ASC metal can polypro caps: ground the metal can to AC ground?

jarthel · 5th September 2006, 04:13 AM

your thoughts?

thanks for the help

dsavitsk · 5th September 2006, 04:55 AM

Yes, if they are outside the chassis where they can be touched.

jarthel · 5th September 2006, 06:13 AM

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?

CLS · 5th September 2006, 09:04 AM

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.

Klimon · 5th September 2006, 11:43 AM

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...

Simon

Tom Bavis · 5th September 2006, 06:08 PM

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...

rdf · 5th September 2006, 07:37 PM

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.

jarthel · 5th September 2006, 10:31 PM

so the good idea is to ground it to AC?

tubelab.com · 6th September 2006, 01:34 AM

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.

rdf · 6th September 2006, 02:50 AM

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.

5th September 2006, 04:13 AM	#1
jarthel diyAudio Member Join Date: Jan 2002 Location: somewhere in Australia	ASC metal can polypro caps: ground the metal can to AC ground? your thoughts? thanks for the help

6th September 2006, 01:34 AM	#9
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	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. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

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5th September 2006, 04:55 AM	#2
dsavitsk diyAudio Member Join Date: Jan 2005 Location: Chicago	Yes, if they are outside the chassis where they can be touched.

5th September 2006, 09:04 AM	#4
CLS diyAudio Member Join Date: Jun 2005 Location: Taiwan	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.

5th September 2006, 06:08 PM	#6
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	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...

5th September 2006, 07:37 PM	#7
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	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.

5th September 2006, 10:31 PM	#8
jarthel diyAudio Member Join Date: Jan 2002 Location: somewhere in Australia	so the good idea is to ground it to AC?

6th September 2006, 02:50 AM	#10
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	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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