I am gearing up to work on the amp as I am almost ready to put them together to test. I only have a laptop,putting a sound card or others are not as easy. I do have quite a few older laptop......well not that old, I have a first gen I3 and a 3rd gen I5( not very reliable). What can I do to use those for measuring distortion?
I do have a Presonus audio box for recording and Studio One software that I used for recording guitar and other instruments like a multi-track recorder. I know I can make a complete song using this on a laptop.
thanks
I do have a Presonus audio box for recording and Studio One software that I used for recording guitar and other instruments like a multi-track recorder. I know I can make a complete song using this on a laptop.
thanks
I never bother measuring distortion.
If it sounds good then I am fine with it.
You can buy software that uses the sound card on your laptop to measure distortion.
If it sounds good then I am fine with it.
You can buy software that uses the sound card on your laptop to measure distortion.
There are two basic methods. Both starting with a sine wave source that is as pure as possible. The first method then attenuates and filters out the frequency of the sine wave. The attenuation makes the amp output signal the same amplitude as the input. Once signal is filtered out with the notch filter, what's left should be distortion induced by amplifier.
Second method is tougher to pull off but more forgiving of source quality. Basically the test signal is split and inverted. Inverted signal goes directly to meter circuit while non-inverted feeds amp. When attenuated signal from amp is summed with inverted signal they should null out all but distortion.
Doc
Second method is tougher to pull off but more forgiving of source quality. Basically the test signal is split and inverted. Inverted signal goes directly to meter circuit while non-inverted feeds amp. When attenuated signal from amp is summed with inverted signal they should null out all but distortion.
Doc
With an Audio Precision APx525... 🙂 😎
Less expensive options do exist. You can get quite far with a quality computer sound card and some software (True RTA comes to mind). Set the software to generate a sine wave and measure the amp output. You'll probably have to use a voltage divider as the sound card can't handle the full output swing of the amp. Use the RTA software to measure the FFT (harmonic spectrum) of the output signal. From this you can estimate the THD. In some cases, the software will do the estimate for you and report the THD number.
The older HP test gear can be useful as well. The HP3562A and 8903A or 8903B are excellent instruments. They can measure down to 0.01 % (-80 dB) THD+N according to the spec sheet, and typically down to 0.002-0.003 % (-90~-95 dB) at 1 kHz, 1 V.
If you want to go a step beyond the typical sound card, I suggest looking at Quaint Asylum's QA400.
Tom
Less expensive options do exist. You can get quite far with a quality computer sound card and some software (True RTA comes to mind). Set the software to generate a sine wave and measure the amp output. You'll probably have to use a voltage divider as the sound card can't handle the full output swing of the amp. Use the RTA software to measure the FFT (harmonic spectrum) of the output signal. From this you can estimate the THD. In some cases, the software will do the estimate for you and report the THD number.
The older HP test gear can be useful as well. The HP3562A and 8903A or 8903B are excellent instruments. They can measure down to 0.01 % (-80 dB) THD+N according to the spec sheet, and typically down to 0.002-0.003 % (-90~-95 dB) at 1 kHz, 1 V.
If you want to go a step beyond the typical sound card, I suggest looking at Quaint Asylum's QA400.
Tom
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Start with the free Visual Analyser software. My problem with PC sound card solutions is that I never know if they're giving me a reasonable number until I check the system with a traditional bench unit. In theory you can calibrate with two known amplitude signals, but I've only done that with my Cordell unit.
the QuantAsylum QA400 looks very interesting. I have to read through the specification. Sounds like it's a "ALL IN ONE" unit, generating it's own signal and read back the output from the amp ( maybe through a voltage divider) and do the whole thing.
As I said, I only have laptop and I can't just put in sound card as easy. then I still have to worry about the frequency source as you need to have a pure sine wave. OR you have to do summing and subtracting to get the distortion. I guess if you have to tweak and read, it's a lot easier with a all in one self contain unit.
I need to read in more detail to make sure it really do everything I described to justify the $199.
Thanks
Yes, and also a 331. Got so used to the 331 I can null a 334 faster than the autonull. Best friend owns an 8903.
Doc
Doc
I look at 8903.....$$$$
I just post question on the Q400 in another thread. Which one would you prefer if you have your choice? I have no idea on these, I used spectrum and network analyzer before, but those are $$$ big time.
Looking at the situation that I only have laptop, I think going to either of these two might be the cheapest way after all.
thanks
That oresonus should be a decent starting point. You got a model number?
You'll also need a reduction jig to match the level or sending the amp's output directly into the input will fry the latter.
You'll also need a reduction jig to match the level or sending the amp's output directly into the input will fry the latter.
What is oresonus? do you mean Personus? Attached are the pictures. I bought it over a year ago to do demo on some guitar electronics. I have not use it since and I have to dig it up in the garage!!!
This is the link on ebay of the same unit:http://www.ebay.com/itm/Presonus-Au...304?pt=LH_DefaultDomain_0&hash=item4633db6e18
This is quite far off from using as spectrum analyzer, I just know it has ADC inside to digitize music😀. Also, the digitizing rate is slow for hifi testing.
I am pretty sure I need a good sine wave source or do tricks in using the input and the attenuated output to do carrier subtracting to get the distortion harmonics.
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One evaluates PCs as signal analyzers by the usual means: Loop back and measure the residuals.
It is theoretically possible that the distortion in the generator compensates for the distortion in the analyzer, but that is actually pretty rare and it affects any test set, PC or otherwise.
VA is a worthwhile tool, but it is not unique.
There is a freeware tool known as the Rightmark Audio analyzer that runs a fairly complete suite of tests automatigically. It is pretty widely used.
The biggest problem with PC's as signal generators and analyzers is that they lack the ability to handle a wide range of signal levels which proper test sets are designed to do.
That is the Audiobox Two and is of sufficient quality for RMAA testing. It is able to probably go down a little below -100dB which should be enough for power amp testing, but maybe not DACs or preamps.
Sorry for the typo, the tablet keyboard takes a lot of getting used to.
If you can get that working and sort out the routing, you should be able to take decent measurements with the Audiobox. Yes it will only do 48k but the additional 6 or 8 dB from a 96k unit may not be sufficient initiative to upgrade. Might as well save for a better level of A/D than you can get from Focusrite's entry level boxes and work with this till then.
If you can run a loopback test with just the card, you'll get a pretty good idea of what you can do with it.
Sorry for the typo, the tablet keyboard takes a lot of getting used to.
If you can get that working and sort out the routing, you should be able to take decent measurements with the Audiobox. Yes it will only do 48k but the additional 6 or 8 dB from a 96k unit may not be sufficient initiative to upgrade. Might as well save for a better level of A/D than you can get from Focusrite's entry level boxes and work with this till then.
If you can run a loopback test with just the card, you'll get a pretty good idea of what you can do with it.
HP's 8903 is just over-rated, reminds me of the entire ethos surrounding IBM mainframes before DEC, Cray and DGN.
Despite it's front end limitations, you could do far worse than the QA400. The folks building these seem to have the interest in audio.
Despite it's front end limitations, you could do far worse than the QA400. The folks building these seem to have the interest in audio.
One point is that with the QA400 you are locked in to their proprietary software. If you go the sound card route there's many different software packages you can explore from free to paid-for, each with varying strengths and weaknesses. You can migrate as you build experience. For me this is the only disadvantage of the QA400, but for me a was a show stopper.
Jan
Jan
You could also say that about the Prism or even the AP APx stuff. The virtue of not needing to debug a lot of driver/os interactions and just using the stuff is a real benefit that comes from a dedicated interface. I use both types of solutions myself, depending on what I need to accomplish. I'm looking forward to the QA405 with a lot more capabilities.
I also use a Praxis w/ either an ESI Juli@ or and EMU 1212m or 1616m depending, so I'm on both sides of this fence.
Also, the question is how much to go the sound card route? It's going to be a lot more complicated as QA400 is pretty much all in one.
If you try to use any signal generator, You need to do summing and subtraction to cancel out the harmonics from the signal generator. How much it cost to rig up that. So what is the realistic cost of going to sound card route?
I know the QA400 is $199 plus a switch attenuator box. But the sound card route very likely need active circuits to get the job done.
Personally, I want one to get the job done, I don't really case what fancy option they have, I want to measure THD. If a stand alone box that is all in one to make life simpler, I'll go that route Unless I can do it with my laptop for half the cost of the QA400.
If you try to use any signal generator, You need to do summing and subtraction to cancel out the harmonics from the signal generator. How much it cost to rig up that. So what is the realistic cost of going to sound card route?
I know the QA400 is $199 plus a switch attenuator box. But the sound card route very likely need active circuits to get the job done.
Personally, I want one to get the job done, I don't really case what fancy option they have, I want to measure THD. If a stand alone box that is all in one to make life simpler, I'll go that route Unless I can do it with my laptop for half the cost of the QA400.
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