Noise Suppression: Key to Good Tone

Noise Suppression allows your music to breathe

A rebuilt 1960 AC30 incorporates noise reduction wiring techniques

Noise suppression capacitor used on a Mojave Scorpion power supply. This capacitor reduces switching noise caused by diodes turning on and off at a rapid speed.

Most guitar amps have circuitry which is both high gain and sensitive to small variations in input signal coming from the instrument itself.  This added sensitivity is what guitar players love for dynamics, better detail and increased harmonics but high gain has a price. The added gain comes at the expense of added noise. To resolve this issue, and retain the highly sought after articulation and detail we explore some of the building techniques used by Mojave Ampworks. The culmination of both articulation and detail are what I like to call “String Definition” where you can hear the notes of each sting standing out in a chord voicing yet still get the full effect of punch if that chord is lightly overdriven. Even clean guitar amplification will be subject to the issue of noise.  Noise is not always audible. The signal that is produced has a certain amount of space that allows the guitar harmonics to ring out clearly if there is nothing in the way but guitar signal. Noise will suck the life out of the signal by robbing it of the dynamics and power needed to vary it positive to negative. That swing is what makes your guitar able to express dynamics in the form of volume or sustain. Noise that is not audible will typically be in the form of an oscillation at a frequency above our hearing but nonetheless it is robbing power from the amp and from your guitar signal.

Mojave Ampworks hand build custom Top Boost kits for AC30 amps for the 1960s

There are other noise types which have more to due to mechanical design. The main issue that can become a problem over time is grounding. Incorrect grounding opens the door to unequal grounds from one point to another though out the chassis. This means you will hear the difference in the form of hum and or in severe cases, squeal. Poor grounding also creates funny looking results on the signal line and the addition of a low frequency hum means noise that is also robbing the guitar signal in the form of power. Sometimes a bad ground can also create an oscillation. All these types of problems must be addressed for good performance long term.

This custom made kit uses a ground that is kept isolated and ties into V1 ground to prevent ground loops form developing. This technique was extremely useful in lowering hum levels already high in the early AC30 JMI era amplifiers.

Mojave Ampworks has had many years in dealing with Vox AC30 Top Boost amps, Vox AC 15s and many models of Marshall Plexi model amps. This love afair with the golden area of guitar amps has brought our level of experience to a better degree of understanding having seen how amps age and what the issues are long term. Something might seem like a good idea at the beginning but give it 40 years and you will know for sure!

Mojave Ampworks uses custom made transformers to feed separate heater voltages to the preamp tubes in the Scorpion 50 model amp. Separating the heater supply from the the rest of the amp removes the AC noise created by the power supply switching diodes in the power supply which creates a buzzing noise in the heater voltages. This method means extra work but dead quiet amps that allow for increased dynamics and articulation. This improvement is one of many ways we increase the gain and response for the player to get his extra bit of detail the artist is striving for. Vivian Campbell did his test using a Les Paul equipped with P90s and used his fingers for the majority of the time.  This type of test is what really pulls the finite details to the surface through dynamic exercising and making the amp work to show what it’s got.  The Scorpion preamp is extra hot but without the cascaded or cascode gain, but rather using a unique preamp gain system called Current Tracking which allows for high gain and extra low noise. The pre amps are arranged in parallel. By tying the grids together you effectivly lower the noise level by raising the noise rejection of the input tube. There is a higher current gain in this configuration and this means tiny details are amplified that would other wise pass undetected or with little to no attention paid by a standard preamp design.

Here the Mojave Plexi 45SE has chassis wiring that exemplifies low noise construction. Central Point Grounding, preamp grounds separated form power amp grounds. Dedicated AC line ground. Wiring is held tight to the chassis between tube socket connections and turret board circuitry.

Many times guitar players turn to pedals to add that extra gain into the mix. This works well but almost without question this introduces a large degree of noise into the signal chain and this will always steel detail from your guitar.

Mojave Ampworks offer the Current Tracking preamp in  3 out of its 6 amp line up. If you wish to learn more about how the low noise approach has made it’s way into the Mojave design, check out the information on the Scorpion, the Sidewinder 30 and the Coyote 12. The Coyote 12 watt is also able to run on average at 15 watts and maximum power usually tops out between 15 to 18 watts. Do not be deceived, 12-18 watts is very powerful and loud for most music recording and performing.

In conclusion it is the perspective of Mojave Ampworks that low noise is a vital design criteria and that guitar players are better served having electric guitars that make more harmonic details rather then allowing a layer of static, hum or hiss over the art of the music. Leaving the details to be heard is the goal of our low noise approach and keeping your art and music out front for the listener to hear is our priority.