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sometimes it oscillates
Radio shack used to sell a board that they called a "Stereo Headphone Amplifier", which basically supported a pair of LM386 chips and supporting components. Some years back I found one at a hamfest for some really low price and snagged it. Built the board, put it in a minibox with both RCA and quarter-inch connectors at inputs and outputs, and found a suitable wall wart to power it with (also originally from Radio Shack, as it turns out). There were a few different options for things like gain, rolloff, etc. that you could configure on the board with jumpers, I elected to route these to mini toggle switches.
Sometimes when I power this thing up it'll break out into oscillation. Turning the volume control all the way down will usually put a stop to that, but I'd like to find out what's going on and put a stop to it. *ALL* of the connectors are grounded to the box. Is it likely that this has something to do with it? Something I was reading not too long ago had input connectors isolated from the physical enclosure, due to "ground loops" or something like that. Could this be the cause? -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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testing stability by feedback responce technique question
Hello , I tried to check the stability of the circuit by opening the feedback loop and placing the pertubation as shown below.
How ever I made two plots Vf anole and Vf,Vin in AC responce and I get quite different result.
What is the proper way to test feedback responce? Thanks. /g/electronics101/files/john233/classA_driver_new.asc /g/electronics101/photo/296358/3872575?p=Created%2C%2C%2C20%2C2%2C0%2C0 ? |
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Re: 1KHz AF oscillator with 0.00002% distortion.
I started to build a board that would give me a bunch of frequencies ilkeI used an FPGA. Discovered could only do decade division, otherwise odd harmonics would be created. Never really had time to investigate. I pulled mine when on the roadside. I guess instilling the seed of doubt prior to citation being written is/was more effective than fighting with a prepared and waiting prosecutor in courtroom. Last speed incident involved me going too slow. Was tail end Charlie on a poker run, caught a light and separated from the M.C. Sheriff deputies claim to impeding flow of traffic was thrown out. I do try to drive slower now. Partly due to age, partly due to cost of fuel. Mostly due to the current crop of "Ragers" running around now. Literally appear out of nowhere unexpectedly. ~SD |
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Re: 1KHz AF oscillator with 0.00002% distortion.
On Friday 03 January 2025 07:58:04 am SheldonD via groups.io wrote:
My first, and last, audio reference involved calibration whilst beating against WWV.I started to build a board that would give me a bunch of frequencies ilke that, nowhere near as fancy iu the oscillator part, but I never did get enough 7490 chips to finish it. It's probably still around here someplace. And if I am in a rush, I will just grab my 1khz tuning fork. Pulling that out after getting stopped and questioning calibration has gotten me out of ALOT of speeding tickets.Heh. The last time I tried to fight one of those the officer showed up with a record of calibration, there wasn't any way to fight that. And it ended up costing me more... Most, if not all, were rightfully deserved.The last one I got was several years ago, and I just paid it. These days I tend to take it a lot easier, my vision not being as good as it used to be. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Re: 1KHz AF oscillator with 0.00002% distortion.
On Thursday 02 January 2025 04:40:06 pm wn4isx via groups.io wrote:
Their amplifiers have impressive specs, too bad 40 years of riding a motorcycle and being 73 make HiFi someone ridiculas.Yeah. I have a stereo, along with an octave-band equalizer, in the other room that I haven't hooked up yet, since I moved over here. Which is something like 4-1/2 years ago? I used to have stuff on all the time, not so much any more. I notice that he talks about some huge capacitor on the output of those amps, which suggests a single-ended power supply. I'd rather go with split supplies and no capacitor. But I'll probably end up DIYing something around some of the LM380 chips I have handy here, if I decide that I need another amp. Maybe use 'em in pairs, so I can have a bridged mode. As to needing a 1kHz AF oscillator with 0.0002% distortion.....who said I needed it? Like I said, I'm a sucker for test gear. He who dies with the most wins....not sure what we might win but I'm sure it will be impressive. [That was an attempt at humor.]One would hope. I just completed a PITA "must do" project. We have 20 feet of water pipe above ground. We meant to use a Ditch Witch to bury it but, well knee surgery in June and August meant "That ain't happening." So I added self regulating heat tape with fiberglass insulation then a vapor barrier.My brother used one of those when he put his pool in. I have no idea what's involved in operating one. It was 3 hours of unfun laying on my back installing the heat tape and insulation,the vapor barrier was the hardest part.I've lived with places that needed that stuff before. I'm not entirely convinced of the reliability of it. I added a remote reading AC mains current/power meter. It will be interesting to see how the current varies as the temperature drops to Antarctic levels over the next week.That strikes me as a good thing to have on that setup. Cold weather has already affected my weather station, nothing but dashes on the display in here, it's not getting any signal from the outside part, so it's only displaying the temp and humidity in here, and the data and time. I didn't think that it had been that long ago that we put batteries in that outside unit, and the small solar panel is supposed to take care of most of that end's requirements. Not fun, taking that thing down and getting it in here. There is a chance we might get ice, which could take down the AC mains. Now that'd be a real PITA.I had a non-urgent appointment scheduled for Monday, and I've already rescheduled it. We're supposed to get some kind of crap and there's no way that I'll be driving over the mountain with that going on. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Re: 1KHz AF oscillator with 0.00002% distortion.
My first, and last, audio reference involved calibration whilst beating against WWV.
That got real old, real fast, and started making recordings of decades and octaves from the tuner in band hall. Took 45 minutes to warm up, but never more than a fraction of a cent off. That got old too, so ended up buying audio test CD. Pretty sure was from W5YI. Rock stable signal out of headphone jack of any *1x* cdplayer in a computer. Now ? Last time I needed 1K I took an oven heated / gps derived & corrected 10Mhz reference and divided until I got what I wanted. /10, /10, /10, /10. And if I am in a rush, I will just grab my 1khz tuning fork. Pulling that out after getting stopped and questioning calibration has gotten me out of ALOT of speeding tickets. Most, if not all, were rightfully deserved. ~SD |
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Re: 1KHz AF oscillator with 0.00002% distortion.
wn4isx
Their amplifiers have impressive specs, too bad 40 years of riding a motorcycle and being 73 make HiFi someone ridiculas.
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As to needing a 1kHz AF oscillator with 0.0002% distortion.....who said I needed it? Like I said, I'm a sucker for test gear. He who dies with the most wins....not sure what we might win but I'm sure it will be impressive. [That was an attempt at humor.]
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I just completed a PITA "must do" project. We have 20 feet of water pipe above ground. We meant to use a Ditch Witch to bury it but, well knee surgery in June and August meant "That ain't happening." So I added self regulating heat tape with fiberglass insulation then a vapor barrier.
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It was 3 hours of unfun laying on my back installing the heat tape and insulation,the vapor barrier was the hardest part.
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I added a remote reading AC mains current/power meter. It will be interesting to see how the current varies as the temperature drops to Antarctic levels over the next week.
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There is a chance we might get ice, which could take down the AC mains. Now that'd be a real PITA.
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Re: 1KHz AF oscillator with 0.00002% distortion.
On Thursday 02 January 2025 07:30:51 am wn4isx via groups.io wrote:
I'm a sucker for test equipment, more so for good equipment at rock bottom prices.Some interesting stuff on that web site. It's pretty cool that they're into selling kits, as the outfits that used to ain't doing that any more. This oscillator has a claimed distortion of 2 parts per million (0.0002%).I don't see where I would need something like that. I only have access to test equipment that can measure down to 0.001% and this oscillator's distortion was lost in the noise floor of the test equipment.For strictly analog, that ain't too bad. At $89 this represents an amazing value. Yes you can download their assembly manual and "roll your own" but I doubt you can achieve the performance of this unit.I looked that over, and some of the other ones. Part of their magic is their PCB layout and hand selecting the frequency determining devices. It isn't worth my time and energy to try and copy their PCB and locate accurate parts.What are you going to do with it? Me, I'll probably end up rolling my own of various amps and things. I do have an HP audio generator sitting back there that I picked up at a hamfest that needs a little TLC. One of these days... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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1KHz AF oscillator with 0.00002% distortion.
wn4isx
I'm a sucker for test equipment, more so for good equipment at rock bottom prices. ? A friend dropped an inexpensive audio oscillator by for me to check out. https://www.akitika.com/1kHzOscillator.html#:~:text=Distortion%20is%20very%20low%2C%20typically,only%202nd%20harmonic%20is%20visible.) This oscillator has a claimed distortion of 2 parts per million (0.0002%). ? I only have access to test equipment that can measure down to 0.001% and this oscillator's distortion was lost in the noise floor of the test equipment. ? The frequency was slightly off, well within specs but 1002.31Hz. ? At $89 this represents an amazing value. Yes you can download their assembly manual and "roll your own" but I doubt you can achieve the performance of this unit. ? Part of their magic is their PCB layout and hand selecting the frequency determining devices. It isn't worth my time and energy to try and copy their PCB and locate accurate parts.? ? I'm well know as a cheapskate and I ordered one. ? |
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PC oscilloscope
wn4isx
If you are only interested in looking at audio on an oscilloscope, one decent method is to use a "high quality" USB audio interface. The Behringer UMC202HD is a decent unit that can be found at several music stores for around $100. Behringer enjoys a mixed reputation, apparently if you get a good unit they will work fine "forever." ? My three have been in nearly daily services for 4 years now. They are used as the analog to digital converter as a test instrument and to feed AF into a PC for audio analysis/decoding on a shortwave radio and one is used as an actual musical instrument input device. ? This circuit is used for the oscilloscope input conditioning. PC Oscilloscope Interface https://sound-au.com/project154.htm And these circuits are used for radio to PC, PC to radio PC To PA System Interface https://sound-au.com/project133.htm ? I used parts I had on hand so my circuits are slightly different. ? We use similar circuits to feed PC to/from our church's PA system and I carry a pair with my laptop just in case I find myself pressed into service as PA source or recorder. ? The PC to PA system interface will also function as a basic PC oscilloscope interface. ? For those who wish to study audio distortion, Mr. Elliot has some interesting, and downright weird, techniques. Intermodulation - Something 'New' To Ponder https://sound-au.com/articles/intermodulation.htm#s4 ? And ? Distortion Measurement System https://sound-au.com/project232.htm ? One can get by with a less then stellar USB AF device. Some well respected AF amplifiers show some surprising weaknesses when tested this way. ? |
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Re: scope?
On Monday 30 December 2024 02:53:49 pm wn4isx via groups.io wrote:
The document atThat's what I was talking about. That document is the two peices of paper that came with the unit... I've save a copy of that, as I can read some of it a bit better than the actual print-on-paper and blow it up further if I need to. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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compensating external error factor using main feedback mechanism in FLL
Hello, I have built a system shown below by the attached article.Its a frequency locked loop.
basicky I am using a YIG as VCO to tune it exactly to the cavity resonator. The phase and amplitude of the resonance shown below. The mixer acts as a frequency discriminator by the behavior in photo 3. So if we input a tone at some frequency and look what IF (error voltage) we get at point B as shown in photo 4 and 5 . The main problem I have is the YIG VCO. The YIG has two coils which we tune. A large coil call "tune" and a small coil called FM. The large "tune" coil is being fed near the resonance area,while the smaller FM coil is the coil I use to tune the error of the mixer IF (frequency discriminator) which compares the signal coming from the cavity resonator and the signal coming from the YIG. The second coil is FM coil: 1.5uH inductance and 1Ohm resistance FM coil. sensitivity 400Khz/mA The main problem is that I am tuning the error using the FM coil while the tune coil (which is biased by constant voltage) is not in the feedback fixing mechanism I only have the FM coil to compensate for the gap between the YIG and cavity signals. I was told to use a PI controller(between the IF output and YIG input )to compensate fro the tune drifting. Is there some strategy on how what parameters the PI controller should have to compensate for the exteral frequency drifting caused by the tune coil? Thanks. /g/electronics101/files/john233/High_spectral_purity_microwave_oscillator_design_using_conventional_air-dielectric_cavity%20%284%29.pdf
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Re: scope?
On 30 Dec 2024 at 10:36, John Kohlbach via groups.io wrote:
Hmmmm... I am intrigued. Their stuff is of reasonable cost, and appears to work adequately. I am sorely tempted.... Thank you for the info, John. Ken W7EKB www.w7ekb.com -- This email has been checked for viruses by Avast antivirus software. www.avast.com |
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Re: scope?
On Monday 30 December 2024 01:23:05 pm wn4isx via groups.io wrote:
Sight unseen, could the BNC be a reverse BNC?Nope. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Re: scope?
On Monday 30 December 2024 01:36:25 pm John Kohlbach via groups.io wrote:
Hi Roy, could this be the beastie?Without even looking at the link, I'd say probably. A bit of poking around tells me that this thing is commonly referred to as a DSO-138. The two numbers I ran across are apparently two versions of the kit, one with just the main chip soldered, the other one with all of the surface mount parts soldered The unit I have is completely assembled. Apparently it's good to about 200KHz bandwidth, so I guess it's okay for audio work and some arduino stuff. But that's okay, I have a nice Tek scope on my bench for when it's needed (and I don't remember the last time I turned it on). There appear to be a lot of people selling these. And one company has a newer version out that's supposed to be better. Finding a case has been another thing entirely, it looks like I'll be getting one from china by way of ebay for not very much money. So it looks like I have a new toy here. Dunno when I'll do much of anything with it, though. I haven't yet fired it up. I guess we'll see... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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Re: scope?
wn4isx
Sight unseen, could the BNC be a reverse BNC?
One where the nominal female has a male stinger?
I've ran into them in the oddest places. The FCC requires reverse BNCs, TNCs, and SMAs on WiFi transceiver and some part 15 900MHz equipment.
They are also used on equipment where a manufacturer wants to lock you into using their connectors.
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Re: scope?
Photo?
Ken W7EKB On 30 Dec 2024 at 11:39, Roy J. Tellason, Sr. via groups.io wrote: I was given this little thing a while back, haven't done anything -- This email has been checked for viruses by Avast antivirus software. www.avast.com |
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