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Old 19th October 2011, 11:20 PM   #1
skidave is offline skidave  United States
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Default THD & IM Software Suggestions

Hey everyone. I'm looking for suggestions on software to do THD & IM measurements for basic audio gear testing. It does not make sense to purchase an older Sound Technologies unit based on not knowing if it works properly and calibrates. Trust me, I would love to have a mint condition unit, but I don't think this route is the way to go. I would like to find a software program that can do THD, IM, and other pertinent measurements.

This is only for hobby, but I would like to be able to measure and spec the power amps and tube gear I build. Plus, using software I would be able to save screen shots or export data.

Looking for suggestions and searching the web. The RealRTA looks great, excpet it is for use with a mic to measure room response, etc.

Any info would be appreciated.

Thanks,

Dave
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Old 22nd October 2011, 03:40 PM   #2
Svein_B is offline Svein_B  Norway
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I use ARTA

with a dummy load/attenuator for connecting to the amps output:
Click the image to open in full size.

Samle measurement:
Click the image to open in full size.

SB
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Old 23rd October 2011, 12:32 AM   #3
skidave is offline skidave  United States
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Thanks Svein. I am looking at the Tascam US-100 USB sound card / interface. Mainly because this unit has unbalanced line in / out.

When you test amplifiers, I would assume you are using the line out to feed your amp and then after your attenuator, you feed it to the line in. I see the Zeners to limit the signal to 2 volts.

Do you have control over the weighting (A, C or flat)?

I might have some more questions! Thanks for responding.

Dave
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Old 23rd October 2011, 02:07 AM   #4
Lavcat is offline Lavcat  United States
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[QUOTE=skidave;2751870]Hey everyone. I'm looking for suggestions on software to do THD & IM measurements for basic audio gear testing./QUOTE]

See this thread:

Balanced Soundcard Interface for Power Amplifier Distortion Measurement
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Old 23rd October 2011, 02:35 AM   #5
BFNY is offline BFNY  United States
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Be aware that making a connection from the amplifier speaker out "-" terminal to earth ground can in certain cases be a problem. If it is a problem, and you do it by mistake, (*and* the amp has good protection circuits), it should trip. If not, it may blow outputs if you apply full power for testing.

This refers to especially on big high power class D amplifiers with floating +, - speaker outputs, or any other amp with bridged or floating differential outputs.
If in doubt, check with a multimeter the resistance from speaker "-" to amplifier "ground". On most common amps it will be close to zero resistance. If not, you should check further, as you may need to use a true floating differential input on the measurement side.
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Old 24th October 2011, 01:18 AM   #6
skidave is offline skidave  United States
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Lavcat: thanks for the heads up on the other topic!

BFNY: been there before. I have a few amps that use a three wire power cord. They use the earth / ground connection for the chassis and then 'float' the ground for signal just above chassis (by 10 or so ohms). Yes, I have completely blown the resistors that float the signal ground. I learn as I go!

Keep the info coming!

Dave
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