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Old 6th May 2012, 12:45 AM   #22901
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Originally Posted by Bonsai View Post
It's the change in capacitance with voltage that is really bad also.

I also had a case a few months ago where I had one 'singing' in a snubber circuit. When I held the cap between my thumb and forefinger it stopped.
weird stuff happens!
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Old 6th May 2012, 01:14 AM   #22902
bcarso is offline bcarso  United States
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In one of Hagerman's tube preamp kits he had a series RC snubber across the secondary HV winding. My friend built it up and complained about hearing hum and buzz. When I finally understood him I realized he was talking about acoustic emission. He brought the unit over, and the noise was quite audible in a fairly noisy room. It was all from the capacitor, a high voltage ceramic disc which iirc was one of those with various agency certifications.
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Old 6th May 2012, 02:05 AM   #22903
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Originally Posted by Speedskater
Seldom do US houses achieve 25 Ohms or less resistance to Mother Earth. The first part of the NEC rule is for the 25 Ohm resistance, but to measure this a special meter that costs about $2500 and one hour labor is required. So most residential electricians go to the next part of the rule and just drive a second ground rod.
Older two wire US circuits by rule can be updated with a GFCI receptacle that has an attached label "no ground wire".
(snip)
25 ohms is the maximum permitted. 5 ohms is what the telephone company requires.
(snip)
In US houses it's an either / or requirement.
Either it's measured under 25 Ohms or drive two ground rods.
Most residential electricians go with two ground rods.
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Old 6th May 2012, 04:46 AM   #22904
Bonsai is offline Bonsai  Taiwan
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I discovered the singing because I was varying he sig gen f and driving about 30 V pk to pk on th output. X7R again. I have subsequently removed a few X7R MLCC's from my circuit. Bad stuff and really need to be applied very carefully and IMO no where near audio.
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Old 6th May 2012, 01:06 PM   #22905
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Say NO to CERAMICS! '-)
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Old 6th May 2012, 01:08 PM   #22906
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X7R yes, but you might want to give COG/NPO a try if you haven't John

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Old 6th May 2012, 01:12 PM   #22907
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No good reason to do so. I use polystyrene.
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Old 6th May 2012, 01:17 PM   #22908
godfrey is offline godfrey  South Africa
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I sympathize with John - they all look the same in the junkbox. I struggle to make out resistor color codes these days without a magnifying glass, let alone the writing on TO92 devices. As for SMT: well, I prefer to work with parts I can actually see.
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Old 6th May 2012, 04:47 PM   #22909
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I sympathize with John - they all look the same in the junkbox. I struggle to make out resistor color codes these days without a magnifying glass, let alone the writing on TO92 devices. As for SMT: well, I prefer to work with parts I can actually see.
Ok time to let a secret out. The laser etched markings on semiconductors can best be read when under an "Artic Blue" light. That is light rich in near UV! I used an old "Tensor" lamp for this. It uses an automotive bulb and runs it at a volt or two above it's 12 volt design voltage. Lamp life is about 100 hours as compared to the 1000's of hours it should work in a car. I buy the light bulbs in boxes of ten.

Now for those who have never seen a Tensor lamp, it is a filament transformer in the base a thin gooseneck and then essentially a juice can for the reflector. The deluxe model has a high low switch for those who didn't like the short lamp life.

I would like to tell you it works for sorting resistors, but the problem there is that one manufacturers orange is anothers' red!

I have a large drawer with bins, every other bin is marked with a standard 5% value. Ones that are not a standard value go in the unmarked bin in between. For my good 1% resistors I keep them in a notebook with plastic pages having 12 pouches per page.

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Old 6th May 2012, 06:04 PM   #22910
1audio is offline 1audio  United States
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Quote:
Originally Posted by Bonsai View Post
It's the change in capacitance with voltage that is really bad also.

I also had a case a few months ago where I had one 'singing' in a snubber circuit. When I held the cap between my thumb and forefinger it stopped.
Depending on what you were snubbing the screams would have drowned out the singing.

Do be careful what you touch. . .


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