The sine wave source is RME ADI-2 Pro FS R. I was planning to measure that signal with the oscilloscope. BNC to RCA adapters as well as a normal audio cable works fine for measuring audible frequencies with an oscilloscope.
-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Yes, part of the operational procedure of measuring the amp's -3dB cutoff point is to monitor the output sine of the sine wave generator (RME) on one O-scope channel while simultaneously monitoring the amp's output on another O-scope channel. The RME will not output up to ~200kHz due to the DA process and it's limitation. I say that because good audio amplifiers will sometimes go as high as 100kHz, 150kHz and maybe even 200kHz sometimes at the -3dB cutoff frequency and so the sine wave source needs to have a sine wave output into the 100's of kHz. You may need to purchase a function generator or a sine wave generator. They are not expensive.
What was the purpose of measuring a -3dB cutoff frequency, and can FFT functions on an oscilloscope work well enough?
To determine the frequency response bandwidth of the amplifier.
Not for measuring bandwidth because the sine wave needs to be seen so that if something bad is occurring you have a good visual reference on things. Measuring bandwidth can go south (Amp can oscillate.) if not careful but I've never had a issue because I am careful. Don't touch the DUT while increasing the sine wave frequency into the 50kHz to >100kHz+ and do it carefully but efficiently/somewhat fast so you don't over stress anything. Also the sine wave amp input needs to be seen simultaneously as the amp output because if it decreases as the sine wave generator frequency increases then the operator of the test needs to compensate by increasing the output magnitude of the sine wave generator to ensure the amp input sine wave levels stay the same from start to finish of the test.
What about measuring distortion at 20 kHz with an FFT oscilloscope? If the distortion is low enough, the amp surely has bandwidth. Input and output sine waves can be compared on the oscilloscope.
DonR
Major Contributor
Scopes are too crude to measure distortion below 1%. You would be better off with a THD analyzer like a Keithley 2015.
I don't think distortion FFT measurements and bandwidth measurements are congruent. They are separate things with separate cause and effect when things are not operating to spec. I've seen amps with distortion from over heating voltage amp transistors and the bandwidth was still there.
jsrtheta
Addicted to Fun and Learning
jsrtheta
Addicted to Fun and Learning
It seems every few years the federal government sues GNC for selling supplement products with ingredients which are unlawful to sell, or selling products that do not contain what they say they contain. This has been occurring for decades.
They also sell products from companies that do not contain ingredients that they claim to, or contain much less than they claim. It's a very unpoliced business, for which we in the USA we can thank the former Iowa Senator Tom Harkin.
Input voltage on that one looks too limited for a power amp I believe, but I remember something interesting from the manual of the Technics SU-V7 power amp: "Total harmonic distortion is measured by the digital spectrum analyzer (H.P. 3045 system)".
Specifications from Technics and Yamaha back then look like something that was measured carefully, so I can just look at the sine wave with the expensive oscilloscope I already bought and it should look fine.
DonR
Major Contributor
You would use a voltage divider at the amp output. That is what I had done in the past.
jsrtheta
Addicted to Fun and Learning
There is a difference between what the FTC is empowered to do and what they will actually do. And what they will actually do depends on how scarce their resources are. Like most such agencies, they have plenty of targets but too few resources to go after them. Glancing at the FTC Act, I didn't see a provision for private actions. Some statutes will authorize a government agency to after a bad actor but also allow citizens to sue as well. This act doesn't seem to (though I hasten to add I am not an expert on FTC law and this is not meant to be a legal opinion). Bottom line: Audio enthusiasts are not a large population, and are not suffering the kind of losses that would rouse the FTC to go after, say, cable companies.This thread started with this post, and I'm not sure anybody mentioned the Federal Trade Commission Act. All I had to do was google US misleading marketing practices, not even an American citizen, but I found it that easily. Just like the EU Directive, the Federal Trade Commission of the United States has made this law for suing illegal audiophool companies:
Truth In Advertising
www.ftc.gov
The Consumer Protection from Unfair Trading Regulations 2008 of the United Kingdom may also make that philosophy inconsequential.
Now, if someone's selling space heaters that have a habit of starting house fires, they're could have a lot of problems. But no politician is going to demand prosecution of, say, Synergistic Research.
I think you've hit the nail on the head here.
The resources to protect the interests of 330+ million would have to be very large indeed.
IMHO the Federal Government was never intended to hold the hands of it's citizens from cradle to grave, we've traveled way too far down that road already.
We're way too far in debt already with having to pay for more individual butt wiping.
In the USA, the federal government, acting as the head of the mafioso pharmaceutical and health care business, requires that it be proved that something be effective before it can sold. In most other countries, one only has to prove that the product is not harmful, and it is up to the consumer to decide whether it is effective. Being mostly of libertarian persuasion, I prefer the later. The USA federal government is not protecting consumers, they are protecting the pharmaceutical and medical care industries to maintain their monopoly over health care choices.
For pharmaceuticals (prescription and non-prescription drugs), but not for supplements. They don't have to prove any efficacy at all.
Yes, it’s the false claim that is regulated.
And we have come full circle. Those regulatory laws are specifically aimed at the claims made by the original snake oil salesmen.
Rick “justified under the General Welfare clause of the constitution” Denney
Correct for non-Rx over-the-counter drugs.
The FDA requires proof of efficacy for Rx drugs. The FDA can withhold approval for a drug even if it does have efficacy, if there are already another drug on the market to treat the same conditions and has about the same results. Also, the FDA can unilaterally decide whether a drug is Rx or over-the-counter. Despite what many believe, this is not how it works in some countries outside the USA, where the emphasis is do no harm, rather than require proof of efficacy (which can cost tens of millions of dollars for clinical trials and take years to accomplish).
For non-Rx over-the-counter drugs the FTC (Federal Trade Commission) requires that all advertising claims be truthful, just like any other product. However, they rely heavily on opinions from the FDA as whether a drug has proven efficacy, usually as demonstrated in a randomized placebo-controlled clinical trial. So even if some doctors recommend certain vitamins and supplements to help with certain conditions, the FTC can still ban any claims that the manufacturer or retailer makes about them.
Actually, for Rx drugs, FDA requires (as mandated by law) demonstration of both safety and efficacy. Size of trials and length of time required is related to efficacy/safety; a very effective drug with a good safety profile for a significant disease will require much less time and cost to develop. The rationale is that it is better to require the company that stands to profit from the drug spend the resource to demonstrate that it is safe and effective, rather than having patients (and/or their insurance) spend money on treatments that either do not work or are unsafe. Millions have been spent by vulnerable patients on fake cancer treatments (e.g., krebiozen, laetrile, "immunoaugmentation", shark cartilage..) for which there was not a shred of good evidence to show that they were beneficial.