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Luke's basic amplifier tests


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#41 lukeamdman

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Posted 19 October 2015 - 04:56 AM

Maybe running it with 240v mains would help?
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#42 lukeamdman

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Posted 20 October 2015 - 10:54 PM

I just re-ran the IDP 2400 test at 80hz and 5.5ohm, but this time on the same 240v 30A circuit I did the SP2-12000 tests on.

 

The results were EXACTLY the same for both one channel driven and two. 



#43 Bossobass Dave

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Posted 21 October 2015 - 04:24 PM

Lab Gruppen (1979) ==> TGI Group (2000) ==> TC Group (2002) ==> Music Group (April 2015)

 

Random foreign forum post:

 

We have recently evaluated Labgruppen IPD2400 for compact/mobile duties however we found "weak" in every means. It has around ~20A output capability http://labgruppen.com/view-model/ipd-series/ipd-2400?page=spec
which is hardly enough even for 300W/8Ohms speakers (2 in parallel).
The XD2500 has 45A or so which is lot more stronger, and you feel it in the headroom too..

 

 

The IPD-2400 is purportedly made in Taiwan. Most user-reviews like it for SQ, size and lower price (vs typical LG pricing), but it's obviously not an output monster.



#44 lukeamdman

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Posted 21 October 2015 - 05:14 PM

Lab Gruppen (1979) ==> TGI Group (2000) ==> TC Group (2002) ==> Music Group (April 2015)

 

Random foreign forum post:

 

 

The IPD-2400 is purportedly made in Taiwan. Most user-reviews like it for SQ, size and lower price (vs typical LG pricing), but it's obviously not an output monster.

 

Interesting!

 

I really like the SQ (meaning it's no different than any other decent amp I've heard) and the EQ is great. 

 

However, the power output I'm getting from it isn't making any sense to me.

 

With the 2ohm tests, I was able to get ~10A per channel without bus pumping.  Increasing the levels to ~10.5A a channel, I'd get bus pumping after ~2 seconds into the tone.  That lines up with the 20A figure mentioned in the review you just posted.

 

If the power supply is capable of 20A, why are my 5.5ohm tests limited to about 6A per channel?  Shouldn't I be getting about ~550w per channel instead of ~210w?

 

In my tests, regardless of the resistance, I was limited to ~210w per channel without bus pumping.

 

What am I missing?  Could this be a software/firmware issue?



#45 Bossobass Dave

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Posted 21 October 2015 - 07:07 PM

Interesting!

 

I really like the SQ (meaning it's no different than any other decent amp I've heard) and the EQ is great. 

 

However, the power output I'm getting from it isn't making any sense to me.

 

With the 2ohm tests, I was able to get ~10A per channel without bus pumping.  Increasing the levels to ~10.5A a channel, I'd get bus pumping after ~2 seconds into the tone.  That lines up with the 20A figure mentioned in the review you just posted.

 

If the power supply is capable of 20A, why are my 5.5ohm tests limited to about 6A per channel?  Shouldn't I be getting about ~550w per channel instead of ~210w?

 

In my tests, regardless of the resistance, I was limited to ~210w per channel without bus pumping.

 

What am I missing?  Could this be a software/firmware issue?

I agree that something is not right. Did you try bridging the amp?



#46 lukeamdman

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Posted 21 October 2015 - 07:23 PM

I agree that something is not right. Did you try bridging the amp?

 

LG says the amp isn't bridgeable:

 

 

ipd%20bridge_zpsrlo8a0rs.jpg

 

 

If it really is a "dual mono" design, than what I'm experiencing isn't bus pumping?



#47 SME

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Posted 22 October 2015 - 12:34 AM

If it really is a "dual mono" design, than what I'm experiencing isn't bus pumping?

 

Nope.  What makes you think it's bus pumping?  It sounds to me like you are either draining the capacitor reserves, which would cause clipping, or you are observing a limiting/protection circuit, which could either clip or soft limit.  That you heard frequency doubling suggests a lot of 2nd HD, which *might* be consistent with soft limiting.  I'm betting the clip lights only light when some voltage (near the max) is exceeded.

 

By the way, I expect almost all of these amps will behave this way in the sense that the max power output will drop a fairly short time frame with a continuous signal.  There's a max voltage that an amp can output into any load.  (Bridging doubles this figure.)  If you exceed that, you clip.  If you start pulling peak levels of power from the amp, the capacitor reservoir will be drained as the power supply can't keep them charged at full voltage.  This may cause the max voltage (and clip point) to droop over time.  At some point, the reserve will be drained, and the max voltage will be limited by the capabilities of the power supply.  As more time passes, one of several protection circuits may kick in.  For example, parts of the amp may get too hot or too much current is being drawn from the main supply.  Such an amp can pull much more current from the mains outlet than the outlet is rated for, but only for a short period of time (a few seconds).  After this burst period, the amp must limit current to 80% of the rated load to avoid tripping the breaker.

 

That LP is limiting at a measly 500W?  That's way less than a 120V/15A breaker can supply.  And at 500W, I'm almost certain you're hitting a limiting circuit.



#48 lukeamdman

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Posted 22 October 2015 - 02:15 AM

Nope.  What makes you think it's bus pumping?  It sounds to me like you are either draining the capacitor reserves, which would cause clipping, or you are observing a limiting/protection circuit, which could either clip or soft limit.  That you heard frequency doubling suggests a lot of 2nd HD, which *might* be consistent with soft limiting.  I'm betting the clip lights only light when some voltage (near the max) is exceeded.

 

By the way, I expect almost all of these amps will behave this way in the sense that the max power output will drop a fairly short time frame with a continuous signal.  There's a max voltage that an amp can output into any load.  (Bridging doubles this figure.)  If you exceed that, you clip.  If you start pulling peak levels of power from the amp, the capacitor reservoir will be drained as the power supply can't keep them charged at full voltage.  This may cause the max voltage (and clip point) to droop over time.  At some point, the reserve will be drained, and the max voltage will be limited by the capabilities of the power supply.  As more time passes, one of several protection circuits may kick in.  For example, parts of the amp may get too hot or too much current is being drawn from the main supply.  Such an amp can pull much more current from the mains outlet than the outlet is rated for, but only for a short period of time (a few seconds).  After this burst period, the amp must limit current to 80% of the rated load to avoid tripping the breaker.

 

That LP is limiting at a measly 500W?  That's way less than a 120V/15A breaker can supply.  And at 500W, I'm almost certain you're hitting a limiting circuit.

 

Whatever is doing this limiting, it isn't consistent with either voltage limiting or amperage supply since regardless of the resistance you get the same wattage per channel.  It doesn't matter if it's running 2ohm stereo or 5.5ohm stereo, you'll only get ~210w a channel if you want more than a second or two of output. 

 

At dual 2ohm, it'll supply 10A (or ~20v) per channel just fine.  At 5.5ohm, you only get 6A (or ~34v) a channel.  Through all this, the amp never even gets slightly warm, the fans never turn on, and the limiter lights are never on (you can limit based on either voltage, watts, or dBu).

 

I only guessed it was bus pumping based on what I've read about it recently.  Whenever this behavior manifests itself, it plays multiple frequencies at once and it's "pulsing" rapidly.  The other two class D amps I've tested so far haven't behaved anything like this when pushed to and over the limit. 



#49 Ricci

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Posted 22 October 2015 - 02:02 PM

I agree with SME this has nothing to do with bus pumping. It is already a fully bridged design. Also bus pumping can damage the amplifier in short order so fast acting protection circuits would normally be used to recognize the issue and stabilize the amplifier. Typically this would involve muting the outputs completely among other things.

 

This sounds like the amp is hitting a long term limitation in the power supply, an internal limiter, or severe clipping. Are you sure it does not have some type of current or voltage limiter engaged in the dsp or somewhere else? It may just be that it has a low rail voltage and once the caps are drained it just doesn't have much voltage to work with.



#50 lukeamdman

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Posted 22 October 2015 - 03:19 PM

I agree with SME this has nothing to do with bus pumping. It is already a fully bridged design. Also bus pumping can damage the amplifier in short order so fast acting protection circuits would normally be used to recognize the issue and stabilize the amplifier. Typically this would involve muting the outputs completely among other things.

 

This sounds like the amp is hitting a long term limitation in the power supply, an internal limiter, or severe clipping. Are you sure it does not have some type of current or voltage limiter engaged in the dsp or somewhere else? It may just be that it has a low rail voltage and once the caps are drained it just doesn't have much voltage to work with.

 

 I’ll post some screen shots of the GUI/configuration.  It’s very possible that I could be missing something that’s causing this.



#51 Ricci

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Posted 22 October 2015 - 04:07 PM

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



#52 lukeamdman

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Posted 22 October 2015 - 10:16 PM

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. 



#53 lukeamdman

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Posted 22 October 2015 - 10:20 PM

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



#54 SME

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Posted 23 October 2015 - 02:58 AM

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.



#55 LTD02

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Posted 23 October 2015 - 04:43 AM

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



#56 Ricci

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Posted 23 October 2015 - 01:05 PM

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.



#57 lukeamdman

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Posted 23 October 2015 - 05:54 PM

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. 



#58 Bossobass Dave

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Posted 23 October 2015 - 08:50 PM

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. :)



#59 maxmercy

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Posted 23 October 2015 - 11:03 PM

 

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

whoa-300x223.jpg



#60 lukeamdman

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Posted 30 October 2015 - 08:41 PM

I recently picked up a Crown XLS 2500 that I'll add the list of amps to be tested. 






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