When we left off last week, I was troubleshooting a mid 2000's Crown power amp that had decided to not work for a customer at a gig. It turns out that the pots were a little dirty and the XLR input connections had fatigued. A shot of DeOxit, some solder, and deionized air to blow the dust out and this bad boy is good to go.
While I had it apart, it really admired the construction techniques used. Even though this amp was built in China, the attention to detail and a few little tricks to make the amp road worthy really stood out.
People talk about why one piece of gear is better than the other. Sure, electrical specs are a big part of it, and we'll talk about how to actually read those in another installment. But the bottom line is that if you're a working band and moving your gear from gig to gig, it's got to be able to stand up to that. I've seen some equipment (designed for home use) that sounded fabulous, but wouldn't survive 10 miles in a U-Haul...even in a road case.
So this week I thought I would point out just what makes a piece of equipment "nice". And even though we're just looking at a power amp, a lot of these points apply to any piece of electronic gear you're going to haul around. And this is not an exclusive endorsement for Crown...there are a lot of other companies today building some very good gear at reasonable prices for the average working musician. But on the other hand...there are a lot of 'em that are building some really bad stuff.
OK students...what is the #1 enemy of electronics? What? Who said heat? That's right...proper system cooling goes a long way toward extending the life of the gear. So that's usually the first thing I look at. On that note, starting at the front panel notice the large vent for air flow:
And those aluminum fins that are sticking up...heat sinking for the output transistors. The cooling fans are located directly behind them. What all that adds up to is a straight path for the air to flow and take the heat out of the amp. This is called back-to-front cooling, and just about every amp over 100 watts / channel uses that now. But that wasn't always the case. When I built my first really big PA (2,000 watts) in the late 80's, I used Peavey CS-800s. They had a fan in the back, but exhausted the hot air out the sides of the amp. Put 'em in a rack, and guess what...you're recirculating the hot air! I had to hack up my road racks to get them to exhaust correctly. It's something to watch out for.
Moving around to the back panel, check out the speaker connections:
This amp can output up to 800 watts per channel...far more than a 1/4" connector can safely carry. Crown was one of the first companies to move to Speakon connections which are far more secure and can carry a whole lot of power. Binding posts also give you the option of using banana plugs or wire lugs. This is all standard on high power amps now, but this was cutting edge in 2006.
Moving across the back panel, Crown used two cooling fans for this amp:
Two fans give coverage to the entire heat sink field in the amp. Electrically, they're two speed and thermostatically controlled. They run at half speed (which makes 'em pretty quiet) until things get hot and heavy, and then they cut over to full speed. And in the event that the amp still overheats due to a fan failure or extremely high ambient temperatures, the control system will shut everything down before any major damage can occur. You're not going to find that on a cheap Pyle amp!
Inputs are pretty straight forward, a pair of balanced XLRs. This is one place I've got to pick on this amp...it would have been really nice to have a switch that parallels the inputs. In other words, let me plug into one channel, but feed both of them (useful if you're using the amp for subs). I'm not crazy about the plastic housings on the XLRs, as those 4 screws you see (that go into the plastic) are what are holding that panel in place. A couple of them were stripping out, so I used a filler on the holes to give the screws some new meat to bite into.
But you know what makes up for my gripes with the XLRs? Look under the AC power connection. That's not a fuse, it's a circuit breaker!!!! That's right, if something happens and you pull too much power, this trips. No fumbling around to find a replacement fuse...just clear the fault condition, reset the breaker, and you're back up and running. In bulk, these really don't cost that much more than a fuse and fuse holder...and I really wish more manufacturers would go this route.
Now, there's a few things I want to show you on the inside of the amp. If you remember from article I did a few weeks ago about rebuilding a bass amp, I talked about how the power supply is critical to the proper operation of the amp. Check this out:
There are two things to point out here. First, on the left, are the bulk storage filter capacitors. There's about twice an many as theoretically required. And that white stuff between them...industrial adhesive. Components that are tall have a tendency to physically "rock" (not in a good way), and that can result in lead breakage and failed solder joints. Gluing them all together helps prevent that.
To the right, that round thing...it's a toroidal transformer. This is what steps the line voltage down from 120 to the various voltages the amp needs. Toroidals, because of their construction, have a very small magnetic field around them when compared to a standard rectangular transformer. So why is that a big deal? Easy, magnetic fields can induce hum into nearby audio circuits. A transformer like this makes for an amp with very low background noise.
There's one other construction note on this photo. Right below the capacitors, you'll see a row of white rectangular objects. Those are power resistors (we'll look at some different ones next). These essentially balance the loads going to the output transistors, and they can get hot. By selecting this style of resistor (which is relatively expensive), the heat is not going back into the circuit board and deteriorating it. And notice a bead of silicone across the top of them...again to stabilize them and keep them from moving more than they should.
Finally, there's some construction points that the designers really got right on the circuit board.
There are three things I want you to notice here. In the upper left, there are two power resistors (the grey cylinders with the stripes). These are electrically the same kind of thing as the white rectangular ones above, but in what we call an axial package. They're going to get hot as well, but if you look closely they're not sitting down on the circuit board (which would eventually scorch it). They're set up off the board where they won't do damage and will radiate heat better. That's a small thing that a lot of manufacturers miss.
In the top center is a ribbon cable that connects the front panel (pots and LED indicators) to the main board. Remember last week when we had trouble with a ribbon cable because of the connector? You won't see that here...the ribbon is soldered in! It's more expensive because it increases your manufacturing build time, but you won't have a connector problem.
And finally, this is something I've only seen super high end touring amps. See the red and black wires that are going into the board? Those connections are stiffened with adhesive. Otherwise, those wires would eventually break at those points (I've repaired plenty of them). This cost a fraction of cent to do, but improves the reliability immensely.
This amp has a lot of other things going for it electrically that you can't see. Things like a soft start turn-on (it reduces the inrush current when you power up), and a 3 second delay after turn-on before the speakers are connected...so you don't get that loud "THUMP" when you're bringing your system up. And sonically it's just plain good, but that's all in the specs.
So how about next week we talk about amp specs...what is THD, sensitivity, and damping factor? How do these specs impact what the amp sounds like? And probably most importantly, I'm going to show you how to spot a bogus wattage rating from a mile away. You won't need a calculator, but if you're planning on drinking heavily next Friday night you might want to wait to read this one until Saturday afternoon.
Until then, keep the meters (or LEDs) out of the red.
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
Sometimes bad things happen to good gear. And sometimes things happen that appear worse than they actually are. Sometimes you can recover at a gig, and other times...well, that's why you carry spares, right?
I've had two pieces of gear come in this past week, both failing on gigs for working musicians (which is just the worst). One turned out to be an easy fix...the other one is being a bit elusive.
The first contestant this week was a Carvin B2000 bass amp. Paul, the owner, described the problem as "it would get real quiet, then loud". Immediately, that sounded like a connection problem somewhere in the front end of the amp. We got it on the bench, connected up a speaker and a signal source, and fired it up. Sure enough, it wasn't anywhere near the volume it should be, and what was there had a lot of noise and static.
The problem was in a ribbon cable. "What's that?" you ask. Once only found in computers and other high-tech gear, ribbon cables are used by pretty much every electronics manufacturer out there now. They're an inexpensive way to shuttle a lot of signals around, and it makes assembling a product faster.
There are two ways to implement them...solder them in (preferred), and using push-on connectors. Carvin (and most amp manufacturers) use the connectorized version like so:
Those black cables running between boards....that's them. Here's a close up of a ribbon cable with connectors:
If you're dealing with what's known as "logic level signals" (which are anywhere from 3.3 to 5 volts) these things will work for years without a problem. However, it you're dealing with low level signals (usually a half volt or less), then things sometimes start going haywire.
These connectors can oxidize over time. This gets into a little bit of heady science, but if there's enough current flowing through the connection there's an electrolysis effect that takes place. No, it doesn't remove hair but it does "clean" the contact. Low level signals...not so much. That's where you have to intervene with a good contact cleaner. My favorite is still DeOxit that I mentioned previously. Just remove the connector, spray the pins lightly, and then you want to plug/unplug/plug several times to distribute the cleaner and work the corrosion off.
We did just this with the bass amp, and it's rockin' again. Oh...how did we find it? That's where knowing where you can touch and where you shouldn't in a live amp comes in handy. And actually, I used a pencil and tapped on all the ribbon connections while the amp was output a signal to the amp. When we found it, it was very obvious (it got really loud). Unless you know what you're looking at and understand the risks, I can't condone someone that doesn't have some electronics training doing this in the field.
The next piece of gear that came in was a mid 2000's Crown power amp for a PA. The client had it on a road trip (in a rack, as it should be) the previous weekend. It worked Friday night, but after driving the next day to the Saturday gig it did not make any sound.
Now, let me introduce you to the 7th corollary of Murphy's Law, which states:
"When a piece of equipment is in a position to be diagnosed, it will perform flawlessly".
And that's exact what happened...it passed signal on both channels. I couldn't blame ribbon cable connectors this time. They're used in a couple of locations, but they're soldered in and secured with adhesive.
So...the amp works on the bench but not at the gig. What then? Well...it could be speakers, cables, or drive gear but the guy who brought the amp in has been a road dog as long as I have. When he says he checked those things, I believe him.
One thing that we can deduce by the behaviour is that this is likely a physical/mechanical problem, and not a failing component. Very few electronic components "heal" themselves (but there are actually a couple...nothing in this amp though).
So how do we find the problem? Electronic techs have long had two low-tech tools that we use to sometimes solve some high-tech problem...cold and heat. By subjecting circuit boards and components to rapid temperature swings, we can expose marginal connections. You know, the ones that make connection at room temperature, but when the equipment warms up (and things start expanding) the connection goes away.
OK, heat is easy...we use a hair dryer or heat gun. But cold...how do you do that? We'll there's an app for that...or should I say a can.
This stuff is non-conductive and gets really cold. However, you're not going to find it at your average electronics store (Fry's does carry it). And if I run out of this, I'll use a can of compressed air (like for cleaning out computers). But you hold it upside down. Now you'll get a cold shot (apologies to SRV).
So...we're going to leave it at this point. I'll be working on this today, and will have the diagnosis next week. While I have the amp apart, I'm going to give it a good cleaning too. Because that's the way that Gus Rummell taught me in my Advanced Troubleshooting class at Central Texas College oh so many years ago.
Until then, keep the meters out of the red.
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
In the 30 something weeks we've been having these discussions, I've pretty much focused on gear. PA, amps, speakers, instruments....hooking them up, using them, and keeping them running.
You can have a $20,000 guitar or bass rig, but if you're physically not able to play your instrument all that equipment can do is sit there and look good.
A $50,000 PA just takes up space if you can't sing.
You get the idea...and this week we're going to talk about the most important thing on the stage to keep working right...and that's you, the musician.
Now, before I go any further let me get this disclaimer out of the way. I'm not a medical doctor, physician's assistant, chiropractor, licensed massage therapist, or anything else like that. I'm a 54 year old musician that's taken a bump or two along the way, and now starting to feel the effects of said bumps.
In addition to the usual stuff musicians my age deal with (arthritis, tennitus, hair loss), I've been fighting pain in my right arm and shoulder since about 2009...most likely due to the marathon practicing I did to get up to speed with Buzzfuel.
SInce then, I've been had issues with numbness and weakness in the fingers, and that's drag when you're a guitarist/bassist. I've been to Chiropractors, Orthopedic doctors and surgeons, Neurologists, and Licensed Massage Therapists. Each one helped in some way or the other, but nobody ever found the "smoking gun". So, after a ton of money in co-pays I just decided that it is what it is. I found temporary relief with deep tissue massage, and would usually have that done a couple of days before a show to get me through. But then, the LMT that I was seeing moved away, and at that point I didn't feel like going through the motions of finding anyone else.
The problem has been is that I don't fit a profile. Sports injury doctors ruled things out because as one put it "there's no way you could hurt yourself playing guitar". No way? Challenge accepted.
I'm going to get a little philosophical here...I believe that every job I've had or band I've been in has been for a reason. I was there to either learn something, teach something, or meet someone...or in some cases all of the above. And that's happened again. This time, I managed to meet a guitar player (and a damn fine one at that) who happens to be an Orthopedic Physician's Assistant. He never pressured me, but would say every now and then that he'd be happy to get me in and have one of the docs look at the shoulder. At first I'm just thinking "here we go again", but then realized that with someone that understood the mechanics of playing as well as human physiology, I might actually get somewhere this time.
Long story short, after an MRI, nerve conduction study (now I know how a circuit board feels when I'm troubleshooting it), x-rays, and a cortizone shot it's come back to my rotator cuff (which 2 other doctors "ruled out" 2 years ago). Not a tear or anything that's going to require surgery. It just turns out that I've managed to keep the bursa irritated for a considerable length of time. But then again, there are a lot of folks who would say that I've been a source of irritation for a considerable amount of time as well.
For those of us without medical degrees, I find an illustration very helpful here.
The worst part...that steroid shot into the bursa. But that's what confirmed to diagnosis.
So, the fix? A week of oral steroids and some physical therapy to get some strength back in the muscles I've guarding so far this decade. Yep...that's it.
I guess where I'm going with all of this is that as musicians, technicians, and roadies we can come up with some rather unique ways to injury ourselves. "Playing through the pain" may be viable in our 20s and 30s, but at least for me not so much now.
If something hurts, get it checked out if you can. If it's muscular and you haven't lost movement then ice works wonders. If you're hoarse, don't keep singing. Give it a rest. And if you're hoarse for no reason (you haven't been straining your voice), then definitely get checked out. I've lost 2 friends to throat cancers that started out that way. If they had gone in when the hoarsenss started, they might still be here.
Now, I've gotta give a shout out to Orthopaedic Associates of Central Texas, and especially PA Gregg Langston, Dr. Jeffry DeLoach, and Dr. Michael Valastro for finally getting to the bottom of what was going on.
OK...dry spell is over with now and I'm going to try to get back on track with these posts. I'm not sure yet what next week's subject is going to be. I've got an amp coming in for service, and I'm building a rack for a vocalist next week. I'm sure we can garner some fodder along the way.
Until then, keep the meters out of the red!
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
