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lukeamdman

Luke's basic amplifier tests

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I read that article many years ago, and in some cases, it can be applicable. Keep in mind that you are also driving essentially a dummy resistor load, and the results may be different driving a reactive load, where back EMF is reflected on the power supply.

 

I'm sure someone could find an application for this, but the more I think about it the less it seems worth the hassle.  Wouldn't it be easier to series the load and use the amp in bridged mode like you normally would, and skip the parallel inputs and reversing the polarity on one of the outputs?  

 

Even in the best case scenario of a 15% gain, we're talking about a fraction of a single dB of gain.  

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I'm sure someone could find an application for this, but the more I think about it the less it seems worth the hassle.  Wouldn't it be easier to series the load and use the amp in bridged mode like you normally would, and skip the parallel inputs and reversing the polarity on one of the outputs?  

 

Even in the best case scenario of a 15% gain, we're talking about a fraction of a single dB of gain.  

 

The real answer is it depends. I agree that it may only be a small fraction of a difference. It would be interesting to note the input power to the amplifier to see if the efficiency / breaker utilization changes any, which may be a bigger deal for large systems with racks and racks of amplifiers running off a generator, or in a venue where power is subject to droop. ( older wiring, smaller services )

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On ‎3‎/‎25‎/‎2017 at 9:57 PM, lukeamdman said:

I was asked to test this over 2 months ago but I've been a huge slacker:

 

http://www.prosoundweb.com/topics/sound_reinforcement/fighting_for_power_a_way_for_amplifiers_to_increase_actual_power_delivered_/

 

The basic theory is that if an amp is driven in stereo and both channels are producing the exact same signal, both channels are also drawing current from the power supply at the exact same time/interval.  The author of the article claims that if you parallel the inputs but flip the polarity on the input of one of the channels, causing the sine waves from each channel to be exact opposites, the channels are now "taking turns" drawing current from the power supply.  

This is how Powersoft K series amps operate all of the time. Those guys are smart so you'd have to assume they did that for a reason. This likely only shows up as a measureable improvement when the power draw becomes large and starts to sag the AC line. More useful for pro sound apps where you might have many amps driven hard on one circuit and/or the circuit isn't great to begin with like a generator, etc.

Many years ago Ivan Beaver from Danley Sound showed me how to do this at a GTG. Flip polarity of one input channel in the amp and re-flip/correct at the speaker wiring to bring back in phase. Worked pretty good with a Crown CE4000.

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59 minutes ago, manninen said:

238595829928168.jpg

Wonder if he will "loan" me one for testing? LOL.

What does he expect people to power with these? I guess it could be useful in an arena or very large concert hall. for that price I'd expect some dsp and networking options and maybe a free hat.

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In other amplifier news, SpeakerPower is under new management since Brian has retired.  Retail prices appear to have increased as well.  

 

http://www.speakerpower.net/about-us.html

 

"CEO's Message

Welcome,

I am Justin Ryan, CEO of SpeakerPower.  In 2018, I acquired SpeakerPower from its founder, Brian Oppegaard, upon his retirement.  I am very excited to continue the growth and development of SpeakerPower.  As an experienced executive in a variety of industries, and an MIT trained engineer, I know what it takes to develop exciting new products that satisfy the most demanding requirements of customers for their cutting edge products.  With further investment in new products, I plan to build on SpeakerPower's 16 year track record of delivering high quality, powerful, efficient, and intelligent amplifiers.

For OEM manufacturers in Professional and Home Theater markets, SpeakerPower provides the opportunity to have next-generation intelligent amplifiers in your self-powered loudspeaker line. Our complete turn-key approach means that it is as easy for you to install a SpeakerPower amplifier in your cabinet as a woofer, horn or compression driver. With our proven designs, you will be up and running quickly with minimal up-front investment. And our state-of-the-art digital signal processing and power technology will reinforce your image as a technological leader.  With designs from 200 to 12,000 watts, we can meet your most critical needs.

Users of SpeakerPower amplifiers enjoy high power and high efficiency, with intelligence designed to ensure continuous output in the most demanding applications.  Our products are manufactured and supported right here in California.  Our commitment to quality, technological acuity, and steadfast product support means your loudspeakers are powered with confidence. See what we can do for you today.

Justin Ryan
CEO"

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Yep...I emailed Brian about the SP1-6000 plate amps a few weeks ago and he put me in contact with Justin. Brian says he still does consulting work for SP when needed but otherwise is retired. 

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On 1/9/2019 at 12:58 PM, Ricci said:

Yep...I emailed Brian about the SP1-6000 plate amps a few weeks ago and he put me in contact with Justin. Brian says he still does consulting work for SP when needed but otherwise is retired. 

Someone over at AVS received an sp1-4k or 6k recently and looks like they are using an internal cover again on the plate models. Glad to hear Brian's potentially still got some input there even if he does spend most of his time sitting on a beach drinking rum now.

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40 minutes ago, Pradeep said:

Someone over at AVS received an sp1-4k or 6k recently and looks like they are using an internal cover again on the plate models. Glad to hear Brian's potentially still got some input there even if he does spend most of his time sitting on a beach drinking rum now.

Hey I resemble that remark!

 

2019-01-15 20.20.29.jpg

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The output power of a K20 vs an X4
K20: 
145 V RMS for less than a second at 2.05 ohms both channels driven
Then it limits to 58 V then it goes down to 52. 
This means 10.5 kw per channel for long bursts
1680 watts for 4-10 seconds
1350 watts per channel for almost a minute then thermal protection.

Similar output is offered at 2.5 ohms , 70 V RMS for 4-10 seconds. This time constant depends on the internal temperature.
The X4 can do 2950 W for 2 seconds at 4 ohms, then 1600 watts per channel at 4 ohms for 20 seconds single channel.

2*2650 w for 0.8 seconds then 950 watts per channel at 4 ohms for 12 seconds 2 channels driven

After 20 respectively 12 seconds, the amp shuts down the output, going into protection.
There is also a review of the X4 on Production Partner showing interesting result with all channels driven at the same time with the same signal.

Ipal module is pretty small. Maximum output power is 4500 watt for 0.3 seconds then it will reduce to 2500 watts for 3 seconds then it limits to 700 watts continuous for 35 seconds then down to 400 watts for long term.

K3 at 2.3 ohm load will deliver 3150W per channel for less than 0.4 seconds both channels driven, will then go down to 1450 for a second then slowly down to 500 watts a channel in 1.5 seconds.

Why I receive this thread? Because now Powersoft launched a new model, X4L , a forced bridged X8 amp, that has 4 channels with 300 Vpeak and 140Apeak. If 2 X4 channels can deliver that sustained power and program power, then I believe the new X4L will surpass the K20 if asymmetrical loading is used.

The idea is that a series loaded 2*21Ipal loaded Skhorn presents a pretty high minimum impedance for a K20 so mostly the output is voltage limited in normal use. Bridging the amp would be too much for the long safe run and very expensive. With this new model, voltage will not be a problem anymore, the maximum average output power is high enough for using 8 21 Ipal on 4 channels and. It can be almost 3 dB louder on peak output than with the K20 but with awesome processing and three phase ready.

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Huh???

What makes you say that "all of the amps limit"?

Speakers are not purely resistive loads. The average impedance is far higher than the nominal and even so 3000 watts or so of true average power into a speaker is a TON of power. You can clearly see trends in the sub compression during the sweeps well before the loudest sweep.

There are only a few cases where the amplifier limits during the sweep. Most of them are extremely high power multiple driver cabs (MAUL, Skhorn) or systems with an impedance too low for the bridged K20 ( 1 ohm or 2ohm nominal load,( RF-19, dual 21IPal, SP4 18D1)) or where the SP1-6000 has not enough power. Even in those cases ONLY the loudest sweep runs into amp limitations. In those few cases what is the alternative amplifier that will provide an increase in headroom over a bridged K20 or a SP1-6000? In what case would MORE amplifier than this be put on a single cabinet?

The speakers are tested with both a very long duration signal and also very short duration burst signals. The data is there to make judgments on how the cabs respond to both and what will happen with normal signals that are in between.

The long term output sweeps do not show heating of the voice coil only. They also show the effects of suspension changes and loss of excursion linearity beyond Xmax as well. There may also be some amplifier limiting in the loudest sweep for passive cabs. All of these things are shown in those graphs.

If you want to see the effect of thermal effects only look at the repeat lower SPL sweep taken after the build up to the maximum sweep level. This is the one that shows how much shifting and heating has occurred in the driver with the amplifier and excursion related changes removed.

 

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Thank you @Ricci for the response.

I didn't get the phrasing right, because in fact I know the results are good and verifiable. What I wanted to know in fact is if we could make a correction curve to get the amp out of the way completely, or a variable compensation curve.

I am thinking of using a Rigol oscilloscope to record voltage and current over time in sweeps and then create a power compression file to add to the measured response so that the only result is the drivers PC.

 

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6 hours ago, radulescu_paul_mircea said:

Thank you @Ricci for the response.

I didn't get the phrasing right, because in fact I know the results are good and verifiable. What I wanted to know in fact is if we could make a correction curve to get the amp out of the way completely, or a variable compensation curve.

I am thinking of using a Rigol oscilloscope to record voltage and current over time in sweeps and then create a power compression file to add to the measured response so that the only result is the drivers PC.

 

I dont think it is possible with a sweep signal including low frequencies. Excursion gets too high quickly unless the testing is a much longer duration. I think you would have to use a much different signal type if you want to look at thermal compression only. Something with a lower duty cycle and band limited to Fb and above possibly. 

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8 hours ago, radulescu_paul_mircea said:

Thank you @Ricci for the response.

I didn't get the phrasing right, because in fact I know the results are good and verifiable. What I wanted to know in fact is if we could make a correction curve to get the amp out of the way completely, or a variable compensation curve.

I am thinking of using a Rigol oscilloscope to record voltage and current over time in sweeps and then create a power compression file to add to the measured response so that the only result is the drivers PC.

 

Instead create a thermal model of the driver and then you can just compare thermal models and simulate power compression:

https://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN_19_Nonlinear_Thermal_Parameters_(Convection Cooling).pdf

This can also be extended to combined thermal models of cabs and drivers to optimise cooling. 

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On 6/18/2019 at 8:13 AM, radulescu_paul_mircea said:

Thank you @Ricci for the response.

I didn't get the phrasing right, because in fact I know the results are good and verifiable. What I wanted to know in fact is if we could make a correction curve to get the amp out of the way completely, or a variable compensation curve.

 

Found a solution. Instead of using an oscilloscope to look at the voltage, I got a device with -40 dB of voltage gain reduction, with galvanic separation to be used directly with a sound card. I can now use it to get measurements for sound output in paralel with voltage output. I can even use the output of the amplifier as an input reference for transfer function of the speaker alone, with any nonlinearity of the amp eliminated .

But I can also measure the amp dynamically, in use, which is a nice feature

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On 9/13/2019 at 7:23 PM, radulescu_paul_mircea said:

Found a solution. Instead of using an oscilloscope to look at the voltage, I got a device with -40 dB of voltage gain reduction, with galvanic separation to be used directly with a sound card. I can now use it to get measurements for sound output in paralel with voltage output. I can even use the output of the amplifier as an input reference for transfer function of the speaker alone, with any nonlinearity of the amp eliminated .

But I can also measure the amp dynamically, in use, which is a nice feature

Interesting. Are you planning to do any testing of this setup? What is "the device"?

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http://www.atelier-der-tonkunst.de/produkte/pol-ddi

This is the link to the product. Really good and very low distortion. Capable of taking 200 Vrms at under 1% THD is super useful. I tested it for limiter settings and it works as it should. I will try to get my hand around on how to use it for live Impedance monitoring. That would help me a lot

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53 minutes ago, radulescu_paul_mircea said:

http://www.atelier-der-tonkunst.de/produkte/pol-ddi

This is the link to the product. Really good and very low distortion. Capable of taking 200 Vrms at under 1% THD is super useful. I tested it for limiter settings and it works as it should. I will try to get my hand around on how to use it for live Impedance monitoring. That would help me a lot

What a funny coincidence, this device looks like a slightly less fancy version of the pmillet sound card interface, which notnyt from AVS sent me a few weeks ago. I will also use it for amp testing.

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6 hours ago, Ricci said:

Excellent...I may have to buy one of these units for my tool kit. 

The pmillet is a DIY one thou. Parts are roughly 200$ total, which includes the custom PCB from ebay. You can select your measurement range from 200mV to 200V in 10x steps and it's very clean. It basically turns your PC into and Oscilloscope if you have the right software (which I'm still looking for).

You can read more about it here.

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@Ricci I got some time to test the interface today and found just a single PC Oscilloscope software that was able to use the audio input as input device. It is a little cumbersome to use and not very feature-rich, but offers what I need. The meter on the interface is a true RMS meter but gets a little wonky below 20Hz. I tested my amp and it started limiting at 132V RMS, which is about 187V peak. Voltage peak limiter was set to 190V, interesting!

The software should work just as well with the other attenuation box mentioned, but with that one you won't be able to do ultra clean low level measurements.

 

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