I've been trying to make improvements to an amplifier I've been working on but I cannot see below -150db on my scope and all of the harmonics are below that point. I have a number of improvements I can apply that should provide fairly significant improvements beyond whatever the current measurements are at but I cannot even see what they are before or after the improvements are applied.
What does one do when they require access to a high end distortion analyzer but does not have one?
What does one do when they require access to a high end distortion analyzer but does not have one?
Many instruments can be leased on a monthly or longer basis from a rental company. It's not cheap, though. Electronic Test Equipment Rental l TRS-RenTelco
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I'm at the edges of my means as it is, rental is not really an option. I would at least need only a few moments of time with the analyzer in question for a quick analysis. Anyone in the New England area possess such an analyzer that would be willing to let me come over and use it?
I highly doubt you're seeing -150 dB from your scope!
Good sound card and something like Bob Cordell's distortion magnifier will go a long ways toward your goal. Certainly to -120 dB, which is about as far down as you can go without getting into serious heroics.
Good sound card and something like Bob Cordell's distortion magnifier will go a long ways toward your goal. Certainly to -120 dB, which is about as far down as you can go without getting into serious heroics.
You're right, I thought it was a bit odd the noise floor was lower than usual today. My house has varying amounts of electrical noise day by day so I assumed today was a particularly quiet day. Turns out I just left the scope in DBFS mode. Putting it in DBV mode puts it back at a 130ish noise floor. Still my problem remains.
There must still be competent audio labs around, that will do testing for a fee. Maybe these guys will know about some. The Connecticut Audio Society
Also, to be sure, do you know the difficulty in getting reliable distortion measurements anywhere near -150 dB? That's way up in heroic territory. We have any number of threads discussing oscillators/detectors that may/may not work at that level.
Samuel Groner's excellent work on opamps discusses this issue here:
So do you actually need -150 dB or do you *think* you need -150 dB? My guess is the latter.
Samuel Groner's excellent work on opamps discusses this issue here:
So do you actually need -150 dB or do you *think* you need -150 dB? My guess is the latter.
I need to know the specs of my design for marketing and optimization purposes mainly. My biggest concern at the moment is optimization, I cannot see the results of what I am doing.
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Have you calculated the thermal noise of the input resistor of your product? If you divide the nominal input voltage with this value, some informative figures will come.
No, good point. Using basic online calculator I'm getting -117db value but that is incorrect because the noise floor is about -130db on the analyzer while testing.
I ordered one of those distortion magnifier kits. I am hoping that is enough to get me down to -150db at least when paired with my QA401. I assume the distortion magnifier will eliminate the annoying harmonics induced within the QA401 itself?
Is there a point to purchasing an ultra low distortion audio oscillator if using the distortion magnifier?
Is there anything else I can do to improve the situation?
I'm building a workshop from scratch in an isolated part of my property, is there any thing special I should do in order to make the "room" more fit for measuring low level signals?
Is there a point to purchasing an ultra low distortion audio oscillator if using the distortion magnifier?
Is there anything else I can do to improve the situation?
I'm building a workshop from scratch in an isolated part of my property, is there any thing special I should do in order to make the "room" more fit for measuring low level signals?
A dedicated power line, with an isolation transformer.
For the more fanatical, a Faraday cage.
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I'm currently studying multiple subjects and have seemingly endless work to do, forgive me if I offload some questions to the internet instead spending all my time finding answers to my diverse and obscure questions in the depths of the internet and literature.
Feel free to not respond to my questions if this bothers you.
Feel free to not respond to my questions if this bothers you.
Do please share the make and model number of your 'scope which can show harmonics in an FFT down to -150dB. Mine only shows a DR under 60dB in FFT. It would be great to even have 100dB, let alone 150dB.
That question was answered on previous page. It wasn't showing -150db. I left it in the wrong mode. -130db was the correct number.
Scope is QA401.
Scope is QA401.
Ah I see, QA401 isn't a scope, its an analyser box. That's what threw me.
To see below -150dB you'll need either more points in your FFT or alternatively average several FFTs together. Try recording a 45s chunk of your amp's output at 44k1 using Audacity, this will give you over 2million samples, the FFT gain with 2million input points will be of the order of 60dB.
To see below -150dB you'll need either more points in your FFT or alternatively average several FFTs together. Try recording a 45s chunk of your amp's output at 44k1 using Audacity, this will give you over 2million samples, the FFT gain with 2million input points will be of the order of 60dB.
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