Ask Eddie: It's Clean-Up Time

Jul 1, 2011 9:00 AM, By Eddie Ciletti

HOW ONE AUDIO QUESTION GOES TANGENTIAL

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THE OTHER STUFF:
Routine maintenance includes cleaning pots, switches and faders when possible, replacing when not. The other electronic components are passive (resistors and capacitors) and active (vacuum tubes, transistors and integrated circuits). Finding replacements is an art, knowing when it’s necessary to get the exact part to being creative with what’s available. More often than not, the physical size and footprint has changed, but the quality is often better.

The “fun” in repairing a recording console is that the problems from module to module will be very similar. Akin to wiring a patchbay, replacing the same components on each module is a repetitive process.

Resistors are the least-likely components to be replaced or upgraded unless they are stressed from heat or in a critical, low-noise gain stage. Use metal-oxide and metal-film in these respective applications.

Capacitors come in many shapes, sizes and types. Electrolytic capacitors are the most likely to degrade and fail with age. Axial-lead types have mostly been phased out because Radial types are more space-efficient. (See the figure below.) Replacing Axial with Radial requires cleverness at minimum and occasionally a bit of boldness, as I often drill a new hole so the cap can stand as intended.

Integrated Circuit (IC) Operational Amplifier (Op Amp): At their best, modern IC op amps are transparent (colorless) building blocks, but initially it was their size that provided the vision of the future—more possible features in a smaller space for less money. In many cases, IC op amp circuitry allowed a “transformerless” option (eliminating the need for input and output transformers), further reducing weight, cost and sonic character. There’s nothing particularly desirable about that vintage IC op amp sound, and modern op amps offer considerable room for improvement, if you’re willing to do the homework.

Upgrading IC op amps is not plug-and-play. Unless someone has done it before and can provide detailed plans, the process requires test equipment (an oscillator and oscilloscope), and reasonable knowledge of available IC op amps and their suitability. There are several considerations.

Power Supply, and power-related considerations, lead us to the most technically challenged portion of this exercise. Everything in the consolerequires voltage and draws current. (Just in case you’re curious, voltage x current = power, in watts.) And, just as the goal of proper gain structure is to minimize distortion and maximize headroom, the same relationship applies between the console’s total power requirements and the capabilities of its power supply; the power supply should have more available reserve current than the console requires.

In the U.S., wall power is 120 volts alternating current at a frequency of 60 Hz. Audio circuitry runs on Direct Current (DC)—what batteries make—and amplifiers need clean, quiet DC power to manipulate sound, which also happens to be a form of AC. The typical console power supply converts AC into a handful of voltages required by the audio circuitry. Voltage is only half of the power equation.

In between the power supply and the console could be many feet of cable. Inside the console, the voltages are routed to each module—or channel strip—through ribbon wire or a motherboard outfitted with connectors. However, the more affordable mixers tend to push their power supplies to the limit. Better IC op amps often draw more current than the parts they are replacing, so an op amp upgrade implies a potential increase in power requirements.

In Closing
Obviously, each one of these tangents could be its own, so you tell me, “What do you want to know more about?” Whenever possible, please provide links, schematics and images in advance. I’ll do my best to fill in the gaps by hunting, gathering, annotating and hopefully answering your question.

RESOURCES
For additional information on the topics covered here, you can visit tangible-technology.com and access the following.

Capacitor Video
Capacitor and Opamp upgrade article: Part-1
Capacitor and Opamp upgrade article: Part-2
OpAmp Upgrade Article
Internal power distribution and grounding upgrade: Example-1
Internal power distribution and grounding upgrade: Example-2
Tools (hardware and test equipment)
Basic Electronic Tools
Conventional Soldering
Surface Mount (SMD) Soldering with conventional tools
Article: What is a Cold Solder Joint?
Capacitor and Opamp upgrade article: Part-1


Eddie Ciletti is a former New York studio tech, longtime contributor to Mix and an instructor at the Institute of Production and Recording in Minneapolis. He can be reached through his Website.






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