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Thread: Silver Mica Caps

  1. #1
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    Silver Mica Caps

    Interested to hear opinions from builders on their experiences with using silver mica vs. ceramic caps in various positions in the amp such as the tone stack or frequency bypass on an inter stage attenuator. Especially with regard to reliability. I have seen many SM caps go noisy but not the ceramics. Interested to see if others have had the same experience.

  2. #2
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    I've seen the oposite. Never seen a SM cap go noisy, they typically seem to reduce noise, and they sound a tad smoother.

  3. #3
    Junior Member Robert8192's Avatar
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    I also have a capacitor related question. There appears to
    be 5 kinds of caps: caramic disk, Electrolitic-Caps,
    Poly film (whether axial or in box form) , Mylar (the green guys),
    and silver miva. (probably more out there.)

    I am building the following preamp, and could use sugestions
    as to the ideal caps to use, But also the theory as to why they
    perform the best.. I believe I can pin down when
    an - E-CAP is used... But the cap that is 0.33 ??(#2)?? e-cap
    or film. Please use the RED-numbers I have added..

    I also understand #6 and #9 are coupling caps.. should be larger
    sprague type poly film to attenuate all dc volts out-
    To keep this on topic for this post, where would or could
    silver mica be used??

    Thanks for all the help in advance wizard333 and enzo.

    Robert.

  4. #4
    Senior Member Enzo's Avatar
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    Hi Robert, welcome to the forum. May I suggest start a new thread for your amp design. It is not good forum etiquette to hop in and "hijack" another guy's thread.

    Welcome to SWEINC as well. I never have had a problem with silver mica caps, but while you can find 1500v ceramics or .1uf ceramics, I find the selection of CM caps to be limited. So it is simple to find a 250pf treble cap in either ceramic or mica, finding some large couplers may not be.

    And Robert (See how it gets clumsy trying to answer two different guys in one post?), I think a real important question is what is the B+ voltage in your circuit? Your drawing looks like a commercial schematic for some tube boost pedal circuit. Note the different cap symbols on it? Some of those have a tube but it is running at 12v or something. The listed plate caps are only rated at 100v on the print. SO you don;t need big 600v caps to block 12v of DC.

    Especially in a little pedal, caps may be chosen on the basis of size. Look up a 1uf 50v e-cap at Mouser, and find the dimensions on the data sheet. Now look up the same rated part in some sort of film like mylar. Check the size. How many of those will fit in your little circuit physically?

    I think if you make a chart on a sheet of paper for each cap in the circuit, you will find a very limited selection for some. Run a list of the cap values down the left and the various types across the top. And put an X where you find one of each type in a catalog like Mouser. You will find few over 1uf that are not lytics, at least not in handy sizes.

    You left tantalum caps off the list.
    Education is what you're left with after you have forgotten what you have learned.

  5. #5
    Junior Member Robert8192's Avatar
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    Thanks Enzo, sorry,
    I was going to make my own thread, but I saw this one
    was dealing with capacitors, so I figured..

    I would always go with ceramic disks in a low voltage,
    non-critical area of a circuit. as ceramic capacitors are generally smaller, cheaper although their capacitance varies strongly with voltage
    and they age poorly. - mica capacitors are extremely reliable, stable and
    tolerant to high temperatures and voltages, but are more expensive.



    I knows there are more types :: multilayer ceramic, ceramic disc, multilayer polyester film, tubular ceramic, polystyrene, metalized polyester film, aluminum electrolytic, tantalum., silver mica and even glass.

    Well, you found me out. I am putting together a little preamp based on the
    TK999HT. I am going to be applying a mear 45V to it, so if you
    see any significant changes that might need to be made,
    I could use all the help I can get.


    As I look at this schematic, I would go with

    #1: 1uF Ecap #2: 0.33Ecap #3 :ceramic disk #4 :Ceramic
    #5:ECAP #6: polyfilm

    #7:Ceramic #8:ECAP #9olyfilm
    #10:
    #11: #12:


    For #13 : #14 : #15: #16: #17: I will propably use green mylar
    or some yellow met poly-film. caps mixed together.
    This kind of a tone stack from the Hiwat line of amps.

    #18: #19:
    #20:Ecap #21 Mylar: #22:Ecap

    If anyone has any kind of info- please help me.
    If this is confusing to me, it must confuse other
    new posters, and it holds me back from building
    and planning things. And I was hoping someone would explain
    some of it as there are a lot of real knowledgable people
    in this forum.

    Thanks

  6. #6
    Noodle of Reality Steve Conner's Avatar
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    10, 11, 12, 18, 19 could all be plastic film. 18, 19 could alternatively be ceramic.

    Here are some guidelines on capacitor choice. They're my own personal opinion and may be controversial.

    Below 1nF use ceramic or silver mica. It doesn't really matter which. Cork sniffers will tell you that ceramic sounds harsh, dirty, etc, but I don't believe it. The reason for this guideline is simply that it's difficult to get plastic film caps below 1nF, and they tend to be expensive.

    There are lots of different kinds of ceramic capacitors, and the good ones can be as stable, etc. as silver mica. Others are highly non-linear and temperature sensitive, you should avoid these altogether. But generally the bad parts are the low-voltage, high capacitance ones, which you won't be using anyway.

    Between 1nF and 1uF use plastic film. For audio circuits, the particular kind of plastic doesn't matter. Mylar is cheapest.

    Try to avoid electrolytic and tantalum altogether, but above 1uF you will be forced to use them for physical size and cost reasons.

    When you see a capacitor symbol with one white plate and one black, that means it's polarized. Therefore the schematic is telling you to use an electrolytic (and the white plate is positive) However, I'd use plastic film for the 0.33uF/50V part myself. A 0.33uF, 50V Mylar film capacitor isn't that large or expensive.
    Last edited by Steve Conner; 01-04-2010 at 12:50 PM.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  7. #7
    Senior Member JHow's Avatar
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    Try to avoid electrolytic and tantalum altogether, but above 1uF you will be forced to use them for physical size and cost reasons.
    I second the opinion on electrolytics - you will have to replace them eventually.

    I admit to having a weakness for small 60's era transistor radios. They all need electolytics done - and nine times out of ten, that's the only fault.
    Last edited by tboy; 01-05-2010 at 08:16 PM. Reason: quote tag repair

  8. #8
    Supporting Member tubeswell's Avatar
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    Quote Originally Posted by Steve Conner View Post
    Cork sniffers will tell you that ceramic sounds harsh, dirty, etc
    I'm one-a them. I definitely prefer silver micas (over disc ceramic) for treble caps. YMMV
    Building a better world (one tube amp at a time)

  9. #9
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    Another drawback of ceramic caps is their tendency to be temperature sensitive (with the obvious exception of NP0s). That's one of the reasons why I prefer SM caps for low-capacitance audio applications ( "bright" caps etc.).

    JM2CW

    Cheers

    Bob
    Hoc unum scio: me nihil scire.

  10. #10
    Senior Member Pedro Vecino's Avatar
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    Quote Originally Posted by SWEINC View Post
    I have seen many SM caps go noisy but not the ceramics. Interested to see if others have had the same experience.
    Yes, it is. This was common enough in AC30īs of the 90s made by Korg. I donīt know if the brand and model had relation, but it is a problem that I have seen often in these amps.
    Regards

  11. #11
    Noodle of Reality Steve Conner's Avatar
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    Well, for those who don't like silver mica or ceramic, there is a third option for small capacitances, polystyrene film.

    http://hobby_elec.piclist.com/picture/cond9.jpg
    from
    Capacitors

    These are actually my favourite for treble caps: I've never used silver mica or ceramic in a tube amp build. They have a fair bit of self-inductance though, so you might not want to use them for snubbing, RF filtering, or compensation.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Quote Originally Posted by Robert M. Martinelli View Post
    Another drawback of ceramic caps is their tendency to be temperature sensitive (with the obvious exception of NP0s). That's one of the reasons why I prefer SM caps for low-capacitance audio applications ( "bright" caps etc.).

    JM2CW

    Cheers

    Bob
    Most class 1 ceramics (NP0, C0G, SL) are good in this sense, and you may be hardpressed to tell the difference tone wise from a SM

  13. #13
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    sometimes it's even possible to track down axial metpoly props in pF values, I have been lucky enough to do it a couple of times.... and it is somewhat easier still to track them down as radial box types. Kemet makes some good ones with a 5mm footprint that are perfect for replacing ceramics in a PCB. Wima also makes some, with care an some forethought it is even possible to use them in turret builds, although hard to swap out.

  14. #14
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    Boy, this couldn't be more timely for me. I am re building a 1976 Bassman 100 and the only perplexing question I keep asking myself is ...what types of caps to use. The power supply caps were easy, thats done. The tone stack and coupling caps are another story. Fender uses both ceramic disks and polys. Which is better? Is it a $$$ issue? Then to make matters even worse, I open up the Antique Electronics cat and come accross Alessandro High End Coupling Caps. Come on... a .1 , 630 volt for $19.50 each. Is this the capacitor equivilent of Monster Cable? Is there any definitive info on this forum or others that exams this mystery of life?

  15. #15
    Supporting Member tubeswell's Avatar
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    Quote Originally Posted by nwguy View Post
    Is it a $$$ issue? Then to make matters even worse, I open up the Antique Electronics cat and come accross Alessandro High End Coupling Caps. Come on... a .1 , 630 volt for $19.50 each. Is this the capacitor equivilent of Monster Cable?
    Is $$$ an issue? Well when you see that sort of stuff it sure is. People out there just waitin' to take your money.

    (But pssst, if you want to get your hands on something real groovy, I got some golden tone-reflecting paint in a spray can you can spray on the inside of your cab - extra special price to you today $99.99. Or if you buy today I will chuck a whole extra spray can in for only an extra $49.99 - that's under $150 for 2 cans! Looks exactly like a Dulux can of gold spray paint but don't be fooled Jimmy, this is the real McCoy)

    Quote Originally Posted by nwguy View Post
    Is there any definitive info on this forum or others that exams this mystery of life?
    Plenty of witticisms posted hereabouts on this mystery for sure
    Building a better world (one tube amp at a time)

  16. #16
    Junior Member Robert8192's Avatar
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    Well , thanks to Steve, JHow, tubeswell, and Robert.
    A huge help.
    I have had all my questions answered as to my issues on the preamp.

    Glad to see so many responces. There appears to be some oppinion-oriented

    reasons to like SM and some prefer CD. I think since SM lasts longer, I would go
    with SM on my treble caps, IE in my tone-ckt it is the 470pF (#13, 16, 18)

    As to the question about Alessandro coupling caps?? Since the 1940,s many
    different kinds of amps were built. Many purists took to their favorite
    kind of parts and believe they are best. Remember, that parts and
    manufacturing processes sometimes get better, and better parts can arrise.
    I've even seen on the internet a beeswax-film caps that sell for 55$ for a .4uF and a 6uF was like 155.00$ FOF-LOL- OMG - WTF.
    To nwguy, anything from .1 to .05 Ceramic. and the smaller stuff , make it
    poly.. It just has a better ring to it. But I am knew to this myself..

    Maybe someone having the schematic for the Bassman can list the caps
    compliment by number and give some pointers there...

    So when the smoke and flux fly for nwguy, he's putting in the most
    perfect caps for that old amp. and remember , give Electrolitics about
    5-10 yrs before they die and ceramic about 10-15 yrs before they die.
    (depending on use)
    Again, a huge thanks.

  17. #17
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    Quote Originally Posted by Joey Voltage View Post
    Most class 1 ceramics (NP0, C0G, SL) are good in this sense, and you may be hardpressed to tell the difference tone wise from a SM
    Joey,
    If you re-read my post, you will find I actually dealt with NP0s by stating "with the obvious exception of NP0s" - obvious because NP0 means "no temperature drift, neither positive nor negative". Ceramics with other temperature coefficients (e.g. N750 - standing for Negative Temperature Coefficient, drift 750 ppm/°C) are usually found in RF circuits (e.g. oscillators) to compensate for other components' thermal drifts which may affect the RF circuit's frequency stability.

    Tone-wise, maybe I'm a cork-sniffer, maybe not, but I find ceramics "gravelly", furthermore, they have a known tendency to change their capacitance depending on the voltage applied, so I think I'll stick with the more stable poly (-propylene, -styrene, -whatever) and SM caps when possible, relegating ceramics to the "RF realm" only.

    Cheers

    Bob
    Hoc unum scio: me nihil scire.

  18. #18
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    Quote Originally Posted by Robert M. Martinelli View Post
    Joey,
    If you re-read my post, you will find I actually dealt with NP0s by stating "with the obvious exception of NP0s" - obvious because NP0 means "no temperature drift, neither positive nor negative". Ceramics with other temperature coefficients (e.g. N750 - standing for Negative Temperature Coefficient, drift 750 ppm/°C) are usually found in RF circuits (e.g. oscillators) to compensate for other components' thermal drifts which may affect the RF circuit's frequency stability.

    Tone-wise, maybe I'm a cork-sniffer, maybe not, but I find ceramics "gravelly", furthermore, they have a known tendency to change their capacitance depending on the voltage applied, so I think I'll stick with the more stable poly (-propylene, -styrene, -whatever) and SM caps when possible, relegating ceramics to the "RF realm" only.

    Cheers

    Bob
    Bob,

    I was mostly just clarifying what I meant by "class 1" ceramic, that part may not be too obvious to some

    It is true that ceramics may impose some non-linearities, but yes most noticeable when being run very close to their maximum working voltage, this actually may not be a bad thing though. although I tend to use poly's whenever I can find them.

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