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Sunday, December 30, 2012

What's ahead?

I find it interesting that when I read some interviews with musicians, they talk about looking for their sound, getting a different sound, or searching for something new. Yet when you get to the description of the gear they used on their last recording, it's almost impossible not to find the word "old" or "vintage."  They're trying to think outside of the box while being planted firmly inside of it. On the other hand, some people are already so far outside that I have a hard time keeping up with what they're doing. Instead I find myself wondering how the box we're in is going to grow.

One technology area that's overdue for a good idea is loudspeakers. If you look at a speaker objectively, it's pretty crude--very inefficient, limited in the range of frequencies it can reproduce, delicate--it's made of paper!  Certainly there must be better ideas out there to move air. Piezos may be a first step, and I've read about thin speakers and vibrating membranes, but don't know of any commercial products.

Similarly, magnetic pickups are due for an upgrade. The signal they produce is tiny and prone to noise, plus the magnetic field can interact with the string if it's too close. What about optical sensors? There are several out there already that offer better sensing of the string's vibration and are immune to electrical interference from lamp dimmers and other devices.

Digital signal processing offers some exciting possibilities to make a guitar a better instrument. Here I'm referring to something like the Antares auto tune circuitry that does pitch correction on the notes you play so the guitar plays in tune when it's not, and intonates perfectly. It doesn't have to change the sound of the guitar, although it can (like making an electric sound like an acoustic). But think of the restrictions this removes:
  • the 25.5" scale length of a Fender is critical to its sound, but if you may prefer the 24.5" scale of a Gibson there was no way up until now that you could get the tone 
  • intonation doesn't need to be perfect on the guitar, so you don't need a Buzz Feiten tuning system or Plek setup
  • transposing a song won't affect the chord voicings
Digital modeling amps are a great idea on paper, but the reality of it hasn't panned out. There's something a little off in the sound and the feel. Maybe that's the Turing Test for amps when you can't tell whether you're plugged into a blackface Super Reverb or a digital model of it. Similarly I heard that playing a Variax guitar felt "wrong" for some of the sounds--like playing an electric guitar, but  hearing a 12 string acoustic is "wrong." (Maybe that point above about scale length won't hold true.)

So as the calendar clicks off one more year, I'm wondering what the future will bring.

Thursday, December 20, 2012

Trainwreck amps demo

Just watched a great demo of 3 classic amps built by Ken Fischer, the 2 Trainwreck Express and 1 Liverpool. One Express were owned by George Lynch and the other was Ken's amp until he sold it to Billy Gibbons. The demo is great, using a Strat and Les Paul with different settings and playing. You can really hear the difference among the amps and guitars. Check it out:

Friday, December 14, 2012

The role of rectifiers

The job of a rectifier is to convert alternating current (AC) to pulsating direct current (DC). The filter capacitors that follow it in the circuit remove the pulsations, and provide a smooth DC power source. It seems pretty basic, yet how this is done has an effect on tone.

There are two types of rectifiers: tubes and solid state diodes. In the early vacuum tube days, solid state diodes weren't powerful enough or readily available, so rectifier tubes were used. In the 1960's, solid state technology had advanced enough where silicon diodes could be used. Sometimes several would be strung together to get the voltage rating needed, but now that's no longer the case.

One difference between the two devices is that a vacuum tube rectifier has an internal resistance (which is different depending on the type of rectifier tube used). Another is that tubes are sensitive to the amount of capacitance that is used to filter the pulsations out of the DC, and have a limit to the amount that can be used.

The way these two factors affect tone shows up as:
  • sag or compression in volume when playing loud, and
  • the amount of bass the amp can reproduce.

Both loud volume and/or bass frequencies pull more current through the power supply. Current through the resistance in a rectifier tube produces a voltage drop at the tube (Ohm's law), so the power supply voltage sags below what it is when the amp is idling. If the capacitors following the rectifier tube can't make this voltage up, the B+ voltage dips and the volume goes down slightly. When you're playing loud, or hit a loud note, this sounds like a little bit of compression. Or if there's a lot of bass, the tone changes because the bass is amplified less than the other frequencies.

Diodes don't do this. The voltage drop across a diode is constant and very small in comparison to a tube. They also don't care how much capacitance is at their output, so larger capacitors are often used. This makes an amp play "tighter." Metal players usually prefer diode rectification for its tightness, while many blues players like the looser tube rectification because the compression makes the amp sound like it is singing.

Diodes are cheaper and will last longer then rectifier tubes, but amps still use rectifier tubes for tonal purposes. Most of the time the rectifier type is built into the amp design, but some amps (Mesa) allow switching between tube and solid state rectification. There's also a mod that uses a diode to isolate the preamp and power amp capacitors. This allows the preamp to stay tight, since it stops the power amp's filter capacitors from drawing on the stored voltage in the preamp capacitors when the amp is working hard. It's also possible to build  or buy a rectifier tube socket with solid state diodes wired into it to change the rectification method. (You need to be careful here as this also raises the B+ voltage slightly and may stress aging filter capacitors.) And there are even some solid state rectifiers that have a resistance built into them so you get solid state longevity with tube-like tone.