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Capacitor brand/type for NAD amp?

Discussion in 'Electronic Repair' started by TDWesty, Jun 17, 2005.

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  1. TDWesty

    TDWesty Guest

    My NAD 3125 may need new caps (it is 20 years old). All original caps
    look fine, and are ELNA brand, either RE or CE series. I cannot find
    ELNA online, although I may check a local store. I've been told
    Panasonic FC series are good. Are they a suitable replacement for the
    originals? They are "low impedance" - is this the important criteria
    for audio? ELNA appears to be well respected in the audio world from a
    bit of searching I've done, so I don't want to lose any of the
    original NAD sound by using the wrong caps.

    The one problem my amp has (see earlier post) seems to be isolated to
    the left channel infrasonic filter section. Assuming I can resolve this
    be replacing the caps in that section, should I just quit there?

    Many people have said to just replace all caps on a 20 year old amp,
    but the Panasonic spec sheets show that 20-30 years is a reasonable
    lifespan for caps at near room temps. The 1000-2000 hrs ratings seem to
    be at the max operating temps. Replacing all the caps seems like a
    fair bit of trouble, especially if the result is a possible loss of
    sound quality if the new caps are inferior to the originals, in terms
    of audio quality. Any insight is appreciated!
     
  2. Tim Schwartz

    Tim Schwartz Guest

    Hello,

    I've had good luck with the Panasonic caps. I often order them from
    Digikey (www.digikey.com). I would not 'Shotgun' the entire amp, but I
    would replace the defective caps in both channels, even if only one of
    them was currently bad. I would not worry about the brand change.
    Though I'll warn you that discussing pros and cons of various brands of
    caps can lead to long boring threads on newsgroups. <G>

    Regards,
    Tim Schwartz
    Bristol Electronics
     
  3. Tim Martin

    Tim Martin Guest

    Panasonic FC capacitors are electrolytics. The high-value electrolytics you
    mentioned (50v 4700uF and 1000uF) will be used in the power supply section,
    which is working fine in your amplifier (I think you said your amplifier is
    working fine with CD and DVD inputs, but not with tuner and VCR inputs.)

    For the problem you have - weak signal on left channel when using tuner or
    VCR inputs - you need to establish the cause. I'd guess it's a defective
    switch or connection somewhere.

    It could be a very minor fault, but may take an engineer several hours to
    track down.

    Tim
     
  4. sofie

    sofie Guest

    TDWesty:
    The best advice I can give you is to stay focused and fix the "Left Channel"
    problem.... then you can evaluate the overall performance and make a
    decision about a "shotgun" repair involving ALL of the caps.....
    personally, if the amp is working fine after your specific repair, I
    wouldn't fix it.....
     
  5. I've got a '71 Quad system still working fine. The AM tuner has had a few
    sets of valves, and I've cleaned or replaced a few pots and switches. But
    not one cap...
     
  6. sssayers

    sssayers Guest

    I agree brand doesn't matter. I use Xicon brand from either Part
    Express or Mouser. Mouser's prices and selection of caps is better.
    The big caps are probably OK. I'd replace those in the amp and powe
    supply. You better believe 30 year old caps are bad, or will b
    soon! If you replace capacitors, it's only the electrolytic cap
    that you need to replace
     
  7. Engineer

    Engineer Guest

    (snip)

    Start with the switches, clean them thoroughly. I have fixed several
    recycled and junked stereo receivers from the 1970's an 80's and the
    most common fix is to clean the switches (next is dial lamps.) In one
    case the switch was damaged (no spares), so I jumpered the function on
    the board (only lost the tape-in option, no big deal, still have AUX.)
    Your problem does not suggest faulty electrolytic capacitors.
    Cheers,
    Roger
     
  8. TDWesty

    TDWesty Guest

    I've sprayed all the switches & pots with contact cleaner, and the
    resistance across the terminals off all the input switches are the same
    - about 0.5 ohms. It is a bank of 4 switches (tape, cd, tuner, phono)
    soldered directly to the board, so without a desoldering tool, removal
    looks to be fairly tricky. Tape works fine, CD & tuner are bad in the
    left channel.

    I may try to replace the transistor for the infrasonic filter, which is
    apparently bypassed for the tape input. I need to find one, it is not a
    common one - C1845.
     
  9. kip

    kip Guest

    Common as Dog Poo...MCM / Global has them.
    kip




    essage news:...
     
  10. Asimov

    Asimov Guest

    "TDWesty" bravely wrote to "All" (18 Jun 05 10:48:27)
    --- on the heady topic of "Re: Capacitor brand/type for NAD amp?"

    TD> From: "TDWesty" <>
    TD> Xref: aeinews sci.electronics.repair:50953 rec.audio.tech:21300

    TD> I've sprayed all the switches & pots with contact cleaner, and the
    TD> resistance across the terminals off all the input switches are the
    TD> same - about 0.5 ohms. It is a bank of 4 switches (tape, cd, tuner,
    TD> phono) soldered directly to the board, so without a desoldering tool,
    TD> removal looks to be fairly tricky. Tape works fine, CD & tuner are bad
    TD> in the left channel.

    TD> I may try to replace the transistor for the infrasonic filter, which
    TD> is apparently bypassed for the tape input. I need to find one, it is
    TD> not a common one - C1845.


    Add 2S prefix in front of C1845, you should find a 2SC1845 more easily.
    BTW the 2SC1845 is a "General Purpose" high gain transistor and it can
    be easily substituted by any with a suitable voltage that fits. Not that
    critical a part for audio usage.

    A*s*i*m*o*v

    .... A stereo system is the altar to the god of music.
     
  11. Tim Schwartz

    Tim Schwartz Guest

    Hello,

    Well, that transistor is a 2SC1845, and is really common.

    --Tim
     
  12. If you're not equipped for desoldering a switch, are you sure you
    should be contemplating a recap?
     
  13. TDWesty

    TDWesty Guest

    A fair point. :)

    But each cap can be done one at a time with minimal fuss and an iron.
    The switch bank has 24 pins and 4 switches clipped together in a rail,
    so I don't think it could be removed without a solder sucker.
    I've decided against a recap for now, at least until I get the left
    channel fixed and my speakers back in service so I can judge things
    better.
     
  14. I'd normally remove a multipole switch by clipping the contacts etc to
    minimise damage to the pcb. Many are a pretty tight mechanical fit.

    And I do have a desolder station.
     
  15. TDWesty

    TDWesty Guest

    I've only been able to find one manufacturer for the 2SC1845 -
    Fairchild, and Digi-Key doesn't carry this one for some reason (they
    have other Fairchild parts). Any tips on a substitution chart - I've
    been trying to match V, IC, and HFE closely, but haven't found anything
    DigiKey carries that is close enough. I would prefer to deal with a
    Canadian supplier to avoid border hassles. So far the NTE90 appears to
    be the only other close match.

    I'm confused a bit by your comment about "any with a suitable voltage"
    - isn't the gain significant? I can find some that match the 120V, 50ma
    rating, but very few with a gain of 600. I am assiming that I should
    replace both channels at once to avoid a mismatch, but wouldn't using a
    lower gain transistor cause problems? I don't have the schematic, so I
    don't know the exact function of this thing, but I do know it is in the
    infrasonic filter section. So I'm guessing the high gain is used to
    effect a sharp low freq roll off? In this case, perhaps the gain isn't
    that critical. Sorry if these are dumb questions...
     
  16. Guest

    Guest Guest

    : TDWesty:
    : The best advice I can give you is to stay focused and fix the "Left Channel"
    : problem.... then you can evaluate the overall performance and make a
    : decision about a "shotgun" repair involving ALL of the caps.....
    : personally, if the amp is working fine after your specific repair, I
    : wouldn't fix it.....
    : --
    : Best Regards,
    : Daniel Sofie
    : Electronics Supply & Repair

    Agreed. I have a Marantz receiver that is 30 years old. No reason to go in and
    replace all of the capacitors. It works fine. Fix what is defective. Leave
    it at that.

    b.
     
  17. Guest

    Guest Guest

    : The one problem my amp has (see earlier post) seems to be isolated to
    : the left channel infrasonic filter section. Assuming I can resolve this
    : be replacing the caps in that section, should I just quit there?

    I'd suggest finding the source of the problem vs. shotgunning parts that
    are likely not to fix the problem. The "low impedence" capacitor is probably
    a low ESR capacitor. Impedance is a result of the value of the capacitor
    which is intrinsic, plus the inductive reactance of the leads/foils.

    Most stereo equipment is "step and repeated" in their PC board designs.
    You have one working side and one with low signal. Compare (using an
    oscilloscope) the working side components vs. the nonworking side.
    It's helpful to have a schematic to see where the positions of the
    components are but a skilled technician/engineer can often follow the
    signal paths by the physical layout.

    I have repaired electronic equipment for decades and have never seen a
    need to brute-force "every electrolytic capacitor" in any piece of
    equipment. It just seems foolish to me. Especially if the equipment
    has been in use (electrolytic capacitors do fail by "reversed polarity"

    B.
     
  18. clifto

    clifto Guest

    I have, but the equipment was on the production line. :)
     
  19. You should stop hanging around those wasted, commie, ex-hippie
    college professors.
     
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