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What to measure for and what gear to use?
What to measure for and what gear to use?
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Old 15th June 2019, 05:46 AM   #1
FriedMule is offline FriedMule  Denmark
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Default What to measure for and what gear to use?

I have looked trough this forum and google but have not found an answer for dummies. :-) So I hope that you will try to help a noob. When measuring audio (primarily amplifiers) you look for THD+N, linearity, phase and much more. But what are the "much more" and what gear do you use to test fore all of these values?
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Old 15th June 2019, 08:37 AM   #2
Jazid is offline Jazid  United Kingdom
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The classic tests for power amps are power output to specified level of distortion into differing loads, signal to noise, input sensitivity/gain, input and output impedances, polarity, bandwidth, distortion as THD, THD+N, nature of distortion products (odd/even harmonics), and maybe output offset voltage and power consumption.
For pre amps gain/input sensitivity, output voltage, input/output impedances, signal to noise from the different inputs, distortion at specified output voltages (and its components), headroom, maybe RIAA compliance.
It'll take too long to describe the equipment, maybe you could read some of the RTX6001 analyser thread on this forum for pointers?
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Old 15th June 2019, 02:26 PM   #3
FriedMule is offline FriedMule  Denmark
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Thank you wary much, that was a reply that I clearly understand. :-)
I have looked at the RTX6001 and some of the treads.


On the way I did find the Audio Precision ATS-1, is it capable to do the tests?
https://www.axiomtest.com/documents/...0datasheet.pdf


Edit: forgot to say that, yes I have tried to read about the ATS-1 but again, noob-alert! :-)

Last edited by FriedMule; 15th June 2019 at 02:31 PM.
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Old 15th June 2019, 03:16 PM   #4
Jazid is offline Jazid  United Kingdom
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I'm another relative noob, welcome What to measure for and what gear to use?
Never used AP equipment as I cannot afford it, but I've never heard a bad word about it. It is the range to which all other audio testers are compared
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Old 15th June 2019, 03:23 PM   #5
FriedMule is offline FriedMule  Denmark
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Quote:
Originally Posted by Jazid View Post
I'm another relative noob, welcome What to measure for and what gear to use?
Never used AP equipment as I cannot afford it, but I've never heard a bad word about it. It is the range to which all other audio testers are compared
Okay and thanks, fellow noob:-)
I have decided to afford it by saving:-)
My hope is just to get the best for a home tinkerer.
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Old 15th June 2019, 03:53 PM   #6
BamboszeK is offline BamboszeK  Poland
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I don't think that ATS-1 is best choice today. It is specced for just -92dB THD+N. Most of good amplifiers would exceeds that.
IMHO something like RTX6001 plus software (like Room EQ Wizard, ARTA, Virtins) is much better and future-proof option. I would even prefer some solid audio interface. Not so plug-and-play like ATS-1 or RTX6001 but can archieve same or even better performance while it costs fraction of price. You can check this thread - Howto - Distortion Measurements with REW
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Old 15th June 2019, 08:26 PM   #7
FriedMule is offline FriedMule  Denmark
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Quote:
Originally Posted by BamboszeK View Post
I don't think that ATS-1 is best choice today. It is specced for just -92dB THD+N. Most of good amplifiers would exceeds that.
IMHO something like RTX6001 plus software (like Room EQ Wizard, ARTA, Virtins) is much better and future-proof option. I would even prefer some solid audio interface. Not so plug-and-play like ATS-1 or RTX6001 but can archieve same or even better performance while it costs fraction of price. You can check this thread - Howto - Distortion Measurements with REW
Looks interesting, can it do more then distortion measurements?
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Old 16th June 2019, 10:27 AM   #8
suzyj is offline suzyj  Australia
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Quote:
Originally Posted by BamboszeK View Post
I don't think that ATS-1 is best choice today. It is specced for just -92dB THD+N.[/URL]
Nothing wrong with that. Using a decent source (for example the Frex LT AN67) and a notch filter you can extend that down a further 30-40dB.

I use an old HP 3585B, which really makes only 90dB. I regularly use it to examine THD and distortion at -120dBc

For the OP, in no particular order:
  • A decent multimeter. You need to be able to measure voltages and resistances to some degree of accuracy. I use an old Fluke 87, and recently acquired a HP 3478A.
  • A couple of lab power supplies. Iím fond of old Thurlby supplies, but a pair of anything thatís good for 30+V and able to set constant current will allow you to power things up without losing too much smoke.
  • A signal source. Lots of people use sound cards. I have an Edirol FA-66 which is nice, and my mac has surprisingly good sound output. This tends to be the limiting factor for me, so I have a couple of the aforementioned Frex low distortion oscillators too.
  • A load. Big high-power 8Ω resistor. Put it on a heatsink.
  • Some things to examine the output with. Sound cards are good, but a bit limited both in terms of frequency response (audio only), and input sensitivity and attenuation range. My HP3585B is my go-to instrument here - DC to 40 MHz. I also use a Tektronix TDS320A CRO, which is invaluable as it makes 100MHz, and thus far none of my audio stuff has oscillated above that
  • Cables, attenuators, adaptors, notch filters. I find blown up old minicircuits amps make great project boxes - BNC on each end and room for a few passives or whatever inside.
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Old 17th June 2019, 02:22 AM   #9
FriedMule is offline FriedMule  Denmark
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I have to admit that I may be more towards a "hands on" unit then an computer unit.
I think it's like CNC in wood working, you can program the pc, make perfect cuts and even 3D carvings and then assamble it afterward to a perfect result. But I do prefere my table saw, band saw, hand router and hand tools, even I know that it can never be as perfect as the CNC.
I know that a computer with a great sound card and top notch analytic software maybe could deliver better analyses, better tests and yes better all. But I feel that a unit where I turn the dails, flip the switches and connect cables, is more to my liking. :-)


suzyj: I have thought about the Siglent functions generator series 2000, I do own some handheld multimeters, that I mostly trust, and I have a Rigol MSO5000 oscilloscope.


How much differance is there from the old HP8903b and the old but newer audio precision ats-1?
The price is about 5 times higher!
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Old 17th June 2019, 12:05 PM   #10
suzyj is offline suzyj  Australia
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My computer setup is too dynamic to be relied on for testing. I seem to replace the computer every 3-4 years, and each time I do interfaces change, and operating systems change. I’ve gone pci to pcie to firewire for audio card, and next time I change computers the firewire one will likely go in the bin in favour of usb 3 or thunderbolt or whatever the interface de jour is.

My test equipment, on the other hand, has been static for many years. It just works. So what if I take photos of screens or write down numbers - at least it’ll still be the same five years from now.
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