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post #31 of 1332 Old 11-30-2014, 06:51 PM
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Oh, almost forgot. REW can calculate THD too.

You should be able to use that, once you find a way to get 14,000watts into a soundcard. hehe
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post #32 of 1332 Old 11-30-2014, 06:53 PM - Thread Starter
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Quote:
Originally Posted by BassThatHz View Post
Oh, almost forgot. REW can calculate THD too.

You should be able to use that, once you find a way to get 14,000watts into a soundcard. hehe
Voltage divider, don't need full signal to calculate thd.
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post #33 of 1332 Old 12-01-2014, 05:16 AM
 
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What amps specifically do you want to measure ?
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post #34 of 1332 Old 12-01-2014, 05:57 AM - Thread Starter
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What amps specifically do you want to measure ?
As many as I can. Going to create a database of it. I will have a standardized testing procedure outlined as well so others can contribute data.

Also going to measure idle current draw, noise at 1 foot, and possibly RF noise.
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post #35 of 1332 Old 12-01-2014, 06:07 AM
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Would love to see the QSC g-5 and g-7 measured......
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post #36 of 1332 Old 12-01-2014, 08:25 AM
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As many as I can. Going to create a database of it. I will have a standardized testing procedure outlined as well so others can contribute data.

Also going to measure idle current draw, noise at 1 foot, and possibly RF noise.
If there is anything I (or we) can do to help, you let us know.
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post #37 of 1332 Old 12-01-2014, 08:27 AM - Thread Starter
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If there is anything I (or we) can do to help, you let us know.
Going to solicit feedback once I have some preliminary tests assembled. Then I'll just need gear to test
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post #38 of 1332 Old 12-01-2014, 08:29 AM
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Looking at the scarlett 2i2 for audio interface. Would pref something cheaper, but don't see anything that measures better for the price. The balanced io is necessary here.
Tascam US-366
15% off at Musician's Friend
$50 MIR
Final price: $119

I own it and really like it. I use it as a mic preamp for REW, as a multi-channel DAC, for testing unbalanced/balanced connections to amps, for testing optical, coax, and AES digital inputs/outputs, as a headphone amp, and as a mixer for the kids skits.

Edit: The 15% off at Musician's Friend would also apply to the Scarlett 2i2 making it $127.50.

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post #39 of 1332 Old 12-01-2014, 11:10 AM
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going to measure idle current draw, noise at 1 foot, and possibly RF noise.
I amended my post here to include idle fan noise now, in addition to the temp.

I measured both the front and the back @ 1ft. (They were all different so I figured that capturing both sides might be important to someone).
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going to measure idle current draw
All of the amps I measured drew about 100-300watts @ idle, with the average being about 200watts;
and that power draw didn't change by very much until the output power rose above 80watts per side or the -20db lights (whichever is the most.)


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and possibly RF noise.
I wasn't able to detect any RF noise in any of the amps. (Only a few microvolts up near the 1Mhz range.)
Even the newage switcher amps were only a few micro/milli volts in the 300khz-1000khz range.
[and that was after travelling through 40ft of unshielded speaker cable and hundreds of miles of unshielded transmission lines too!!!]
Hardly worth worrying about considering that nobody can hear above 30khz, nor can few tweeters even play it. (if any at all!)
and under any load it would be drowned out by the music signal and speaker distortions to boot (and XO and coil inductance too.)

There is probably more Nyquist distortions coming off the audio CD @ 10khz, than RF noise coming out of amps @ 400khz.

Last edited by BassThatHz; 12-01-2014 at 11:16 AM.
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post #40 of 1332 Old 12-01-2014, 02:11 PM
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I have a peavey IPR2 3000 just sitting here.

Marantz 7702 Atmos
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Speakers- TBD
subs 2 XXX ported SLLT powered by IPR2-7500.
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post #41 of 1332 Old 12-01-2014, 04:20 PM
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Quote:
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Oh, almost forgot. REW can calculate THD too.

You should be able to use that, once you find a way to get 14,000watts into a soundcard. hehe
I've experimented with Rew V5.0's THD measurements for small signals and found it to be kind of squirrelly. It would increase and decrease in value by orders of magnitude when only changing the frequency in small increments. I have a good soundcard and have put different preamps in the loop with it but the results don't make sense to me.

I'm not saying don't use it. REW beta is supposed to be better in that regard and as an amp approaches it's limits it will have way more measureable distortion than what I was trying to look at. I just wouldn't take it's numbers to the bank without something else to compare to.
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post #42 of 1332 Old 12-01-2014, 07:00 PM - Thread Starter
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I've experimented with Rew V5.0's THD measurements for small signals and found it to be kind of squirrelly. It would increase and decrease in value by orders of magnitude when only changing the frequency in small increments. I have a good soundcard and have put different preamps in the loop with it but the results don't make sense to me.

I'm not saying don't use it. REW beta is supposed to be better in that regard and as an amp approaches it's limits it will have way more measureable distortion than what I was trying to look at. I just wouldn't take it's numbers to the bank without something else to compare to.
I'll be evaluating different software to see which works best for the job. Hopefully next weekend I can get some interesting data posted.
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post #43 of 1332 Old 12-01-2014, 10:35 PM
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Originally Posted by Shreds View Post
I've experimented with Rew V5.0's THD measurements for small signals and found it to be kind of squirrelly. It would increase and decrease in value by orders of magnitude when only changing the frequency in small increments. I have a good soundcard and have put different preamps in the loop with it but the results don't make sense to me.
REW's math seems correct. These settings seem to work best.



But finding a soundcard with sufficiently low noise to do THD calcs above 300hz could be very challenging indeed.

This is my Asus Xonar HDAV1.3; which cost me $180 like 8 years ago...


1% distortion is 1V RMS of 2nd or 3rd harmonic out of a 100V RMS sinewave.
For 1V into a soundcard, that works out to be just 0.01volts.

i.e. -40db.
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post #44 of 1332 Old 12-01-2014, 11:33 PM
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Here is what 10% harmonic distortion looks like on a scope:
(1% was pretty much invisible on a scope, so I had to make it 10 times worse.)

1.4% 2nd+3rd


10% 2nd


10% 3rd
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post #45 of 1332 Old 12-02-2014, 03:14 PM - Thread Starter
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Got some parts... Will end up about 4.5 ohms per channel.



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post #46 of 1332 Old 12-03-2014, 07:16 PM - Thread Starter
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Got my audio interface. Scarlett 2i2. Measures well. I should be able to sufficiently test amps with this.


Sweep, nice and flat..


Intermodular distortion nice and low


Waveform from IMD test


Square waves


CEA 2010 burst
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post #47 of 1332 Old 12-03-2014, 08:24 PM
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F**k yeh.
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post #48 of 1332 Old 12-03-2014, 08:26 PM - Thread Starter
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F**k yeh.
Now I just need a garbage pail and some time

edit: and some parts to setup a voltage divider to feed back to the interface. Need some TLR inputs.

PC -> 2i2 via usb -> AMP via TRS to TRS/XLR

AMP -> heating elements via speaker level outputs.

Need to make some cables with speakon connectors that can feed a voltage divider at the same time, then from there to TRS back to the 2i2. Will have some exposed leads on that board for jumpering in connections from amps that don't have speakon outputs.

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post #49 of 1332 Old 12-03-2014, 08:27 PM
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The first one should be easy to acquire.

Look forward to how things go.
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post #50 of 1332 Old 12-04-2014, 01:03 AM - Thread Starter
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STEPS vs REW for FR and THD, thoughts?
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post #51 of 1332 Old 12-04-2014, 02:37 AM
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Quote:
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STEPS vs REW for FR and THD, thoughts?
Try both and see if there are any differences. ARTA in the free version only disallows saving the results, but you can save screenshots initially so testing it will cost you nothing.
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post #52 of 1332 Old 12-04-2014, 05:31 AM
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What about FR sweeps down to 2hz? Would be good to compare the single digit -3db roll-offs under a light load, say 100watts.
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post #53 of 1332 Old 12-04-2014, 05:37 AM
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Quote:
Originally Posted by notnyt View Post
As many as I can. Going to create a database of it. I will have a standardized testing procedure outlined as well so others can contribute data.

Also going to measure idle current draw, noise at 1 foot, and possibly RF noise.
Awesome! This will be a fantastic contribution!

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post #54 of 1332 Old 12-04-2014, 06:26 AM
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What about FR sweeps down to 2hz?

Yeah, yeah, yeah. Throw us sealed subbers a bone.
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post #55 of 1332 Old 12-04-2014, 10:12 AM - Thread Starter
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Yeah, yeah, yeah. Throw us sealed subbers a bone.
I'll run sweeps from DC....

REW doesn't generate burst tones under 10hz. Wonder if I can modify it. Otherwise I'll just have to find a 5hz cea 2010 burst.
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post #56 of 1332 Old 12-04-2014, 07:19 PM
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I'll run sweeps from DC....

REW doesn't generate burst tones under 10hz. Wonder if I can modify it. Otherwise I'll just have to find a 5hz cea 2010 burst.
Cool. I was messin' around in one of my DAW's and I created this one at 5Hz. I tried to match the length of the waveform and amplitude of the other bursts I saw REW making in the lower frequencies. PM me your address if you want me to email you the .wav.
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post #57 of 1332 Old 12-04-2014, 07:49 PM
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Cool...Been hoping somebody would get this going. I don't know of any program which has a 5Hz Keele burst built in. You'll probably have to make one and sample it. Might be a bit cludgy.

Are you going to do unloaded FR vs 2, 4, 8 ohm?

I would probably just do something like 10, 20, 40, 1kHz, 10Khz and 20Khz for the burst tests. 5Hz would be interesting if it isn't too much of a hassle to generate.

I used to use NCH tone generator to produce some signals I couldn't get like 10 non harmonically related sines all at the same time. I haven't looked at it in a while but it may be able to offer something for 5Hz, IMD or spectral contamination.

Pros for REW. Free, measures down to 2Hz, faster measurements. Can do distortion through the 10th harmonic. STEPS only goes down to 5Hz and lumps the harmonics above the 5th all together. If you set up the STEPS FR measurements for high resolution they can take awhile to run so REW probably makes more sense there. STEPS also has possibilities that REW doesn't though. Whatever you do the first couple of amp tests will probably help you make up your mind on what makes sense and what doesn't and the easiest and most practical way to make it repeatable.
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post #58 of 1332 Old 12-04-2014, 08:15 PM
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Quote:
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Are you going to do unloaded FR vs 2, 4, 8 ohm?
There's no point really. The determinant for the LF roll off is a coupling cap and the speaker load isn't going to change it.
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post #59 of 1332 Old 12-04-2014, 08:19 PM - Thread Starter
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Quote:
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Cool...Been hoping somebody would get this going. I don't know of any program which has a 5Hz Keele burst built in. You'll probably have to make one and sample it. Might be a bit cludgy.

Are you going to do unloaded FR vs 2, 4, 8 ohm?

I would probably just do something like 10, 20, 40, 1kHz, 10Khz and 20Khz for the burst tests. 5Hz would be interesting if it isn't too much of a hassle to generate.

I used to use NCH tone generator to produce some signals I couldn't get like 10 non harmonically related sines all at the same time. I haven't looked at it in a while but it may be able to offer something for 5Hz, IMD or spectral contamination.

Pros for REW. Free, measures down to 2Hz, faster measurements. Can do distortion through the 10th harmonic. STEPS only goes down to 5Hz and lumps the harmonics above the 5th all together. If you set up the STEPS FR measurements for high resolution they can take awhile to run so REW probably makes more sense there. STEPS also has possibilities that REW doesn't though. Whatever you do the first couple of amp tests will probably help you make up your mind on what makes sense and what doesn't and the easiest and most practical way to make it repeatable.
Yep.. will be doing unloaded vs different loaded sweeps.

I may poke the REW author to add 5hz capability to signal generator if possible, or dig into the code. That would be ideal. If I'm reading right, STEPS has the benefit of delays between measurements, so you're not depleting the power with a high level swept sine wave right away.

Thanks for the feedback, much appreciated.

REW also does dual test tones now so I'll be posting IMD data as well. Once I get my electronics all setup (l-pad components coming tomorrow) I'll outline full test procedure, go through a test, post the data, and seek feedback.
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post #60 of 1332 Old 12-04-2014, 08:20 PM - Thread Starter
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There's no point really. The determinant for the LF roll off is a coupling cap and the speaker load isn't going to change it.
FR from amps, especially on the high end, will change based on the impedance of the load.
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