Yes , I noticed the tyco med. grades use better caps with lower values , higher resistance values .... trading leakage for HF rolloff and general performance.Yes, Yet another thing to consider.
OS
When you're using a filter with Y caps (that's the ones from line to earth), your attenuation is only going to get as good as the earth connection you have. Which in most cases is inductive and several uH. So in my view Y caps aren't really worth bothering with - they're impossible if the kit is class II anyway. Ferrites are the way forward.
Where would you put them?
Circuit please. The web is lacking in discrete RFI filter material ... only finished modules. Just a general idea , I am good at "filling in the blanks".
OS
Well they'll probably be used as the core of the common-mode choke, so they're already there. We just need to make sure they're the right kind. Usually ferrites are chosen for having low loss. Here we definitely want the opposite - ferrite with lots of loss! I wonder if non-laminated steel would have an effect at the lower frequencies, we might need several filters in series each targeting a particular freq band. Higher frequency ones first (nearest the inlet).
What's wrong with low leakage? I dont understand how this would be a neg and not a pro...
I discussed this subject with a friend and we came to the conclusion that EACH offender on the same line then the hi-fi system must be filtered with a good, discrete RF filter of size proportional to the power consumed.
Prevention sometimes is better than cure.
Besides, a way to filter the GROUND is needed for all audio equipment that do NOT use a SMPS psu themselves.
If you compare the two versions of a pre-built mains filter, the normal one and the medical variant, you'll find there's a difference in rejection of noise. That's because the values of Y capacitors are smaller in the medical variant, hence less HF filtering effect. On reflection, this isn't always bad for audio, its only bad where there's a good earth which can be used as a sink for the interference. If the earth is poor, or non-existent (as for a class II setup for example) then a medical grade filter could well be better.
Here's an interesting paper I dug up as a result of the issue coming up on the JC Blowtorch thread. I offer it here to those interested in the effects of RF on IC amps:
http://www.analog.com/static/imported-files/tutorials/MT-096.pdf
http://www.analog.com/static/imported-files/tutorials/MT-096.pdf
Here in italy the earth isnt very good.
Now that you mention class II regulation, that could be the reason why a certain british amp sounds so good when you wouldnt say looking at the inside -no dirty ground to pollute it.
If the earth is not good , pound an 8' (foot) rod in the ground. Get #6 copper wire , create a "technical ground" for 30-40$. (used in recording studios)
OS
I wasn't actually thinking of earth as a national phenomenon.
Rather there will be a connection at your local substation (probably) between neutral and earth. How good a connection there is between your local earth and that one is the question.
I noticed nobody mentioned using shielded speaker cables. Not instrument cables but shielded speaker cables. Do you think they do not help? Waste of money or what?
Older Gibson Les Pauls have a metal "can" that covers the electronics in the back of the guitar so maybe Urgon is on to something with the metal boxes. On an old Les Paul the electronics are mounted on a metal plate and the can fite over the top of it sealing all the electronics inside a metal compartment. The input jack also has a metal can around it and so does the toggle switch.
Older Gibson Les Pauls have a metal "can" that covers the electronics in the back of the guitar so maybe Urgon is on to something with the metal boxes. On an old Les Paul the electronics are mounted on a metal plate and the can fite over the top of it sealing all the electronics inside a metal compartment. The input jack also has a metal can around it and so does the toggle switch.
AVE...
This is all because of engineering need to separate RF modules from low frequency modules and to protect them from all kinds of noise. Ignition coils and alternators generate huge amounts of electromagnetic noise, and this is main reason for shielding. In modern cars all computers are in metal boxes not because they need mechanical protection, but because they need to be shielded from all that radio garbage...
In my opinion it's rather overkill. Even if speaker cable picks RF signals, there are no semiconductors to demodulate them and the signals are too weak to move membrane of speaker...
Do you know, why all shortwave transceivers, CB's and normal radios have so many shields inside? Open any car radio and look inside. First of all: the whole radio is in a huge, metal box grounded to car frame. Then RF circuitry is almost always in metal box. I had nice CB radio where whole modulation/demodulation/tuning circuit was in box, and C-class output amplifier had separate box inside that one...
This is all because of engineering need to separate RF modules from low frequency modules and to protect them from all kinds of noise. Ignition coils and alternators generate huge amounts of electromagnetic noise, and this is main reason for shielding. In modern cars all computers are in metal boxes not because they need mechanical protection, but because they need to be shielded from all that radio garbage...
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I would reccomend having a look around either of these sites, one US on UK. There will be somthing that covers ALL the topics being discussed. There is a wealth of EMC engineering and knowledge out there. There are articles and design information covering every aspect of EMC engineering.
EMC Journal portal | EMCJUSA
http://www.compliance-club.com/
And the Daddy of EMC Engineering, Henry Ott, if you are serious about EMC you realy require his book as a start point and a reference (Electromagnetic Compatability Engineering).
Tech Tips
EMC Journal portal | EMCJUSA
http://www.compliance-club.com/
And the Daddy of EMC Engineering, Henry Ott, if you are serious about EMC you realy require his book as a start point and a reference (Electromagnetic Compatability Engineering).
Tech Tips
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Even my $129 Mexican Strat has some attempts at shielding. Why? First off the signal generated by the guitar is in the millivolt range. It is also quite common to have more than a little extra gain in the preamp section of a guitar amp for that cranked to eleven sound. It is also common for a guitar to be used on a stage that is lit by killowatts of lighting that is fed by 60Hz dimmer circuitry that generates sharp transients with harmonics throughout the audio range. Shielding and humbucking pickups are needed to "keep em seperated."
Shielding technology has come a long way, so has RF design. It is true that many circuits in a radio or other RF design need to be isolated from the other circuits. It has become more important now that we stuff microprocessors and DSP's inside radios. THe digital electronics generate square waves at RF frequencies in the 2.5 to 5 volt peak to peak range. The receiver is trying to pick up signals in the same frequency band that are in the microvolt range, over a million times weaker. Metal cans and multi layer PC boards are your friends here.
When cars first started getting digital fuel injection, the cell phone became popular. I found several cases where a well placed phone inside the passenger compartment could stop a running car. The newer cars with drive by wire have better shielding and RF control. I haven't found one that I could whack with a cell phone yet. I would still be wary of standing in front of a Toyota with a high powered radio!
Agreed it is probably not necessary, except in a few odd cases. I grew up in a house located about 2 blocks away from a 10 KW AM radio station. It got into everything I made. THe entry point was usually the input circuits, especially my early attempts at solid state guitar devices. The old Tone Bender and Fuzz Face circuits don't work in a plastic or wood box! I can't recal having a problem with speaker wiring and that is a near worse case situation. You can always test using a GSM or iDEN cell phone against your speaker wires several feet away from the amp (to aviod direct coupling into the amp).
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