Testing amps.

[Drock]

Hey guys, I'm obsessed it seems, to learn more about amps how they work, testing, comparing, all that jazz.
Anyway, I have watched a few videos on how to do a clamp test to measure the output on an amp.
So I pulled out a few amps this morning and tried it out.
I have tested as follows, please give feedback whether or not a) I'm doing this right. b) can you actually compare an amp this way, or is there another method?

I tested
1: t13500.1
2: elite.1
3: The One

This is all done on my test bench at roughly 13.5 v

First I set all the bass boost at 0db. Then lp freq as high as it goes. Subsonic filter set at 55Hz. (As high as it goes).
I then with no speaker attached and a dmm set the gain to 80v AC ( I'm not trying to measure what the amps can produce, just what they do at equal gains) I then hooked up a dd3512d4 sub run at 2 ohm. Then a clamp meter around the positive speaker wire at the amp.
My source is my iPod set full volume and plays a 55hz tone.

This is my results ( keep in mind that I have set all gains at 80v AC before hooking up the speaker.

Ti3500.1
66vac x 14.42 amps = 951.72 watts

Elite.1
73vac x 14 amps = 1022 watts

The One
80vac x 20 amps = 1600 watts
This amp at this volume was a very obvious difference it output.

The one thing I noticed was that even though I set the gains exactly the same 80vac, both the ti and elite dropped in AC voltage quite a bit.
The One amp did not budge, it stayed at 80vac.

Unless I did something wrong, IMO this goes to show you how efficient The One amp is.

Anyway need some input from some experienced guys, and then I'll keep testing more amps. Have lots more. I'm curious now.



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[trickyricky]

What are you trying to measure? You cannot use a subwoofer as a load, you have to have a resistor (very large, high wattage/a device with a purely resistive impedance exhibits no phase shift between the voltage and current.) and several meters to measure more than just one output.

You have to measure your voltage (before testing and when testing) at the same time measure the DC current this is for your B+ input.

Same thing will be needed for your output (speaker terminals), meter measuring the AC and another the AC current.

You will need a scope to make sure your sine wave is not clipping, set your amps to max prior to clipping and measure away .

After testing (shouldn't take more than a couple seconds to write down the numbers) measure the resistors while their hot, they wont change much. Do some math and you'll fine out the real output of the amplifiers, even its efficiency.

[Drock]

Wow, that's a lot more than any of the videos I watched.
All they did was put a dmm on the speaker terminals to measure volts AC and a second clamp meter on the positive speaker wire and measured the amps.
Then multiply the volts x amps = watts.
This was there way of determining the amps output.
And in the vid they used a sub for the test with a 50hz signal.

I did see in one video a guy use a bunch of resistors.
I know the sub will very in resistance compared to the resisters for load. But I thought since I did the same test to all amps it would be the same difference across the amps.

Clearly after one reply I have a lot more to learn.


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[trickyricky]

A lot of those guys, at least the ones I've seen, don't have a clue on what they're doing. They do it wrong and get high numbers and believe they got a special amp or underrated.

That's why I ask what where you trying to measure, or compare. If its their total output power, then the way I mentioned on the second post is the way to go. Unless your lazy, don' want to do the math and have 3k to spend on SMD's Amp Dyno....


I use several resistors for different loads, the ones I have are 300watt rated and when combined I can get up to 15kwatts bursts. Having the proper power supply is a different story,

[Drock]

Thanks for helping out. I want to learn to do this right.
No need to cut corners. What resistors did you use. I will order a few


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[trickyricky]

I use 16ohm 300watt (http://www.mouser.com/ProductDetail/Ohm ... gbvn2Gg%3d), but mouser now has these bad boys available http://www.mouser.com/ProductDetail/TE- ... uGQxp50%3d.


Its not cheap, you have to have meters as well (two will do....a current clamp and the RMS dmm). You will just have to remove them from the power wires to the speaker wires. Now if you have two of each you can just place them on each side and record all numbers at once. You can skip the scope if you have a scope dmm such as a TPI 440 (or similar hand held scope).


If your patient enough you might be able to find them on ebay for less than half the price that's on mouser. Heres a bad ass one that I wish I had...... FSE100002E1R00KE available at Digikey, its 1ohm 1kwatt and if you read the datasheet it will let you know what its actually capable.

http://www.digikey.com/product-detail/e ... -ND/270007 for the 1ohm 1kwatt resistor

[Drock]

I'm making a shopping list. Finding a scope and learning to use it might be a challenge. But I'll figure it out.


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[Drock]

That link does dot work.


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[trickyricky]

They both seem to be working. Just search for "wirewound resistor" select the ohm and make sure wattage is above 300watts, or the 1kwatt that will take up less space (instead of many resistors, its just large one).

Scopes are cheap, you can get an old school tek 465 on ebay for around 200-250 shipped and those are way nicer than the hand held (the CRT display is much more better when looking for clipping signals). The hand held ones you can barely see it clip because of the resolution of the screen sucks.


Don't be afraid of the scope, its easy and I will be more than willing to help or point you to the right tutorials.

[ByBlaZeD]

Nice info here! Always wondered myself... may have to dig some out and play myself Lol

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[Drock]

I thought it would be a good skill to have. I've been checking out different forums and there appears to be a lot of guys that are doing this wrong. I have stayed away from making comments as I am not well educated in this area.

I figure it's time to learn some more technical info than just hooking up a few wires and owning high end gear. I want to know what power I'm actually doing. I don't want to talk shit, I just want the facts.


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[Mr. Wild]

Why did you have the subsonic on and set to 55Hz? Thats just blocking your 55Hz test tone by several dB.

[Drock]

That was just the dial setting turned all the way. Just easy to set all amps the same. Turning the dial the other way would be 5hz.
And was not trying to measure the spl, just the power output at the speaker terminals.
Again I'm just learning here so any advice is very helpful. Thanks


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[trickyricky]

X overs and filters on amps have to be bypassed. With dummy loads you don't have to worry about subsonic fhz.


Don't get scared when you hear music or the sIne waves coming out of the resistors, lol.

[Drock]

X overs and filters on amps have to be bypassed. With dummy loads you don't have to worry about subsonic fhz.


Don't get scared when you hear music or the sIne waves coming out of the resistors, lol.

Thanks. Going to a local shop today to see if they have anything that will work. If not I'll order from above link.


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[Drock]

Well no luck on the resistors today. Guess I'll have to order some online.


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[ajaye]

I've been looking into making a dummy load(s) unit that would be flexible for multiple channel and variable impedance, less for analytical purposes than for just functionality testing. I think one important thing it sounds like trickyricky's advice gets at is to drive both (or all) channels at once to get real results. No one really hooks up all 4 channels of an amp and then listens to one channel at a time. A lot of manufacturer's specs are with only one channel driven though, especially home theater stuff with 9.2 channels.

The amateur radio community has a ton of good info out there for diying all types of test setups, and sometimes stupid amounts of power dissipation. May be worth checking out as well. Toasters' and ovens' heating elements seem to be a popular budget starting point, and reading some of the dudes talking about using liquid oil baths for cooling and forgetting to vent the paint can full of oil end in hilarity.

[trickyricky]

You make your own, get four 4ohm 1kwatt and call a day (they cost a little over 50 bucks each, hardware is extra), that way you can test four channel amps with 4 ohm loads, or you can test two channel amps with either 4 or 2 ohm loads, and the mono's @ 4, 2 or 1 ohm loads (with all four resistors in parallel, or use all four and make a single 4ohm load capable of handling 4kwatts).

When testing YOU HAVE TO put a load on all the channels, if you bridged them or have them separate it wont matter as all channels will have or share a load. The reason for this is if you have a 4 channel amp and test one channel at a time then you might get higher numbers than the actual ones when all 4 channels have a load and the power supply has to provide power to all FOUR channels.

For example... below I will use two channel amps. This is to explain the fact that you don't need many wirewound resistors.

Having a 4ohm load on each channel is the same as having a single/mono 8ohm load.
Having a 2ohm load on each channel is the same as having a single/mono 4ohm load.

Below I have a four channel amp.

Having a 4ohm load on each channel is the same as having two mono/bridged 8ohm loads.
Having a 2ohm load on each channel is the same as having two mono/bridged 4ohm loads.

See where am going with this, am pretty sure you guys already know this. So there is no need to have lots of resistors or for it to be that flexible. You just need to know what your doing when testing. That's why I choose 16ohm loads, but I suggest you get FOUR 4ohm 1kwatt resistors.

[Drock]

Sounds good. I'm just having issues using the links. Seems they don't work on my phone. I dont have a computer


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[trickyricky]

Its HLZ30007Z8R000KJ for digikey, those are 8ohm 300watt resistors. I got lucky and found a 1ohm 1kwatt resistor on ebay for 30bucks shipped...its about 50.00 on digikey (not including S&H).

So be patient and you'll find what you need. If your in a hurry to get the parts, you'll end up paying a lot more.

[captainobvious]

Dont bother trying to build your own at great expense...

http://www.ebay.com/itm/200W-4ohm-alumi ... 51b4b848e9

This seller offers a vast variety of impedance loads and power ratings for them as VERY reasonable prices. Hope this helps

-Steve

[freshkryp69]

Drock, Ebay is the place to get them cheap!!! Ive seen them as low as 10 bucks each.. they never last long.. Look for Vishay/Dale resistors.. they are the high end brand, very high quality..

[Drock]

Thanks. I'll keep an eye out.


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[captainobvious]

Just make sure you get a high enough wattage from the get go so that you can test more powerful amps down the road if desired. Oh, and remember that to get a true output measurement, you'll need to apply a load to all channels of the amp

[bigdwiz]

What about the 1000W "braking" resistors on eBay? They are your best $ per watt

http://www.ebay.com/itm/1000W-2-4-8-16- ... 1332826290

I built a few banks using ceramic and wirewound resistors, but these braking resistors are a much better deal