jd@uofm-cv.UUCP (Joseph B. Douds) (08/05/84)
Has anyone had success using a varistor to kill the effects
of transients in a stereo system? It gets really annoying
when someone cranks up a blender when I'm recording. Any
advice will be greatly appreciated.
In real life: Joseph B. Douds
University of Michigan
Electrical & Computer Engineering
(actually, I'm an aerohead or I might
already know the answer to this)
(313) 763-9712
Computerese: jd@umich-ciprnet
...!ulysses!gamma!epsilon!mb2c!uofm-cv!jd
...!ihnp4!uofmcv!jdgnome@olivee.UUCP (Gary Traveis) (08/06/84)
I'm affraid that a varistor alone will not actually get rid of "blender noise" coming through the power line. A 60hz low pass (LC) filter will help a lot but is not as easily slapped together. A compromise can be made by putting a set of .047 to .1uf 300v non-polarized caps across the power line and to earth ground (very solid earth ground). >-----------------------------------------------> | ----- ----- | --------- | | ----- /// ----- | >------------------------------------------------->
newton2@ucbtopaz.CC.Berkeley.ARPA (08/08/84)
It's unlikely a varistor will help deal with RFI, whether conducted or radiated, from a universal motor. Try experimenting with the physical arrangement of power cords on the audio equipment, with lifting some AC power grounds, or with other ground-loop breaking approaches. Shielding (foil) may help in the less-likely event that the interference really is radiated rather than power-line conducted. Remember that AC power cords make effective antennas (they're actually used for such in radios). Good luck with a frustrating and elusive problem.
gnome@olivee.UUCP (Gary Traveis) (08/10/84)
Regarding my last posting of the two-cap line noise reducer, I would like to add that the 300vac rating on the caps only applies if you have a set of 135-150vac MOVs hooked into the circuit. Also, if you do use MOVs to get rid of line spikes, don't forget to fuse the input. If something really nasty happens to the power line, it is better to have the fuse blow and quickly isolate everything from the overvoltage.
hbb@houxt.UUCP (08/14/84)
Jim Muller suggested "...spending $75 or so on a powerline filter
intended for Apples, TRS80's, PC's or whatever?"
I have been having the 60Mhz-hum problem with my amp and tried
using my power-filter (made by Electronic Specialists) to
correct the problem without success.
I am not an EE, but it would seem likely to me that the sort of
interference the power lines give off has a different effect
on computer equipment than on audio equipment. Hence, power-
filters designed to correct power related computer problems
(voltage spikes and brown-outs) will not be as effective in
reducing audio related problems.
--
Harlan B. Braude
{most "backbone" sites}!houxt!hbbgnome@olivee.UUCP (Gary Traveis) (08/16/84)
There are a few different types of power-line related noises that can pop up in an audio system. 1) Hum - a 60hz hum that is sitting in the background and stays mostly the same amplitude over time. :This could be caused by the following circumstances. a) A ground loop caused by too little or improper grounding. AC neutral is NOT the same as ground! b) A transformer nearby a sensitve area of the system. Namely a power transformer or video device too close to preamp or pickup. c) A bad power supply with ripple in preamp or power amp. 2) Buzz - A constant buzz (low freq) that comes and goes. a) Flourescent light or ballast near audio system. b) A light dimmer being used on the same or nearby AC power line. c) Bad or dying rectifier in amp(s). 3) Whine- A variable or intermittant whine/buzz that comes and goes. Often in bursts. a) A blender, variable speed drill, vacuum cleaner or other AC/DC motor that uses brushes internal to the motor or unit itself. 4) Pops - A loud or moderate pop heard from time to time. (sometimes random crackling) a) Any capacitive or inductive load being turned on or off. Flourescent lights that use starters will flicker and cause popping on power-up. b) Non-positive switches. Bad wall switches, or aquarium heater thermostats can induce noise on both audio and TV/video systems. That covers most cases -- oops! I forgot HAM and CB interference! Well, once the cause of a problem is discovered, then the proper fix can be sought. A power line filter (a good one) can get rid of most of the above problems, but not all! Gary (hplabs,ios,fortune,allegra)oliveb!olivee!gnome - with no more time today...
wunder@wdl1.UUCP (wunder ) (08/19/84)
#R:uofm-cv:-58200:wdl1:2200001:000:291 wdl1!wunder Aug 18 15:44:00 1984 If it is your blender (or you are friends with your neighbors), you can put an RFI filter on the blender's cord. This is sometimes more effective, since it stops things at the source. The Radio Amateur's Handbook used to have a good section on do-it-yourself RFI elimination. w underwood
muller@inmet.UUCP (08/19/84)
#R:uofm-cv:-58200:inmet:2600098:000:708 inmet!muller Aug 17 13:18:00 1984 ** Re H. Braude's response, I suppose you mean 60 Hz, not 60MHz! Since 60 Hz is the nominal frequency on a power line, you don't want to get rid of it. However other electric appliances may generate harmonics of it (120, 180, etc) as well as higher frequency spikes. Your power supply should filter out the 60 Hz and its lower harmonics, but may not be good against the "really" high stuff, since that isn't NORMALLY part of the power system. With regards my comment on computer spike-protectors, they should indeed only keep out spikes and surges (if designed for both), but I wonder about their ability to handle much of a load. Except for CRT's, computers don't really draw lots of power. Jim Muller
muller@inmet.UUCP (08/25/84)
#R:uofm-cv:-58200:inmet:2600097:000:351 inmet!muller Aug 10 21:15:00 1984 *** Has anyone thought of going into your local computer store or mail order house and spending $75 or so on a powerline filter intended for Apples, TRS80's, PC's or whatever? Of course, maybe you are trying to avoid spending another $75, but if you have spent 10 times this on your speakers, then your priorities should be obvious. Jim Muller