The Beast

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Re: The Beast

Postby Harry Dalek » Thu Jul 22, 2021 3:06 pm

Steve Anderson wrote:The 'Audio Soundcard' above looks OK, but without downloading the datasheets (yet) I can't find any reference to sample rates or other specifications...unless that's in the soundtrack with the video (I haven't played it yet).

It's also just the output side, i.e. playback only, no record function, unless I've missed that as well...entirely possible!! Of course the hardest part is the record function...

Steve A.

In your added text 192kHz sampling is mentioned which in theory can record up to 98kHz, assuming it can record. Again that depends on the input anti-aliasing filter (if there is one)....and again you end up with bloated file sizes.

Having had a quick look at the first datasheet for the PCM270xC on the very first page it says, "Sampling Rates: 32 kHz, 44.1 kHz, and 48 kHz" No mention of 96 or 192kHz anywhere that I can see...

Now this is becoming confusing...why then is there a second D-A that can go at 192kHz? (the PCM1794A). Maybe I'll come back to this once the coffee kicks in...

OK, the caffeine has done its job...but I'm still confused! No problem, the fact is the PCM1794A can go at 192kHz and the device is playback only. Now where did this all start?...

FYI The PCM1794A is around US$16++ each at Digikey. Not only can it handle 192kHz but is 24-bit.


IS play back only a problem ? i suppose if you had a camera and wanted to record a higher bandwidth is some thing i didn't think about ,i was more thinking outputting to a monitor ....but good point

If its worth it if this is a project or not as it could be just a matter of buying a fully built thing or module or come down to as you say a chip if there's a lot of saving here ....worth the time for the improvement ? i am curious !

Before the other day i knew nothing about all this apart from i knew you could have an external sound device .
If any thing this one you mentioned must improve of a standard sound card ,i do want to do that test on what the sound cards can and can't do nearly finished on the monitor move onto this .
i was was look at the data sheet sample up to 200khz maximum ,seen other USB DAC's saying they can sample over 300khz if true must be more pricy

I see there is some sort filter in this device ,if this is a good bad thing !

Any case i just have a look around what's built with this chip so far .Just reading your new post Steve
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Re: The Beast

Postby Harry Dalek » Thu Jul 22, 2021 3:21 pm

Steve Anderson wrote:Going back a few steps, I mentioned an 'up to' 100kHz oscillator so you can confirm or otherwise a sound card indeed has that input filter required.

Ideally as you sweep up the input frequency toward half the sample frequency the playback output should drop very rapidly - really very rapidly!

At a sample frequency of 48kHz as the input frequency gets near 24kHz the output should vanish. If you go beyond 24kHz there should be zero, absolutely nothing. With a poor or non-existent filter with an input frequency of 25kHz - you'll get 1kHz out! At who knows what level - hardly useful! With 26kHz input - 2kHz out, and so on...

So using a sampling rate of 192kHz the response should be up to (in theory again) 96kHz, hence the mention of a 100kHz oscillator...

Steve A.


Arrrr i see This would show what your sound card really can do that's a good test really show what it can't keen to give it a go .
I can use the mic input for an oscillator i can feed in or a first quicker test software produce sweep a oscillator not sure they go passed 20khz perhaps 40khz for those with better sound cards as we are chatting about .
Should the waveform be sinewave or does not matter can be square wave ?
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Re: The Beast

Postby Steve Anderson » Thu Jul 22, 2021 4:05 pm

Harry Dalek wrote:...Should the waveform be sinewave or does not matter can be square wave ?

Sine wave, a square wave contains bucket-loads of harmonics which will alias and lead to a totally confusing mess, in fact any waveform that is not sine...a sine wave should contain one frequency and one frequency only, any other - any other without exception, contains harmonics...sometimes sub-harmonics...

Steve A.

A square wave has a distribution much like the 1kHz version below...loads of harmonics...in this case all odd harmonics, 3rd, 5th, 7th and so on...
Spectrum_square_oscillation.jpg
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Re: The Beast

Postby Steve Anderson » Thu Jul 22, 2021 4:53 pm

The most useful instruments (not tools) in an electronic workshop are 1) A multimeter, 2) An oscilloscope, then 3) an oscillator that produces audio and logic level frequencies over a reasonable range, then you get into stuff that is very useful, 4) Bench power supplies, 5) A decent scientific calculator, though that could be viewed as a tool...after that it tends to depend on your specialisation or interest...somewhere way down the list is the humble PC...as a generalisation my PC is mostly use for communication, e.g. here...Oh! And drawings...though that's communication, just in a different form...

If you haven't got a sine-wave oscillator in your arsenal - get one or build one...you can also create sine-wave tones in Audacity, they're not perfect, but a start, and better than nothing, and actually not that bad...save them as a sequence of sine audio frequencies (tones). However, beware, they're fine in the mid-audio range, but at the extremes of frequencies there's no guarantees...that (yet again) depends on your 'sound card'.

Steve A.
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Re: The Beast

Postby Klaas Robers » Thu Jul 22, 2021 6:32 pm

Steve, all you write is true for audio. But Harry wants to use it for video. Then the problems are different. The high notes then are only in transients, not in pure high notes. However if a televised person wears a shirt with a fine pattern, you might see a moiré pattern when played back. I see these things rather frequently in the digital TV programs. Already from the past I know that actors are advised not to wear that type of shirts. That is the best anti-aliassing filter.
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Re: The Beast

Postby Steve Anderson » Thu Jul 22, 2021 7:14 pm

Klaas, entirely correct, cross-colour was often a problem with subcarrier based colour TV systems. However, let's bring this back to fundamentals.

What are we trying to do here? As I see it...record and playback an NBTV waveform with minimal degradation. Now given a nominal baseband NBTV bandwidth of 10kHz, sampling at 20kHz or more is sufficient. Now that's a push-over for any respectable 'sound-card'. Signal-to-noise, distortion, also forget it, no issue. If you desire to stray into the higher line-rates or bandwidths, well, that's a whole new subject!

Our issue, rather conversely, is the LF performance...as you have mentioned on the NBTVA website, a response down to 2Hz or so being a goal to aim for. Agreed. Lower even better. So let's get out of all this theory and build something that actually performs!

I did start a thread which addressed this very issue, DC-to-around 15kHz as I recall, but that has stalled, for no particular reason other than it seemed not many were interested...correct me if I'm wrong, and I'll get on with it...

Steve A.

I may as well go ahead, I've got nothing on my plate at the moment and submit it to Jeremy...in other words, I need a challenge! Though this is quite a simple one...
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Re: The Beast

Postby Harry Dalek » Thu Jul 22, 2021 8:56 pm

Hi Steve and Klaas
Klaas yes for sure you are right in what i want from the idea ,also i think there is a name to the strobing effect on those patterns people wear causing the problem ,i think you were saying its still happening on todays Television which is surprising .

If you haven't got a sine-wave oscillator in your arsenal - get one or build one...you can also create sine-wave tones in Audacity, they're not perfect, but a start, and better than nothing, and actually not that bad...save them as a sequence of sine audio frequencies (tones). However, beware, they're fine in the mid-audio range, but at the extremes of frequencies there's no guarantees...that (yet again) depends on your 'sound card'.


I do have software signal generators but top range depends on what you mentioned ,they do sinewaves top range i would not think over 20khz but have to look again .

Hardware I have a 2 small ones one i know can do sinewave waveform it's a DDS signal generator kit i made a few years back i decased it a while back and have to replace two pots ,cross my fingers it still works been stored away for a year or 2 .
My little kit below

The attachment DDSsignalgeneratorF7LTANBIXLA7NZX.pdf is no longer available




What are we trying to do here? As I see it...record and playback an NBTV waveform with minimal degradation. Now given a nominal baseband NBTV bandwidth of 10kHz, sampling at 20kHz or more is sufficient. Now that's a push-over for any respectable 'sound-card'. Signal-to-noise, distortion, also forget it, no issue. If you desire to stray into the higher line-rates or bandwidths, well, that's a whole new subject!


At first i didn't think of the recording side at all but that would be logical for camera build recordings over Standard NBTV which there isn't really a way at the moment fully electronic ,i was thinking wouldn't it be good using the PC to do what it does for standard NBTV and play back higher bandwidth video .
Even a little more The USBDAC seems it might help can't be any worse than a standard sound card sound device i would think a touch better how much is the Question seems be be from your calculation's, i see your point on what the filter if there would do to video ?

Our issue, rather conversely, is the LF performance...as you have mentioned on the NBTVA website, a response down to 2Hz or so being a goal to aim for. Agreed. Lower even better. So let's get out of all this theory and build something that actually performs!


Yes looking at the high end here but i understand low end is important to .

I did start a thread which addressed this very issue, DC-to-around 15kHz as I recall, but that has stalled, for no particular reason other than it seemed not many were interested...correct me if I'm wrong, and I'll get on with it...

Steve A.

I may as well go ahead, I've got nothing on my plate at the moment and submit it to Jeremy...in other words, I need a challenge! Though this is quite a simple one...


8) Hard to do exciting subject on bandwidth need Albert for a exciting posting title ! Full bandwidth NBTV Hell only Albert is good at it ! ! if you have a need or people see there's something they can get they didn't before it will get their interest , We all would like to improve on the last go at a project ,i would say Show as in a image what the result would be with the idea and that will get every ones interest as they say a picture speaks a thousand words...so working on the low end and here working over the high end of NBTV standard ,got my interest.
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Re: The Beast

Postby Steve Anderson » Fri Jul 23, 2021 12:41 pm

That little DDS generator is fine for what we need in NBTV, up to 65kHz+ and with an 8-bit resistive D-A a low enough sine distortion of around 0.4%. Not good enough for measuring distortion in hi-fi amps, but good enough for here. Being crystal controlled the frequencies should be more than close enough.

Box it up, add a power supply (as shown) and you've got yourself a very useful piece of gear!

Steve A.

You could add a 74HCxx type of buffer and have a proper 5V TTL logic output also...from pin 33 of the micro...a 74HC00 would be fine in most applications...
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Re: The Beast

Postby Harry Dalek » Fri Jul 23, 2021 3:26 pm

Steve Anderson wrote:That little DDS generator is fine for what we need in NBTV, up to 65kHz+ and with an 8-bit resistive D-A a low enough sine distortion of around 0.4%. Not good enough for measuring distortion in hi-fi amps, but good enough for here. Being crystal controlled the frequencies should be more than close enough.


As i recall wasn't to bad ,i wanted to get going today but ended up having to work lock down ended for my job ,but look into getting it going tomorrow . i have to solder 2 pots back in place .

Box it up, add a power supply (as shown) and you've got yourself a very useful piece of gear!

Steve A.

You could add a 74HCxx type of buffer and have a proper 5V TTL logic output also...from pin 33 of the micro...a 74HC00 would be fine in most applications...
[/quote]

Well i sort of did case it up with power supply but i picked a case that was too large which made it not so portable ,i took it out to recase it ,i think they sell a case for these things so look into that i should of got it first go but wasn't sure it would work i got 2 frequency meter kits from some one else same model's both seem to be duds so i was a bit ify paying for a case if it didn't work in the first place but this one worked fine .I will look into the buffer idea ,that did not cross my mind ! know what you are doing you see the possibilities may be one day i will too :wink:
a better look at the DSS
https://www.electronics-lab.com/project ... generator/
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: The Beast

Postby Steve Anderson » Fri Jul 23, 2021 10:22 pm

Eek! I wouldn't use such an immense PSU for such a small unit (A PC ATX PSU). It's also switched-mode, dirty, (electrically), noisy (a fan) and some without a minimum amount of load produce excessive output voltages. Use something like that is suggested, a simple 78xx/79xx type-arrangement. Where do these people come from? Notice there's no photos of the power supply as it would dwarf the little oscillator unit!

Why use a 300W PSU when this device probably uses less than 0.3W?

Aside from that it looks quite a nice little and useful unit!

Steve A.

Apart from this item, I advise you to steer clear of that site...and this oscillator isn't even mentioned...at least I didn't find it...Jeez, there's some crap out there! I'm always wary when the words, 'cheap', 'simple', 'easy' crop up in a title...as that's exactly the sort of results you'll probably get...

Need a white-noise generator for doing noise figure measurements? I just happened to find this one kicking around the workshop, cheap, simple and real easy! Here it is, generating noise even as the photo was taken! Though if cooled to −273.15 °C it would practically cease that behavior...
Noise Generator 1.jpg
Noise Generator 1.jpg (73.29 KiB) Viewed 623 times


I should perhaps stop being so cynical...

Excuse the grimy work-top, they get like that after a while!! At least it shows its being used! I'm always suspicious of those with clean and tidy workshops...
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Re: The Beast

Postby Harry Dalek » Sat Jul 24, 2021 6:15 pm

Steve Anderson wrote:Eek! I wouldn't use such an immense PSU for such a small unit (A PC ATX PSU). It's also switched-mode, dirty, (electrically), noisy (a fan) and some without a minimum amount of load produce excessive output voltages. Use something like that is suggested, a simple 78xx/79xx type-arrangement. Where do these people come from? Notice there's no photos of the power supply as it would dwarf the little oscillator unit!

Why use a 300W PSU when this device probably uses less than 0.3W?

Aside from that it looks quite a nice little and useful unit!


Me either i like small as possible i had mine in a big case transformer power supply supplying it but even that was too big . i would like to run it off a battery but dual supply ..

I got mine going today testing it below top of the range the wave form is touch less sinewave looking on the higher KHZ range and a few hz off what i can seeing on the scope frequency meter .

DSCN6422.JPG

DSCN6423.JPG


Apart from this item, I advise you to steer clear of that site...and this oscillator isn't even mentioned...at least I didn't find it...Jeez, there's some crap out there! I'm always wary when the words, 'cheap', 'simple', 'easy' crop up in a title...as that's exactly the sort of results you'll probably get...


No no i was just looking for some thing extra schematic and on it as i have misplaced the instructions

Need a white-noise generator for doing noise figure measurements? I just happened to find this one kicking around the workshop, cheap, simple and real easy! Here it is, generating noise even as the photo was taken! Though if cooled to −273.15 °C it would practically cease that behavior...
The attachment DSCN6422.JPG is no longer available


I should perhaps stop being so cynical...


I can't say i have ever needed one ! didn't even think much about this setting ,i got the waveform generator many as i was thinking this might come in handy one day perhaps this is the day :idea:

Excuse the grimy work-top, they get like that after a while!! At least it shows its being used! I'm always suspicious of those with clean and tidy workshops...


Mine was a mess today looking into this Signal generator i just had to do a clean up ..it sure helps when you have a little room to move i bet it would not matter how much table room you have it will end up the same way !

ON the circuits power supply and testing the device today i found it would glitch on turn signal off and back on, you have to turn the power supply off and back on again ,i looking to the this dual 12 volt and 5 volt supply it was asking for on the circuit board ,i test it on just dual 5 volts and so 12 and 5 volts same now and negative 12 volts swapped to negative 5 volts and problem went away and seems to work better ....Arrrr these kits !

Looking into the case it seems they only sell the newer models which doesn't fit mine so plan 3 coming up ,i was almost going to work some thing out today but thought it was best to test the thing first see if it still worked ,the power supply could be simpler now .
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Re: The Beast

Postby Steve Anderson » Sat Jul 24, 2021 8:11 pm

The change from a sine-wave to triangle at higher frequencies is probably down to the LM358 having a quite limited frequency response (related to slew-rate). If it's in an IC socket swap it out for a TL082, same pin-out, no other changes required. Plus I hope you're using a proper scope probe in x10 mode, that can easily fool you and the scope...especially if using a croc-clip on a piece of string instead...

The circuit shows no 100n supply bypass capacitors (again), add them (disc ceramic) whether you change the op-amp or not. One across +5V to ground near the micro, and one each from +12V and -12V to ground near the LM358/TL082. Seriously, do it! You may be surprised at the difference.

As for the frequency display, I think I would trust the scope rather than the in-built kit version. Who knows what reject pile they get the crystal from for the kit, the crystal in the scope should be somewhat better. Even the supply bypass above caps could well help here...it may be worth getting a new crystal, it looks like 16MHz on the circuit, but the can will (should) have the frequency on it...they're quite cheap...

Other than those suggestions it's down to how good(?) the code is in the micro, whatever, there's not much you can do about that...

Steve A.

Needless to say, it appears they've put this together in possibly the cheapest way that is possible...and it tends to show....they obviously have no pride in what they produce...again, those words, simple, easy, cheap...

Note: The power supply suggested will require C1 (2200uF) being at least 45V rating - they don't mention that of course...
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Re: The Beast

Postby Harry Dalek » Sat Jul 24, 2021 11:04 pm

Steve Anderson wrote:The change from a sine-wave to triangle at higher frequencies is probably down to the LM358 having a quite limited frequency response (related to slew-rate). If it's in an IC socket swap it out for a TL082, same pin-out, no other changes required. Plus I hope you're using a proper scope probe in x10 mode, that can easily fool you and the scope...especially if using a croc-clip on a piece of string instead...

Oh i didn't check the x10 on the probe i'll check now Oh no it was on x1 arrrrrr ! thanks for the advice on the opamp i will swap that over tomorrow and test again .

The circuit shows no 100n supply bypass capacitors (again), add them (disc ceramic) whether you change the op-amp or not. One across +5V to ground near the micro, and one each from +12V and -12V to ground near the LM358/TL082. Seriously, do it! You may be surprised at the difference.


Yes no decoupling camps, i will add ,i believe you always has helped ,i suppose they just try and get away with minimum parts in these kits .

As for the frequency display, I think I would trust the scope rather than the in-built kit version. Who knows what reject pile they get the crystal from for the kit, the crystal in the scope should be somewhat better. Even the supply bypass above caps could well help here...it may be worth getting a new crystal, it looks like 16MHz on the circuit, but the can will (should) have the frequency on it...they're quite cheap.
..

i will have a look at that as well ,yes i was thinking that too scope frequency meter over the programmed frequency meter on the kit ,its close few Hertz off not too bad for a cheap kit .

Other than those suggestions it's down to how good(?) the code is in the micro, whatever, there's not much you can do about that...


Thats ok is what it is seems to be good enough here ,i would be happy if i can clean up the sine wave with your suggestion's

Needless to say, it appears they've put this together in possibly the cheapest way that is possible...and it tends to show....they obviously have no pride in what they produce...again, those words, simple, easy, cheap...


Sell a lot quick i suppose ,well got one out of me !,since i am not really good at building this sort of thing from scratch i have to either go this way or buy it built.

Note: The power supply suggested will require C1 (2200uF) being at least 45V rating - they don't mention that of course...

[/quote]
OK look into that as well , least i have a lot of suggestions to improve on it thanks Steve i will work on it tomorrow morning .
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Re: The Beast

Postby Steve Anderson » Sun Jul 25, 2021 1:35 pm

Harry Dalek wrote:Oh i didn't check the x10 on the probe i'll check now Oh no it was on x1 arrrrrr ! thanks for the advice on the opamp i will swap that over tomorrow and test again.

Always, always use a scope probe on x10 unless you really, really need that extra input sensitivity, very rare. On x10 it puts a 9M (9 Meg-Ohm) resistor between the probe tip and the input capacitance of the scope and more so the capacitance of the probe cable. Make sure you've compensated for the probe capacitance...it should be in the instruction manual...if you don't you'll end up with very odd and inaccurate waveforms at higher frequencies. Measurements then become useless...really useless.

Look for "Probe Compensation" in the manual. Google "Oscilloscope Probe Compensation" for an explanation as to why...here's one...

https://www.tiepie.com/en/fut/probe

Steve A.

This applies to anything that uses an attenuating probe, spectrum analysers, wide-bandwidth meters and others...

Often when using x1, and you scope the output of an op-amp, it shows oscillation. Op-amps don't like capacitance of a few hundred pF (in x1 mode) or more on their output, they go unstable. In x10 the input capacitance is reduced to 10-15pF, oscillation (usually) stops.

If trying to scope very small signals (unusual in NBTV) build or buy an external pre-amplifier.

When the time comes to replace the probes (you WILL have replace them well before replacing the scope) buy non-switchable ones that are always in x10 mode. No errors and far more reliable as there's no switch that's always the thing that fails...
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Re: The Beast

Postby Harry Dalek » Sun Jul 25, 2021 3:27 pm

Steve Anderson wrote:
Harry Dalek wrote:Oh i didn't check the x10 on the probe i'll check now Oh no it was on x1 arrrrrr ! thanks for the advice on the opamp i will swap that over tomorrow and test again.

Always, always use a scope probe on x10 unless you really, really need that extra input sensitivity, very rare. On x10 it puts a 9M (9 Meg-Ohm) resistor between the probe tip and the input capacitance of the scope and more so the capacitance of the probe cable. Make sure you've compensated for the probe capacitance...it should be in the instruction manual...if you don't you'll end up with very odd and inaccurate waveforms at higher frequencies. Measurements then become useless...really useless.

Look for "Probe Compensation" in the manual. Google "Oscilloscope Probe Compensation" for an explanation as to why...here's one...

https://www.tiepie.com/en/fut/probe

Steve A.


Ok Steve i have to keep an eye on that i think i push the switch on the probe when measuring some times and forget about it ,i will read the link .


This applies to anything that uses an attenuating probe, spectrum analysers, wide-bandwidth meters and others...

Often when using x1, and you scope the output of an op-amp, it shows oscillation. Op-amps don't like capacitance of a few hundred pF (in x1 mode) or more on their output, they go unstable. In x10 the input capacitance is reduced to 10-15pF, oscillation (usually) stops.

If trying to scope very small signals (unusual in NBTV) build or buy an external pre-amplifier.

When the time comes to replace the probes (you WILL have replace them well before replacing the scope) buy non-switchable ones that are always in x10 mode. No errors and far more reliable as there's no switch that's always the thing that fails...


Yes it would be better coming in either x1 or x10 keep me from pushing it to the other setting but i will have to keep and eye on that and i will take all that in .

On to todays tests on the signal generator ...i added the decoupling caps(on power supply and both ics ) and replaced the opamp with a Tl082 and checked the crystal ,results were may be a touch better still the waveform was not a nice sinewave over 30 or So KHZ still .
DSCN6432.JPG
DSCN6436.JPG


Over this you see it sort of looks more triangle wave once it get to top of the generators range.

DSCN6435.JPG


Now i noticed when the power was switched off i could notice the waveform going for a short time to a nice sinewave ,while on i looked around the opamp and what's going into the opamp pin 2 and its a very nice sine wave at any frequency ,so some thing is up in the opamp's design as its waveform isn't as nice out of it .

At least i know i can get something good enough out of this thing to test the sound card ,the question is do i need the opamp at all or does it need a redesign ?
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DSCN6443.JPG
Last edited by Harry Dalek on Sun Jul 25, 2021 3:42 pm, edited 1 time in total.
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