Conference napalm::guitar

    I played rock music in the 70's on an ES335 for a few years.  I had no
    problems until I had to play at larger clubs at higher volume.  I could
    only control the feedback by fiddling with the bass/treble controls
    and/or distance I stood from my amp.  Eventually I fixed it permanently
    by buying Les Pauls/SG's.  I could not bring myself to tape/stuff, or
    otherwise spooge up a beautiful cherry red ES!  
    
    I could, on demand, get all the feedback/sustain I wanted, tho!
    
    dawg

    I used to play an ES335 at HIGH VOLUME in the early 80s.  I had
    .012's on there, and that thing just used to SCREAM!  Granted,
    I needed a "kill" switch, as the sympathetic resonance alone 
    would kill you even with the volume off, but it sustained for
    days.

    I remember when I used to go for the intentional feedback/sustain (on
    Santana tunes when I would drag out a solo for a few days), the string
    that was providing the effect would vibrate so violently, I could watch
    it shake......and then I had to go back between sets and tighten up the
    screws that held the tuning pegs on!   
    
    \   /
    O   O
   (  *  )
    vvvvv
    ^^^^^
    dawg (lying about the loose screws part, of course)

    Does it *hum* or *feed back* or both ?
    What frequency(ies) ?
    Paul
    

    Paul
    
       It produces a constant low hum with occasional feedback. This is at
       approximately 5 ft from amp. at half volume. Tone controls both set
       half way. I'm afraid this will be even worse at on stage conditions.
       I find it lessens the feedback by removing treble, but this really
       impacts the sound. Almost forgotyt I'm plugged into the low gain 
       channel.
        Bob
    

    Bob,
    
    It's important to separate hum from feedback, so let me define them, at
    least temporarily: hum is an electrical phenomenon, feedback is an 
    acoustic phenomenon.  Given that definition, are you still getting hum?  
    If you are, then you've got some kind of signal problem: cords, 
    connectors, etc.
    
    Acoustic guitars usually get feedback somewhere around B to D on the 
    low E string if'n you turn the suckers up loud.  For example, I have a
    Gibson L-7C, a big fat jazz guitar that feeds back at C#.  I cured it
    by putting a graphic EQ in line with the guitar signal and dropping the
    offending frequency 3 to 6dB.  A better solution, IMHO, would be to use
    a parametric EQ in line, to better tune the center frequency and adjust
    the filter width.  

    John
    
       I tried things out last night and you were right. It is a low
    frequency feedback and not a hum. By muting the strings the hum
    went away. So' I played with the EQ and was able to filter out
    the low feedback and the occasional high feedback. I was able to
    turn up to stage volume. The only problem I find is the sound
    quality. It has lost the acoustic guitar sound I wanted. I can 
    actually adjust my tone controls on my Les Paul and produce a
    nicer tone. Over the weekend I hope to get some time to try a
    few experiments. Such as make up something to cover the sound
    hole to see what that buys me...try by passing the internal mike
    and use a external mike.
    Thanks for your help. An accoustic in the hands of a solid body
    electric player is a dangerous thing.
         Bob
    

    In .5, you say that this occurs when you are 5 ft from the amp at half
    volume.
    
    I'm trying to ask this without sounding like a wiseguy, but could you
    spring for a longer cable?  Five feet sounds like you're too close no
    matter what else is or is not functioning properly.
    \Gary

    Gary
    
       Its not the chord length. I'm trying to practice under what I
    believe will be normal stage conditions. Blues clubs tend to have
    small stages. Last night matter of fact I was less than 4 ft. 
    from the amp. So' I guess I'm trying to debug the problem before
    I bring it out on stage.
          Bob
    

    How big is the room you rehearse in???
    
                                                  stig

    Stig
    
       Rehearsal room is large enough I can easily stretch out 10' cords. I
       fixed it over the weekend. The sound hole disc I mentioned cures the
       problem. It works great. I know have the tone I want. At the volume
       I need. I was actually able to get within three feet of the amp 
       before it started feeding back. Pops on and off for use plugged or
       unplugged. Picked it up for $12.00. Cheap investment.
    
                             Regards
                               Bob
    

    Bob - 
    Glad for the happy ending.  I'll be honest with you, I still have
    trouble picturing an Ovation acoustic/electic on a small stage in a
    smoky lowdown juke joint... that's why I was wondering why you were
    standing so close.  Now if you'd have said an ES-335...   ;7)
    \Gary

    Gary
    
    The accoustic is for cashing in on some (Clapton unplugged) tunes. You
    are right, usually the other guitarist uses a ES-330 1960 version that
    had two single phase pickups and I use a Fender Strat.
    He uses a Martin D-28 accoustic with an internal mike. I don't know
    what the difference is in the mikes but his doesn't feedback as bad as
    the Ovation. Then again an Ovation is nice, but it ain't a Martin. Of
    course it doesn't carry the price tag either.
    Bob
    

    I think I'll send you E-mail on feedback vs. hum just for reference. In
    the meantime, there's another idea that can be useful in some settings.
    Run the Ovation through a small amp set to sound exactly like what you
    want at modest volume, then mike the small amp through the PA system.
    This works for such "nasties" as cupped hands over a blues harp. You
    might also try replacing your amp & speaker with something that doesn't
    resonate near the same frequency as the Ovation. You'd be surprised
    what you can come up with as the "perfect" combination of equipment
    when you have something that's as cantankerous as that Ovation seems to
    be.
    
    Paul
    

Hi Bob,

     I trust you've read LUNER::KELLYJ's note (2705.6). If I heard it, I 
could tell you what it is ("feedback" or "hum"), & probably what's causing it.  

     Let's sketch some possibilities:

     	HUM: I'll define this as unwanted electrical signals either induced, 
        conducted, or radiated into the signal path such that they produce 
     	unwanted audible noise especially 60 &/or 120 Hz. When sufficient 
     	nonsinusoidal components or other harminics are present, this can be 
     	heard as "buzz". This may be greatly exacerbated by "noisy" power lines,
     	or nearby radio transmitters.

     The most common sources of this are: 
     	dirty (resistive) connections
     	low battery in active preamp or effects boxes.
     	lousy shielding (including improper wire type or incorrectly wired 
        	cables)
     	bad or missing ground connections 
     	ground "loops"
     	cold solder joints
     	noisy tubes (not applicable for all solid state equip.) 
     	reversed mains (which can be due to improper house wiring, etc.)
     	inductive pickup from transformers (proximity & direction sensitive)

     Proper grounding & shielding are the basic cures:
     	Clean all signal carrying jacks & plugs with rubbing alcohol.
     	Replace batteries regularly even though they may check "good".
     	Make sure all signal cables are shielded type with the shield connected
     to ground & the signal carrying lead enclosed in the shield. 
     	Sometimes a loose or broken connector will cause an open ground. Cables
     without strain relief will eventually become frayed.
     	There may be "ugly" connections inside the amplifier or effects boxes 
     as well. You can probably test for this by swapping instruments.
     	Cold solder joints &/or unshielded wires may be inside the guitar as 
     well. Pickups are notorious for this.
     	If you are using a tube amp, remember that every tube has a socket & 
     they *do* get dirty. Tubes themselves can give rise to both hum 
     (buzz/noise) and feedback (microphonics). It's easy to swap them to 
     isolate these problems.
     	Some AC power wiring is different from what the building codes 
     prescribe. If your amp has a ground reversing or "polarity" switch, plug 
     in a guitar cord with nothing on the other end and flip the "polarity" to 
     the position of least hum & noise. You should first make sure that you 
     don't have power line ground loops by disconnecting other AC operated 
     equipment from the amp undet test. 
     	Transformer pickup can be brutal, but is certainly worse when any of 
     the previous problems are present. Most transformer noise tends to be very 
     sensitive to position & orientation of the guitar pickup with respect to 
     the offending transformer. In a room full of transformers (Every amp has 
     one ... "and they all stink!") this type of interference may not seem to 
     be proximity or orientation sensitive. Good cabling & shielding can help 
     a lot, but there are probably cases where you just have to move out of 
     range of the transformer. Some household appliances & industrial machinery
     may be just overwhelming.


     	FEEDBACK: I'll define this as unwanted effects caused by a portion of 
     	the signal being coupled ("fed back") into the signal path in phase 
     	with the original singal so as to cause unwanted regeneration, 
     	oscillation, or ringing, sometimes erroneously referred to as "hum".

     There are really two distinct types of "feedback":
     		A. Electrical/electronic &
     		2. Acoustic(al)

     	"Electrical" feedback is most commonly a microphonic tube or a 
     miswired or damaged connection, though in properly functioning solid state 
     equipment, these both become unlikely. Sometimes a bad connection (see 
     above section on hum) can cause oscillation, & it is possible to get into 
     trouble if your speaker cables or speakers are too close to your 
     instrument cables, though you almost have to try to make this happen. 

     	All of this brings us finally to "Acoustic(al)" feedback. Hollow body 
     electric & acoustic guitars are world famous for this stuff. You can take
     a perfectly balanced PA setup & make it feed back simply by putting an 
     acoustic guitar close enough to the microphone. The cavity inside such an 
     instrument is nicely "tuned" to accentuate certain audible frequencies & 
     of course this functions like a (Helmholtz ?) resonator when you put it 
     near a microphone.
     	Note 2705.6 mentions ways of compensating for anomallies at specific 
     frequencies, & you may want to design your own little "equalizer" network
     to do what a parametric would do. This would take some experimentation, 
     but the final circuit would most likely be a lot cheaper & more reliable 
     than a parametric EQ.
     	
     	I was going to post this in the notes file, but it got kind of big & 
     unfocused. Also I don't know if there are many people who care, since by 
     the time a person understands this stuf well enough to be confident to fix
     the problem, that same person can usually afford to avoid it in the first 
     place. On the other hand, "notes" is exactly the right place for such 
     ramblings, so I may post it if I can figure out how to cram a file into a 
     note.

     					Good luck,
     					Paul

    Paul,
    
    Looks like you got the technique for entering a file into Notes...glad
    you did, there's a lot of good information in .15.  I think Bob nailed
    it down to the last type of feedback you mentioned: acoustic. 
    
    One tiny nit: I don't think rubbing alcohol is good for cleaning 
    anything except guitar strings at the end of the gig, because it
    contains water.  For doing electrical cleaning, I use some contact 
    cleaner I got through the mail: Cramolin.  Those audiophile-type-geeks
    say it's the greatest for cleaning and then preventing 'scrunge' or
    'gloop' or whatever the hell that stuff that builds up is called!

    Yeah, there are lots of cleaners on the market both spray & dip that
    are much better than isopropyl. Cramolin is probably the high end of
    the bunch. Fluids that were intended for tape heads tend to evaporate
    quickly & leave no residue. 
    I've found that if you're gonna break down & clean a lot of connections
    at once that the best way to do it is to get a large bottle of
    commercial ethanol solution dip in a swab & while cleaning all the
    contacts, drink the rest of the ethanol. Then by the time you're done,
    you'll be so drunk you won't care what it sounds like. 
    *Warning*: We are professionals. Do *NOT* try this with isopropyl or
    "rubbing" alcohol. (The low cost version involves fermented hops, but
    this usually works better when your TV is already operational.) ;hmm
    

    I herr that would alcoahol causes brain dammage, I donn delive it.

    re: .17
    
    I don't know how expensive Cramolin is, but my favorite solvent for all
    sorts of things is automotive brake parts cleaner.  It's used to clean
    brake pads and discs and clutch parts, things that have to have *no*
    oil or grease on them before assembly.  It's also good for stubborn
    heel marks on the kitchen linoleum, and goodness, just all sorts of
    things.  %^)  It may be cheaper than Cramolin at about $3.00 (US) for
    an aerosol can (12 oz.?), and it really doesn't leave any residue.
    
    re: .18, Greg
    
    Rollin'!
    
    Dave

    There's a product by the people who make Cramolin called Deoxit that
    I've heard good things about. It's supposed to do the jobs of both the
    red (cleaner) and the blue (lubricant) Cramolin.
    
    Greg

    For good sound, you want to clean & lubricate & prevent further contact
    oxidation. Check out what Walt Clark has to say about Cramolin in the
    AUDIO conference. I've never used the stuff, because most of my work
    has revolved around getting things to work *at all*, but it looks like
    a winner (~$12 each for an aerosol can of "red" or "blue"). 
    Those "AUDIO geeks" are a good bunch of geeks to know, unlike some of
    the dweebs at music stores.
    Paul 

    Don't get this sh*t in your eyes!!!  Wear specs!
    
    jc

>    Don't get this sh*t in your eyes!!!  Wear specs!
 
    I can HEARTILY agree, I've done it...  Spent the better part of the
    evening in the emergency room and had sore eyes for a week.   
    
    I noticed Deoxit in the Manny's mail order catalog for about $9 a can.
    
    Greg