The CB1 was designed after the preamp built for Jerry Garcia by John Cutler. It is a "Wide Band Unity Gain Buffer" amplifier. The original design used a bipolar OpAmp in an inverting mode. On the CB1, we used the same circuit topology, but compressed it enough to fit into any guitar — even a Fender Stratocaster.
Initially, some players told us that the CB1 preamp was too bright. While this didn't make sense to us at first, it soon became clear that, after living with a "dark" sound for so long, the true, pure sound produced by the preamp actually sounded too bright by comparison. Most players had compensated for the dull sound with other sound modifiers, tone control settings, changing tubes, speakers, or adding effects to get the brightness back. This demonstrates that the preamp works and does what it is designed to do — buffer the guitar signal and preserve the natural sound.
The CB2 was designed around the samd basic concept as the CB1, but with two important design changes. First, we changed the "band width" to limit the high frequency response down from the CB1 limit of 100K Hz. to under 10K Hz. This made the sound a little less brilliant for those who ended up with too much top end sound.
Second, we used specially designed coupling capacitors to get the sound quality we were looking for. We tested hundreds of caps. It took a year of testing until we found the magic combination that worked for us. Then we had to have our engineers work with the capacitor engineers to fine-tune the parts to exactly what we needed. The last important step in the final assembly process of our preamps is to "hand test" every part and label the polarity. This testing is a very valuable detail that does, in fact, affect the sound quality of our preamps. We achieved the Ultimate in Tone!
All CAE Preamps are designed to allow easy bypass switch installation. We've made every effort to ensure that the bypass switch will not "pop" when used.
Although it adds complexity to the wiring scheme (and is not part of the standard installation instructions), we recommend adding a "hardwire bypass switch." We also suggest keeping the preamp in the signal path at all times. However, many players want the option to go back to non-buffered sound for some special effects.
It is NOT recommended that the bypass switch be used to turn the preamp power on and off. This can cause and audible "pop." The power to the preamp should remain on while in use.
Our wiring scheme for the bypass switch is designed to completely remove the signal from the preamp while in "bypass mode." This is called "hardwire bypass." Old guitar efects did not completely disconnect the signal from the electronics when the device was switched out. Such a connection would tend to "load" the signal down and change it somewhat. In our circuit, we use a "two-pole" switch and a jumper wire to bypass the guitar signal around the preamp completely. When the preamp is switched IN, both the Input and Output of the preamp are connected via the switch contacts.
There is a wiring diagram schematic on our web site. Any technician can easily read and follow it. If you'd rather do it yourself, we are now working on a pictorial diagram with a mechanical view of the wiring.
You may purchase a prewired kit from us by special order. Please e-mail us for details.
Download drawing: Bypass Switch Wiring Schematic for the CB2 Guitar Buffer
Most guitars are "passive" devices — you must vibrate a string in order to produce any output. The string vibration generates electricity in the pickups. Next the selector switch picks the neck or bridge signal and sends it through Tone Control to the Volume Pot.
The volume control pot impedance is selected to not overly "load" the pickups and dull the sound. Typical values are 250K, 500K, and 1 Meg. These values contribute to signal leakage in the guitar cord, which also dulls the sound.
CAE preamps address these problems by buffering or strengthening the guitar signal and driving it through the cables and effects to your amp. Our preamp lowers the impedance so a much lower-value volume pot can be used, which, in turn, reduces leakage and preserves tone. We recommend using a volume pot value of 25K ohms.
Adding a bypass switch can create new problems. Bypassing the preamp with a switch and loading the pickups with the 25K pot is going to darken the tone again. We've developed a solution to this dilemma. CAE now offers a custom dual section volume control pot that has one section for the passive value of 500K ohms and an active section for 25K ohms to work with the preamp.
The wiring is a little trickier, but it is not too much more complex than the bypass switch alone. Basically, we just add the pot inside the preamp circuit so it is switched out in the passive mode and the stock value replaces the hard wire jumper.
Our pots are a very high quality plastic film type element. The small size makes it fit in almost all guitars. The two elements are on the same shaft, so switching modes does not cause the volume to change. The standard diameter shaft fits many generally available knobs. The pot values are 500K for passive mode and 25K for active mode, and both are Log or Audio Taper for a good feel.
Diagram: Guitar Wiring Diagram: Dual Element Volume Pot and Bypass Switch
Download schematic: Guitar Wiring Schematic: Dual Element Volume Pot and Bypass Switch
CAE Guitar Preamps run on a 9 Volt transister radio battery. We recommend Duracell brand batteries for trouble-free operation. We tested our preamps using the Duracell MN1604 9 Volt battery. [Click here to view the full Duracell specs.]
We have determined that the sound quality of the preamp will begin to degrade when the battery voltage drops down to 8.5 Volts. We measured the time it takes to drain a new battery down to 8.5 Volts under continuous operation (see results below). You may get a bit longer life from the battery if you don't use it continuously. At 8.5 Volts, the sound will not stop or cut off, but you will begin to notice reduced sound quality.
CB1 ................. 10 Hours
CB2 ................. 10 Hours
Jangletone ........ 6 Hours
If your guitar is wired per CAE installation instructions, pulling the plug out of the guitar will automatically switch the battery power off. We suggest replacing the guitar Output Jack with a Stereo Jack and using the "ring" connection as the On/Off switch. When a mono guitar plug is inserted into the jack, the sleeve of the plug will ground the ring connection turning on the preamp. If you unplug your guitar cord during set breaks, the preamp power will shut off, prolonging battery life.
We don't recommend cutting power to the preamp with the bypass switch, as this will cause a "pop." The power to the preamp should remain on while in use.
YES! You can power your preamp with an external power supply, although this option requires some custom equipment and special wiring in the guitar. Our standard installation instructions don't show this configuration, since it requires special equipment not supplied with the basic preamp packages. Using an external power supply also prevents you from playing as a stand-in performer, since you must have your own equipment with you. Configuring the preamp for use with an external power supply will be discussed at length in another document.