MIMF

I have been making pickguards for archtops for about 8 years and have experimented with piezo transducers (disc type) as well as magnetic pickups, mostly the "slimbucker" type, which fit all models except guitars with very low string clearance (1/2 inch or less).

Some pictures of my work are here on Pinterest:

https://www.pinterest.com/indigomoonjaz ... stom-made/

I would like to hear some opinions about your experiences with these and share some of my knowledge as well.

The units I make require no preamps (piezos) and use standard volume and tone circuits which work well.

These can also be combined with magnetic pickups on the same guard in several ways.

This is what I use for a true acoustic sound. Adding a magnetic pickup is something I have thought of for a long time. So far I haven't needed to switch from acoustic sound to electric sound on the same gig. With that said what would you suggest for my Eastman that currently does not have a pick guard?

Many moons ago a preamp system was designed by Vlad Ardelean for blending a magnetic and a mic or a piezo pickup and was posted on the forum as the MIMF preamp. It had several flavors including one for an archtop that would fit under the pick guard with slide pots and watch batteries. I built one and it worked great. Here is a link to the file:

http://www.mimf.com/old-lib/mimf_preamp.pdf

Thanks for posting this information, guys.

The condensor microphone is probably a great idea to record the true acoustic sound of the guitar.
Two disadvantages come to mind: sensitivity to feedback. Long ago i tried something similar with a violin - horrible in that respect, but otherwise great sound). The 2nd disadvantage: the clip cannot be safely attached to most metal tailpieces.

A while ago i built a solid body guitar with a spruce body using a low impedance pickup. A modified tele neck pickup mounted in the 90°-scale position typical of musicman basses.

Even on the solid body with the strat bridge i achieve a surprisingly acoustic sound.

And that's not surprising: a Low-Z-magnetic pickup has a much smoother and wider response than any piezo, especially when it has a small aperture (i.e. is a single coil or a stacked humbucker).
Some experimentation has to be done with the position of the pickup: only the positions close to the bridge will catch the full range of harmonics of a string. On the other hand there is some danger of weak fundamentals. The 90% position appears to be a reasonable compromise between these contradicting requirement.

Back to the pickup itself: i have been using 500 windings of really thick wire. It can drive the microphone input of a mixing console but it is still powerful enough to drive a guitar amp. A preamp with a gain of 20 dB should bring its output into the range of high impedance pickups - but that is not really necessary. Due to the low impedance of the pickup the volume pot can also have a small impedance - 2.5 kOhms! - which will not affect tone when the volume is decreased.

I can only recommend to experiment in that direction. The only disadvantage of such pickup system is that it requires the use of a pickguard.

Ken Parker apparently uses a similar approach on his archtops, and he whites that he avoids piezos because of their sonic disadvantages.


Another idea which i am still thinking about: if the main criterium for the sound of an archtop bridge is its weight, it might be possible to make a hollow bridge, give it a bone saddle with a piezo wire underneath, squeeze a 3.5 mm stereo jack in the treble side and a "Till-Jfet-preamp (a JFET with two resistors...)" in the bridge body, and chances are good that the acoustical tone is affected hardly or not at all. All the rest - volume, tone, power supply - is put into an external breakout box.

What Do You think? (I am considering to design such a bridge for my problem child archtop as soon as i am sure that i finally succeeded. Which will require quite a few months of observation)

Barry Daniels wrote:Many moons ago a preamp system was designed by Vlad Ardelean for blending a magnetic and a mic or a piezo pickup and was posted on the forum as the MIMF preamp.

After a quick look at the schematic my impression is that the values of the resistors are pretty large. This has the advantage that the power consumption will be small. It has the disadvantage that the resistors will produce noticeable thermal noise, according to the well known formula

A modification to smaller values of the resistors (and to suitable JFETs) will not involve any changes in topology, i.e., the printed board layout will remain unchanged. Another issue might be that in the past most JFETs of interest for us have run out of production.

It is my understanding that several of the components are no longer in production and some modifications may need to be made. I did buy parts for several when I made mine. If someone really wanted to try the stock board I might be persuaded to part with a set.

I play in a 16 piece big band with my clip on condenser microphone. I have no issues with feedback. And no issues clipping on to the tailpiece.

The latest generation of opamps for audio are outstanding and many of the suggested schematics will give a solid starting point for a dual buffer.

Indeed, but high quality opamps often have a significant power consumption and thus are not well suited for operation from a battery. And You always have to check for the headroom. The buffer i built for my archtop around a TDA1034 (a meanwhile old high quality opamp which does more or less require an external power supply) has a somewhat limited headroom when it is run at 9 V.

But power supply is always an issue if the guitar is mainly an acoustic archtop with all the electronics under the pickguard.

But back to my earlier question: what Do You think of the idea of putting everything, piezo and buffer, into the bridge? (And of course using a lightweight and small jack plug.)