On Mon, Dec 9, 2024 at 06:03 PM, wn4isx wrote:

You want someone there who knows how to do CPR and a working telephone.

I don't know if this is still taught, but in vacuum tube days, where lethal voltages were often exposed, they used to say to have a walking-cane nearby.? It must be wood.? And with the curved handle.? The cane is used to pull someone's arm or torso away from a "hot" circuit without becoming part of the circuit yourself.? Wood is a pretty good insulator when not wet.

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And from first-hand experience, the cane also comes in handy for daily exercises if someone is getting shoulder-related PT.? :-)? Or if you have trouble walking and actually need one to safely walk, as we get old.? :-(

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Andy,

It’s this model (excstly) :

Originally they came with just one probe and nothing else. ?Now they include second probe as well as few other accessories. ? Those other accessories doesn’t have insulated plastic cover over the BNC twist cover. ? That seems to be a weak point (having metal exposed for operator’s touch).

The BNC connector on the scope itself is recessed so that if 2 probes are connected, then it’s actually harder to touch the exposed metal connector.

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What do you think about them as test devices for mains voltage ?

Jong?

A few comments on taking measurements on AC Mains.

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With the exception of rated battery operated DVMs or neon testers, don't unless you know exactly what you are doing, what you are measuring, why you are measuring it.

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AC Mains waveforms are boring, do you have a good reason to look at them?

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You want a safe work station with an obvious power off switch that does not take down the room lights.

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You want someone there who knows how to do CPR and a working telephone.

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I've played with direct mains powered devices since I was 8, I'm 73, and I've been knocked silly more times then I can count.

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I am extremely lucky, care to try your luck?

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Over 400 people are electrocuted in the US every year, better them 1 a day, 4000 are injured, more then 10 a day, feel lucky?

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Ground fault interrupters (residual current device in Great Britain) can help but also make you careless. Properly used isolation transformers can also help but again can make you careless.

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Ask yourself, is this project work dying over?

There weren't any harmonics but the audio sounded, and I hate this discriptor, muddy, smeared.

There might have been a very weak comb effect.?

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I fed band width limited white noise, sharp cut off at 20,000kHz, 9dB/octave, ran the amps at 10W and the mid range, ~1000 to ~4000Hz was "depressed."?

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In one of his good amps, the peaks of the white (random) noise form a nearly straight line, in the 'bad' amps, the midrange is down about 6dB.?

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I've seen noise spectra of many amps and never anything like this. I'd have expected the upper frequencies to be messed up.

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And the need for a ferrite bead in the collector lead as well as the base and a 10pF cap between base adn emitter....

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This was a dozzy!

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We modified enough transistors for 5 amps, they all worked fine and then we went out for a nice steak, his treat.

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On Mon, Dec 9, 2024 at 12:58 PM, jong kung wrote:

…. What is the industry opinion on using a portable ?/ floating (DMM style) scopes on mains voltage ?? ? Is it considered just as safe as using HV differential probes ??

On Mon, Dec 9, 2024 at 02:46 PM, wn4isx wrote:

The new transistors are oscillating at about 1GHz, the frequency is frequency modulated by the incoming audio!

I am trying to figure out if this is the start of a new conversation, or if it is meant to be a reply to another one.? Without any context, I assume it is the former.

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(It is quite challenging for me, trying to keep up with so many conversation in every interesting group.)

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With regards to RFI, oscillations, and changing,silicon, we do live in interesting times.? :-(

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Andy

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The new transistors are oscillating at about 1GHz, the frequency is frequency modulated by the incoming audio!

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The cure was a ferrite bead on the base and collector (now that's a first for me) and a 10pF SMD capacitor between base and emitter.

I grabbed my Tiny SA on a wild hunch, found a spike and borrowed a Signal Hound USB spectrum analyzer to confirm the oscillation.

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The semiconductor industry constantly "improves" their products.

Original 1N4004 switch slow enough to be a minimal EMI source, modern 1N4004 switch fast enough to be EMI sources from hell.? The silicon is purer, the junction is thinner and the turn off time is a lot faster.

Someday really soon I hope to post a simple test device to see how much commutation noise a diode produces.

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There are no license free bands or frequencies in the 700~800 spectra.

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At the moment, December 9, 2024, the FCC has allocated 902-928MHz for license free part 15 operations.

There are many restrictions that might be both difficult to understand and comply with. However an industry group wants to steal some of the 900MHz part 15 frequencies.

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The FCC allows 2W operation on some FRS channels as part of the FRS license free system.

This would probably be more practical.

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Hi group,

About an hear ago, I saw a portable (battery operated) 2 channel scope for approx $120-$200 (depending on max bandwidth) and bought one. ? While I never work on mains voltage, I figured it would be nice to have such unit just in case I ever get the urge (to probe a 120v device). ?And sure enough I later decided I want to see the voltage wave form out of my battery backup UPS device.

But …. What is the industry opinion on using a portable ?/ floating (DMM style) scopes on mains voltage ?? ? Is it considered just as safe as using HV differential probes ??

Jong?

P.s. ? about my battery backup UPS - crappy waveform output. ?Luckily all my devices connected to it uses some form of switching power supply, so I’m hoping that’s good enough to undo the evils of “modified” sine wave?

If someone knows that an electronic component can fail or misbehave under unusual but possible conditions, there is nothing off-topic about it.

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Andy

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I apologize, I thought the helium kills MEMS oscillators to be vaguely related to electronics but not related enough to stay "live" and intended to provide enough information for those interested in a relatively obscure failure mode of a device that is growing in popularity to be worthwhile posting.

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In the future I will try to only post stuff I consider valuable and relevant enough to remain live.

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My 'I won't delete' stuff wasn't about my own posts it was about posts with what I consider to be directly in violation of either US law or Groups IO rules.

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A "go here to steal this copyrighted material" falls under both categories. Even if the poster didn't fully appreciate the full legal ramifications of the post.

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I talked with a lawyer about a family legal mater, I own about 50 acres in Eastern Kentucky I want to donate to a trust for that side of my family. The land is worthless, no minerals, farmed to exhaustion by the wrong farming techniques, home to way too many copperheads, but the land has been in our family since a Revolutionary War land grant. I'm 73, have no children and wanted to protect the land after I'm gone. At 73 with total knee replacements in both knees, the chances of me ever hiking there again are remote.

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Our family lawyer is a junior partner in a local firm, she's also a cousin. She brought in a senior lawyer to discus possible conflict of interest because she owns the adjacent ~50 acres and wants to place her land in the same trust.

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The senior lawyer's specialty is intellectual property so I asked about the link to allow direct access to IEEE papers and was told that link was illegal and would be viewed in a copyright suit as furthering a criminal enterprise and the person posting it could well face criminal charges and a civil tort with significant financial losses. Group IO could have received a 'take down order' for this entire group.

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Of course I have no idea what the odds are the IEEE would ever find out, or if they are as draconian as some reports suggest, so I played it safe. an act I regret more then you can possibly understand or accept. If I had it to do over, I'd comment mentally to myself and carry on ignoring the post.

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My "I won't delete" applied to any post by anyone other then myself if I have reason to believe it violates the law or Groups IO rules. I will not delete anyone else's post if it includes detailed directions for obvious criminal acts such as "This is how to run a drug ring." This group is on it's own from me for that perspective.

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In the future I will try to refrain from posting topics that relate to electronics but are not clearly part of this groups mission, or might have a very small group interested in some arcane topic, as I understand it.

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In spite of my "I won't delete" if I realize I post something that violates Group IO policy, criminal law, or places me at risk of a civil tort, I will delete such posts without hesitation.

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However I doubt that will ever happen because I am extremely careful about the links I post.

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Sidebar as they said during a widely publicized trial....

When my department got our first Internet access, Bill Clinton had just given a speech and I was asked to find it. So I typed in Whitehouse.xxx, not knowing anything about domains I had no idea the proper domain would have been ".gov". Instead I brought up a webpage with naked women leaning out of every window in a photo of the Whitehouse. The entire office staff was there, 3 female producers, and 4 female administrative assistants. I froze in shock and disbelief for about 30 seconds before fumbling for the power switch and eventually turning the PC off. I was told later my freckles looked like dots of black ink against my white skin. We were visited by the 'campus porn patrol' later that day and given a stern warning about accessing such sites. The division head made it clear it was an innocent error, that none of us understood the xxx part of a webpage.

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So I accept being careful isn't always enough.

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It is possible, though extremely unlikely, I'll mess up the xxx and place a link to somewhere I don't mean to by accident, or a typo in the header of an address which could lead someplace unwanted.. Or a web page creator could let his lease expire and someone else take over who might post odd stuff. I'll admit if the later happens sometime after I make a post I'll probably never know about it unless someone flames me for the link. If I find out about such an incident, I will delete my post without hesitation.

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Again, please accept my apology and a promise to never ever post "OT will delete in x days" again along with a promise not to play Group IO's watchman and censor.

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If I post something I intend for it to remain online until Groups IO goes away.

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The only other exception to the "I won't delete' I can think of might be if I decided to leave this group, then I reserve the right under US copyright law to protect my material by deleting it. Since I'm not planning on leaving, that is unlikely and frankly I don't see that anything I've written and posted online in any group is worth that much effort.

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Without getting into the weeds or being accused of practicing law, under US Copyright law, the person who writes something other then a set of data owns what they wrote. There is no requirement to file a copyright form and copy of the material with the library of congress or to specifically claim copyright pm the work, the act of creating it makes it protected under US law.? ]paraphrased from the US Copyright office[

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J.D. Salinger, of Catcher in the Rye, stopped publication of letters he wrote based on the fact he owned the copyright of said letters.

[note the law then required filing forms to obtain copyright ownership.]

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Not that anyone would be the least bit interesting in collecting much less publishing the wit and wisdom of wn4isx.

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On Thu, Dec 5, 2024 at 10:08 AM, john23 wrote:

Hello , I have built a PLL system based on the following article.

I have designed the amplifier to have some input voltage current output behavior.

but in the lab I sat that when i plug the the input I get oscilations at the output.
what could cause the situation?

Feedback.

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Coupling.

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Andy

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For those interested in the somewhat esoteric world of High End Audio....I offer some links to speaker simulators

Note: Speakers are not nice stable loads, even a single speaker rated at 8 ohms might be 8 ohms a some frequency, mount it in an enclosure and the impedance will be extremely different depending on the type enclosure.

A closed box will behave on way, a single port another, a transmision line speaker (yes they do exist) will have yet another set of impedances.

And the impedance will be a mix of inductance, coil resistance and any resonances of the cone as modified by the enclosure.

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This is one test load

https://www.stereophile.com/reference/60/index.html

Note the Zobel Netork on page 2, they can be critical in some situations.

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This site covers some of the interaction between speaker cables and real world speakers.

Loudspeaker Cable Characteristic Impedance

https://sound-au.com/cable-z.htm

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Passive crossovers

https://sound-au.com/lr-passive.htm

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Loudspeaker Enclosure Design Guidelines

https://sound-au.com/articles/enclosures.htm

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Phase Angle Vs. Transistor Dissipation

https://sound-au.com/patd.htm

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Driving a 4 or 8 ohm resistive load is easy peasy, driving any real world speaker is fraught with possibilities. Some speakers present loads that cause some very high quality amplifiers to oscillate.

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I worked part time at an electronics shop. The owner sold high end audio equipment to the demented. Great American Sound offered Son of Godzilla. And amp that would drive damn near anything, we used it to make a drill variable speed. [Hey we were bored] However when connected to a pair of KEF studio reference monitor speakers, the GAS amp went insane, destroyed the speakers in about 4 seconds. KEF withdrew that set of speakers and it isn't listed in their history. KEF claimed that speaker had constant phase correction.

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Those KEFs sounded good with my Sansui AU555A, a rather mediocre amp by any definition.

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Effects Of Source Impedance on Loudspeakers

https://sound-au.com/z-effects.htm

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At some point everything in an audio chain has an influence. And it is next to impossible to pinpoint every variable.

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Audio Wattmeter - Measures?True?Power!

https://sound-au.com/project189.htm

Shows some speaker electrical characteristics.

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DIM/TIM (Dynamic or Transient Intermodulation) Some older references call it SIM (Slew rate intermodulation)

From https://www.aes.org/par/i/#IM

"DIM/TIM (dynamic/transient intermodulation distortion)?A procedure designed to test the dynamic or transient behavior, primarily, of audio power amplifiers. The other IM tests use steady-state sine wave tones, which do not necessarily reveal problems caused by transient operation. In particular, audio power amplifiers with high amounts of negative feedback were suspect due to the inherent time delay of negative feedback loops. The speculation was that when a rapidly-changing signal was fed to such an amplifier, a finite time was required for the correction signal to travel back through the feedback loop to the input stage and that the amplifier could be distorting seriously during this time. The most popular test technique consists of a large amplitude 3 kHz square wave (band-limited to ~20 kHz). [Historical Note: This test proved that as long as the amplifier did not slew-limit for any audio signal, then the loop time delay was insignificant compared to the relatively long audio periods. Thus, properly designed negative feedback was proved not a problem. Subsequently, this test has fallen into disuse."

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Note: I can make any audio amplifier display TIM, but not with any music, even the cannon fire in the William Tell Overture has a fairly slow rise time.

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Now a 9mm pistol shot captured with a condenser microphone on a 96K digital recorder and played back into an audio amp might cause TIM. I'm not sure the microphone's rise time would capture the actual event's risetime...and the blast might destroy the microphone.

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This might be worth reading

https://sound-au.com/articles/distortion+fb.htm

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On balance, just buy a decent audio amp and speakers and use your time for more productive projects. Unless of course understanding the subtleties of high performance audio amps is your thing.

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And just when you think you've seen every crazy idea on earth....

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My friend's dummy load has inductors and capacitors with large wattage resistors to simulate a 'regular' spkeaker.

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BTW, the problem is in the driver stage of the AF power amp.

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One steady state and slow swept tones they check out identically (well within expected variance, one amp might have 0.001%THD/IMD and the other 0.099%.

He lacks the ability to do really short, 1ms, white noise pulses.

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I'm wondering about TIM, something I've tended to dismiss (with the exception of Crown DC-300).

TIM (transient IM) would can happen if your negative feedback loop was so slow some signal made it through before the negative feedback arrived at the front end to apply correction. Given the speed with which signals flow, outgoing and return feedback, that shouldn't be an issue with any decent design (which clearly excludes Crown DC-300.)

We'll do the Hafler test, found a very detailed "how to" and the Baxandall (spelling?) compare the output with the input. The two tests should produce similar results.

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This is way out of my comfort zone, feels nice to stretch the brain a bit.

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Somehow I suspect the manufacturer changed the manufacturing process and something very subtle is different.

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As might be suspected, I absolutely hate the DC-300. It sounded gritty with muddy midrange.

We installed 20 in a sports complex. For a PA system, they were adequate, with proper LF input rejection and output DC offset protection.?

I'd loved to have been able to do the Hafler test on the DC-300. Their smaller amp (DC-75 of DC-150) sounded great.

The DC-300 had a slew rate of 8V/uS, slow by today's standards.

I need to pull up the diagram of the DC-300 and study their feedback loop....

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