Phoenix Gold Phorum

Actual

stipud wrote:Actual

Thank you very much... I may need to tune it a little more now. Just curious... I heard some bad things about my left and right voltages being different. I set the front right to 17.7v then check the front left and it's 16.5v. what the hell? is my amp damaged? It sounds awesome but still? maybe thats why my frontstage sounds a little off. grrrr.

try swapping the rca's and see if it moves to the other side.

ttocs wrote:try swapping the rca's and see if it moves to the other side.

Great idea! I think I remember having trouble with this setof rcas before. I will let you know what I find.

stipud wrote:Just type it in google...

voltage = sqrt ( impedance * wattage )
voltage = sqrt ( 2 * 1200 )

So google "sqrt ( 2 * 1200 )"...
sqrt(2 * 1200) = 48.9897949

I really like this post... I have come back to it on multiple occasions. My question is... When setting the gains on my Arc audio 2500CXL am I going to use the left negative and right positive to adjust the voltage? or do I switch it from mono to stereo and adjust each channel seperately? The amp seems to power the Peerless XXLS subs beautifully but I would like to get it all dialed in. Thanks for your help and everyone else on here who takes the time to give advice.

Here are the specs on the 2500CXL...


2 x 270W @ 4ohms
2 x 525W @ 2ohms
1 x 1050W @ 4 ohms bridged
THD: <0.05%
Freq. Response: 20Hz 20kHz
S/N Ratio: 105dB
Damping Factor: >2000 (1kHz)
Max. Current Draw: 135A
Fuse: 3 x 30A

so i found this chart online how accurate is it and i lost my birth sheets for my amps so whats the best way to find true power. example my 1000.2 is supposed to be

Into 2 ohms Stereo @ 14.4 Vdc = 500x2
Into 4 ohms Bridged @ 14.4 Vdc = 1000x2

but the birth sheet says about 10 watts short of 1300

This is kind of a late add on but it seems that it would be 10x easier and 10x less confusing with zero math if someone posted a chart of rail/output stage voltage for each amp and you just tuned the gain with a DMM to reach this voltage with a 60 hz 0db wav file with your volume set at 3/4.
If you had a line driver or line output converter you would want to do the same trick on it first (knowing your voltage target would be the max output listed on the spec sheet OR the max input voltage of your amp i.e. 2v on old amps to 8v on many others). Naturally you would set the gain to minimum on the device and ease up until you just hit it.

I would also think that you could measure this by playing the track with speakers off the amp and then turn gain up while measuring to see what voltage it peaks/plateaus at. Any thoughts on this?

If you really want to do this properly and maximize your clean output, you should use an oscilloscope and a range of sine tones to test and set the gain structure.

Step One:
Figure out the clipping volume point on your head unit. Keep all EQ and sound field processing off. Note that if you use these features, you're boosting the signal up into the clipping range after you set this properly. It's recommended to not use these to boost, only cut as stated previously in this thread.
It's very important that you measure EACH and every rca output on your head unit with this process. They will not all always clip at the same point or frequency.
Connect your oscope to rca output 1 of the head unit and set your volume at max. Play a RANGE of sine tones from 20hz up to 20khz (I like to use about 10 different ones, burned to a test cd about 10 seconds a piece and let them play through each track with the oscope connected). If at any point the waveform is clipped, back down the volume on the head unit until just before the clipping point. Wehn you make it through the 10 test tones with no clipping, record that volume setting number. This is the clipping point on RCA output 1.
Follow the same process for each of the RCA outputs. When they are all done, take the lowest unclipped volume setting from them. This is the max volume you can play your HU at before clipping any of the outputs. It is very important to understand that even between the exact same model, your unit may clip at a different volume setting than your buddies unit. The reason for this is poor board component tolerances in head units. And if you think it's limited to low dollar units, you'd be wrong. Even on big buck SQ decks like the Pioneer P99RS, this is still the case.
With that said, you've now found your HU's clipping point. From here out, keep your HU one volume setting below the clipping point for all gain setting going forward.

Step Two:
Choosing a gain overlap that is acceptable to you and adjusting. What is gain overlap? First lets look at how we are setting gains and what we're using to do it. Typically, a series of sine wave tones are used to aid in locating clipping points. These tones are usually recorded at a level of 0db, or maximum signal. However, a sine tone is a far higher duty signal than typical dynamic music that you'd actually listen to. It will take a much stronger musical signal to reach the output level of the sine wave. Because of this, if you set your amplifier gains with 0db tones you may be wasting some of that available power that you paid big bucks for with your amplifier. Gain overlap is achieved by using a lower intensity range of sine tone recordings so that you actually adjust your amplifier gain to a higher point to account for some of that difference. For example, instead of using 20hz@0db and 40hz@0db tones to set gains on your subwoofer amp channel(s), you might choose to do 5db of additional overlap by using 20hz@-5db and 40hz@-5db tones. Just how much overlap you'd like to include is dependent on your equipment and application. The more gain overlap you include, the higher the noise floor becomes. Think about it- when you turn up the gain on your amplifier, there is more noise included in the signal. Some amplifiers are much cleaner than others. In addition, you might choose to go with more gain overlap on low frequency drivers (perhaps -10db) like midbass and subs and less on midranges and highs (maybe -5db) where noise is more easily distinguished.
To set these gains on the amplifier, disconnet your speaker cables and attach your oscope to the first output you want to adjust. With your HU on one click below clipping volume, and with it playing the sine tones you wish to use (lets say -5db for now), adjust the gain on the amplifier for that channel until just before the clipping point. You've now set that channel up for 5db of overlap and will notice a significant increase in your output over 0db tone settings. If you'd like to measure output and to be more accurate, you could attach a dummy impedance load that is the same as what you'd be connecting to this amp channel and measure the AC voltage from your DMM. Do the math to convert it to watts and you've got a very good idea of your unclipped output with the current gain overlap setting.
Repeat this process for each of your amplifier outputs. Again, it's important to note that amplifier outputs will not always clip at the same point as well. Lets assume you have a gain knob for "front" and "rear" output on an amp. You need to check both the front left AND the front right and adjust to just below clipping for whichever one clips first.


Step Three:
Listen and enjoy! However- before you pop in music and listen...turn it down...it will be siginificantly louder than tuning with 0db tones.
Try playing a 0bit digital silence track and turn up a bit. Listen for noise and decide if it is acceptable for you or if you want to go with less gain overlap on certain drivers. If you dont have any noise, you may even want to consider adding a little more gain overlap with the process.