Recent Posts

1

General Technical Chat / Re: new propellantless drive company

« Last post by coppercone2 on Today at 11:06:59 pm »

That is no reason to investigate an effect. Then its just boring physics instead of popsci physics.

I recall reading that it was significantly above photon drive levels though (according to their experiments), IIRC the whole point was that there is a force that is bigger then the force expected from photons.

2

Beginners / Re: Convert US standard 115V to International 230V

« Last post by IanB on Today at 11:03:04 pm »

I insist that with lower frequency (everything else being equal) the voltage at the filter capacitor falls further. Model an AC voltage source, followed by a rectifier bridge, a capacitor and a constant current load. My prediction is that the voltage at the capacitor and load falls further with decreasing frequency. It must be obvious to anyone.

I understand what you are saying, but surely the design would have to be very marginal before this had an impact on the following section of the power supply?

3

Repair / Re: Please help! TANNOY PRECISION 8D dead

« Last post by Valden on Today at 10:59:55 pm »

Hello to owners of Tannoy Reveal 6D and 8D monitors. I've just completed another repair, which is written up in the link below where there's a useful thread. Rather than duplicate, here it is ...

https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-audio-equipment/15433-tannoy-reveal-6d/page10?view=thread

4

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by KungFuJosh on Today at 10:55:51 pm »

I meant I get a clean sine wave up to 841MHz.

Ah, I see. Well, that's just one point in time, and the display persistence hides the deviation of the peaks from the real value. What we're interested in is observing dynamically how the waveform becomes wobbly as the signal frequency increases and gets closer to that point.

It's clearly better than the Rigol, though, which is much worse at 1/2.5x the sampling rate. I wonder how the SDS800X HD scopes perform in this scenario.

Here's, BTW, a 500 MHz sine wave captured at 1.25 GSa/s sampling rate:

I didn't get any wobble within normal range, and then I still don't get anything as crazy as what you showed in your screenshot. It mostly shrinks and the counter gets farther and farther off. Near the end before it resets, it looks a little wonkier.

Let me know if you want different parameters than what I've got here:


TSA Ultra set at 800MHz with a 10s 500MHz sweep.

5

Projects, Designs, and Technical Stuff / Re: How is a motor run capacitor sized?

« Last post by aroby on Today at 10:53:03 pm »

If you're making your own board, then presumably you can change the footprint, so long as it's not too big for the case.

Have you measured the voltage across the capacitor? Does it actually get anywhere near 106V, the RMS voltage with a peak of 150V? As mentioned above, the voltage rating is probably selected for the size.

I would use two 68µF low ESR capacitors connected back-to-back, to form a 34µF non-polarised capacitor. Choose as larger case size as you possibly can, given the space constraints and voltage rating, which presumably doesn't need to be above 50V, although check first to be sure.
[/quote]

I'll investigate that. Trouble is the actuator is 1,300 miles away!  The board is quite space challenged and has a DPDT switch on the underside that pokes through the case and secures the board.   When you say 2 68uF back to back, I assume that is two polarized caps joined on the -ves and with the +ves connected to the motor?

6

Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by moffy on Today at 10:51:53 pm »

I keep wondering what that 1N4148 is even doing there? It's the oddest circuit I've seen.

It's probably to stop the loop voltage drooping unnecessarily, it is working like a peak hold with a slow discharge time set by the resistors, it might make more sense if we knew what the phase comparator was doing.

7

Beginners / Re: Convert US standard 115V to International 230V

« Last post by soldar on Today at 10:51:21 pm »

The frequency of mains supply after rectification 100Hz or 120Hz depending on where you live. AND THERE IS NO SIGNIFICANT BEHAVIOUR CHANGE OF AN ELECTROLYTIC CAPACITOR BETWEEN 100Hz AND 120Hz AT 20 to 25C^o It makes no damn difference whether it's on a linear supply or an SMPS. That tiny change in Value and ESR between 100Hz and 120Hz won't make a damn bit of difference to the ripple voltage. Electrolytic capacitors have as much as 20% tolerance in value and your saying that a fraction of a uF can make a significant difference to ouptut ripple?  That's absurd! Just to reduce the output ripple voltage by half, the capacitance needs to double.

Canadian, eh? Now, now, there is no need to be rude. I see you don't get it and you get defensive.

I insist that with lower frequency (everything else being equal) the voltage at the filter capacitor falls further. Model an AC voltage source, followed by a rectifier bridge, a capacitor and a constant current load. My prediction is that the voltage at the capacitor and load falls further with decreasing frequency. It must be obvious to anyone.

This is my last word to you on this topic as I have no interest in putting up with rudeness. Maybe others can chime in if interested.

8

FPGA / Analog video output with FPGA ?

« Last post by Jaunedeau on Today at 10:48:31 pm »

Hi,

  I'd like to output an RGB video signal on an old CRT TV. The resolution would be at least 160x200, 320x200 if possible. So I need to output three analog values, with value changing at approximately 5MHz but they need fast transitions (e.g. if I use PWM, I guess I need at least 4 PWM periods in one pixel).
  I could use dedicated video DAC, the problem is that they seems to be harder and harder to source and since this is for an open source project that I hope may live for a few years and the price is apparently higher than the fpga I need (probably a gw1n 1k)... Is there any interesting chip I missed ?

  I have seen several people using r-2r ladders for this, but they only use 3 to 5 bits per components, I need 8. Can I use an r/2r or r ladder with trimpots on the higher bit to adjust the DAC, or will other factors (such a temperature drift ?) make it a bad idea ? (I won't mass produce so calibrating each piece once is acceptable)
  Should I build a PWM or PDM DAC inside the FPGA ? (in PAL, with 52us per line, 320 columns, 256 possible values and 4 PWM cycles per pixel, that would mean  6gHz clock... probably cheaper to save on the FPGA and use a DAC, but maybe PDM would be doable ?)
  Another solution I can think of is a 10 bits r/2r ladder, and and hardcoded calibration table to compensate for the resistors variation... any better solution ?

Thanks,
J.

9

Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by moffy on Today at 10:47:22 pm »

OK so Arcam had it perfect 30 years back!?

Isn't that when they made their name and reputation for good audio? Newer doesn't necessarily mean better, take the ubiquitous 1N4148 diode which has been around for decades but still is probably one of the most widely used small signal diodes.

10

Altium Designer / Re: Altium V15 - Dup designators that won't fix on board level annotate

« Last post by Psi on Today at 10:45:57 pm »

As for the board level annotate, you might need to delete the annotation file from the project and start over once you get.any underlying issues resolved.

yeah, I've tried deleting that file but no luck. Definitely still an issue somewhere.

I think I will make a copy of the project and just start deleting sections, see if I can do a binary search and locate any problem area. Assuming it is a specific area causing the issue.
The dup designators themselves don't seem to be limited to any section but it's hard to tell exactly.