lukeamdman

Luke's basic amplifier tests

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It's a long shot but it there any chance that the signal being sent into it or the inputs are clipping?

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It's a long shot but it there any chance that the signal being sent into it or the inputs are clipping?

 

I don't think so, but I'll double check.  With one channel driven the volume on my preamp will get to about -9.  With two channel driven, only -12db. 

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Here are screenshots of the GUI:

 

ipd-1_zpsn3ckqmwk.jpg

 

 

 

ipd-2_zpspoohuaje.jpg

 

 

ipd-3_zpsqopdkxuc.jpg

 

 

 

ipd-4_zpsb3t6gkme.jpg

 

 

 

ipd-5_zps9hvqa3bb.jpg

 

 

 

The limiter settings are still at the defaults:

 

ipd%20limiter_zps1nd5jxnd.jpg

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I'll post this link from the Speaker Power web site again.  While we can't really consider this to be an unbiased source, it's interesting that a similar performance pattern is shown for the Lab Gruppen FP14000.  Long term power output (before thermal) is shown to be limited to 1500W no matter the impedance.  All lower impedance does is reduces the time it takes for output to be limited.

 

From what Luke has described, I'm almost certain some kind of protection or limiting system is activating.  If anything other than his amp were clipping, it would almost certainly be present as soon as the signal was played and not after some length of time.  The fact that the amp is limited to a fixed wattage further supports this because if the voltage were clipping anywhere in the circuit, the max power output would still change with differing impedance.  Could it be clipping inside the amp?  I don't think so.  Not with the "pulsing" that Luke describes.  That sounds more like the work of a soft limiter.

 

I don't see anything in the pictures that suggest any kind of user-selectable limiter is enabled.  In the other amp thread, there was some discussion about "protection circuits" and what constitutes good "protection circuits".  In the case of modern amps, I believe the firmware logic is more important than the parts used.  I am not an EE, but I do know a lot about software and have studied a fair bit of control systems theory.  Leaving aside the more technical issues, one must make decisions that balance performance, safety, and reliability among other things.  What both Luke's and SpeakerPower's (not sure whose name to credit here) results suggest that the protection circuitry in the Lab Gruppen amps is very conservative.  We are left to wonder why this is so.  Perhaps it ensures that it won't overheat, even if it's being used in full sun in the Persian Gulf, or maybe it's supposed to protect connected drivers from damage in the event of abuse or unexpected faults.  Maybe I'm just giving too much benefit of the doubt to the product.

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the test signal is a constant sine wave, no?  perhaps a 5-7 cycle tone burst would allow the amp to meet its spec?

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Looks similar to the Armonia GUI.

I assume you are measuring the rms voltage during your tests Luke. Note that the voltages shown in the GUI and LG literature will be peak numbers. 98 volts peak would equate to roughly 69.4 volts rms.

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the test signal is a constant sine wave, no?  perhaps a 5-7 cycle tone burst would allow the amp to meet its spec?

 

I'd need better/faster equipment to measure that.  It takes the Fluke 117 about a second to read the RMS voltage, so a 5-7 cycle burst would happen too fast for it give a reading. 

 

 

Looks similar to the Armonia GUI.

I assume you are measuring the rms voltage during your tests Luke. Note that the voltages shown in the GUI and LG literature will be peak numbers. 98 volts peak would equate to roughly 69.4 volts rms.

 

I just noticed the peak voltage thing in the GUI, and yes, I'm measuring RMS voltage.

 

So far I've only been able to barely squeeze out 50v RMS with one channel driven at 5.5ohm, and that only lasts about a second. 

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It might be worth trying the exercise of repeating the test with the VPL set to decreasing values until it actually kicks in?

 

BTW and FYI, Music Group (who has owned LG since April of this year) is Behringer. :)

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Have you tested the 2500 yet? Interested to see how (if) it goes belbow 20 Hz.

 

I'm waiting on the FTW-21 drivers to continue testing.  If Mark is still on schedule, they should ship out next week. 

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I'm also modifying my spreadsheet to make the results easier to read.  Currently it's a little too busy, and I'm removing the SPL numbers since that requires more work and additional strain on the amps/subs since I have to run another max power/output test but this time watch for SPL in the room. 

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Can one conclude that the Behringer inuke nu6000 puts out more power than the Crest 7.5 based on the results of lukeamdman test compared to this test:

http://forum.speakerplans.com/behringer-inuke-nu6000-vs-kam-kxd7200-bench-tested_topic69202.html

 

The nu6000 puts out 1,800 watts for bass duty at 4 ohms and the crest 7.5 puts out 1,668 watts at 2 ohms.  I would assume the crest 7.5 wouldn't put out 

any more watts at 4 ohms compared to 2 ohms.  Looks like the power supply would prevent this from happening.  

 

I have the peavey ipr2 7500 and I heard it's power supply is even worse.  Am I right in this conclusion?  Kind of disappointed I paid double for the peavey ipr2 7500 compared to the nu6000 if this is the case. 

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Can one conclude that the Behringer inuke nu6000 puts out more power than the Crest 7.5 based on the results of lukeamdman test compared to this test:

http://forum.speakerplans.com/behringer-inuke-nu6000-vs-kam-kxd7200-bench-tested_topic69202.html

 

The nu6000 puts out 1,800 watts for bass duty at 4 ohms and the crest 7.5 puts out 1,668 watts at 2 ohms.  I would assume the crest 7.5 wouldn't put out 

any more watts at 4 ohms compared to 2 ohms.  Looks like the power supply would prevent this from happening.  

 

I have the peavey ipr2 7500 and I heard it's power supply is even worse.  Am I right in this conclusion?  Kind of disappointed I paid double for the peavey ipr2 7500 compared to the nu6000 if this is the case. 

 

The only way to know how the inuke6k or ipr2-7500 would perform compared to the 7.5 would be for me to run the same test under identical conditions.

 

If I could measure the amperage draw at these maximum output levels we'd have a much better idea of the actual power output.  I know the starting resistance, but as power and excursion increases that resistance is going to change. 

 

Additionally, an amp most certainly could provide more power in 4ohm stereo vs. 2ohm stereo because lower impedance loads require more amperage from the power supply.

 

For example:

 

2,000w per channel in 4ohm stereo = 89.4v and 22.3A per channel

2,000w per channel in 2ohn stereo = 63.2v and 31.6A per channel

 

If the power supply can only provide a total of 45A, it'll hit 2kw per channel at 4ohm but will only provide 1kw per channel at 2ohm stereo. 

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for bass duty

 

The other aspect you need to look at is frequency.  The power ratings for most amps are given at 1,000Hz if I remember correctly.  Based on my informal, real-world experience, the IPR2-7500 has more power down low, below 20Hz, which would lead me to the opposite conclusion than yours, which is the IPR2-7500 has the stronger power supply.  But it would be interesting to see if Luke's tests would bear this out so we could have some true data.

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I'm just hoping that whenever the Crown XLS amp gets tested we can put to rest this 20hz highpass thing and see in the real world what effect if any it has on the SPL of a sub.

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I'm just hoping that whenever the Crown XLS amp gets tested we can put to rest this 20hz highpass thing and see in the real world what effect if any it has on the SPL of a sub.

 

I'll post raw responses (no eq or xo) from every amp I have driving the sealed 21s.  I'll also test the XLS, among other amps, for max power at 25hz, 20hz, 15hz, 10hz, and 5hz. 

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The other aspect you need to look at is frequency.  The power ratings for most amps are given at 1,000Hz if I remember correctly.  Based on my informal, real-world experience, the IPR2-7500 has more power down low, below 20Hz, which would lead me to the opposite conclusion than yours, which is the IPR2-7500 has the stronger power supply.  But it would be interesting to see if Luke's tests would bear this out so we could have some true data.

 

I was going to compare the 7.5 to my nu4-6000 (basically a inuke-6k when bridged), but I sold the 7.5 with the Ghorns a couple months back...

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The other aspect you need to look at is frequency.  The power ratings for most amps are given at 1,000Hz if I remember correctly.  Based on my informal, real-world experience, the IPR2-7500 has more power down low, below 20Hz, which would lead me to the opposite conclusion than yours, which is the IPR2-7500 has the stronger power supply.  But it would be interesting to see if Luke's tests would bear this out so we could have some true data.

 

I think an amplifiers power output down low (compared to higher frequencies) has more to do with said amps high-pass/DC block filters than how "strong"  the power supply is. 

Hopefully,  some protection circuit would jump in before the ps is in trouble, no matter played frequency. 

 

Basically the amp with the lowest cutoff freq of the high-pass filter would output more power down low than another,  equally powerful amp would with higher cutoff freq HP filter... 

 

Just my thoughts though,  nothing tested... 

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I think an amplifiers power output down low (compared to higher frequencies) has more to do with said amps high-pass/DC block filters than how "strong"  the power supply is. 

Hopefully,  some protection circuit would jump in before the ps is in trouble, no matter played frequency. 

 

Basically the amp with the lowest cutoff freq of the high-pass filter would output more power down low than another,  equally powerful amp would with higher cutoff freq HP filter... 

 

Just my thoughts though,  nothing tested...

 

I was generically referring to the power supply as a system rather than the individual components involved. But I would think it would be the capacitance and quality of components as much as anything else, which is why the sister Crest ProLite 7.5 is preferred (presumably due to power output) over the same design of the Peavey IPR2-7500. But who knows what sort of protections and filters have been implemented as you surmise.

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I think I'm going to give this a try:

 

http://www.amazon.com/Fluke-i400-Current-Clamp-Banana/dp/B000EA1ETC/ref=sr_1_1?ie=UTF8&qid=1450396077&sr=8-1&keywords=fluke+i400

 

The specs say it has a "usable frequency" range" of 5hz-20khz, with the most accurate of that range being 45-400hz.  

 

I'll be able to directly compare it with a meter wired in series, so if it's way off I'll know.  

 

If this works out, I'd know the resistance of the load at the peak output levels and we'd have a much better idea of actual power being delivered.

 

http://en-us.fluke.com/products/all-accessories/fluke-i400.html#techspecs 

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Nice find!  It's a bit pricey, but I think that might be nice to use for power handling studies too.  My thinking is that impedance increases should correlate quite well with voice coil heating.  This can be used to measure temperature versus time for different amounts of power input (and possibly different frequencies/excursion) to understand how well the woofer dissipates heat, both in the short and long term.

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I pulled the trigger on the clamp meter.  Should be here tomorrow.

 

I was also looking into a scope and an amp probe, but the probes have the same "accurate" frequency range as the clamp meters.

 

Similar to a simple multi-meter that can be wired in series with the amp/sub (but is limited to 10A), is a there a device that can be used in the same way but can handle loads up to ~80A?  My searches have come up empty, but it's very probable I'm searching for the wrong thing since I'm so green to this. 

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Oh snap, an electrical engineer buddy of mine is onto something. 

 

I'll post the details when I understand them, but basically by using a very low resistance wire-wound resistor wired in series with the load, by measuring voltage you're also measuring the current. 

 

Here's the resistor he recommended:

 

http://www.mouser.com/ProductDetail/Vishay-Dale/NH050R1000FE02/?qs=sGAEpiMZZMtbXrIkmrvidDNaDpN5VXc5CiNzBrP%252bceM%3d

 

That's the lowest resistance I could find for a non-inductive resistor. 

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