THD & IM Software Suggestions

skidave · 19th October 2011, 11:20 PM

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

Svein_B · 22nd October 2011, 03:40 PM

I use ARTA

with a dummy load/attenuator for connecting to the amps output:

Samle measurement:

SB

skidave · 23rd October 2011, 12:32 AM

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

Lavcat · 23rd October 2011, 02:07 AM

[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

BFNY · 23rd October 2011, 02:35 AM

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.

skidave · 24th October 2011, 01:18 AM

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

19th October 2011, 11:20 PM	#1
skidave diyAudio Member Join Date: Jul 2006 Location: York, Pennsylvania	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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22nd October 2011, 03:40 PM	#2
Svein_B diyAudio Member Join Date: Oct 2005	I use ARTA with a dummy load/attenuator for connecting to the amps output: Samle measurement: SB

23rd October 2011, 12:32 AM	#3
skidave diyAudio Member Join Date: Jul 2006 Location: York, Pennsylvania	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

23rd October 2011, 02:07 AM	#4
Lavcat diyAudio Member Join Date: Dec 2009 Location: New Jersey USA	[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

23rd October 2011, 02:35 AM	#5
BFNY diyAudio Member Join Date: May 2004 Location: Saratoga NY	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.

24th October 2011, 01:18 AM	#6
skidave diyAudio Member Join Date: Jul 2006 Location: York, Pennsylvania	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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