Low Noise

I’m often asked how it is that my Texas Tone amps have so little hum and hiss compared to many other tube amps, and yet have such sweet tone. It’s by design.

So many tube amps today are descended from amps in the mid-1950s to the mid-1960s. Many builders today make tube amps that are either clones or replicas of those amps. Texas Tone tube guitar amplifiers are not clones or replicas. They are new designs that are inspired by those iconic amps of the past. In those rare cases where we make a traditional amp design, it’s updated for low noise and safe operation.

Why not clones or replicas?

Safety

In some cases, the choice is clear – safety. Guitar amplifiers of the past had two-pronged non-polarized AC plugs. Turning the plug upside down reversed the polarity, which was interesting because there was no way to know which end was up. The danger of this is that the so-called “ground” side of the amp chassis could become “hot” and vice-versa. Tube amp builders made compromises and concessions to this. Two of these were the Ground switch and what became known as the “Death Cap.”

The Ground switch reversed the polarity of the plug (equivalent to turning the plug over, when you didn’t want to turn off your tube amp). I recall that the trick was to get all the amps on stage to the same polarity.  How did we do that?  Hold your guitar strings and tap a microphone. If you got shocked, you needed to flip your Ground switch or turn the AC plug over.  Ouch!

The Death Cap was a capacitor wired to one side of the AC power, or to the Ground polarity switch. It was intended to get rid of hum if your polarity was reversed. The reason it’s called a Death Cap is that if the capacitor fails, then your amp chassis, and by extension your electric guitar, could become hot with 120 Volts AC, a most unpleasant situation. Today, all amplifiers are built with a three-prong AC plug and a power ground, or at least they should be.

Noise

The noise floor of many vintage amps (new ones, too) is quite high. Many guitarists just get used to the noise and hum. I know one who doesn’t like tube amps because they hum and hiss.  I told him, “mine don’t.”  Some guitarists buy noise gates or noise filters or line filters to help reduce unwanted noise and hum. This noise is due to two things – component selection and wire lead dress. A little background may help.

Grounding

Many amps are built with poor grounding techniques, with multiple ground points throughout. This is a recipe for noise, as multiple ground points cause ground loops, a main contributor to noise. Texas Tone amps are built with solid electrical engineering ground scheme to eliminate ground loops and ensure low noise operation.  Well-respected electrical engineer and amp builder Randall Aiken has a nine-point plan for proper grounding.  As he states, “Grounding isn’t rocket science.”  Makes me wonder why some amp builders don’t follow basic grounding rules.

Lead Dress

In the mid-1960s Leo Fender sold his company to a large conglomerate. They immediately instituted cost-savings, partially due backorders of items sold but not yet produced. The Fender General Manager, Forrest White, had implemented a quality bonus program to ensure high quality work, but this was one of the first things scrapped to increase production numbers. Due to the rush to push product out the door, and without the quality incentives, amplifiers were built without proper attention to wire lead routing, called “lead dress”. Poor lead dress can lead to hum, hiss, oscillations, squealing, and generally negative impacts. Rather than fix this, the company changed their circuits to add anti-oscillation components, and changed component types and values to save money. The end results was that guitarists began to seek out the older amps that sounded better.

Components, Wire, and Lead Dress

Texas Tone tube guitar amplifiers are built exclusively with aerospace grade military specification wire. It’s flexible and yet holds its shape, even with right-angle bends, is conservatively rated at 150C (300F) and 600 working volts. I’ve seen some tube amps use 105C or even 85C wire rated as low as 300V. Since most tube amps produce between 300 and 500 Volts DC, using 300V wire is asking for trouble.

I make sure that the wiring inside Texas Tone amps does not induce noise, by ensuring that high voltage wires are kept away from signal wires.  Any time wire paths cross, they do so at right angles and sufficient air space.  Many sensitive signal wires are shielded.  There are lots of current spike and noise in transformer center-tap wires and choke wires.  These are kept away from sensitive preamp nodes.  I’ve seen some amp builders, in the name of neatness, bundle wires together with tie wraps – a sure recipe for noise.

Amps of the 1950s used carbon composition resistors. Why? Because that’s what was available and cheap, not because of some “sound mojo”. Allegedly, and subjectively, carbon comp resistors are said to be somehow warmer sounding.  Huh?  Many of these resistors aren’t even in the signal path!  Carbon comp resistors have notoriously loose tolerances, poor drift and noise characteristics, and are responsible for most of the crackling and frying sounds heard in most old tube amps.  I’ve also tested 220k carbon comp resistors that read anywhere from 185k to 240k!  Not good when the circuit calls for two 220k resistors tied together, or using one as your supply voltage for a gain stage.  Rest assured, the gain and distortion characteristics of a preamp with a 190k versus a 240k are quite different.

Most of these carbon comp resistors are rated at 350 Volts, not a happy situation in tube amps that routinely see more that 400V!  The resistors used in Texas Tone tube guitar amplifiers are known for their stability, high temperature and voltage rating, and extreme low noise, and they don’t drift like carbon comp resistors. Here’s a comparison:

Type Tolerance Temperature Voltage Low-Noise
 Carbon Comp 1/2 Watt  ±10% 125C 350V NO
Texas Tone USA ±1% 175C 500V 0.10 μV/V
Texas Tone 1 Watt ±5% 155C 500V -10x Carbon Comp

Not only are these components low-noise, high voltage, and high temperature, they have tighter tolerances and they don’t drift, so they maintain your sound.  You want your sound to be consistent, night after night, gig after gig, session after session. You want a reliable musical instrument, not one that crackles, pops, hums, and is unreliable.

When you hear a Texas Tone amp, you’re not hearing hum and hiss, you’re hearing yourself at your best!  When you sound your best, you play your best.  Your tone matters.

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