Well, you know what they say: Those who can, do, those who can't, teach ....
jd
And those who can't even teach, "coordinate".
The one relevant study of this sort I could find is by two guys from IBM, Allen and Segall, but it dates back to 1974, before computer switching supplies were in wide use. You're probably referring to something other study.
Allen, G.W. and D. Segall, “Monitoring of Computer
Installations for Power Line Disturbances,” IEEE Winter
Power Meeting Conference Paper, WINPWR C74 199-6, 1974
A more recent paper:
D.S. Dorr et al, “ Interpreting Recent Power Quality Surveys to
Define the Electrical Environment,” IEEE Transactions On
Industry Applications, Vol. 6, No. 6, November/December 1997,
pp. 1480-1487.
reviews a few different surveys of power line disturbances, in particular one cited quite a bit, by NPL.
However, what I often find frustrating in this thread is that you guys will not talk straight. You go ahead and hint at some stuff, but then not say what you mean, and one has to pull it out of your mouths with the pliers, so to say. What's up with this? If you want to say something, say it. If not, then don't.
In particular, does RF interference matters to audio amplifiers? If it does, then what are the levels that one should start to be concerned with, and what are your preferred techniques for dealing with that?
You may want to adjust your expectations. Many contributors in this place are not here for teaching or sharing with others purposes.
I guess that's the one.
Well, that can be had online, following this link.
But I think the results are a bit dated.
This is not the paper. It would be in one of the Transactions that I subscribed to at the time. Consumer Electronics, Circuits and Systems, or Solid State Circuits, to name 3. Others will follow, if this is not a complete enough list. The 'Proceedings of the IEEE' might be also included. However, I suspect 'Consumer Electronics' the best candidate.
Ikoflexer, it is also important that you read my follow-up input as well, before giving conclusions.
Ikoflexer, it is also important that you read my follow-up input as well, before giving conclusions.
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John, a shot in the dark here. Could it be "Closed space RFI testing" by I.M. Bell? The abstract says this:
"An efficient closed space RFI testing method has been developed to assure competitiveness of the new designs. This paper discusses the RFI testing philosophy as well as development considerations regarding procedure, presentation of results and acceptance criteria."
This appears in Consumer Electronics, IEEE Transactions on (August 1999), 45 (3), pg. 860-8
"An efficient closed space RFI testing method has been developed to assure competitiveness of the new designs. This paper discusses the RFI testing philosophy as well as development considerations regarding procedure, presentation of results and acceptance criteria."
This appears in Consumer Electronics, IEEE Transactions on (August 1999), 45 (3), pg. 860-8
Aw, come on, remember I'm the beginner here, I need to read stuff.
John, I like that, full citation
If anyone's interested in this paper, PM me.
Attachments
let me ( as a very ordinary DIY audio builder with basic electronics understanding) - how do anything from 1Mhz to 200MHz power line noise spctrum go through the step down transformer ( with a very poor bandwidth - ) and how much of this noise coming in to the rectified filtered DC modulate the line amplifier signal? We assume that line amplifier has much higher bandwidth than 50 Khz bandwidth normal to audio. Do I miss something without going through this IEEE paper?
sk
sk
The arrl article I posted a few posts ago may be funny, but does it point to the possibility of other points of entry for RFI, besides the psu? Is this something that anyone would take seriously?
syn08, you don't seem very concerned about any of this. I'm just asking for opinions, share experiences?
syn08, you don't seem very concerned about any of this. I'm just asking for opinions, share experiences?
Hi kannan,
Also remember that even though a circuit may not respond past a certain frequency, the individual parts sure do! Even if they don't, every PN junction is an AM signal detector. Then, is if that isn't bad enough, various frequencies may mix with each other. The end result may be a collection of odd noises in the audio band.
Another effect may be that certain parts of a circuit may be operated at high enough levels to cause distortion. Once your clean audio signal arrives to this overloaded stage, it gets "bent, folded and mutilated" as well.
I know of an area not far from here where RFI is so bad that many CD players simply refuse to operate. Wrapping these affected units in tin foil, grounding same to the chassis ground cured the problem. If you can imagine that none of these would misbehave in the shop ..... Now they look like art (not good art), but at least they work. Many phono stages suffer similar issues, except they are simply extremely distorted. Even FM tuners can have their IF stages overloaded by harmonics of the detected AM station.
Fun - wow!
Anyway, noise on AC supply lines may or may not affect a piece of equipment. It really depends on levels, frequencies and how good (bad?) the shielding is. A simple power supply with poor HF shielding allows higher frequency RF to ride right on through.
-Chris
Most high frequency noise will come through capacitively between the windings. Also, don't forget that once the noise is "in the box", even before it runs through the transformer, it may radiate out exactly where we don't want it.
Also remember that even though a circuit may not respond past a certain frequency, the individual parts sure do! Even if they don't, every PN junction is an AM signal detector. Then, is if that isn't bad enough, various frequencies may mix with each other. The end result may be a collection of odd noises in the audio band.
Another effect may be that certain parts of a circuit may be operated at high enough levels to cause distortion. Once your clean audio signal arrives to this overloaded stage, it gets "bent, folded and mutilated" as well.
I know of an area not far from here where RFI is so bad that many CD players simply refuse to operate. Wrapping these affected units in tin foil, grounding same to the chassis ground cured the problem. If you can imagine that none of these would misbehave in the shop ..... Now they look like art (not good art), but at least they work. Many phono stages suffer similar issues, except they are simply extremely distorted. Even FM tuners can have their IF stages overloaded by harmonics of the detected AM station.
Fun - wow!
Anyway, noise on AC supply lines may or may not affect a piece of equipment. It really depends on levels, frequencies and how good (bad?) the shielding is. A simple power supply with poor HF shielding allows higher frequency RF to ride right on through.
-Chris
Thanks Chris
now we have no answers to this - what frequency max and what amplitude of this range can cause problems in a line amplifier?
Can we assume that 3 mm Aluminium enclosure would adequately shield a line amplifier from radiating RFI? I am excluding Phono Amplifier or AM detector kind of circuits in this question. I also assume that PS line should get to the rule so defined for RF noise( If John can give us some guidelines on Freq/amplitude guidelines for PSU noise - will be nice?)
Kannan
I am concerned, within reason. I don't think potential RF ingress issues require any special or outstanding measures. To my experience, common sense practices like good grounding, proper shielding, smart wiring (reducing loops), filtering, decoupling, ground loops (or lack, thereof), RF input filters, etc... are addressing 99.99% of the potential issues. No need to get paranoic about, and shielding audio gear like a RF transmitter, designing power supplies for tenths of MHz rejection, etc... is a waste of time, energy and money. Of course, there are always pathological cases like people living in the proximity of RF transmitters, but I don't think they should set a design target.
For example, while I absolutely agree that toroidal transformers are allowing some (?) RF ingress through the winding capacitive coupling, I have never seen any shred of evidence or credible study about the impact (and superiority, thereof) of (e.g.) R-core or even split bobbin transformers on the audio performance. Moreover, if such impact exists, the transformer is not necessary the evil part. To me, (e.g.) building a gain stage with virtually zero PSRR, then complaining about the transformer/power supply allowing RF ingress, is plain wrong design.
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