BillFitzmaurice.info

I have been confused and trying to solve this mystery on my own but to no avail. So I come asking for a hint or some help.

I have the Crown XLS2500 rated for:

8-ohms/440W (per channel) that should equal to around 59 volts if my math is correct.
4-ohms/775W (per channel) for about 56 volts.

I thought this would be a good match to run my 2 T30's with their lab12's (needing to be limited to 50V) on one channel in parallel (800W at 4-ohms) and then my OTop 12 (starting the build this weekend) on the other.

However, when I stick the multimeter in the back of the binding posts (set to AC 200) and run a 50 hertz sine wave from a tone generator, I only read about 43 volts. I don't have the crossover or any filters on while doing the reading. Volume knobs are all the way up on the amp, but without the thermal light coming on.

43 volts at 8-ohms equals only 231W versus its 440W rating.
43 volts at 4-ohms equals 462W versus its 775W rating.

Am I doing the math wrong? Am I missing something?

The only audio file that even brings the amp close to that 56 volts is a 60hertz sine wave at 0db that I downloaded, it fluctuates between 44 volts and 51, 2 clicks down from full on the volume knob because turned all the way up the thermal light starts on.

Thanks in advance for the hints or help.

what input source are you feeding the amp with?

The tone generator is from my iPhone, with the volume all the way up.

The 60 hertz sine wave file is from my laptop headphone output, volumes all the way up.

Is the iPhone the culprit in the equation?

I just created a 50 hertz sine wave in Audacity, played from laptop and now getting around 53 volts on the reading, one notch below full volume, with the thermal light occasionally blinking.

2 notches back from full, averaging about 39 volts with no thermal light coming on.

I know I need to pick up a PA+ or equivalent to brick wall limit it, but just curious if I am doing this right or wrong. It seems right now I can't even get close to the 50 volts mark without the amp getting angry (thermal light).

all an amplifier does is amplify the input signal. those knobs on the front are not output attenuators, they are input attenuators. if you cant get the 53 volt signal out of it with the ipod maxed out and the amp knobs maxed out, its because the ipod is not producing enough input signal.

Thanks sine. I'll keep at it.

Did I get the right amp for the job? I thought I had this mostly figured out but now I am having doubts. Do I need an amp with more headroom? I have a suspicion that I should run one T30 lab12 on each channel (8ohms at the 440W's) and then get a second amp for the OTop. Or am I off-base with that line of thinking?

Sorry, I hope these are not too horrible of questions, I don't really know of anyone locally that I can chat about this stuff right now. Trying to work on that.

Cheers.

chrisj360 wrote:
Did I get the right amp for the job? I thought I had this mostly figured out but now I am having doubts. Do I need an amp with more headroom? I have a suspicion that I should run one T30 lab12 on each channel (8ohms at the 440W's) and then get a second amp for the OTop. Or am I off-base with that line of thinking?

Sorry, I hope these are not too horrible of questions, I don't really know of anyone locally that I can chat about this stuff right now. Trying to work on that.

Cheers.

It's all good Chris

The XLS 2500 has ample output to run 2 x t30's to 50V on one channel and Otops on the other.

Couple of things:
50V is 50V. Two cabs wired in parallel max at 50V. Continually converting back to watts is not helping your cause. When you get there, simply limit to 50V!

When it comes to inputs, when using your laptop, is all your volume settings on the little speaker icon/radio button for "volume" down the bottom on your right all up to max when you double click to bring up max volume and line input output etc?

After all is said and done, music programme content through the amp isn't generally as intensive as hitting the amp with a sine wave. That's why you set with a sine wave.

Just check those levels and see if you can get up to where you think you should be in output.
I don't recall anyone much saying the Crown XLS drivecores don't output to spec...

Perhaps your phone or laptop don't have a strong enough output to drive your amp to its maximum output.
Consumer devices operate at -10 dBV while professional devices ( like your amp) operate at +4 dBu.
You might try driving the amp with a mixer or other device with higher output levels.
http://en.wikipedia.org/wiki/Line_level

+1 on the 'iPhone not producing enough output' theory. 'Consumer' level output of your phone is around 12dB lower than what your 'professional' (level) amp is expecting to see. It isn't that your power amp is too weak (in fact it is ideal!!), but rather your iPhone's amp.

To be 100% sure of this (as you are sounding a little worried), measure the output from your phone connecting your meter to an RCA/jack of the audio link cable (use a sinewave, just as you do when setting the limiter). In order for your iPhone to drive the amp to it's full rated output, you need this to measure at least 1.4V RMS (this is the amp's sensitivity spec in the crown manual). Any lower than 1.4V would explain the behaviour you are seeing.

Thanks for the insight and help with this everyone. I'll do some more reading up on this stuff and let you know when I get it all sorted out.

Thanks again and cheers!

A friend was using a XLS through the RCA inputs and noted that he didn't get full power out until he switched to using the balanced inputs, which matches the other suggestions. Try it through a mixer or an adaptor box?

escapemcp wrote:+1 on the 'iPhone not producing enough output' theory. 'Consumer' level output of your phone is around 12dB lower than what your 'professional' (level) amp is expecting to see. It isn't that your power amp is too weak (in fact it is ideal!!), but rather your iPhone's amp.

To be 100% sure of this (as you are sounding a little worried), measure the output from your phone connecting your meter to an RCA/jack of the audio link cable (use a sinewave, just as you do when setting the limiter). In order for your iPhone to drive the amp to it's full rated output, you need this to measure at least 1.4V RMS (this is the amp's sensitivity spec in the crown manual). Any lower than 1.4V would explain the behaviour you are seeing.

A big + 1 on this.

I use an XLS1000 on my bass rig and these amps are well known in the bass world for people popping up on forums saying that their Crown isn't anywhere near the right wattage because it's not as loud as their old amp that "they only had to turn up to two o clock".

Invariably, it is because they are trying to drive it with a preamp pedal of some sort that only puts out .75 or 1 volt. When they match the output voltage of what they're driving it with to the 1.4 volts that the Crown needs for full output, the problem is usually fixed.

This is an interesting discussion because this past weekend I could not get squat out of my Crown 802 using a sine wave signal. The Asus card notes: Output/Input Full-Scale Voltage :
Line output (RCA, 3.5) : 2 Vrms (5.65 Vp-p)

I went from the line out and the RCA outs. No difference. I had made up a cable to be able to connect 1/4 mono plug to the XLR input of the Crown wired properly for unbalanced in. 1 Channel out from the computer.

I was mistaken reading my meter I discovered when I simply played a song through the system as I was trying to break in the speakers. With a sine 35hz via Audacity I was lucky to get just under 1 volt at max everything. With a song playing, the Crown on the second notch was going to 2 volts or more so the 10 would have been easy but it would have been loud and the speakers might have been bouncing a bit off the floor. Never mind 50v.

I tried my Lenovo pad which I have an app that is an RTA along with a generator for all sorts of noise, tones etc. Still could not break 1 v with a sine wave signal.

So my speakers ran for 12 hours on 0.010 V stupid me. It's a new meter and it's why my old analog meter didn't register a thing.
I could hear the tone coming out of the speakers and feel them but I was just not thinking clear reading the decimal point.

I could repeat this using the board at our practice studio, but I'm thinking I'll just go with what Eminence notes regarding breaking in speakers.

is your hipass engaged?