Resistive Load for Amp Testing

[Sonnie Parker]

I'll add that what you don't get for that price is a set of Kelvin test leads. I didn't bother but if you are serious about making low-Z measurements, you will want them.

I ended up getting the Fluke 287... works good and a reliable trusted brand for the most part. A little pricey, but I think it's worth it.

 

[Sonnie Parker]

And the tank is built... in the process of installing the speaker connectors and wiring those up.

 

[Sonnie Parker]

All wired up... and mineral oil is here.

 

[Sonnie Parker]

So the tank with the water elements is a bust... the elements are inductive. For some reason we were thinking they were non-inductive, but tests have verified otherwise.

I can probably still use it for non-critical testing of higher powered amps.

Back to the drawing board on resistor loads. I'll have to build a board full of resistors to get where we need to be.

 

[linearphase]

Well that sorta sucks. I thought that might be an issue. Might I ask how inductive is the load? Did you measure the whole load or just a single element.

 

[JLM1948]

So the tank with the water elements is a bust... the elements are inductive.

How much inductive?
When you know, you can probably apply a corrective RC network.

For some reason we were thinking they were non-inductive, but tests have verified otherwise.

There is nothing in the real world like zero inductance; you must specify what your limit is.

I can probably still use it for non-critical testing of higher powered amps.

Of course.

 

[Todd Anderson]

Ugh... I know you put a lot of work into that! Interested to see where this goes...

 

[Sonnie Parker]

Yeah... I have not measured it in mH ... trying to decide on what oscillator to order, which will be needed for that.. The increased harmonic distortion is different for each connection, so the induction will likely vary as well. If I use one pair of terminals, I get one reading... if I use both terminals (and they are nothing more than wired in parallel) I get another reading.

I tested it with a cheap 12.5 watt resistor and got zero increase in harmonic distortion.

I have some high wattage resistors on order. The non-inductive ceramic resistor route is ultimately less expensive, but not if you've already spent close to $1,000 on the water element system.

 

[linearphase]

Yeah... I have not measured it in mH ... trying to decide on what oscillator to order, which will be needed for that.. The increased harmonic distortion is different for each connection, so the induction will likely vary as well. If I use one pair of terminals, I get one reading... if I use both terminals (and they are nothing more than wired in parallel) I get another reading.

I tested it with a cheap 12.5 watt resistor and got zero increase in harmonic distortion.

I have some high wattage resistors on order. The non-inductive ceramic resistor route is ultimately less expensive, but not if you've already spent close to $1,000 on the water element system.

The easiest way is to use an LCR meter like that described above. But you can do it cheaper.
Do you have sound card? With that and REW you can measure impedance over the entire audio range and also meter Inductance , capacitance and resistance, impedance is really why you need to know. Just google impedance test fixture or looks in the REW help file. Double check all your connections for tight solid low resistance..
You can do that with your Fluke. Just remeber to short the leads then zero the ohms measurement before starting.
In the 80’s I measured hundreds of amplifiers up to 400 watts and found that even slightly loose connection resulted in wide variations in THD.

 

[Sonnie Parker]

I have some resistors coming for temporary usage, and they might work out in the long run, dunno yet.

OhMite is working on a configuration for me to net a few 8-ohm assemblies using ceramic slab resistors at +/- 5% tolerance. It will look something like the image below.

8 resistor on each assembly and each resistor is 150 watts at 64 ohm each... all wired in continuous parallel to net 8 ohms. The resistors we will use are the 510SP model (not 510AS that is pictured), although they are roughly the same size. Net we'll have 4 assemblies at 1200 watts each with 8-ohm loads. This will also give me 2400 watts into 4 ohms when connecting two assemblies in parallel, and then if I connect those two I can get to 4800 watts at 2 ohm, but not in stereo... only mono single channel testing for 2 ohms loads... unless I end up buying 8 assemblies instead of only 4.

 

[Head_Unit]

acinfinity fans! OR those mega orange things from Home Depot. Couldn't you glue aluminum heatsink onto each ceramic? Or would that give some slight inductance? Ugh, makes my head feel twisted thinking about it