| jarthel |
your thoughts?
thanks for the help :) |
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| dsavitsk |
| Yes, if they are outside the chassis where they can be touched. |
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| jarthel |
| quote: | Originally posted by dsavitsk
Yes, if they are outside the chassis where they can be touched. |
but not all metal that can be touch are grounded. say a metal knob for a volume control? |
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| CLS |
I don't know ASC metal can, but I'd been shocked by some unshielded aluminum tops of electrolyte caps.
Ouch!
Those caps were originally fixed onto metal chassis directly by nylon cable ties. After I was shocked, I cut those cable ties & put some more thich cardboard between caps & sheet metal, then re-fixed them. As the thin heat-shrink film seems vulnerable. |
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| Klimon |
| quote: | | but not all metal that can be touch are grounded. say a metal knob for a volume control? |
True, but ungrounded, touchable, conductive elements are only dangerous when high voltage carrying wire gets loose and makes contact with the element. There's usually no high voltage around the volume control...:D
Simon |
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| Tom Bavis |
| A metal knob on a volume control is connected with the shaft, which has a sliding contact with the case, which is mounted to the metal chassis... so it IS grounded. If the pot's case ISN'T grounded, expect hum problems... |
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| rdf |
| One general caveat I recently discovered, grounding a metal-bodied signal cap should be considered carefully. A coupling position isn't likely with an ASC but it's common with Russian Telfons, K40Y-9 PIOs and Russian silver mica. A Fluke DVM measured a whopping 70pf between either terminal and exterior case on the latter. That equated to (a probably not very linear) 70pf shunting the driver to ground in my amp. Even though it measured flat floating the cap body still cleaned up the sound significantly. |
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| jarthel |
| so the good idea is to ground it to AC? |
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| tubelab.com |
If the cap is inaccessible to the user, leave it floating, and keep low level signal leads away from it. If anyone can touch it GROUND IT. The can will often collect enough electrons to zap you. If it internally shorts, it can kill you.
Connecting the can to an AC ground will still put the previously mentioned 70pF to ground.
I have received the same unwanted experience from some Panasonic electrolytics. The big ones have a plastic cover over the can. The 100uF 350 volt ones do not, and the can will shock you. |
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| rdf |
| Hi tubelab. In situations where the cap is in the signal path and the capacitance to ground a detriment, what do you think about using a bleed resistor? 70 pf in series with half a meg might be fine. |
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| tubelab.com |
That should work, but I have never tried it. If the cap develops a short, it could still be deadly if it can be touched.
I usually sell the amps that I build after I have grown tired of them (can't keep them all), so I must make sure that there are NO hot parts that can be touched by the user. I always make sure that every metal part on the amp has continuity to the ground pin on the power cord. |
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