Two...you have to keep in mind that I built automated lighting for 8 years, so once I started into this it became an endless string of acronyms, buzz words, and technical jargon that at times required trigonometry. And seeing that this comes out on Saturday morning (which is prime hangover time), I didn't want to risk exploding any heads. So, maybe another time.
In the last couple of months, I've gotten back into servicing other peoples gear (albeit on a limited and referral only basis). It starts off with "hey...I heard you know how to fix amps...can you look at mine?" The next thing you know, I got gear waiting to be looked at.
As many of you know, I'm an Engineering Electronics Technician by trade. At my day gig, I'm dealing with very low power, and units of measure that are ridiculously small like nanovolts, picoamps, and femtoseconds. That's all well and good, but when I get the chance to get my hands on something in the range of hundreds of watts...well, this is where you insert that Tim Allen grunt. I'll admit it...there's a certain rush to working on a piece of equipment that has the potential to kill you!
Lots of gear snobs go on and on about how good the "vintage" amps from the 60's sound. And some of them are really great. If I had a few thousand dollars laying around I would love to score a mid 60's Marshall JTM-45. But I would never take it out...so much of that stuff from that era was so fragile.
It was in the late 70's that manufacturers figured out how to build good sounding amps that could stand up to being thrown in the back of a van and driving down 200 miles of washboard road by a ticked off roadie who has been up for 3 days on bathtub crank.
Recently, I've had a couple of bass amps from the 80's come across my bench...an SWR and a Gallien Kruger that I'm finishing up today. Both of these amps represented some really outstanding engineering and manufacturing processes. I mean, we're talking 30+ year old equipment that's been working...not sitting in a closet some where.
Both of them just needed some TLC to their power supplies. The GK had a blown output transistor, but it was one of the originals from with a date code on it from 1984! The owner really loves this amp, so we're completely rebuilding the output section in addition to the power supply. This amp will hopefully run another 30 years.
Which brings me to the heart of the article today...what can actually wear out in a piece of gear?
First, let's get the vintage thing out of the way. If you have a 30 plus year old amp that gives you a tone that defines "your sound", then by all means keep it running. It pains me to know that thousands of pieces of vintage instruments and gear have been bought up by foreign investors and have left this country. So anything we can do to keep part of our history here is OK by me.
Stuff Wears Out
In general people think that tubes in amps are the only things that wear out and require replacement. Solid state amps (like most bass amps) just keep running forever.
WRONG!
Even the solid state stuff will wear out after time. You want to know the number one enemy of electronics? It's heat. Yep...it wears things out more than you realize. This is a real generalization, but for every 10 degrees Celsius (18 Fahrenheit) that you can reduce the temp on electronics, you double the life! Yeah, you read that right. This is why tube amps typically need to be serviced more...they just run hotter. And this leads to...
The Power Supply Is Everything
Without adequate and clean power, the rest of the amp can't perform. I've seen some brilliant designs that were compromised by cheaping out the power section (although one amp, the Vox AC-30, actually capitalized on this as part of their sound).
Here's the power supply from the GK amp I'm working on now:
All of those blue cans...those are the electrolytic filter capacitors, and that's the primary component that wears out (or should it say drys out) in amps. Yeah, there's actually a liquid in those things that makes them work. Their job, when they're working right, is to take all of the ripple and junk out of power that's going to amp. When they're not working, you'll notice an increase in hum in your amp even when all of the controls are turned down.
They're also used between the stages in your preamp to couple the audio through. When they start failing there, your sound tends to start getting thinner. In tube amps, your gain is all off because the tube stages are getting voltages there weren't designed to take (the technical term is "incorrect bias").
These things aren't the cheapest things in the world ($5 to $10 each, depending on the value and size), but if your tube amp is over 10 years old or solid state amp is 15 years or more, it's probably time to change these things out. If you let them completely go, they can eventually short out and take out a lot of other stuff in the amp.
Hey Man...You Got Any Scratchy Pots?
Noisy potentiometers (you know...those knobs on the front of the amp) are a very common complaint. Now, if you take your amp in for service, a good technician will clean these for you while he has the amp open (and I'm a good technician).
But whether it's on your amp, one of your guitars, or an effect this is something you can take care of yourself if you're so inclined.
First, I'm guessing that most of you don't know how a pot actually works. Well, it's not really that complicated. And it doesn't matter if it's servicing as a volume, tone, balance, or whatever control...the hardware is pretty much the same.
This is what's going on inside of potentiometer...or as they're also know a variable resistor:
Not the greatest picture in the world, but the important parts are that black semicircle and the wiper arm. The semicircle is called the resistive element. It can be carbon, conductive plastic, or a number of other proprietary things. The wiper arm is what actually moves when you turn the knob.
If you get a bunch of dust / dirt / nicotine / body fluids on either the resistive element or the wiper arm at the point of contact, you get that oh-so-annoying scratch when you turn the knob.
So, how do you clean it? Well, the good news is that most pots have an opening in them, like this one:
If you're doing this in an amp, make sure it's been off for a while and unplugged. DeOxit isn't conductive, but you shouldn't be monkeying around in a powered amp unless you're looking for trouble (literally).
If you have slide pots (like on a mixer or EQ), just shoot it in the front and move the slider. There, that was easy.
If your pot is still scratchy after this, it's likely that the resistive element has worn out (it happens). At that point, you're looking at replacing the part.
DO NOT USE WD-40! I've made a small fortune replacing pots (especially the slider type) because someone thought it was a good idea. Don't get me wrong, WD-40 is a great product...on case casters. But not electronics for two reasons. First, it attracts dirt, and that's what we were trying to fix in the first place. Two, it's reactive with some modern conductive plastics. I once replaced 32 very expensive slide pots (these were $50 each my cost) on a guy's mixing console thanks to WD-40. What's sad was he knew he was supposed to use something like DeOxit, but the WD-40 was "so much cheaper". Yeah, right. I think that total bill was almost $2,400. Tell me again how much you saved?
Speakers....not usually.
Here's something that doesn't wear out unless you blow them, and that's speakers. Sure, the cones can be damaged. Sometimes the glue holding them together fails. And although you typically don't see speakers with foam surrounds in pro audio gear, occasionally I come across one where the surround has rotted away. In all those cases however, the speaker can be saved with a recone. They take the frame and give you a new cone, voice coil, and dust cover where applicable.
But here's what cracks me up, and that's when someone claims that their speaker's magnets have lost their power. I'll ask them if they've had an MRI done on their amp, or if they've been close to a nuclear detonation (in which case we wouldn't be having this conversation). In every case so far, then answer has been "no".
Good, it ain't the magnet.
In full disclosure, I used to wonder about this too. So I called a friend at Electro-Voice, another at Meyer Sound Labs, and emailed an engineer with Celestion in the UK. I got the exact same answer from all three, which I will paraphrase here.
- When you initially power a speaker up, it will loose about 1% of it's magnetic flux
- It will loose another 1% during the first year or so of operation
- It will take about 100 years of continuous operation before it looses another 1%!
Yeah...100 years! So OK, maybe Keith Richards' amps are getting close, but none I've come across.
Here's The Good News
I can say that audio techs and amp repair guys are (in general) the most honest service people out there. TV Repair, automotive, appliance...I've had attempted rip-offs by all of 'em, but never another amp tech. I guess I attribute that the fact that most of them, like myself, are musicians. They understand how import your gear is to you, and know that 99% of us are not swimming in money.
A good tech will walk you through everything they've done, and hand you the parts they pulled out when you pick up your gear. Just things to keep in mind.
Next week ought to be interesting. We'll talk about fixing stuff, but not equipment. Let's talk about taking care of ourselves. I've been fighting shoulder and arm pain in my right arm since 2009, and haven't found answer for what's going on. Recently, I've been very lucky to meet a musician who is an Orthopaedic Physician's Assistant by day. I'm going to see him next week, and want to share what we find out. Because after all, you can have the best gear in the world...but if you ain't working....
Until next week, keep the meters
Ken
Ken Carver has been a musician and performer since the early 70's, and involved with live music production since the mid 70's. He worked for 15 years as a broadcast engineer, building numerous studios and transmitter sites around Texas. He's also worked in Critical Care Communications for the medical industry, R&D for an automated lighting manufacturer, and owned Project Lighting & Sound in the 80's. He currently heads up an R&D Hardware Technician Team at National Instruments in Austin, and still performs on the weekends in the Central Texas area. You can reach Ken at itsjustlogistics@gmail.com
