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Ask Eddie: It's Clean-Up Time

HOW ONE AUDIO QUESTION GOES TANGENTIAL 7/01/2011 5:00 AM Eastern

I sometimes help people solve problems by remote control. When it’s stuff I don’t know intimately, my clients and I learn together. From there it seems a natural progression to bring this private interaction into the light of a public forum—my new blog at mixonline.com—the essence of which will be distilled into this new monthly column, “Ask Eddie.”

This inaugural article is a composite of several related email questions and is typical of the many “tangential threads” that a single question can generate. Be sure to check in at mixonline.com for the blog and watch for regular answers in your MixLine e-newsletter. As they say in O Brother, Where Art Thou?, “We’re mass communicatin!” Let’s start the show.

The Electrodyne 711 module includes a discrete transistor amplifier, input transformer, 2-band-selectable EQ, one aux/FX send (three routing options) and “Gliss” wire-wound glass fader.

The Electrodyne 711 module includes a discrete transistor amplifier, input transformer, 2-band-selectable EQ, one aux/FX send (three routing options) and “Gliss” wire-wound glass fader.

Q: I just got a ’70s (or ’80s or ’90s-era) analog recording console. What’s the best way to prioritize the resurrection process?
A:
The simple answer is to have a trusted tech advisor onsite to determine the condition and then discuss the challenges. Trust the tech to differentiate the essential repairs from the wish-list upgrades. Be sure to get a price breakdown so that everyone knows the limitations of the budget. Be sure to factor in the “unseen costs” by your multiplier of choice. When passion drives the purchase, you need to be extra cautious; you need to know what’s under the hood. Pull a module and look for signs of damage and sloppy repairs. Once powered up, a few custom cables may have to be fabricated to get signal in and out of each module.

Consider the common user-interface components—faders, pots and switches—as they are most likely to require service or replacement. If you hear “scratchiness,” then the “Device Under Scrutiny” has audio going through it. Faders that provide a control voltage to a VCA will not sound scratchy because the control voltage is filtered. If a fader sounds okay but feels funky, take it apart. A switch that controls a relay doesn’t have to be super-clean, just reliable, so go through an entire module’s worth of switches to be sure you didn’t pick the one switch that works.

AMPLIFIERS: That certain pieces of recording gear have their own unique sonic character implies that amplifier design is a key player, along with the equalizer type, frequency options and dynamics processors. Nowhere is that more true than the early ’70s classics. Each manufacturer’s design was unique back when each amplifier was built from discrete transistors sandwiched in between an input and an output transformer.

Each technological development improved specs, but many would lament that the reduced distortion sometimes robbed recording electronics of its desirable and unique sonic character options. There are times when we need our audio signal to be transparent-clean from start to finish, and times when it’s okay to “distress” it!

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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