FRAP - finally dialed it in

[M Hayden]

I've got an older rosewood dread from the 1970s that has a FRAP installed on the treble bridge plate, similar to where Michael Hedges had his. For years, it's frustrated attempts to get a sound out of it (don't have the FRAP preamp). I've tried a Baggs PADI, a Fishman ProEQ Platinum, Headway gear, Radial PZ Pre, et cetera - all gear which is usually pretty easy to dial in. I'd pretty well written it off as a pickup which just didn't work or which needed its own electronics in order to get any kind of usable sound, and was preparing to extract it and replace it with something new.

Tonight I plugged into a Raven Labs PMB-1 (older but still very good preamp) on the high-impedence input, and with a small mid cut, there was the sound - clear, not boxy, absolutely excellent. It's a totally usable sound through the PA with a little reverb added, and for an SBT it doesn't feed back very easily.

Now I see why Neil Young still uses them (his setup is stereo) and why Larry Cragg still recommends them. This thing sounds great when used with a really top-shelf preamp with the right input impedence. Arnie Lazarus was onto something when he came up with this design....

[SpruceTop]

Originally Posted by M Hayden

I've got an older rosewood dread from the 1970s that has a FRAP installed on the treble bridge plate, similar to where Michael Hedges had his. For years, it's frustrated attempts to get a sound out of it (don't have the FRAP preamp). I've tried a Baggs PADI, a Fishman ProEQ Platinum, Headway gear, Radial PZ Pre, et cetera - all gear which is usually pretty easy to dial in. I'd pretty well written it off as a pickup which just didn't work or which needed its own electronics in order to get any kind of usable sound, and was preparing to extract it and replace it with something new.

Tonight I plugged into a Raven Labs PMB-1 (older but still very good preamp) on the high-impedence input, and with a small mid cut, there was the sound - clear, not boxy, absolutely excellent. It's a totally usable sound through the PA with a little reverb added, and for an SBT it doesn't feed back very easily.

Now I see why Neil Young still uses them (his setup is stereo) and why Larry Cragg still recommends them. This thing sounds great when used with a really top-shelf preamp with the right input impedence. Arnie Lazarus was onto something when he came up with this design....

Congratulations! Is yours the FRAP IT which is a single transducer?

Trance Audio Amulet products have taken up where FRAP left off but with somewhat different designs. If you're thinking of adding an SBT setup to any of your other guitars, I recommend Trance Audio Amulet products.

[jseth]

Yep... those old FRAP pickups were about as good as you could get, back in the 70's...

I had one for my Martin D-35, but I never did have it permanently installed; I just stuck it on the bridge with the a little wad of the beeswax that FRAP included with the pickup. Had a little red preamp with it; only a volume "pole" (not really a knob but a knurled post) and took a 9v battery... thinking back on it, there was probably a gain setting internally, but I wasn't all that "tech" savvy back then.

Of course, my FRAP was the "baby" version, not the stereo rig like Neil Young used, but I remember that it sounded pretty good. Probably would've sounded MUCH better if it were mounted tot he bridge plate inside the guitar.

At one point, the other guitarist in the band and I both had these FRAP units... we used them to amplify our keyboard player's acoustic piano, trying to get more usable volume out of it before feeding back when we played loud on stage... didn't really work all that well, but hey! We were trying anything to make the kind of noise we wanted to hear!

I thought I could still track down that little red preamp, but it has apparently gone to the "seldom used equipment graveyard"...

[guitaniac]

The only Frat which I've dealt with (as a soundman) was in a beautiful old '70s Mossman. The owner was using it with a K&K preamp and it sounded very in-the-cave. He finally gave up on it and started using a soundhole pickup which worked much better for his light-handed playing style.

Congrats on finding a good preamp match for yours.

[TOCS]

I'm using an Acoustic Lens pickup by Trance Audio (which is based on the same patent as the FRAP, AFAIK) to a Schatten Design preamp. It sounds pretty good. It would probably sound better with a preamp that has an input Z of 20 megohm, however, there are very few preamps out there with such high impedance.

[M Hayden]

It is the FRAP single transducer on the treble side of the bridge plate. It had previously displayed the in-the-cave sound pretty badly with all the preamps I named, but the Raven's input impedance or something just dialed it in....it's amazing. Just for fun I put a Sunrise in and ran the lead out the soundhole, and put that into the second channel (lower impedance) on the Raven and it sounded huge.

I've been looking at a Trance Amulet M to replace another SBT on another instrument; they really sound amazing, and no battery in the instrument!

In terms of input impedance: There's a little JFET preamp I've made (it's a commonly available circuit design, using a bog-standard J201 n-channel JFET) which can have adjustable input impedance just by adding a switch to select between one of several resistor values. I usually set them up to switch between 1 x 10megohm 1/4w, 1 x 3megohm 1/4w, and one 820kohm 1/4w. It's useful for instruments like old Ovations or weird violin or zouk pickups which are passive but have weird impedance values, and improves the sound markedly, for about $10 in parts and a 9vdc power source. It doesn't provide balanced out but it feeds DIs that *do* have balanced out just fine....

[TOCS]

Originally Posted by M Hayden

It is the FRAP single transducer on the treble side of the bridge plate. It had previously displayed the in-the-cave sound pretty badly with all the preamps I named, but the Raven's input impedance or something just dialed it in....it's amazing. Just for fun I put a Sunrise in and ran the lead out the soundhole, and put that into the second channel (lower impedance) on the Raven and it sounded huge.

I've been looking at a Trance Amulet M to replace another SBT on another instrument; they really sound amazing, and no battery in the instrument!

In terms of input impedance: There's a little JFET preamp I've made (it's a commonly available circuit design, using a bog-standard J201 n-channel JFET) which can have adjustable input impedance just by adding a switch to select between one of several resistor values. I usually set them up to switch between 1 x 10megohm 1/4w, 1 x 3megohm 1/4w, and one 820kohm 1/4w. It's useful for instruments like old Ovations or weird violin or zouk pickups which are passive but have weird impedance values, and improves the sound markedly, for about $10 in parts and a 9vdc power source. It doesn't provide balanced out but it feeds DIs that *do* have balanced out just fine....

I'm not that experienced with the actual effect that impedance has on the signal and sound. Right now I'm getting a pretty strong signal from the strings. There's some of the familiar piezo quack, but I'm not sure if that's because the impedance levels aren't matched properly. It doesn't respond too much to hitting the guitar body either. But I suppose placement of the pickup has a lot to say on that too? I heard Hedges used to tug his into the brace at the treble side of the bridgeplate.

[M Hayden]

The impedence is mostly about matching the pickup's desired impedence with the input that the amplification device wants to see. When it's mismatched it doesn't usually sound good - the input energy is wasted.

Ervin Somogyi had a great demonstration of an impedence mismatch at one of his Healdsburg show lectures some years ago.

The demonstration was conducted with a heavy bolt hanging on a rubber band.

Impedence was well matched when he moved the hand holding the end of the rubber band only slightly and the bolt swung in a wide arc - that represented effective amplification of the input signal.

By contrast, when he moved the hand holding the end of the rubber band in a jerky fashion, the inertia of the bolt overcame the input signal and despite more energy input, it did not move as much as when the signal was smaller but well-matched.

(For the record, Ervin Somogyi is, if you have not seen him speak, a brilliant teacher who uses effective examples to drive his points home.....and this is in addition to being a great guitarmaker).

Here's the circuit I have used:
http://www.till.com/articles/GuitarPreamp/
Putting in a switch that allows for switching R1 between 820kohm, 3megohm, and 10megohm allows adaptability to a lot of pickups. I haven't gone over 10megohm but there's really no reason you couldn't try it and see if it helps.

It's an easy circuit to build, too - fits into an Altoids tin with more than enough room for the battery and two 1/4" mono jacks. And it can be phantom-powered but it doesn't fit in an Altoids tin, then - it needs an actual project enclosure to hold an XLR connector.

[TOCS]

Originally Posted by M Hayden

The impedence is mostly about matching the pickup's desired impedence with the input that the amplification device wants to see. When it's mismatched it doesn't usually sound good - the input energy is wasted.

Ervin Somogyi had a great demonstration of an impedence mismatch at one of his Healdsburg show lectures some years ago.

The demonstration was conducted with a heavy bolt hanging on a rubber band.

Impedence was well matched when he moved the hand holding the end of the rubber band only slightly and the bolt swung in a wide arc - that represented effective amplification of the input signal.

By contrast, when he moved the hand holding the end of the rubber band in a jerky fashion, the inertia of the bolt overcame the input signal and despite more energy input, it did not move as much as when the signal was smaller but well-matched.

(For the record, Ervin Somogyi is, if you have not seen him speak, a brilliant teacher who uses effective examples to drive his points home.....and this is in addition to being a great guitarmaker).

Here's the circuit I have used:
http://www.till.com/articles/GuitarPreamp/
Putting in a switch that allows for switching R1 between 820kohm, 3megohm, and 10megohm allows adaptability to a lot of pickups. I haven't gone over 10megohm but there's really no reason you couldn't try it and see if it helps.

It's an easy circuit to build, too - fits into an Altoids tin with more than enough room for the battery and two 1/4" mono jacks. And it can be phantom-powered but it doesn't fit in an Altoids tin, then - it needs an actual project enclosure to hold an XLR connector.

What about going above the actual impedance level of an input device? How does that affect the sound? I've heard tests being made with a K&K pickup into a variety of different impedance levels, and it seemed as long as it met an input Z of 1 megohm or higher it didn't really change the sound. I.e. there was no difference between the sound when comparing 10 megohm and 1 megohm input Z.