Ferrite beads in power cords?

edited September 9 in Hardware
So I am seeing these modern psu units with ferrite beads on both ends, just like this:

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I was wondering if these could also be used with the old sinclair bricks.

Well, I could add a pair to my (already overworked 8-} ) +2 grey brick but any real benefits are to be expected?


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Post edited by Renegade on

Comments

  • edited September 9
    The spectrum is so electrically noisy I doubt it would make any noticeable difference to its emissions at all.
    Particularly as it's a transformer not a switching power supply.
    Post edited by guesser on
    My rubbish website including the redrawn Amstrad schematics and the new home of the Sinclair FAQ wiki.
  • To get into a real debate about interference, I fully recommend joining a ham forum and start a post saying how you think those BT routers that transmit there signal through houses via the mains wiring are the best invention ever. :))
  • Is there a reason you want to fit these?

    The reason that they are fitted by some manufacturers, is an attempt to further reduce RF interference from escaping along and out of the cables. However, really this should be done inside the equipment. As a user could just buy another cable and use that...

    In regards to the ZX Spectrum, as Guesser says, there is little point in using them, as the machine itself emits a wide band of RF frequencies. There being at the time, no significant regulations requiring manufacturers to pay any attention to the interference levels emitted by consumer equipment.

    If you do decide to use them, they should be on any cable that is connected to the ZX Spectrum, as close to the computer as practical. There is no need to fit them to the Sinclair PSU mains lead. Or on the output lead at the PSU end. As the PSU is a conventional type and does not emit any significant RF interference.

    Mark
  • 1024MAK wrote: »
    Is there a reason you want to fit these?

    The reason that they are fitted by some manufacturers, is an attempt to further reduce RF interference from escaping along and out of the cables. However, really this should be done inside the equipment. As a user could just buy another cable and use that...

    In regards to the ZX Spectrum, as Guesser says, there is little point in using them, as the machine itself emits a wide band of RF frequencies. There being at the time, no significant regulations requiring manufacturers to pay any attention to the interference levels emitted by consumer equipment.

    If you do decide to use them, they should be on any cable that is connected to the ZX Spectrum, as close to the computer as practical. There is no need to fit them to the Sinclair PSU mains lead. Or on the output lead at the PSU end. As the PSU is a conventional type and does not emit any significant RF interference.

    Mark

    Ok, that seems logical.
    But I was more concerned regarding the possibility of the leads acting like antennas and picking up RF interference.
    I mean, I suppose these days we are surrounded by all sorts of wireless devices unlike in the early 80's.
    When my neighbour next door receives a call on his cell phone the picture on my crt monitor starts to shake and the speakers buzz. I know we're separated by "thin" brickwalls but couldn't the spectrum also pick up this interference?
  • Oh those are not random magnets? First time I hear about it... Well, I might have heard about it but that would be so long I can't even remember.
  • Yes, anything can pick up interference. In my real world job, I once had a telephone which was reported as picking up a radio station. Actually it appeared to be picking up multiple stations, as it was hard to make out the words... Had to replace it!

    Back on topic, the Spectrum itself is unlikely to be affected, but the cassette system and TV/monitor may well be affected. By all means try fitting ferrite beads. They won’t do any harm. But keep in mind that the interference may be getting in via any number of ways including the fixed house wiring. And ferrite beads often only offer a slight reduction in the interference level.

    Unfortunately often the only solution is to increase the distance between the item causing the interference and the item being affected. Have you politely asked your neighbour about his phone and informed him that it’s affecting your TV?

    Unfortunately mobile telephones are well known for this kind of thing. Analogue radios and TVs were never designed to cope with such relatively high power RF transmitters at close distances.

    Mark

    Thanked by 1Renegade
  • As others said, the ferrite bead is primarily to prevent RFI from the device going back up the mains lead and into the mains system. It will do *some* good even with a Spectrum (it will attenuate a lot of the higher frequency noise that would otherwise make it up the cable), but don't expect to be able to use a medium wave (AM) radio anywhere near your machine. Some 80s machines such as the BBC Micro had some RF suppression built into their power supplies.

    Similarly, the ferrite bead will help stop RF from getting into the machine, but generally this isn't a problem in any case. I've only ever witnessed one case of RFI affecting a Spectrum - back in the day, I was at school on the school's machine, and a taxi was outside, and we heard the taxi driver's radio transmission come out of the speaker! I've never heard of this happening again, though - there was probably a very specific set of circumstances that allowed this to happen (and it would have happened because there was enough signal strength, and the Spectrum's rudimentary audio amp would have worked as an accidental radio receiver - in exactly the same way as you hear the interference from a mobile phone).

    On mobile phones etc. the trouble with GSM is it has a very harsh envelope, and the "bip-b-b-bip-b-b-bip-brrrrrrrrrr" noises you hear when a phone is near any audio equipment is basically the equipment acting as an accidental radio receiver. Any semiconductor junction that's present where the RF gets in from the phone will act as a detector (like the diode in a crystal radio), and demodulate the signal as if it were AM, in other words, those noises you hear are the envelope of the RF signal. It's absurdly easy to make an AM radio receiver, even by accident - so easy that the first AM receivers worked by essentially putting a wire in the right place on a lump of galena.
    Thanked by 1Renegade
  • ohh i just brought some... to try on a couple of amstrad cpc 464 that i am working on ...... they seem more prone to screen interference than the specie with switchable supplies ..although the 464 lacks anything to smooth the supply as it was meant to be regulated by the the monitor . didn't make any difference at all... i did notice when i used one type that if i plugged it into a different outlet to the tv the interference was a lot less ... i was thinking ground loop but then i confused myself by asking google ! i found some reasonable supplies on Mr Ebay that work nice for the specie for a good price after switching the polarity of course ...
  • If you are using “modern” “switching” supplies (what I call SMPSU), then cheap types have cheap filtering, as in, not very good filtering.

    For safety reasons and for better filtering, I recommend you buy them from a reputable shop/seller in your own country. Preferably from a manufacturer who gives detailed specifications on the output regulation, ripple and noise figures. And from somewhere where you will have no trouble returning it.

    Electrically there is a big difference between any old ‘DC’ output and a low noise regulated and properly filtered ‘smooth’ DC supply...

    Oh, and by the way, the power feeds from the Amstrad monitors comes from a SMPSU inside the monitor.

    Mark
  • yeh i only get power supplies from uk now ,,, i tried a few on the 464's even the one from the cpc shop gave a small amount of interference and that was a good spec...the only supply i have found that is totally without interference on them is pc supplies, ..i have got some micro ATX supplies that supply 5 volt 2 amp on the stand by rail .. although i'm a bit apprehensive of using that for any length of time .. the last time i brought power supply from china it was actually advertised as being for zx spectrum +2 when it came it was max current of 1 amp.. !! totally inadequate for a +2
  • You could add a 220uF 16V low ESR electrolytic capacitor in parallel with a 470nF multilayer ceramic capacitor, both connected across the +5V and the 0V/GND line at or near the power input on the PCB board of the computer. This may help.

    Mark
  • Winston wrote: »

    Similarly, the ferrite bead will help stop RF from getting into the machine, but generally this isn't a problem in any case. I've only ever witnessed one case of RFI affecting a Spectrum - back in the day, I was at school on the school's machine, and a taxi was outside, and we heard the taxi driver's radio transmission come out of the speaker! I've never heard of this happening again, though - there was probably a very specific set of circumstances that allowed this to happen (and it would have happened because there was enough signal strength, and the Spectrum's rudimentary audio amp would have worked as an accidental radio receiver - in exactly the same way as you hear the interference from a mobile phone).

    When I was a kid I had this a few times on my speccy with the broken speaker. I had to swap the ear leads round and press play on my tape recorder to get sound. A few times I'd get voices! Made me jump :D
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