though. P.S. also, i checked the voltage w/ the sub connected to the amp. u just touched to (+) and (-) terminals on the amp w/ the meter when the sub was connected...it read 22.3V instead of 24.5V. |
Gold Member Username: Jonathan_fGA USA Post Number: 1735 Registered: May-04 | You need to connect the resistor as you would a sub: one end of the resistor to the + terminal and one end to the - terminal, then the voltmeter in parallel to that. It's not accurate to put the voltmeter on the sub since it's a reactive load(impedance changes with frequency because of inductance), that's not gonna tell you much in this case. Try that and see if anything changes. You could also try the 2 ohm resistor like I said above, but voltage would have to raise again. And Fishy, yes it's disconnect the sub while the amp's on, and then set the gain with a voltmeter. Regulated power supplies can be less efficient, it's just in the design. The JL 500/1 draws about 60 amps as well. Totally depends on the complexity of the amp and the design. Sometimes even though an amp is 360W RMS, the transients can do much more than that, requiring a larger fuse. |