Replies to This Discussion

Permalink Reply by Wichita Sam on February 6, 2010 at 3:10pm

to limit feedback thru a piezo you can either sandwich the piezo in insulating material such as mouse pad or strips of wood before affixing it to the underside of the top... When I build a bridge plate, I recess the plate and place the piezo between the bridge plate and the top of the CBG (filling the recess with silicone caulk).

The easier and more common way to handle the problem is to affix the piezo (brass disc side) to the underside of the top with CA glue and then encapsulate the open back (the ceramic side of the piezo) with some insulating material such as hot glue, silicone caulk or a piece of mouse pad....

hope this helps,

the best,

Wichita Sam

Braxton Nagle said:

Which are you referring to?

Wichita Sam said:

Not sure, but stuffing the box with balled up newspaper probably kills any acoustic volume... It's clear why it works, it insulates the open back of the piezo from ambient sound waves, which when they gain amplitude, causes feedback.

But, when it is so easy to limit feedback in ways that don't kill acoustic volume of the instrument, why not do it a better way?

No rules,
JMHO,

the best,

Wichita Sam

Travis "SlackJack" Woodall said:

Not sure if anyone suggested this, but one of my friendly CBNation pals suggested to me that I use a balled up page out of a newspaper inside the box. The last CBG I finished, my 23rd total, played great and sounded great but had enough feedback to shoot me to the moon. I tried it, balled it up loosely to where it just makes enough contact with the lid to stay in place...I can crank up the volume and NO FEEDBACK. That, along with my usual encasing the piezo in walnut,is now my standard for all of my build that have a piezo pickup in them. Hope that helps. Good luck!!

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Permalink Reply by Jerryrig240 on February 7, 2010 at 12:01am

I am wanting to build a new box with a peizo inside, I bought some liquid electricl tape the other day and dipped a peizo in it a couple of times....it coats the wires nice, but still hisses and moans reall bad. So, I bought this thing from the dollar store...it is for suporting your couch on the carpet so you don't make a hole in the carpet. All I can descrbe it as is a reall tough peice of felt. It was only a buck and I cut it into 4 peices, took two of the peices and glued them together with the peizo inside. I don't notice as much feedback....I am just trying it on a diddley bow right now, but the clean channel to my pedal sounds fine, but when I hit some distoration, it sounds like crap. I am starting to think that peizo's just don't like distoration.

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Permalink Reply by Greg on February 7, 2010 at 7:54am

Anyone tried one of these?

grizzly.com/products/Samba-Acoustic-Transducer-End-Pin/H6054

You'll have to cut and paste this. Not sure how to make a link.

No soldering. Ready to go. Might help with the feedback the way it's encased.

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Permalink Reply by James Bush on February 8, 2010 at 8:10am

Most feed back can be reduced by using a RCA style cable. Meaning a shielded conductor like a coaxial tv cable but a lot smaller. If you use two wires with no shield you will have a lot of feedback when near the amp speaker. Also get some of that plumbing insulating foam tape ( 1.75" wide ). It works great for giving your piezo a louder volume and secures the disc to the wood neck without any other glues needed.

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Permalink Reply by jeremy james a scriver on February 14, 2010 at 1:49pm

I was told and it worked to sandwich them in wood so I put it between the neck and the box top. You have to use just the disc no plastic cover. Shielded wire helps to

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Permalink Reply by Wichita Sam on February 14, 2010 at 2:54pm

difference of opinion.... shielded vs unshield wire should have nothing to do with feedback... feedback has to do with the transducer picking up ambient vibrations.... what kind of wire you're using has nothing to do with it...

I have used unshielded wire on over 150 piezo equiped cbgs with no feedback issues, once the installation issue was settled...

I doubt that the issue of interference, which can be a wiring thing is in play here either like it can be on a wound pup... the difference in the way a piezo works, just doesn't seem to lend itself to this problem... The only time I've had noise issues is a result of a bad solder or a stray wire....

again, just opinion based on 200+ builds...

the best,

Wichita Sam

cite>jeremy james a scriver said:

I was told and it worked to sandwich them in wood so I put it between the neck and the box top. You have to use just the disc no plastic cover. Shielded wire helps to

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Permalink Reply by crissy b on February 15, 2010 at 7:42am

Hi not to keen on the transducer things but in a didley bow i built it sounds great cos the way it picks up so much when you strike the box just adds new dimentions to the sound .I always put mine in the middle of the box at the bottom by the latch encased in sponge this seems to work fine hope this helps the thing with c b g,s is that everone i put together is different but i love them ime messing with making me own pickups now a magnett some wire just trying to keep the sound like it was in the depression pure gritty blues

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Permalink Reply by Grizz on February 15, 2010 at 8:08am

Might be the type of pot you used. As I discovered there are two kinds; logrithmic and linear. They function differently.

Linear taper potentiometer

A linear taper potentiometer (uses the letter 'B' in the designation eg 100kB) has a resistive element of constant cross-section, resulting in a device where the resistance between the contact (wiper) and one end terminal is proportional to the distance between them. Linear taper describes the electrical characteristic of the device, not the geometry of the resistive element. Linear taper potentiometers are used when an approximately proportional relation is desired between shaft rotation and the division ratio of the potentiometer; for example, controls used for adjusting the centering of (an analog) cathode-ray oscilloscope.
[edit] Logarithmic potentiometer

A logarithmic taper potentiometer (uses the letter A in the designation eg 100kA)has a resistive element that either 'tapers' in from one end to the other, or is made from a material whose resistivity varies from one end to the other. This results in a device where output voltage is a logarithmic (or inverse logarithmic depending on type) function of the mechanical angle of the pot.

Most (cheaper) "log" pots are actually not logarithmic, but use two regions of different resistance (but constant resistivity) to approximate a logarithmic law. A log pot can also be simulated with a linear pot and an external resistor. True log pots are significantly more expensive.

Logarithmic taper potentiometers are often used in connection with audio amplifiers.

I've found that using a Radio shack potentiometer (I think it's linear) the volume doesn't really kick in until around 9 or 10.

jason peterson said:

i have been putting the piezo between two pieces of thin wood and that has been working good for me, the first build i just used the piezo without a volume control and it worked great no feedback but the second build i wired in a volume pot with the piezo and i get i buzzing sound if i don't have the volume turned up to 9 or 10 on the cbg ,does anyone know why this is happening?

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