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New "Business Card Amplifier and Enhancer" for Banjos

Posted by yellowdog on Wednesday, September 5, 2012

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(The following includes several updates added near the end which were written on September 7, 8, 11, and 14, 2012.)  

Over the last week or so I have been experimenting with a very simple mechanical amplifier and tone enhancer which is easily and quickly made from an ordinary paper business card and a few pieces of Scotch brand "Gloss Finish Transparent Tape".  The improved volume and sound quality has totally amazed me!  I now use one of these "business card amplifiers", but mounted in different ways, in my Gibson Mastertone tenor tuned CGDA, (which I use without its resonator to play one-hour solo performances), and in my 17-fret Gold Tone "CC Irish Tenor" without its resonator tuned GDAE which I use to play in weekly Irish pub sessions.  It is really too simple to patent so I'll describe it here and you can make one yourself.  I might sell them later, or you can, for banjo players who don't want to go to the trouble of making one, but making one is hardly any effort at all.  I'll describe it briefly here and will post pictures in my homepage "Photos" section soon.

The particular type of Scotch brand tape, "Gloss Finish Transparent Tape" has the unusual capability of efficiently (for a tape) conducting sound surface waves - the minute deformations on all surfaces of a musical instrument that are inaudible representations of the music created by the instrument.  This tape is essential for the device to work so don't waste your time with any other type.  Fortunately, it is easy to find in office supply stores, "dollar" discount stores, hardware stores, stationery stores, and some supermarkets in the school supplies area.  Look for the red and black plaid pattern on the side of the dispenser or box.  Dollar Tree stores sell it two rolls for a dollar in 3/4-inch widths.  I prefer the sound using 1/2" wide tape but you can easily cut the larger tape to the 1/2-Inch width.

Here's how to make one:  Select a business card without a lot of printing or background color or use it to trace a pattern on plain "card stock" which is 110-pound paper.  Apply about a two-inch strip (which you will later shorten) to the center of each end of the card so that about 1/2-inch of tape sticks to the un-printed side of each end. (Suggestion: If you need to remove the tape from the card later be sure to lift the tape edge that is farthest away from the edge of the paper and then lift (or "roll") the tape toward the edge of the card.  If you try to pull up the tape at the edge of the card it will probably tear up a layer of paper from the surface of the card.)

Next you mount the card in a certain way in the banjo depending on the type of banjo and the sound that you want.  The good news is that you can try many mounting positions because the card with tape is easily moved about and re-stuck in different positions.

When properly mounted in the banjo the card forms a paper arch with the top of the arch about 1-1/4 inch above the wood rim and both ends of the card are slightly above the wood rim - perhaps 1/8" from it.  The tension of the bowed paper pulls up on the tape which causes the bowed card to "float" above the wood rim, which makes it very sensitive to the very small sound surface wave undulations on the tape that the tape picked up from the wood rim and, most important, also any metal parts that the tape touches.  (Can you see where this is going?)  

If you can see the tone ring looking in the banjo (as you can in a Gibson), stick a third piece of the tape over about 1/2" of the tone ring next to a corner of the card and run the other end of the tape over about 1/2" of that corner of the card, stick it down while cutting off the excess tape.   This third piece of tape carries the wonderful high harmonics that are on the tone ring and deposits them on the top surface of the card.  Waves of the same or similar frequencies from the three different tapes will amplify wherever they meet on the card because they will meet coming from different directions.  If you can't see the tone ring and your banjo has rim bolt heads, stick the tape to one or both rim bolt heads.  You can add another short (and narrow) piece of tape crosswise over the first tape to keep it from pulling up off the rim bolt heads.  This cross tape will add volume as well as help the first tape hold.  If the tape still pulls up you can tailor the length of the card so that it will still arch up when the edges of the card are pushing against the sides of two rim bolt heads and this will keep the card from rising.    Keep all tape as short as possible for the best sound quality.  If your banjo has no visible metal inside, add a small square or rectangle about 3/4" x 1/4" of thin steel (cut from a steel can) or brass only partially under one end of tape and you will add brightness to the sound of the banjo.  If sound quality of the highs from the banjo is poor, cut the metal so that no sides are parallel and that should solve the problem.  (Parallel sides on the metal shape will amplify the waves but can also cause time delays which sometimes degrade sound quality.)

I prefer to locate the card inside the banjo so that it is a few inches below the end of the neck when the banjo is in the playing position.  When the banjo is played in a seated position this portion of the banjo is not touching the left leg or body of the player.

The tape at the end of the card can, in some circumstances, become loose enough to work its way around and stick to the inside surface of the card.  This will degrade the sound so this is a good thing to check if the sound degrades in volume or quality.

Don't forget to shorten the tape at the ends of the card to be as short as possible and still hold everything in place.  You can do this as a last step after you have tried locating the card in various positions for the best sound.


The metallic sound surface waves on the rim bolt heads brighten the sound but are surely of overall poor quality since they have to come through about four metal-to-metal connections including one which is threaded. After thinking this morning about a better source of high quality sound surface waves on the banjo I repositioned the business card arch, with its two pieces of tape still attached, between the rim bolt heads so that they didn't touch. Then I picked up the tape dispenser and stuck the end of he tape to the outside of the tension hoop (on the outside of the banjo) at a point which was in-line with the tape at one end of the card. I bent the end of the tape over the top of the hoop and stuck it down on the top but let the very short (1/8"?) end of the tape stick out in the air over the banjo head. Then I reeled off enough tape to bring the tape around the wood rim bottom and back up to cross over the tape at one end of the business card. I wasn't concerned about what the tape touched between these two locations. This long strip of tape brought the almost pure sound surface waves on the tension hoop onto the tape at one end of the card. Since the two tapes were attached at 90-degrees their waves added. Their combined and amplified waves were carried by the shorter strip to the top surface of the card. The result was a very loud and bright sound that was much more pleasant than before. Then I did the same thing for the other end of the card with a second long strip of tape between the hoop and the tape, just as before. The sound was even brighter, louder and still very, very high quality.

But surprise! When I looked at the card closely I noticed that one corner of the card was touching the underside of the head! (Bad?) So I moved that end of the card and tape over slightly so the card wouldn't touch the head thinking that surely this would improve the sound. I played the banjo and the sound wasn't nearly as good! I moved the card back so that the same corner of the card touched he underside of the head just as before and same great sound returned! (Whoo....Time to think!)

On reflection, this made good sense and is one of those things that you wished you'd thought of and hadn't happened accidentally. First, the purest sound surface waves on a banjo are probably on the head of the banjo. Second, sound surfaces waves on a surface are transferred to a second surface most efficiently at an edge of the second surface, which in this case was the edge at the tip of the card. Third, these very pure sound surface waves entered the card at a third location from the two tapes at the ends so the new waves from the head intersected the ones already there at an angle which amplified them wherever they met. And fourth, they entered from or near the tip so were immediately reflected, mostly in phase, from the two edges either side of the tip into the body of the card.

The two long tapes running around the outside of the banjo between the hoop and the tapes at the two ends of the card on the inside touched many other things on the banjo so that probably had some effect. But who cares? Not me with this banjo sounding as good as it does!  (END OF PORTION QUOTED FROM MY FORUM POST)

The great sound from the Irish tuned Gold Tone when the corner of the card touched the underside of the head caused me to go back and see if the same thing would work in the Gibson - as Bayes famous theorem says I should.  (New knowledge should be included in a revised input when solving problems.)  Also, I was a little unhappy in the lack of immediate response of the Gibson after practicing the very fast 1920's tune, "Running Wild", which showed that the Gibson was simply too slow for the tune.  So I detached the strip of tape which ran from the edge of the tone ring, where it meets the wood rim inside the banjo, to the tape at one end of the card.  Then I lifted the tape at the end of the card closest to the center of the banjo and moved the corner of the card up (or over) until its corner touched the underside of the banjo head.  To hold it there I attached a very short piece of tape to the opposite corner at the same end of the card and pulled that corner down very close to the wood rim.  I played the banjo and got a great sound and the response of the banjo was greatly improved too.  Any limitation playing "Running Wild" very fast now would be my fault and not the banjo's.  (How could there be much delay when the surface wave output device, the card, was now touching the ideal surface wave source, the banjo head.)  Then I thought, why not run another short piece of tape from the other near corner to the wood rim and get more waves from the wood rim onto the card, and from a different direction which would cause more amplification.  This would give the card four different input locations with tape plus a fifth input location without tape, the one touching the head.  The volume increased again and the quality of sound was excellent with no significant delay on fast tunes.

I don't know if this is the end of this long road of changes with the business card amp but I doubt it.  Time will tell.  

I hope that you have enjoyed reading this description of my new "business card tone amp".  I tried to include some of my thinking, both good and bad, which led to it.  If you did or if you are interested in the processes of design and problem solving you will probably enjoy reading, "The Theory That Would Not Die", by Sharon Bertsch McGrayne", Yale University Press, 2011.  It is a very entertaining and thoroughly fascinating book about the history and many applications of Bayes Theorem, including its use in searches for enemy submarines and mariners lost at sea, cracking enemy codes, and other highly significant and challenging problems.



This afternoon I made two more improvements on the business card amplifier mount in/on the 17-fret Gold Tone CC Irish Tenor (without resonator).  I'll include these changes at the end of my homepage blog.  (The blog now has a running summary of these and other changes.)
The first improvement made today can be described with one word - "Humdinger"!  Recall that there were two long strips of 1/2" wide tape running around the outside of the banjo around the back to the two ends of the business card.  These carried high quality sound surface waves from the hoop to the ends of the card. This tape connection worked OK, but any tape, even this recommended one, is not very efficient because all tapes absorb wave energy.  So this afternoon I replaced both tapes with a 1/2"-wide strip of .005 thick common brass and attached the two strips to both the hoop and the card ends with two very short strips of 1/2" wide tape at the ends of the brass.  As you might expect the banjo sounded wonderful with this change.  Highs and lows were louder, clearer and had the bright, ringing sound of brass which most players like from a banjo.  This very thin brass is easily cut from a sheet with ordinary scissors and is sold in hobby stores.  Be sure to ask for "embossing brass" which is kept in the artists supplies department not the models department.  
Another change was extending the two pieces of tape at the ends of the two brass strips near the hoop so that they covered not only some of the hoop but also about 1/4" of the head next to the hoop.  I listened to the banjo with the tape touching the head and not touching and preferred the sound with it touching the head.  There was a slight but noticeable difference.
The last change was pulling the corner of the card which was touching the head away from the head, because it seemed unnecessary.
The depth of the banjo will determine the length of the brass strips.  These strips used on the Gold Tone CC Irish Tenor were 3-3/4" long which was long enough to be bent around the bottom of the wood rim with about 1/2" or so on the inside of the banjo next to the card.  Tape covered this 1/2" of brass and extended over to the card.  It is easy to attach this tape to various parts of the end of the card and/or its attached mounting tape and compare sounds.  - For example, covering the corner of the card, covering the input tape to the card from the wood rim or both.  All sound very good and which sounds best is a matter of opinion.
Because the brass is very thin the edge can cut so be careful working with the brass.  The location of the brass strips on the banjo, just below the heel of the neck, is a good position not to damage anything under normal circumstances.


I was finally able to take pictures of the business card amp and put them on my photos here and with a discussion on the forum.  Here is the link to the forum post with the photos and discussion:

Make Your Own Banjo Business Card Tone Amplifier - Discussion Forums - Banjo Hangout



I was a little surprised when I played my 17-fret Gold Tone CC Irish Tenor with the Business Card Amplifier yesterday.  It just sounded OK and I didn't hear the wonderful clear, loud and bright sound that I had been enjoying since removing the second steel strip so that there is only one.  It didn't take me long to find the problem and it was on the outside of the banjo next to the steel strip.  

I always leave a nylon strap attached to the banjo and sometimes don't put it on and it just lays across my left leg when I play.  There are two soft leather ends to this nylon strap and one of them was very near the steel strip just below the heel.  I realized that it could easily touch it if the strap wasn't taut, so I took the strap off the banjo and the great sound returned.  The sound surface waves on the steel strip were moving into the leather and were being absorbed instead of arriving at the business card.  So be sure that NOTHING is touching or can touch the side of the steel strap because that will definitely destroy the great sound of this tone amp.  

I'm looking forward to playing it at our Irish session this Tuesday, September 18th at the Roswell Tap in Roswell, Georgia and will give a report on the amp's performance here and in a comment on my post after that.  Come see it and hear it if you are in the Atlanta area.  We start playing around 8:00 PM.







1 comment on “New "Business Card Amplifier and Enhancer" for Banjos”

privard Says:
Sunday, September 9, 2012 @2:39:49 PM

Frank, a few photos would go a long way to supporting the ideas expressed in the text. THanks.

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