Dynamic microphone into RCA input?

Discussion in 'Pro Audio' started by dmar, May 4, 2006.

  1. dmar

    dmar Guest


    I have what may seem like an odd question: Can I use an adapter to plug
    a dynamic microphone with 1/4" plug directly into the RCA "Line In"
    input of a cassette deck, for recording purposes? Is it simply a
    matter of getting a 1/4" to RCA adapter, or are there issues with
    levels, impedence....or other...? Is the RCA input different in any
    way from the 1/4" microphone inputs that are on many cassette decks?

    Why would I want to do that? Here's the background: I recently picked
    up a decent, but old, Denon cassette deck on EBay for recording my band
    during rehearsal. I did not want to get involved in multi-track
    recording -- just simple stereo recording to listen back easily. And,
    well, I'm trying to do all this on the cheap! The deck works great,
    except that the 1/4" microphone inputs on the front of the unit are a
    bit sensitive -- if a cord gets jostled, the connection shorts and a
    very pronounced "hum" results. Jiggle the cable and I'm back in
    business, but often only after much of a rehearsal session is over and

    So I can probably get the deck serviced, but first I am wondering if a
    couple of simple 1/4" to RCA adapters will do the trick for me.

    Thanks in advance...
    dmar, May 4, 2006
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  2. dmar

    GregS Guest

    Good question is where is the connection problem. Is it the mic cord
    or the tape jacks. Have you tried cleaning. You would need a preamp or mixer to
    use the rear tape jacks.

    GregS, May 4, 2006
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  3. dmar

    Mike Rivers Guest

    Not unless you're recording things like explosions. The line input
    doesn't have sufficient gain for normal sound levels going into a
    microphone. That's the microphone inputs are for.
    Yes. The microphone inputs have enough gain for a microphone.
    Get a spray can of contact cleaner and spray it sparingly into the
    jack. You have a bad connection. Or it might be the cable on your
    microphone that's defective. Get what's broken fixed and you'll be
    Mike Rivers, May 4, 2006
  4. dmar

    Chevdo Guest

    the loose connection requiring a melting of solder is far more likely than a
    dirty jack, in my opinion. A jack would have to be incredibly dirty to act
    like that. I've also NEVER fixed a bad pot by spraying it with contact
    cleaner, which is always the first suggestion for a noisy pot on the repair
    newsgroup (and I've encountered a lot of bad pots)...
    Chevdo, May 4, 2006
  5. dmar

    Chevdo Guest

    in fact, now that I think about it, I've never fixed anything with contact
    cleaner. Even the one application you'd think it would work hasn't in my
    experience - that is, to clean off crud from battery terminals from corroded
    batteries. And in that case a scrape from a knife does what contact cleaner
    can't. I'm going to go out on a limb here and suggest that contact cleaner is
    entirely useless, or at the very least, not nearly as useful as it would need
    to be to warrant being mentioned as often as it is as a fix for so many things
    it doesn't fix...
    Chevdo, May 4, 2006
  6. dmar

    Carey Carlan Guest

    Yes, but the levels will be very low. You'll either not hear much
    signal, or hear it with lots of hiss. You'll want a pair of mic preamps
    to do this properly (the electronics sitting behind those Mic In jacks
    on the front of the deck).
    The "hum" indicates an open circuit, not a short (shorts are silent).
    One side or the other of the connector is not making contact.

    1) Is it the cassette deck or the cable that's failing? Have you tried
    other cables? Other microphones? What shape is the tip of the cable?
    Some cheap microphones come with slightly odd shaped connectors that
    don't seat well in some jacks.

    2) If all your cables and mics have the same problem, then it's the
    cassette deck. Test it with the cover off and see if anything is loose.
    If not, clean the connectors inside. Ideally you can hit the jacks with
    a bit of sandpaper followed by some Cailube or equivalent. Nothing more
    should be necessary.
    Carey Carlan, May 4, 2006
  7. dmar

    Chevdo Guest

    ...except the solder to fix the loose wire to the jack...
    Chevdo, May 5, 2006
  8. dmar

    Mike Rivers Guest

    know which end of the soldering iron to blow into, much less how to
    repair a faulty connector. However, he did say something about when
    wiggling the plug in the jack, it got noisy, so let's hope it's a dirty
    jack. He did say "hum" but not everyone actually means "hum" when they
    say it. That would suggest a broken shield, but contact cleaner is
    safer and it might solve the problem.
    We're not talking about noisy pots here. Have you never had a noisy
    jack? I have, and I keep a can of contact cleaner next to my patchbay.
    Mike Rivers, May 5, 2006
  9. dmar

    Mike Rivers Guest

    You mean you've never used it to clean switch contacts? It doesn't
    really "fix" a pot, but it can sometimes get you through a session or a
    gig in an emergency.
    I think it's quite inappropriate for that. If the're akaline batteries,
    you use vinegar. If they're acid-based batteries, you use baking soda.
    Right - it removes the plating or tinning from the contacts, making
    them get cruddy faster. However, abrasive cleaning is appropriate for
    the lead terminals on a car battery, or for a bare copper bus bar.
    It rarely does harm unless you use too much of it, and while it might
    not be a permanent fix, it might help to diagnose a problem. For
    instance, if you spray a crackly pot and it still crackles, that might
    mean that there's a leaky capacitor putting DC on the element. Or if it
    doesn't fix a switch or jack contact, it could mean that the metal is
    Mike Rivers, May 5, 2006
  10. dmar

    Chevdo Guest

    I spray it on, it never seems to bring any dead switches back to life or reduce
    noisyness of switches or pots. I guess I have used it effectively to clean the
    heads of a cassette deck..
    tinning/plating on a battery contact? I've never seen such a thing, but then
    again I actually have only seen several dozen..
    Chevdo, May 5, 2006
  11. dmar

    Chevdo Guest

    I've never had a noisy jack that could be fixed with contact cleaner. Are you
    dipping your plugs in mud before inserting them into jacks? I seriously doubt
    your environment is cruddier than mine, for years I was razzed for being a
    two-pack-a-day smoker with yellowed walls and yellow crud on the windows. And
    still, that yellow crud never prevented a jack from working properly. I think
    your can of contact cleaner next to your patchbay is superstitious, but if it
    makes you feel better, then your sessions are libel to run more smoothly..
    Chevdo, May 5, 2006
  12. dmar

    Chevdo Guest

    By the way, I've also installed about a dozen 1/4" jacks to various casio and
    radio shack synthesizers that only had speaker output, so I am quite familiar
    with the physical properties of a 1/4" jack. If you look at how it works, you
    will see that it would be very difficult for most types of dirt or grime,
    besides large amounts of goopy material that hardens, to prevent a connection
    from being made. The ring will make contact no matter what, so only the tip
    has to hit the end of the jack where the piece of metal it makes contact with
    is. The tip makes contact by having the bent piece of metal slide into the
    dip between the tip and the sleeve, which is what causes the 'click' you
    hear/feel when you insert the jack. That action causes a significant
    amount of force, and leaves a large surface area of the metal making contact
    with the tip. Any obstruction would have to be particularly solid,
    substantial, and strongly affixed to the metal, to prevent that connection
    connection from being made, and in fact, the jack wouldn't be able to be
    inserted all the way if there were something that significant obstructing it.
    The 1/4" jack is a nice design, it should work like a charm under the worst
    conditions imaginable.
    Chevdo, May 5, 2006
  13. dmar

    Ty Ford Guest

    Probably not.

    There -10dB inputs more than likely.

    Ty Ford

    -- Ty Ford's equipment reviews, audio samples, rates and other audiocentric
    stuff are at www.tyford.com
    Ty Ford, May 5, 2006
  14. dmar

    Mike Rivers Guest

    Troll alert!
    Mike Rivers, May 5, 2006
  15. dmar

    Mike Rivers Guest

    There are many types of 1/4" jacks. Some are better than others. Some
    are not 1/4" (as are some plugs).
    The problem isn't dirt, grime, and goop., It's a very thin layer of
    corrosion that you often cant' see. It makes the plug-to-jack contact
    like a semiconductor and you get distortion from the rectification
    action, as well as low signal level.
    But it doesn't always make solid contact. The hole in the jack is
    always larger in diameter than the sleeve of the plug (otherwise you
    couldn't get it in and out easily) and they all wobble a bit. Long
    frame jacks wobble less, but I'm sure you're not using those on your
    And what do you get when you have a straight piece of metal contacting
    a round shaft? You get a single point contact area. That doesn't leave
    a lot of room for anything that might insultate it. And some of them
    don't have much pressure and don't wipe very well.

    You're very lucky that you've never had a problem with a jack, and
    you're using the wroing kind of cleaner if you have never had success
    with it (unless your contacts are just so badly corroded or dirty that
    it's beyond chemical cleaning.
    Mike Rivers, May 5, 2006
  16. dmar

    Bob Quintal Guest

    Just spraying it on the back of a closed switch or pot rarely
    works, you have to get it inside the switch or potentiometer.
    Cleaning jacks sometimes is easier, but again, spraying is not
    very effective. I apply stuff with a syringe, and it does a much
    better job.

    Depends if you mean an automotive battery, versus the batteries
    used in electronics. the AA, AAA C and D cells as well as the
    9Volt MN-1604 are almost always tin or chrome plated.
    Bob Quintal, May 6, 2006
  17. dmar

    dmar Guest

    Thanks for the good constructive information everyone - well, other
    than the comment that the "poster wouldn't know which end of the
    soldering iron to blow into". I'm a little further along than that,
    although I have to admit I'm not sure I am ready to try to replace the
    jacks myself, if it comes to that.

    First I'll try the contact cleaner, since there's nothing to loose in
    trying. It is definitely the cassette deck, incidentally, and not the
    cables -- that's the first thing I checked, but they work (and the
    connections look) fine.

    Also, I appreciate the suggestion from GregS regarding a mixer. After
    a little research, it appears a mixer would be a great option. Seems
    like that would give me lots more flexibility in recording, and I've
    seen some basic/inexpensive models (eg, Behringer MX602A) selling on

    I did open up my deck and remove the front of the unit, but because of
    the design of this unit (a Denon DR-M4), the jacks are still buried
    beneath lots of stuff (front controls & assoc. board). It appears I'd
    have to do major surgery just to get to the jacks. For what it is
    worth, they did not look like the 1/4" jacks I've seen in speaker
    cabinets, etc. They were basically little black plastic cubes - it
    looked like the tops snap off to get at the insides but again I
    couldn't get to them to see more.

    Interesting to learn about the differences between the line in and
    microphone inputs. Certainly makes sense...I figured they would differ
    in terms of level or something similar. Interesting too that a "hum"
    is an indication of an open circuit, not a short. What I am
    experiencing is most definitely a hum, and a pretty abnoxious one at
    that - it registers on the meter and gets recorded onto the tape, which
    of course is the whole problem. And when there is the hum, there's
    nothing coming from the mic - it's either all hum, or all mic as fas as
    I can tell.

    One thing I did notice is that the plug seems loose in the jack -
    certainly not that snug "snap" you typically get.

    Anyway, I'm rambling now. Thanks again for the great info. I'll post
    again, for the record, if the contact cleaner works : )
    dmar, May 8, 2006
  18. dmar

    Mike Rivers Guest

    That's a metaphor for
    Those are the worst kind of jacks for reliability. They're designed to
    be very compact, and aren't built with very much spring tension. Also,
    some of them have plastic bushings with just a single strip of metal
    along the length for the sleeve contact. That doesn't always make good
    contact. But you can't replace them with anything better, just new ones
    of the same type. And, yeah, you can snap the top off, but that snap
    you hear will be the sound of the jack housing breaking. Just spray
    contact cleaner in through the hole where the plug goes in.
    That's the problem with this type of jack. But it's a very common type,
    used on many, many consumer products. I guess they figure that most
    people will outgrow the unit before the jack wears out (in truth, very
    few people use mic inputs on their cassette recorders unless it's a
    portable recorder), but it does make for problems when people buy
    worn-out decks on eBay.
    Mike Rivers, May 8, 2006
  19. dmar

    Daniel Fox Guest

    Uhhh... if you've never seen the surface plate come off from abrasive
    substances or "scratching" tools (like a knife) you haven't seen
    "several dozen" battery contacts.

    And re: contact cleaner and potentiometers. Where are you spraying?
    It goes inside the pot.

    Daniel Fox, May 8, 2006
  20. dmar

    GregS Guest

    I hate nickel plated materials for contact. Seems to me the orginal phone plugs as used by the
    telephone people, were like brass or some soft metal that cleaned itself with
    each insertion. Silver is like that.

    Sometimes I have drilled little holes into pots to squirt some fluid in. I had a terrible
    time with a Nicolet oscilloscope where I tried cleaning many times, but
    only after figuring out how to bend the case, was I successfull.

    GregS, May 8, 2006
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