Reactive Load Tests?

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EnvisionAudio

EnvisionAudio

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Joined 2002
#1
I'm looking for the best way to load a new amplifier tester I'm building. In the past, I've used simple high wattage resistors for basic power output (zero phase angle), but I'm getting more sophisticated and need reactive loads for more accurate stability tests. I'm not necessarily looking for a speaker-simulated impedance curve, but a set phase angle change.

I found something similar to what I would like to do at the Audiograph PowerCube site:

• 8 ohm +60, +30, 0, -30, -60 degrees +/- 5%
• 4 ohm +60, +30, 0, -30, -60 degrees +/- 5%
• 2 ohm +60, +30, 0, -30, -60 degrees +/- 5%

Any hard and fast rules for making this happen? The tester will be designed to handle ~600W RMS per channel. Hand winding inductors is not out of the question.

Thanks All!
 
#7
dirkwright said:
So, has anyone built a DIY version of Audiograph's Powercube?
AudioGraph Power Cube - Stand Alone System

What's inside that box anyway?
Click to expand...

Wow. That looks like the kind of box I sent Jon Risch a block diagram of back on 3/26/2007 via my g-mail account. Luckily, I kept that e-mail on record..

This is the block diagram. By altering the gain of the control side, you can simulate different resistances. By altering the sine/cos feed to the control load, you can change the impedance parameters you desire.

The way it works, if you want 8 ohms and the load is 8 ohms, the control out is zero. If you wish 4 ohms, drive the control side at a gain of -1, that makes the middle of the 8 ohm load remain at zero volts...the higher you make the control gain, the zero point of the load resistor will move closer to the amp under test, it will look like a lower resistor.

The phase angle works the same way, but just by altering the sine/cos mix.

Cheers, jn
 

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#9
dirkwright said:
Thanks. I don't think Audoiograph does that, since they have a liquid cooled version... on a cart in a big box of course...

Have you built something like this?
Click to expand...
Yes. Back in '86 IIRC.

Mine had modifications to present as a constant resistor load, a constant voltage, or a constant power. I used a swtpc as the control amp. I never tried the phase aspect however.

Why would liquid cooled be different?

Cheers, jn
 
#10
jneutron said:
Yes. Back in '86 IIRC.

Mine had modifications to present as a constant resistor load, a constant voltage, or a constant power. I used a swtpc as the control amp. I never tried the phase aspect however.

Why would liquid cooled be different?

Cheers, jn
Click to expand...

So, we'd need a pretty powerful control amp then?

From what I can see from their website, the stand alone Power Cube has a bunch of electronics in it, whereas I think the Load Box is a set of passive components in a box with many switches. I think the load box would be an easier thing to build.

I just thought that the liquid cooled version was funny... like liquid cooled computers and amplifiers.
 
Last edited:
#14
in the 90'ties

I ran many, many tests on AudioGraph's Power-Cube system, and it is an excellent system that allow you to evaluate any amplifiers ablity to handle reactive loads and to deliver lot's of current. We created a very comprehensive library of measurements on hundreds of amplifiers at that time.
I do not know how it is today, but back then the load-box switched through a number of combinations of resistors, inductors and capacitors in order to create the reactive loads with phase-angle of 0, +-30 deg and +-60 deg.
It measured the amplifier distortion in order to establish amplifier clipping, using a high-speed fft, and finally it measured the high current capability by loading the amplifier with 0,1 ohm, using a short burst. And if the amp went into oscillation during the test it reported that and abandoned the test.

Beautifull stuff! Everybody should have one. Not everybody can afford it. it was $20K back then, probably not less today.

Steen
 
#15
smichael said:
in the 90'ties

I ran many, many tests on AudioGraph's Power-Cube system, and it is an excellent system that allow you to evaluate any amplifiers ablity to handle reactive loads and to deliver lot's of current. We created a very comprehensive library of measurements on hundreds of amplifiers at that time.
I do not know how it is today, but back then the load-box switched through a number of combinations of resistors, inductors and capacitors in order to create the reactive loads with phase-angle of 0, +-30 deg and +-60 deg.
It measured the amplifier distortion in order to establish amplifier clipping, using a high-speed fft, and finally it measured the high current capability by loading the amplifier with 0,1 ohm, using a short burst. And if the amp went into oscillation during the test it reported that and abandoned the test.

Beautifull stuff! Everybody should have one. Not everybody can afford it. it was $20K back then, probably not less today.

Steen
Click to expand...

Right. I have since figured it out and developed my own (but have not built it). It would cost about $3k and require some DAQ cards for a PC. The cheap version would be controlled using some relays and require manual interaction. However, I am less inclined to do this because I feel anything less than fully automated operation could result in damage if something went wrong.
 
#16
EnvisionAudio said:
Right. I have since figured it out and developed my own (but have not built it). It would cost about $3k and require some DAQ cards for a PC. The cheap version would be controlled using some relays and require manual interaction. However, I am less inclined to do this because I feel anything less than fully automated operation could result in damage if something went wrong.
Click to expand...

Well, that's what fuses are for... <j/k>

I'd settle for a load box full of resistors, capacitors and inductors with manual switches therebetween. Maybe a fancy version would have an ammeter and voltmeter on it...
 
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