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Author Topic: LR Baggs Piezo-Pickup preamp  (Read 23969 times)

blues dog

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LR Baggs Piezo-Pickup preamp
« on: September 21, 2011, 11:43:28 AM »
My effort of tracing the LR Baggs Piezo-Pickup preamp from a Godin guitar (the guitars belongs to my customer). I triple check the trace.. Hope don't miss something there..  :D






phatt

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Re: LR Baggs Piezo-Pickup preamp
« Reply #1 on: October 05, 2011, 10:04:50 AM »
Thankyou for the effort,, but I'd check that again as Q4 does not seem to go anywhere?
Phil.

J M Fahey

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Re: LR Baggs Piezo-Pickup preamp
« Reply #2 on: October 06, 2011, 12:12:40 AM »
Q4 looks suspiciously like a gyrator, peaking some frequency.
Too sleepy to calculate it just now, might provide sparkle, body, or anything the designer thought was needed.

blues dog

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Re: LR Baggs Piezo-Pickup preamp
« Reply #3 on: November 02, 2011, 09:30:44 PM »
Agree with JM. Q4 used to maintain some freq for the piezo.
I guess this make the preamp character for the piezo sounds smooth in treble area.

BTW I succesfully made the circuit for the owner of this preamp.
So now he has 2 guitars with similar preamps:
- Godin (I forget the model) with this original LR Bags preamp
- budget Greg Bennet Les Paul with the "replica preamp"

Both of us love the tone. Even the customer feel sooo satisfied with the project   :)

J M Fahey

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Re: LR Baggs Piezo-Pickup preamp
« Reply #4 on: November 03, 2011, 03:57:50 AM »
Goooooooood !! Congratulations !!
PLEASE post some pics of your work. :tu:


Hey !! What a funny thumbs up we have now !!
Dear joecool, are you sure it´s OK?

joecool85

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Re: LR Baggs Piezo-Pickup preamp
« Reply #5 on: November 03, 2011, 09:34:14 AM »
Hey !! What a funny thumbs up we have now !!
Dear joecool, are you sure it´s OK?

New forum software, new emoticons.  I'll see what I can do though.

**edit**
Fixed and even added a double thumbs up ->  :dbtu:
« Last Edit: November 03, 2011, 09:59:41 AM by joecool85 »
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
thatraymond.com

J M Fahey

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Re: LR Baggs Piezo-Pickup preamp
« Reply #6 on: November 06, 2011, 04:24:29 PM »
Well, all I can say is  :dbtu:

zedonetx

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Re: LR Baggs Piezo-Pickup preamp
« Reply #7 on: October 28, 2015, 06:22:27 AM »
do you know the model of this Godin guitar? I need something for my classical-flamenco guitar. and i want to make a good natural tone Preamp. :)

J M Fahey

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Re: LR Baggs Piezo-Pickup preamp
« Reply #8 on: October 28, 2015, 08:59:40 AM »
That L R Baggs preamp is *very*  good.
I just calculated the "mystery gyrator" frequency and it's surprising (or not? ) 95 Hz
Clearly it adds body to turn usually famigerated "Piezo shrillness" into nice warm fat sound, without losing top frequency transparency.
AFn excellent design ... although you'll have to design your own PCB .

This one is for dual mics, Piezo and Magnetic, if you use just the Piezo, you can simplify the design quite a bit, since you need neither the Magnetic preamp nor the mixer, in that case V1 volume pot can straight go to output jack.

Enzo

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Re: LR Baggs Piezo-Pickup preamp
« Reply #9 on: October 28, 2015, 01:51:12 PM »
And Baggs and others already make a selection of such pickups and preamps.  Unless you are just into making a project, you might consider a commercial product, one that has a pickup designed to work with it.  My friends at Elderly can help you, and other places like Sweetwater as well.

http://www.elderly.com/accessories/cats/PUA.html

http://www.sweetwater.com/c985--Acoustic_Guitar_Pickups

dogbox

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Re: LR Baggs Piezo-Pickup preamp
« Reply #10 on: November 02, 2015, 08:27:52 PM »
That L R Baggs preamp is *very*  good.
I just calculated the "mystery gyrator" frequency and it's surprising (or not? ) 95 Hz
Clearly it adds body to turn usually famigerated "Piezo shrillness" into nice warm fat sound, without losing top frequency transparency.
AFn excellent design ... although you'll have to design your own PCB .

This one is for dual mics, Piezo and Magnetic, if you use just the Piezo, you can simplify the design quite a bit, since you need neither the Magnetic preamp nor the mixer, in that case V1 volume pot can straight go to output jack.

That's very interesting JM. Can you explain how you calculated the frequency affected by the Gyrator, I'm geussing the Gyrator (i had to google gyrator to find out what it was :-[), acts as an Inductor, so is it some kind RLC filter..maybe a bandpass?? Am I completely on the wrong track?? I've been recently playing around with some homemade piezo disc pickup/contact mics. Still yet to get that magic sound. There sure are a lot of schematics on the web and ideas about how to tame these piezo devils.

Have tried Tl072 chargeamp based circuits, and various well known things like Tillman and offshoots. I got a some largeish discs, some salvaged from buzzer, and these really small ones that are very trebley/high end. Have tried mounting the bassy one and the treble disc feed into a 2 stage jfet preamp that I found on a ham radio site, I added 10m input resistor. I then added a passive mixer - just 2 -  10k pots - 10k resistors. It works but the larger disc really over powers the smaller. I only have 1k, 10k, 20k pots on hand. I tried a 20k pot on the smaller and got more signal in the mix. But it lacks a bit of sparkle, and its now lost a bit of volume.

keen to give this one try on the breadboad before I get out the soldering iron and commit to my lastest version. I have mpf102, and some BC 54x . Would they be ok this LR Baggs circuit?? If you have suggestions..I'm here to learn..cheers

phatt

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Re: LR Baggs Piezo-Pickup preamp
« Reply #11 on: November 03, 2015, 06:27:58 AM »
This might help explain some of the issues you will face.

http://www.ozvalveamps.org/pickups.htm

I know it's fun to muk around with pz elements but there are many hurdles to overcome.
These days piezo elements are cheap and plentiful and all the initial bugs are already well researched.

Even with the above sorted the preamp can be a mine field. I doubt few manufactures take the type of guitar into account as most just use of the shelf electronics in cheap plastic cases and no matter how impressive the specs Low frequency Feedback is often big issue with ElAcoustics.

Any large cavity with two parallel planes (Classic acoustic Guit shape) will resonate in sympathy at certain frequencies. The smaller body guitars tend to have less FB issues.

Ovation may not be everyone's fav axe but they did get one very important factor dead right, that is the bowl back minimizes the dreaded feedback. <3)

As I play a lot of open mic gigs these days I've resorted to a cheap plastic Acoustic and although unplugged it will never compete tone wise with Martins or most other exotic instruments it's a massive sound when amplified. I've been asked many times about how I get such a huge sound.  8) 8)

The guitar is a Hornby Skewes Vintage Synergy Vr6 with a bridge piezo and onboard Fishman Isys preamp. it has no tone controls just a volume and a contour push button,, oh and a stupid tuner which I hardly ever use.  See here; http://www.jhs.co.uk/vintageelectroacoustic.html

Like a lot of these preamps the output signal can be anywhere from average to insane loud causing many headaches.  :grr :grr :grr My unit's output was too hot past halfway and that was rectified by simply wiring a passive 25k master volume control on the output. The first volume is then used as a gain control and hardly ever gets moved.

The added passive master volume is mounted on the face which makes for super fast volume changes.
When playing solo you can't access side mounted controls fast enough and that is very frustrating for me as I use volume control a lot on both Electric and Acoustic.

All the rest of the sound comes from a dedicated tone circuit I designed > then pedals and amplifier setup do the rest.
Hope it helps, Phil.

dogbox

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Re: LR Baggs Piezo-Pickup preamp
« Reply #12 on: November 03, 2015, 01:24:42 PM »
Thanks Phatt that was a great link you posted. Yeah it is a bit like re-inventing the wheel, but playing around with piezo is fun, and educational..and safe for the kids (as they say). Currently living in Bengkulu , Indonesia and chances of me being able to get brand name pickup are slim to none. I've only got an Indo made acoustic nylon string, masonite fretboard, and cheap but surprisingly good sounding ukulele. I really want get some kind of rig together so I can jam with a few mates.

I just try get as natural sound, try eliminate the bass loss as much possible. My rig is a powered no name one hung low PA bin that definitely needs something between the piezo and the amp. Straight piezo with no buffer equals, distortion, horrible tone..feedback, due to its 100k input resistance, this thing was designed for fynamic mics. Been trying various simple preamps on a breadboard. They all work to an extent, but feedback is defintely an issue, and certain notes on certsin strings can cause a vibrational buzz. Fine tuning the placement of the piezo on the body can get different tones, using a couple at the same time yields better results when attached to the outside. In the Oz valve article, he talks about putting a couple of caps in series, I geuss hes really talking about use of piezo into a valve amp. I just bypassed my preamp and a tried a couple of cap values as suggested 5000pf and worked pretty good..one cap is ok, 2 is better. Its late and I can't crank the amp, but i just fed my passive blender into the caps..totally surprised..sounded pretty good??? Why?. LOL

I have got the Baggs circuit on my breadboard, minus the gyrator. Not sounding any better/worse than the ham radio one i already had. Gonna add the gyrator tomorrow see if magical sparkle appears :). The passive circuit defitely seems to tame this disc, and still getting a nice amount of bass tones. How it that even possible??
Anyways mate....cheers for the info

phatt

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Re: LR Baggs Piezo-Pickup preamp
« Reply #13 on: November 04, 2015, 08:40:21 AM »
Ok now I think I understand ,, you want to do this as cheap as possible.

Then go with the first schematic and tweak until you are happy. :tu:

My only concern is that some of these circuits require specific Fets to work correctly.

If it helps there are a lot of Ovation drawings here:
http://www.ovationtribute.com/Schematics.html

Also this is very simple to build and may work ok with your idea.
http://www.hawestv.com/amp_projects/fet_preamp/fetpreamp2.htm

Yes try a small value cap directly across the piezo element it may help, maybe start with 50nF
better minds here may know more about selecting values. all my research was a long time ago but I did once mess around with some ceramic transducers and found them to be very quirky things to work with. You can't directly mount them and expect good sound as they need a small amount of mechanical suspension otherwise they feedback.

Try a strip of double sided tape or something similar between the element and sound board.
If you are familiar with those old ceramic phono pickups (found on old budget record players) you will notice the needle is not directly mounted to the ceramic strip,, it's got a small rubber shock absorber between the needle and ceramic element. Without that tiny rubber mount the sound would be very peaky and likely render it useless. :'(
I did once remove the needle and just rested the tiny rubber foot onto the sound board of a guitar and got signal that was passable but hard to mount it all and gave up.
Phil.

dogbox

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Re: LR Baggs Piezo-Pickup preamp
« Reply #14 on: November 08, 2015, 05:40:25 AM »
After a little bit more experimenting with ideas contained in ozvalve I'm convinced that you can improve the performance of the piezo by soldering a cap and resistor directly to the disc. My results...
I tried a 100n/1m resistor. Just that on its own was enough to open up the disc and get all useable  frequencies passed. I was able to plug directly into my macbook laptop audio port which has 20k impedance. I recorded some audio ..ended up a pretty low level around -10db to -20db., and it is obvious that the disc i used must have a resonant frequency around 2.5-3k hz. That makes sense I geuss those are the most easy to hear frequencies for humans, and these disc are generally used as alarms. When I pulled those frequencies down in the mix with a parametric eq plugin, it really sounded pretty good. So I geuss my next step is to create a preamp that boosts the signal, and has a filter/ pot that allows me to reduce those frequencies that make it sound harsh. I also tried a band stop to roll off the high frequencies afte 10k..that helped a bit too. The bass didn't really need much..pretty well all there. On k&k sound website they say for contact mcs to try nd get the pickup direct onto the guitar body, if you use tape put it over the back of the pickup. I definitely got better results that way. But maybe playing into amp, or with a pre it might be too hot a signal. Having fun playing around. Definitely worth experimenting with a couple components on the disc. With my limited knowledge I believe i have set high pass filter on the disc..thus reducing the need for a such a high value input resistor in the preamp?

 

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