Home » Audio » Thermionic Emissions » Mylar cap polarity - Help
Mylar cap polarity - Help [message #9047] Wed, 29 June 2005 17:12 Go to next message
colinhester is currently offline  colinhester
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Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
Just some 10uF 400VDC mylar caps and there are no polarity markings. How do I tell which end is which? I contacted the seller and he was not quite sure either and emailed the mfg......Colin

Re: Mylar cap polarity - Help [message #9048 is a reply to message #9047] Wed, 29 June 2005 17:41 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
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Registered: January 2001
Illuminati (33rd Degree)

Mylar capacitors are non-polarized. They are like other caps with a plastic dielectric, polypropylenes, polystyrenes, etc.


Re: Mylar cap polarity - Help [message #9049 is a reply to message #9048] Wed, 29 June 2005 17:55 Go to previous messageGo to next message
colinhester is currently offline  colinhester
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Registered: May 2009
Location: NE Arkansas
Illuminati (3rd Degree)
That's what I thought, but I just needed to double check. The schematic for the SV811-10 amp shows polatity on the Mylar caps, and that's what kind of threw me......Colin

Re: Mylar cap polarity - Help? [message #9050 is a reply to message #9048] Wed, 29 June 2005 21:50 Go to previous messageGo to next message
Poindexter is currently offline  Poindexter
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What about the outer foil / inner foil thing? You know anything about this?

When I use nonpolarized caps, I just make sure that they are (channel-to-channel) oriented the same; I send the signal down the print on the outside, presuming that they are manufactured consistently.

I am presuming presumptuously?

Heh,

Poinz

Re: Mylar cap polarity - Help [message #9051 is a reply to message #9049] Wed, 29 June 2005 22:09 Go to previous messageGo to next message
Steve is currently offline  Steve
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Hi Colin,

Some manufacturers specify which way to connect the cap, while others don't. I know one brand that outer wraps the caps randomly, so it is an individual cap situation. Mylars may not be that critical as there sonic signature is usually fairly strong.

Take care.
Steve

Re: Mylar cap polarity - Help [message #9052 is a reply to message #9051] Thu, 30 June 2005 10:24 Go to previous messageGo to next message
Thermionic is currently offline  Thermionic
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Which direction the cap is installed won't make a difference in the sound, but which way it's installed WILL make a difference in how much noise can be coupled into the cap, which will of course indeed make a difference in sound.

Always connect the outside foil to the lowest impedance, not the lowest voltage as many recommend. Voltage has nothing to do with it, it's the lowest *impedance* that you want! That'll most always be the plate of the first stage, versus the control grid of the second stage. The control grid is an extremely high impedance itself, with (usually) a bare minimum of 100K all the way up to a 1 Meg resistor to ground.

OTOH, the impedance of the first driver stage (which is the product of the internal plate resistance in parallel with the load resistor), will most always be much lower. Even a very high plate resistance triode like a 12AX7 will only have about 40K output Z when the cathode resistor is bypassed, unbypassed still less than 70K depending on the cathode resistor value. So, the outside foil goes to that side for the best electrostatic shielding.

Thermionic

Re: Mylar cap polarity - Help [message #9053 is a reply to message #9052] Thu, 30 June 2005 11:11 Go to previous messageGo to next message
Steve is currently offline  Steve
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Yes, it can make a sonic difference/sound, depending on the quality of the cap and quality of the components.

A low value capacitor, say 0.05uf is generallly more critical in respect to the outer foil vs a higher value cap, say 2.0uf. The outer foil should be to the lower Z for sure if the cap is small.

Good shielding and design will minimize or eliminate noise, interference problems to begin with.

Take care.
Steve




Re: Mylar cap polarity - Help [message #9054 is a reply to message #9053] Thu, 30 June 2005 11:13 Go to previous messageGo to next message
Steve is currently offline  Steve
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Registered: May 2009
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Forgot to add, the mylar is fairly poor, so it may not make a sonic difference.

Steve

Re: Mylar cap polarity - Help? [message #9055 is a reply to message #9050] Thu, 30 June 2005 13:55 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
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Registered: January 2001
Illuminati (33rd Degree)

Some film/foil caps have markings to indicate the outer layer. Some people prefer to treat these as signal inputs. But not all caps are marked that way.


Re: Mylar cap polarity - Help [message #9056 is a reply to message #9052] Thu, 30 June 2005 14:09 Go to previous messageGo to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18677
Registered: January 2001
Illuminati (33rd Degree)

Audience (Auricap) recommends connecting the outer plate as signal input to the capacitor, probably under the assumption that output impedance of a prior stage is lower than input impedance of the stage following. But I like your suggestion that outer plate goes to lowest impedance, regardless of signal direction. If you know which is the outer foil, it makes sense to tie it to the lower impedance connection, where it will act more as a shield.


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