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  1. #1
    Im building a small cmoy amp and my goal is to reduce it to SMD parts only, now I have a friend who repairs various electronic equipment and I asked if I could replace it with a lower voltage. He said yes along at its higher than the highest voltage on the power rail, anything above plus 20% would be a waste.
    So heres my question in your opinion could I replace 1.0 F 100V metallized polyester capacitor with EEE-FC1V1R0AR . Also why would he choose a 100v Cap on an 18v max rail?

    All info I have tried to put in the attached picture including the circuit

    Click image for larger version. 

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    From the creator of the amp at Tangentsoft :

    C1 (film)
    To understand the issues involved in deciding whether to add C1 or to put a jumper across this position, read my article Input Capacitors for Headphone Amps.
    Many types of capacitors will fit here, up to 0.4" pin pitch. You will probably have to go with metallized polypropylene or polyester to fit a usefully high value cap here.
    Optional? Yes, jumper across it.
    Largest Part Size: 13mm 6mm. Lead spacing 10mm.


    I read the article but there was nothing about voltage

    Fiction is far more plausible when wrapped around a thread of truth

    Nothing great was ever achieved without enthusiasm.
    Ralph Waldo Emerson

  2. #2
    I don't think you can replace that capacitor with an electrolytic.
    The original one is a pass through and will need to see currents in both directions.
    I would tend to go with the designers schematic as I would assume he has done some form of testing.
    Electrolytes are used to smooth dc.

    Peter

  3. #3
    Quote Originally Posted by ptjw7uk View Post
    I don't think you can replace that capacitor with an electrolytic.
    The original one is a pass through and will need to see currents in both directions.
    I would tend to go with the designers schematic as I would assume he has done some form of testing.
    Electrolytes are used to smooth dc.

    Peter
    Hi , thanks for the answer , do they do a pass through SMD replacement for the cap ? How would I search for the part, bit new to this sorry :)

    Actuall I might just replace all the resistors with SMD and leave the rest as through hole I think I will have enough room in the end.
    Last edited by Fivetide; 16-07-2013 at 06:09 PM.

    Fiction is far more plausible when wrapped around a thread of truth

    Nothing great was ever achieved without enthusiasm.
    Ralph Waldo Emerson

  4. #4
    Voltage should be pretty much irrelevant for an input capacitor unless your source has a massive DC offset. Making it a bit higher than the supply seems a reasonable start - the original may well be specified as 100v just because that's one of the more common voltage ranges for that type of capacitor - metallised polyester don't seem to go below 50v and 100v is more common than 63v which is the lowest common voltage in farnells list.

    Definitely don't use an electrolytic. The article you linked to describes the choices pretty well - basically work out the value for the amount of bass attenuation you can live with and then go down the quality levels until you find something that will fit at an acceptable price.

  5. #5
    I think that the reason they use the polyester type is to get a more uniform part.
    The high voltage is just really an indication of the capacitors construction type in that the polyester has a high breakdown voltage.
    You will have to trawl the catalogues to find the smallest physical size for that type of capacitor, if memory serves most of that type will be on the larger side!

    peter

    Try these quite small http://www.futurlec.com/Capacitors/C1000UPF.shtml
    Last edited by ptjw7uk; 17-07-2013 at 08:26 AM. Reason: add link

  6. #6
    Thanks for the link I actually use this part on another project never thought of using it on this :) doh !

    Fiction is far more plausible when wrapped around a thread of truth

    Nothing great was ever achieved without enthusiasm.
    Ralph Waldo Emerson

  7. #7
    Slightly off topic (curiousity has got the better of me)...the schematic you posted shows a bipolar supply, so why are they using a virtual ground IC in the power supply section?

    There are parts of your schematic cutoff from view so maybe that the bit of the puzzle I'm missing!
    Last edited by HankMcSpank; 17-07-2013 at 06:30 PM.

  8. #8
    I work in one of the UKs best HiFi R&D departments so I could answer this one!

    People think higher voltage elec. caps sound better as they are meant to be more linear with change in voltage on their plates. Film is the best to use in this application. Use a large ECHU capacitor perhaps use two 470nF in parallel rated at 10V or 16V is absolutely fine.

    Slightly off topic (curiousity has got the better of me)...the schematic you posted shows a bipolar supply, so why are they using a virtual ground IC in the power supply section?

    There are parts of your schematic cutoff from view so maybe that the bit of the puzzle I'm missing!
    If you mean R3 and R4 they form the global closed loop feedback.

  9. #9
    Oh yes if you want to make an ultimate headphone amplifier use an LME49600 driven with a LME49990 with the 49600 in the 49990 feedback loop. Very simple similar to the one you post just much better.

  10. #10
    Quote Originally Posted by Boscoe View Post
    I work in one of the UKs best HiFi R&D departments so I could answer this one!

    People think higher voltage elec. caps sound better as they are meant to be more linear with change in voltage on their plates. Film is the best to use in this application. Use a large ECHU capacitor perhaps use two 470nF in parallel rated at 10V or 16V is absolutely fine.



    If you mean R3 and R4 they form the global closed loop feedback.
    Thats awsome thanks for the advice Boscoe :) Do you think I can convert this to SMD ? As your the first real sound expert I've talked to. I've spent months trying to learn this stuff but i'm just scratching the surface, what i really need is a good CMoy design that I can use SMD parts on so I can get it small enough and cheap enough to shoehorn into a tabbaco tin with 2 x 9v batteries. Any ideas ? :) I wont lie, I intend to sell them, I need the money lol

    Fiction is far more plausible when wrapped around a thread of truth

    Nothing great was ever achieved without enthusiasm.
    Ralph Waldo Emerson

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