Mesa/Boogie DC3 manual Here’s a question we often hear

Page 19

BIAS ADJUSTMENT: (Part of a continuous series)

Here’s a question we often hear:

CATHODE

GRID ( ,

SCREEN

GRID ( )

“Why doesn’t Mesa put bias adjustments in their amplifiers?”

Well, there’s a short answer and a long answer to this question.

( )

)

....

....

..

....

..

...

..

..

.

Structure of a 6L6 / 5881 Beam Power Pentode.

BEAM-

CONFINING

ELECTRODE ( )

PLATE

( , )

The short answer is that during my 12 years of repairing Fenders, one of the most frequent problems I saw was bias controls that were either set wrong or that had wandered out of adjustment due to vibration. As any honest tech will tell you, there’s lot’s of easy money to be made by sprinkling “holy water” on amplifiers ... uh, what I meant to say is “Your amp needed biasing.” See what I mean? What customer is going to argue with that?

It only takes a moment and a volt meter: The Fender diagram shows how: “Adjust this trim pot for - 52 volts.” That’s it. Nothing more.

Now don’t be fooled into thinking that tubes “draw” more or less bias, they don’t. The way a bias supply is connected to a tube is akin to a dead end road, it just trails off to nowhere without really completing a circuit. It’s a static voltage and regardless of what tube is in the socket — or even if the tubes aren’t plugged in at all, it doesn’t change the bias voltage a bit.

So the end of the short answer is this: Since a bias supply needs to put out the right voltage and never vary, I wanted to build amplifiers that were individually hard wired to the correct values and NEVER needed adjustment. And for 25 years, that’s how Mesa/ Boogies have been built.

Time to change tubes? Just plug our tubes into any one of our amps and you’re DONE. No tech needed. NO bills and no BS about biasing. And most important: The Bias is RIGHT because it can’t change!

Now, you want the long answer? Here’s more information on how our hard-wired bias avoids trouble. Please read on.

But first, let’s make an important distinction. Our business is designing and building high performance amplifiers. And for this we need tubes whose variance is within a narrow range. Our warehouse is full of rejects ...oh, they work — they just don’t perform within our tolerance range. We have a very sophisticated computer - based tube testing system (nicknamed “Robotube”) that matches and measures tubes over seven important parameters. It can even predict which tubes are likely to have a shortened lifetime — even though they work perfectly during the test.

Because our business is building quality amps, we can afford to reject a lot of wayward tubes. The guys you hear complaining because Boogies don’t have bias adjusters are primarily in the business of selling tubes - not amps. They don’t want to throw away 30 percent of their inventory, so they promote the idea that tubes outside our parameters can be used to “customize” amplifiers and they criticize us because our amps can’t be adjusted to accommodate their out-of-Mesatolerance tubes.

Now you might be thinking, “But I thought you just said that tubes don’t “draw” bias, therefore they don’t effect the bias supply and thus it doesn’t need to be adjustable.”

When you set the bias (whether it’s by selecting the right resistors, as we do, or adjusting a trimmer — which is quicker) what you are doing is establishing the correct amount of idle CURRENT that flows through the power tubes. But you can’t adjust the current directly, you can only change it by adjusting the amount of bias VOLTAGE that goes onto the tubes’ control grids.

PAGE 15

Image 19
Contents Dual Caliber DC Hello from the Tone Farm USE Common Sense and Always Observe These Precautions DC-3 DC-3Operating Instructions Gain POWER-UPUse of the EQ. see page 5 for more information on EQ Bass TrebleMidrange Purpose MID Control From 0 to aboutMaster PresenceAround INPUTdominant in the mixGraphic EQ Output LevelPower Toggle Switches Rhythm / LeadOn / Standby Ing tradition and save the replaced set as spares FuseEQ Select Ftsw EQ/REVSilent Recording FX Loop Send / ReturnFX MIX RecordingSpeakers SlaveChannel SamplePersonal Settings 12AX7 Tube Noise & Microphonics Diagnosing Power Tube FailuresTube Noise Diagnosing PRE-AMP Tube Problems Here’s a question we often hear Why doesn’t Mesa put bias adjustments in their amplifiers?Bias Adjustment Cheers Randall Smith Designer & President Your amp needed biasingRear View DC Front View DCMesa Boogie 707 778-6565 FAX no

DC3 specifications

The Mesa/Boogie DC-3 is a highly regarded guitar amplifier known for its versatility, power, and distinctive tone. Introduced during the early 1990s, the DC-3 has become a staple among musicians who appreciate its unique blend of classic and modern sounds. The amplifier is part of the Mark series, renowned for its innovative design and exceptional sound quality.

One of the standout features of the DC-3 is its all-tube preamp, which contributes to its warm and rich tonal characteristics. The amplifier utilizes three 12AX7 tubes in the preamp stage, providing a dynamic response that enhances the natural tonal qualities of the guitar. This all-tube configuration is complemented by a powerful 2x6L6 power tube setup, delivering a powerful 30 watts of output. This combination allows the DC-3 to produce a wide range of tones, from clean and sparkling to thick and saturated drive.

The DC-3 is equipped with a unique two-channel design, offering a Clean channel and a Lead channel, each with its own set of controls for ultimate tonal shaping. The Clean channel is characterized by its bright and articulate sound, making it suitable for a variety of genres, including jazz, pop, and rock. The Lead channel, on the other hand, offers greater gain and sustain, perfect for heavier styles like hard rock and metal. These channels can be blended together using the shared EQ, allowing for a truly customizable sonic experience.

Mesa/Boogie's innovative graphic equalizer further enhances the versatility of the DC-3. It features a five-band EQ that allows players to sculpt their sound with precision. This feature makes it easy to dial in the perfect tone for different performance environments, whether in the studio or on stage.

The DC-3 also includes a built-in reverb, adding depth and ambience to the overall sound. This is a valuable addition for musicians looking to enrich their performances without the need for additional effects pedals.

Robust construction and attention to detail are hallmarks of Mesa/Boogie amplifiers, and the DC-3 is no exception. It is built to withstand the rigors of touring and the demands of professional musicians. With its impressive tonal palette, reliable performance, and durable design, the Mesa/Boogie DC-3 continues to be a favorite among guitarists, making it a worthy investment for anyone serious about their craft.