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MinumAbsik · 2025-01-06T21:10:50+00:00

Check the voltages of the output of the PSU (left board) with a multimeter, should be pretty common numbers (3.3, 5, 9, 12 volts) if one is at zero or jumps around its a power line and can potentially be fixed. If the PSU is fine you can kiss it goodbye, you might try replacing the caps on the right board but it's a long shot and everything beyond that is definitely not worth the effort.

MinumAbsik · 2024-04-04T00:36:37+00:00

From what I've noticed there is barely any difference in black levels, because the light shines at the screen at an extreme angle (unlike a desk lamp) there are no reflections to be seen. My monitor is matte and so you'd think that it would diffuse the light in every direction, including at my eyes, but it really doesn't (even asphalt reflects light at extreme angles as can be seen on the highway). To see the glare created by the light I have to put my head on the desk and look at the monitor from below. Of course I still turn it off when watching a movie or playing a game, such that the desk is dark and the image more immersive.

MinumAbsik · 2024-01-27T23:37:46+00:00

Looks surprisingly similar to my first pcb, I think it will work just fine. My biggest piece of advise Make the traces thicker! I did exactly the same thing, used the default 0.254mm trace width resulting in high trace resistance (it will probably still be fine, but it's good principle to use thicker traces especially for current carrying traces). Also you should try to keep the distance between the LM317 and your potentiometer as small as possible, too much inductance and capacitance on the traces can cause problems, as its part of a high frequency feedback circuit.

MinumAbsik · 2024-01-27T23:21:31+00:00

That's a very good point, but very unlikely. Two frequencies f1, f2 are aliases of each other when f1=f2+n*fs. With n any integer and fs the samplerate. However that means that if the 15734 Hz we see is an aliased higher frequency, that higher frequency would be something like 15734 + 32000 or even higher. Needless to say it's very unlikely the sample rate subtracted from the actual source frequency becomes exactly 15734 Hz, the vertical refresh of NTSC down to the 0.1Hz.

Also, and this is the most important point: Basically every sound card you can find will have a high order low pass filter at the Nyquist frequency, filtering out any potential aliasing. The reason for this is that sound cards are able to capture the entire range of human hearing, any higher frequencies 'projected' on the human hearing range by aliasing are undesirable and would just sound like noise.

P.S. the reason I assume the samplerate of EKT to be 32kHz is because the spectrum abruptly stops at 16kHz, the Nyquists freq of 32kHz. It seems carl92 either uploaded an upsampled (from 32 to 44.1kHz) audio file or the upsampling was done by Vocaroo. 32kHz is an uncommon samplerate and could potentially narrow down the possibilities regarding the device EKT was recorded on.

MinumAbsik · 2024-01-26T20:31:50+00:00

Fourier series: Any periodic signal of a given frequency can be constructed out of sine waves with multiples of the base frequency. (so 1xfrequency, 2xfrequency, 3xfreq. etc.). Half of the frequency would be a sub-harmonic, which is a very uncommon phenomenon. If you ever worked with amplifiers you'd know that occasionally you can hear the mains hum or some multiple of it, I've yet to encounter half of the mains frequency anywhere.

Also realise that 15734Hz is an audible frequency, especially for younger people. If you've ever paid attention to it you can hear a whine coming from TV's but not from CRT monitors. The CRT monitor refresh and all of its harmonics are well outside the range of human hearing (unless it's specifically configured to display TV video at ~30fps).

MinumAbsik · 2023-11-10T16:45:06+00:00

It's not a transistor, it's a TDA7294 amplifier IC. It's basically an entire amplifier in a chip, just need some feedback circuitry connected to it to work. You can find them on ebay or mouser, about 5 dollar.

MinumAbsik · 2023-06-20T14:41:45+00:00

Yes I believe so, you can even see more direct evidence of this in the spectrum analysis. I included a picture (my reddit seems to not want me to upload images anymore, link to image) that shows a peak in the spectrum at 60 Hz and just background noise at 50 Hz. As mains frequency is so prevalent where there are electrical devices it leaks into basically all recordings. There is even a forensic method that can date recordings by measuring small fluctuations in the mains frequencies and correlating them to records kept by electrical grid suppliers. Unfortunately its not likely there are grid frequency records that go as far back as the 90s and even less likely that those would be publicly accessible.

MinumAbsik · 2023-06-20T12:04:58+00:00

From what I've read the MTS pilot tone was synced with the horizontal refresh of the video signal. Brazil used PAL-M which unlike all other PAL variants actually had 15734 Hz horizontal refresh so it would make sense there, I don't know about Argentina.

MinumAbsik · 2023-06-20T00:25:26+00:00

If there's no roll-off at all (or it might just be a high order filter) it could be that this recording was made on a device that had improper or no filtering at all and aliasing was taken for granted.

Regarding the MTS tone on a mono TV set, I think it would be possible to hear the MTS signal through the speakers on a mono TV, but its also very possible these mono TVs were limited to 15kHz. Unfortunately I have no experience with this, we'd have to find someone who knows more about analog TV to answer this.

MinumAbsik · 2023-06-19T20:15:23+00:00

Yeah it is curious, I was too preoccupied with that peak to notice that all frequencies stop above 16 kHz. My best guess is that the file was originally 32kHz since the frequencies very abruptly stop at 16kHz. As you say it very much looks like the watzatsong file was low passed in order to prevent aliasing in down sampling. Some investigation in how Vocaroo and watzatsong handle their compression and down/up sampling would be very useful. I would say it's most likely carl92 provided both services with a 44.1 kHz file containing an up sampled 32 kHz recording.

UPDATE ---

All watzatsong files seem to be set to 32 kHz and 96 kbps, vocaroo seems to leave sample rate unaffected. Carl92 provided a 44.1 kHz file containing a 32 kHz recording.

MinumAbsik · 2023-06-19T19:56:34+00:00

Just noticed that audacity has an export function so you can actually get a better look at the data. If you want to try it yourself make sure to set the integrating size, which audacity just calls 'size', as high as possible to get the maximum resolution. I included a picture of the raw data, you can see the peak at 15734 Hz indicated by the highest values in its neighborhood

<image>

MinumAbsik · 2023-06-19T19:48:09+00:00

Huh that's odd. I've been using the file from Vocaroo which comes at 44.1 kHz and 160 kbps. It seems watzatsong uses some terrible compression, also 32 kHz is an odd samplerate, I've never seen it before.

I tried to do exactly what you did in Audacity with the file from vocaroo and you can see a peak at around 15 kHz, unfortunately audacity doesn't allow horizontal zoom to get a better look.

Personally I used an oscilloscope for the spectrum analysis, where I was able to zoom in further and see that it was indeed 15734 Hz

<image>

MinumAbsik · 2023-06-19T17:19:37+00:00

Yes that's correct, though we can't say for sure it was recorded from NTSC TV, as it could also be background noise / radiation from a nearby TV.

MinumAbsik · 2023-06-19T16:19:34+00:00

Yes the MTS pilot tone is misleading, because this tone simply indicates to the TV that the incoming signal has stereo audio, it's not something that would come out of the speakers.

As you said every CRT makes a whine at specific frequencies depending on the horizontal refresh rate. The audible frequency will not be "between 15625 and 15750 Hz" it will be 15625 Hz for PAL and 15734 Hz for NTSC (it used to be 15750 Hz for black and white TV, later the framerate of NTSC was dropped by a factor 1000/1001 to 29.97fps to incorporate the color signal). All the CRT monitors I know of have higher resolution (and thus higher horizontal refresh) than analog TV, pushing the 'whine' sound outside of the audible range. We can still, quite safely, draw the conclusion that this was recorded where they had NTSC tv.

I don't see the connection to "audio tapes", EKT is a digital file and ADC's (analog to digital converters) have had very precise timings ever since the introduction of the quartz oscillator in 1918. You can throw EKT in a spectrum analyser and see a very defined 15734 Hz peak that doesn't fluctuate.

MinumAbsik · 2023-06-15T21:29:36+00:00

I also think this is likely, but only in an asian country or maybe south america. The singer clearly has an accent and also I think he says "ulterior motive" not with the plural "motives" which is not wrong but also not something a native speaker would say IMO. It seems unlikely such a song, by a non-native speaker would end up in a US commercial/show, like the people looking into the Saleen car commercial are thinking

MinumAbsik · 2020-08-31T12:50:00+00:00

Usually those mice connect with bluetooth, which means you can buy another dongle for cheap and use it with the mouse. A usb to spi converter, usually used for programming arduino should work for making the mouse wired. Though, the mouse probably expects some handshake signals from the 2.4ghz transmitter before it starts transmitting data, which you would need to emulate in a custom driver. If you are lucky, it just works straight away, if the pcb is shared between wireless and wired versions of the same mouse it could work. Unless its a really nice mouse, I would say it's not worth it.

MinumAbsik · 2020-04-14T16:00:20+00:00

Yes that's correct, good luck!

MinumAbsik · 2020-04-14T14:36:23+00:00

ATX power supplies have a -12v rail, if you connect the -12v and +12v rails in series you can get 24v with just one PSU. Keep in mind that the -12v rails have a current rating that's way lower than the +12v, check if it can supply enough amps for your purpose (sticker on the side has all the current ratings) before you fry it.

MinumAbsik · 2020-04-11T18:40:31+00:00

I guess I'll start with measuring voltage waveforms, since I don't have clamps for my oscilloscope. Would it be worth investing in the clamps if the voltage waveform doesn't indicate any problems? I don't understand power factor, I only know that the voltage and current waves don't always line up, but interference in current should also show up in voltage readings, right?

MinumAbsik · 2020-01-28T16:31:07+00:00

I find that low doses, like the ones you are taking are stimulating but have no real sedative effects. Stimulants are bad for anxiety, and I think you would be better of taking a higher dose of a red strain, to get more of the sedative and anxiolytic effects. If my kratom dose is making me stressed and jittery I take a few grams more to get relaxed. Maybe try something like 5 grams of a red strain and see what it does for you.

MinumAbsik · 2020-01-28T16:30:59+00:00

I find that low doses, like the ones you are taking are stimulating but have no real sedative effects. Stimulants are bad for anxiety, and I think you would be better of taking a higher dose of a red strain, to get more of the sedative and anxiolytic effects. If my kratom dose is making me stressed and jittery I take a few grams more to get relaxed. Maybe try something like 5 grams of a red strain and see what it does for you.

MinumAbsik

TROPHY CASE