Upgrades, Switches and Pots

May 1, 2005 12:00 PM, By Eddie Ciletti

MAINTAINING CLASSIC (AND JUST OLD) GEAR

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Audio gear has a metamorphic history of first being essential, then “standard issue” and later disposable, until it's ultimately reborn as a “classic.” Some gear is timeless in that it can be reincarnated with affordable off-the-shelf parts throughout its many lives. And then there are the exceptions.

During the past five years, I've written at least two articles about component upgrades — capacitors and op amps — and applaud everyone who has taken the plunge. While I'm very much into remote consulting, I'm hesitant about helping people choose op amps at a distance because of potential tweeter-damaging oscillations. So far, that's not stopped anyone.

My other concern is the inspiration for this month's column — the need to prioritize the work. That is, to determine if routine service should take precedence over an upgrade.

It's been more than 10 years since I made regular house calls, but my memory is still very good. Most consoles with some years on them — such as the Neve 8128, MCI/Sony 600 Series and Trident's Series 80 and Series 65 — had developed very scratchy pots and switches, even back then. Any time a customer reported a few funky modules, a quick survey proved that many more modules exhibited similar problems. I can't imagine them being in any better condition now.

My recent experience in the educational environment bears this, not only with a Trident Series 80 (a '96 reissue) and SSL 4000, but also with outboard gear. There is always something to clean, repair or replace. For example, the switch that activates on the front/rear pan pot on the SSL I/O module may not get used, but it is the link to the mix bus. Fortunately, the switch has an open back. A cotton swab dipped in 99-percent alcohol and placed into the opening will put enough fluid into the contact area. A little exercise and it comes back to life. That's only half of the procedure.

WHEN “DIFFERENT” ISN'T COOL
When chemical treatment does not work, finding a source for new parts can be challenging. While switches are mostly off-the-shelf items, many potentiometers (aka pots) have been customized, which is costly whether or not the manufacturer is still in business and supporting the model in question.

On older products, rotary pots and switches were connected by wire to the PCB. This provides the user with great freedom when upgrading and replacing. But, as late-model products crammed more parts into less real estate — by directly soldering to a PCB — every dimension, including pin spacing, becomes critical.

In terms of quality, it's fairly easy to upgrade a pot — from “open-case” carbon to conductive plastic, for example — but sometimes that opens the proverbial can of worms: The original knob may not fit on the “better” part. In single and small quantities, off-the-shelf pots sell from $1 to $15 when purchased from a distributor such as Digi-Key (www.digikey.com).

Most off-the-shelf pots are singles, while many circuits, such as sweep EQ, require two or more resistive elements. Multiple element pots are priced exponentially higher — costing around $50 — because they are considered custom and, as such, require a setup charge and a minimum quantity purchase. Customized pots also have dimensional issues, such as bushing size, shaft length and diameter. In addition, resistive taper can be logarithmic (as in audio), linear or some variant.

Conductive plastic parts are considered better, both in terms of materials and precision, as well as being sealed so that dirt does not get in. Carbon is a cheaper material and the pots typically have an “open” metal casing that is less protected from the elements, but more easily treated when they get funky. Sealed pots may last longer, but when they do get scratchy, cleaning is not an option. I'm not big on spray cleaners and prefer the pinpoint applicator because it is not as messy. (See the “Better Audio Through Chemicals” sidebar.)

CONSTRUCTION AND DESTRUCTION
Well-designed electromechanical devices — pots and switches — should be self-cleaning, but that requires pressure and enough material to survive tens of thousands of exercises.

Panasonic's 9mm (single) and 12mm (dual) audio pots are good for 10,000 to 15,000 turns, respectively. Keep in mind that these standard-issue parts cost $1 to $3 in single quantities. Clarostat's conductive plastic pots range in price from $5 to $15 and are good for 25 to 50K cycles of abuse. These are single-element parts only. Most sweep equalizers and total recall parts require two to five elements.

Cheaper pots typically use carbon as the resistive material and are open, making it easy to inject a cleaner or lubricant. The older a pot is, the more likely it can be fully disassembled for a more thorough cleaning. More expensive pots are sealed and are therefore a done-deal. Carbon is not a bad material, but certain manufacturers have used cheaply constructed pots that will not respond to any treatment and are destined for the trash can.

Switches come in many varieties, but the most poplar in vintage gear is the latching type — push once for in, push again for out — as required by EQ in/out, bus assign and insert routing switching. The ITT Schadow switch was most popular from the 1970s into the '80s. Some versions can be disassembled.

HOLY LEGS
Early transistorized gear, like API and Neve designs, used single-sided PCBs. By 1975, dual- and multilayer boards became more common. Although wire jumpers and pins can be used to link one layer with the other, it is more common to “plate” a through-hole with conductive material. The problem with the plating process is that it changes the hole's dimension, and if that space must be shared with a component, then the original through-hole size must have a larger diameter to compensate.

One console that suffers from undersized through-holes is the MCI 600 Series. Extreme care must be taken to remove all solder first, and even then, it is very difficult to remove pots, switches and IC sockets without pulling out the plating and damaging a PCB trace. It is sometimes easier to cut all of the component legs first and then individually remove each leg.

SOLDER BE GONE!
There are two ways to remove solder: Use suction or a flux-treated wire braid. Solder suckers come in two flavors: manual and motorized pump. The former is used with a conventional soldering iron; the latter is an integrated iron using special tips with various hole options, depending on the type of components being extracted. The manual type is okay for small jobs; the motorized variety is better for massive overhauls. Both require frequent cleaning and tip replacement to maintain full functionality.

De-soldering braid is a woven copper mesh that is placed between the soldering iron and the work. I prefer Chemtronics' Chem-Wik®. It comes in various widths; a 25-foot spool of the 0.05-inch width is $7.49 at www.hosfelt.com. Both de-soldering methods sometimes require that solder be re-applied if things don't go well the first time around.

UPGRADE?
So now you see why I might have several reasons to defer an op amp upgrade. If you need one more reason, then try pumping 40 Hz through your favorite pot or switch — it's very revealing.


For more Eddie Ciletti, visit his Website at www.tangible-technology.com.

BETTER AUDIO THROUGH CHEMICALS
Gold is most resistant to corrosion as it's the only precious metal found in nature in its raw form. It is also the most expensive. All of the other metals, including silver, attempt to return to their natural state by recombining with airborne agents, such as oxygen, sulfur, chlorine and fluorine. Silver is one of the more popular contact materials for switches and XLR connectors, for example. Surely, you've seen it turn black. That's silver oxide, and it behaves as a diode if the mating contact doesn't self-clean on insertion. Silver sulfide is a non-conductive and less-obvious film that gets in the way of signals. Cigarette tar and nicotine also contribute to the contamination process.

For visibly exposed contacts such as connectors, a cotton swab or cloth, alcohol and a little elbow grease will remove most oxides and sulfides. But for contacts you can't see or access, it's worth trying products that are specifically designed for oxide and sulfide removal, such as those manufactured by Caig and Stabilant. Both manufacturers offer various application-dependent concentrations.

Due to the wide range of products offered, the support section on Caig's Website (www.caig.com) provides a mentoring card — a PDF download — detailing the entire line and some basic FAQs and tips. In essence, a two-step process is suggested for cleaning pots and switches, starting with DeoxIT to remove surface contaminants.

Follow-up treatment depends on the environment: ProGold for typical studio applications and PreservIT for more aggressive environments. Components should be exercised to help the process along — you may even want to allow DeoxIT to work overnight before moving on to step two.

I am less familiar with Stabilant [reviewed in the March 2004 Mix — Eds.], but the site intrigued me as it offered a bit more insight into the product and its application, as did www.posthorn.com, the product's American distributor. Both concentrated and diluted versions are available; the diluted version includes isopropanol and ethanol. Stabilant recommends using an applicator filled with isopropyl alcohol to flush out contaminants and old lubricant from switches before applying its product.

No matter which product you choose, I prefer the needle dispenser over spray cans, as it concentrates the solution where it's needed most.






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