Heading Off Trouble

The last few weeks have been pretty technical, so I promise...no math this week!

We've spent a lot of time here talking about how to troubleshoot your systems when they fail.  And being able to do that is a skill that will carry you far.

But as most of you know, one of my big mantras is that you shouldn't be fixing things at a gig...you should set up, play, and load out.  Or, as one of my past co-workers said, "Show, blow, get the dough, and go!"

To that end, there's a lot to be said for preventive maintainence.  In a couple of my previous careers, preventive maintainence (or "PM" as we called it) was crucial.  As the chief engineer for a number of commercial broadcast stations, my job was simple...keep the stations on the air and legal.  To that end, I would schedule time monthly (usually on a Monday morning at midnight) to take a station off the air and go through the transmitter.  I would look for loose components or connections, anything that looked like it was getting hotter than it should, and give the cooling paths a good cleaning.  As a result, I had an excellent record for minimal down time. 

You can adopt the same mentality for your PA systems and instrument rigs.  There's nothing really hard about it...it's just talking yourself into doing it.  A few hours a couple of times a year can really save you a ton of aggrevation and frustration at a gig.  If you get the entire band involved, it's something that can be knocked out very quickly.  And unlike the radio stations, you don't have to wait until the wee hours of the morning (unless that's when you function the best).

So...what would preventative maintainence look like on a PA system?  Well, in check list form, it would probably look something like this:

• Test all audio interconnect connect cables (with your trusty cable tester).  Identify any that fail and quarantine them for repair.
• Inspect all cables for knicks or cuts.  Repair with either heatshrink tubing or electrical tape.
• Clean all cables, including power. (Just pull them through a damp cloth as you coil them up).
• Inspect amp racks for loose connections and hardware.
• Clean any fans or filters on force-air cooled gear.
• Exercise all audio connections (disconnect and reconnect them a few times).  Cleaning the connectors with DeOxit is highly recommended.
• Hook your PA up and run some music through it at a low level.  Now, listen to each individual speaker component and make sure everything is still working (I do this every gig).  It's possible to blow a woofer or midrange speaker and not realize it when everything is going full blast.
• Speakers vibrate...vibration causes things to work loose.  Check the mounting hardware for your speakers!
• Any case hardware (handles, latches, or casters) that's busted should be repaired / replaced at this time.  You curse that broken caster every time you load in...get rid of now!
• Replace any missing labels on any equipment.  Remember the 4x4 test!
• Check all of the pots on your main console for quiet operation.  Slide pots are easy to clean, so take care of that now. 

Your personal rigs should be checked in a similar manner.  And don't think that because you don't gig that much that you don't need to do this as often.  I find more problems with systems that sit idle for an extended period of time than those that go out on a regular basis, especially with the connectors in amp and effects racks.

Yeah, I know...this isn't the most "rock star" thing you can do with your band time.  But the payoff is that you're going to lower the stress level at your gigs by not having to troubleshoot/swap out/fix something 10 minutes before show time.  And that (at least to me) has a great deal of value to it.

Next week, I'm going tech on you again!  We're going to talk about one of those oft-quoted but rarely understood terms in electronics, and that's "balanced" wiring.  We've all heard of it, but who really understands it?  We'll break it down next week.

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

I Feel So...Used.

Nice, shiney new equipment is cool.  It's fun to open up the box and get that whiff of "new electronics". Pulling it out of the box, setting it up, and then carefully peeling the protective plastic off the front panel (although some friends of mine frown on that...probably because their grandparents had heavy vinyl covers on the couch).

There's a lot of reasons to buy new gear.  But sometimes, used ain't a bad way to go.  Certain items, I wouldn't think twice about looking at used gear.  Other things...it just doesn't make sense.  So this week I thought I would share my thoughts on used equipment...what makes sense to consider, and what makes absolutely no sense.

First off, I'm not going to talk about instruments and instrument amplifiers.  Once you start getting into that "vintage" thing, I think people loose a lot of their common sense.  Yeah, some older amps sound pretty good.  But others....they sounded like a broken speaker at Sonic Drive-In.  But, because it was from the 60's some folks will convince themselves that they're in tone nirvana.  So, I'm not going there.  We'll limit our talk to PA equipment only.

Speaking Of...
Speakers are something that as long as they don't look like they've been dragged behind a truck are safe to consider.  But, you definitely want to look things over carefully and actually fire them up before you hand over your money.  Take a flash light to shine through the grill (or better yet, ask if you can take it off) to inspect the speaker.  You're obviously looking for tears in the cone, but also look for water/beer stains...especially if it's a monitor slant.  Speaker cones are (for the most part) paper, and they don't like liquid.  A lot of liquid spilled on a speaker will shorten it's life and affect the sound.

If you get the grill off, gently push the speaker in using your finger tips on both hands.  Push about halfway between the center and edge.  What you're looking for is if you feel like anything is rubbing or catching.  The speaker should move freely.  If it doesn't, that indicates that the voice coil is damaged or not aligned properly with the magnet.  That's caused by either excessive power, over excursion (from too much bass), or the thing was dropped from a significant height.  Fixing that calls for a re-cone.  Figure $50 to $150 dollars depending on what brand, model, and size of the speaker.  For me, that's usually a deal breaker. 

Listen to each speaker in a system individually.  You don't want to find out after you get home that one of the woofers in a dual 15 cabinet isn't working.  Unless you run them at a low level and put your ear right up to the cabinet, it's hard to tell.

Getting Amp'd Up
I used to have no trouble buying used power amps as long as they were less than 8 years old.  Why that age?  Well, after 10 or so years most gear needs to have the electrolytics capacitors replaced.  That's something I do all the time, but unless it's just a killer deal I don't want to have to do it immediately.

Again, check out the physical condition.  If it's scratched up, no big deal.  But, if it looks like a corner or front panel is caved in, the amp could be hiding circuit board or component damage inside. 

In addition to listening to the amp you really want to look at it.  If it's filthy to the point that the air intakes / exhaust are clogged, I'l pass right there.  That tells me that the owner gave it no maintainence whatsoever, and that the components have been running at an elevated temperature.  And as I previously mentioned, every 10 degrees C (18 degrees farenheit) the temperture is elevated, you cut the life of some components in half!  People that treat their gear like that typically don't change the oil in their vehicles at the appropriate intervals either.  Here's a photo taken right off of Craigslist:



 

That filthy air filter on the bottom would kill the deal for me.  That, and the Power Base series wasn't exactly one of Crown's best amps.  They were built for a price point first and foremost, and performance / reliability second.

 

That said, it doesn't have to be operating room sterile.  Here's that fan intake on an XLS 402 (one of Crown's best amps for the money) that I consider normal use:

 

Yeah, I'm good with that.  And the fact that I know this amp inside and out.

 

He Ain't Heavy...Wait, Yeah He Is

Now, my biggest arguement against buying used power amps now...weight!  If I'm going to install them in a fixed installation, no big deal.  But if I'm moving this stuff in and out of clubs several times a month, it quickly becomes a consideration.  The pounds-per-watt has been coming down rapidly in the last few years thanks to improvements in switching power supply technology (and that lets the transformers get small and lighter).  It's at the point now where I can get into something in the range of 1000 watts (real ones) that weighs under 15 pounds.  In the late 80s I was using Peavey CS-800s.  Almost the same power, but almost 60 pounds.  A rack of 4 of those was absolute death when you loaded out at 3:00 in the morning!

 

And The Rest Of The Stuff...

Consoles, EQ's, Compressors, Crossovers...the low level signal stuff.  That stuff very rarely fails due to electrical problems.  It's almost always physical damage or dirty potentiometers.  Equalizers are especially susceptible to dirt, but they're also the easiest to clean.  What you do want to look for is evidence of something getting spilled into them.  Beer is tough to clean out.  Sodas...forget it.

 

Missing knobs (if there's just a couple)...no biggie.  I can usually get replacements from the manufacturers.  But ones where the shafts are sheared off...again that's showing some potential physical abuse. 

 

And then, it comes down to the brand.  Quality brands Rane, White, Ashley, DBX, BSS...hard to go wrong with that stuff.  It's built well and can be repaired if needed.  One brand of rack gear I will never buy again is Behringer.  Period.  The first thing that fails on their gear is the pushbutton switches.  And here's the kicker...you can't even disassemble the stuff to clean them.  Or I should say you can't reassemble it when you're finished.  Why?  Because they put that stuff together with double-sided tape!  Yeah, you read that right.  To fix their stuff, you literally have to duct tape it back together.  I've thrown away a crossover and two 4-channel compressors for this very reason.  Naw...screw those guys if they can't even use screws to put their stuff together.  That stuff was replaced with DBX and Presonus gear, and I've never looked back.

 

Check The Spare When You're Kicking The Tires

Whatever you're looking at buying, make sure you check every single function on the device unless you like being surprised later on.  That means every button, knob, and switch.  If the seller is rushing you along or gives you the "don't worry about that...it's fine", then ask them what kind of warranty they're giving you.  If they offer a return period, as them to give it to you in writing (or better yet, ask them to send you an email to that effect with their contact into).  If they don't want to do that, then they're either hiding something or just douche bags.  Either way, you don't need to be dealing with 'em.  Your time and money are better than that.

 

The Bottom Line

I've reached the point that I only buy used gear if:

• I'm saving at least 50% off of the new street price
• It's a killer deal with a problem that I'm reasonably confident I can fix
• It's some oddball piece of gear that's no longer made that I want to make up for selling the same thing when I was younger.

 

And there you go...Ken's guide to used gear.  Take it for what you will.  And just remember that only you can decide if a deal is a good deal.

 

Until next week, keep the meters out of the red (even if the red is a little faded)

 

 

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

 





We Are The Road Crew...

Most of our discussions here have revolved around working on your own sound system and how to get the most out of it.

But sometimes that's not the case.  In downtown Austin it's fairly common for a venue to have a house sound (and sometimes lighting) system.  And if you're lucky enough to be playing on a festival, it's almost guaranteed that the production is going to be hired in. 

Of course, like everything else in the music biz there are companies and people that are really good at what they do and are equipped to deliver a professional product...and then there are those "sound companies" that are little more than "a friend with a lot of stereo equipment".  When you've been doing this as long as I have, you can walk into a venue and in 30 seconds and have a pretty good idea what you have to work with.

So this week, let's talk about things you can do as a musician to make interfacing with a house or hired production team easier for all of you.

Plotting To Take Over The World
First and foremost, if you don't have an up to date stage plot...make one!  It doesn't have to be anything fancy...just something that lets the sound guys know how many inputs they're dealing with and where things need to go.  Here's one I did for The Michael Ingalls Band:

There's actually a lot of information in this drawing.  From one sheet of paper, the sound man can tell:

• How many mics/channels we're requesting
• The brand of mics we're partial to
• Starting points for what we like in our monitors
• Where we need AC power drops
• The frequencies our wireless gear operates on, just in case they use any wireless stuff.

If you had tried to verbally explain all of that, how long would it have taken?  Yeah, a while.  And don't worry that your drawing isn't all pretty and to scale.  A sharpie and the back of the flyer from the band that played there last week works just as well.

If the sound man is worth a flip he will appreciate this because it makes his job faster and easier.  But I'll warn you now that there are more than a few guys that have been mixing crappy bands in crappier clubs a lot longer than they should have, and they'll blow this off.  Instead, they cop a "you'll get what I give you" attitude.  They're burnt out and fed up with the endless parade of Prima Donna bands that come through thinking they're the next big thing.  I feel bad for those guys, but at that point their putting themselves through it.  All you can do is not be another one of those Prima Donnas, work with them the best you can, and play the best show you can.  Then you decide if you want to go back to that venue again...or not.

Checkin' In
Since these guys are (hopefully) a lot more familiar with their sound systems than you are, let them run the sound check.  All the pros pretty much do it the same way, build the mix from the bottom up starting with the drums.  Standard sound check etiquette applies here...keep your instrument quiet while someone else is sound checking.  You will get your turn.

The first step is usually a line check and EQ.  Next, I like to see the monitors done.  Finally, you play and let 'em build a rough house mix.  I've run across one sound man that had us play before the monitors were up.  I tell you, that's painful and difficult in a big room (and it was a big room).  Sound guys...if any of you are reading this please don't do that to the bands you're mixing.  You won't get a good sound check because we can't hear ourselves singing and will hold back.  And speaking of monitors....

Monitoring The Situation
Sometimes this is the hardest part of the sound check...getting the monitors dialed in.  Keep in mind that when you're setting up your monitor you'll likely have things too quiet (because the whole band is not playing).  Remember that in 5 or 10 minutes, sonic chaos is going to be competing with that monitor slant in front of you...plan accordingly.

And again...don't everyone shout at the same time for something changed in your monitor.  There's an old joke that applies here:
     Q:  What's the difference between a monitor engineer and a toilet?
     A:  The toilet only has to deal with one a$$hole at a time.

During the show, if you need something changed then use the universal monitor adjustment sign language.  Get the sound man's attention, point the the source or person you need adjusted, point to your monitor, and then point up or down.  If you're pointing to a singing guitarist, then mouth the word "vocal" or "guitar" while pointing at them.  Otherwise, you don't know what you're going to get.

OK...but what if the sound man is reading a book or has walked away from the board to get a beer?  See "burn out" above.  You just have to deal with it.

A good sound man will have his eye on you during the show, and won't walk away from the console unless something needs to be fixed on stage.  A good sound man will also not try to make you significantly alter how you set up and perform.  Which brings me to...

One Bad Apple...
I played a show several years ago in Waco with The Rhythm Dawgs where there was house PA and lights.  We got there early to set up, and geez...what a pile of crap.  There were probably 8 different manufacturers speakers piled up on top of each other across the back of the stage.  I thought it was just for looks, but the sound guy (who showed up about 15 minutes before we were scheduled to start) was going to use those as monitors.   Really....monitors behind the band???  Nope...don't think so.

He also wanted us to break our amps down and move them to the side of the stage pointing in...and then tried to BS us with some mumble jumble about cross-fire phase cancellation resulting in a cleaner sound out front.  (By the way, have I mentioned that a good soundman will not try to make you change the way your perform).  At that point, I told him that if he had been there when he was supposed to be (over an hour ago), we would have tried to accommodate him.  But now, our amps were up and were staying where they're at.

Then, no sound check...no line check...nothing.  His excuse..."I know this room, I'll get you dialed in by the second song."  He may know the room, but not the band.  He didn't have it dialed in by the second set!

I really couldn't believe how bad this guy was...until I saw him across the street on break toking up.  Later on he was bragging about how he was a "prescription drug and medical marijuana user".  Sorry dude...the only thing you are is a stoner.  Needless to say, we never went back.

The Friend With The Stereo
Sometimes you walk into a situation where you've got good well meaning people that have no idea what they're doing.  Even worse, the equipment they bring is better suited for an iPod in a dorm room than mixing a band.  I walked into one of those situations back in the 80's.  The guy had a DJ mixer.  Seriously...a Numark DJ mixer that he was going to do a 5 piece rock band with.  His first question..."How many of you sing?".  "Four" I told him.  "Uh...I can only do two mics...can you work with that?". 

No..we can't.  So being the nice guy I am I pulled our 16 channel board and our mics from the truck.  I then asked where the mains and amps were.  He pointed to a Kenwood AM/FM receiver and two Sansui stereo speakers.  "It kicks, man...just try it".  We did, and the amp went up in smoke during the first verse.

At that point, I told the event planner that we could do one of two things...we could bring in our PA system (for an upcharge), or we could keep our deposit, leave, and promise never to come back.  They took the latter, which was fine by us.

The point I'm trying to make here is that when you get into these situations, concentrate on what you have (not what you don't) and how to make it work.  But sometimes...it's beyond saving.  Yelling at people don't get it done.  Either try to fix it, deal with it as is, or shake hands and walk away.

It Will Not Be Perfect
Even with the best gear and the best crew operating it, when you're playing on a hired or house system it's not going to be perfect.  Period.

The big tours...there are usually a couple of weeks of pre-production somewhere to work out all the kinks.  Two weeks...at least.  For folks like us...we've got maybe a half hour.  Maybe.

Do the best you can, be cool, and thank everyone at the end of the night.  Be the band that the makes the crew smile when they see you walk in...not the band where the crew all says "geez...not those guys again".

It don't cost nothing to be nice.


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

Seeing Specs Before My Eyes

Last week, we talked about all the ways that the wattage on an amplifier can be grossly overstated and that finding out the true power capabilities can be a game of cat and mouse.  This is especially true of the manufacturers of lower end gear.

This week, I wanted to at least touch on some of the other specifications you will typically see on a power amp.  You don't see these exaggerated near as much...mainly because most folks never get past the wattage spec.  But, they are there, and I thought you might like to know how them impact the way an amp sounds.

First off, let's take a look at the specs our trusty Crown XLS 802.

So, for a live sound application which specs are we really concerned with?  While I can make a case to consider all of 'em, the first 4 are really the important ones.  Let's talk about what they are.

Sensitivity Training
The spec for sensitivity of an amp is actually one of the easiest to understand.  The spec for this amp is 1.25 volts.  What that means is that if you turn the gain controls on the amp all the way up, it will take 1.25 volts at the inputs to drive it to full power.  This is a reasonable spec, as most modern mixers and crossovers can output several times this. 

The trick is that console outputs are almost always spec'd as dBu.  To convert that to voltage requires....ah hell, I'll just give you the answer today.  My Presonus StudioLive can do +24dBu.  That works out to a little over 12 volts...plenty to drive the amp.  (We'll do an article on decibels for non-math majors one of these days).

But decibels are funny critters, being logarithmic.  That means they're kind of like the Richter Scale they use for earthquakes...where a 7 is a whole lot worse than a 6.  If your console can output +18dBu, then that's about 6 volts.  And if it can only do +4dBu...that's right at 1.25 volts...which means you'll have to have it floored to max your amps out.  It also means you're completely out of headroom on your console and you're probably clipping the signal.
And once the signal clips at the console there's nothing you can do to clean it up later. ...you're S.O.L. at that point. 

Freq Out
The frequency response of an amp is the range of frequencies that it can pass.  Almost every amp will have that spec, but 80% of them are incomplete.  A frequency response without a tolerance on it is really useless.  The spec for this amp is 22Hz to 20kHz, but notice the numbers after that...+0 dB, -1 dB.  That means the amp is flat to within 1dB which is incredibly good. 

Most amps are spec'd +/- 3dB which is still perfectly acceptable for live work.  But when you start seeing numbers like +/- 10dB...it's a BS spec.  That means you're going to have to put a lot of EQ in front of that amp to get it to flatten out.  And if there's no tolerance...well...that just means they're hiding something.

Now, how much frequency response do you need for live work?  Unless you're using concert grade subwoofers and doing electronic dance music, you're not going to need to reproduce much of anything below 40Hz.  And going to the other way, most PA systems start rolling off at 12 kHz.

So why do amp manufacturers spec the frequency response outside of this range.  While you may not be able to hear (or a speaker pass) anything about 15kHz, an extended high frequency response can be an indication of how "fast" an amp is.  There's a spec not mentioned about called slew rate, and you'll usually see it on consoles and preamps.  Slew rate can be a scary looking spec, but what it amounts to is "how fast can this amp move on a waveform".  It's usually expressed in volts per microsecond.  An extended high frequency response can mean that the amp has a decent slew rate.  What that that translates into sonically is amp that sounds clear and punchy.  The slew rate along with the damping factor (we'll talk about in a bit) has a large impact on the "sound" of a power amp.

Bring Da' Noise
The signal to noise ratio (frequently abbreviated S/N) gives you an idea how much background noise the amp produces on it's own.  Here again, a bigger number is better.  For this amp, they're saying that the noise is 100dB below the signal.  Putting that into more familiar terms, it means that the noise is 1/100,000th of the signal...pretty darned quiet.  The difference between weighted and unweighted is that the weighted number is filtered and limited to what we can actually hear.  The weighted number is more meaningful in the real world here.  But even the unweighted is still pretty impressive. 

Again, how much do you need?  Keep in mind that your system S/N can not be any better than the worst component in the chain.  So, if you amp is 100dB, but your Behringer console is only 55dB...then that's as good as your system can get.  Personally, I look for 80dB or better unless the client just has no budget and is only going to be playing $#!+ hole clubs.

Distorting The Truth
When most musicians here the term "distortion" they think of the pedal a guitar player steps on before the intro to "Satisfaction".  (OK, bad example...that's a fuzz box). But where I'm going with this is that while distortion is usually desirable to a guitar (and some bass) players, it's not in a PA system.  So this is where a smaller number is better.

Now, how many of you actually know what "distortion" is?  The technical definition for the intellectually curious is any non-linearties introduced into a signal.  For the mere mortals, it's probably easier to explain how it's measured.

To measure distortion in an amp, you input a single tone (1kHZ is the standard, but some folks use 400Hz) and measure the output signal level.  Then, you filter out the original tone at the output and measure the signal level again.  The crap that's left over...that's your distortion.

Again, how much (or little in this case)?  It depends on the application.  If this amp were going into a studio or other critical listening environment, I would want 0.1% or less.  But for live work, I'll generally accept anything at 1% or below.  This amp has 0.5%, so it's fine.

But remember, for the distortion numbers to be meaningful it has to be a rated power.  And this is where you can get tripped up.  The Crown spec above is written to say that distortion will never be worse than half a percent.  But other manufacturers will bound the distortion measurement by doing things like spec'ing it at a lower power or not over the entire frequency bandwidth of the amp.

If you don't see this number on a spec sheet...it's likely because the manufacturer doesn't want you to know that it sucks.

Et All
The other numbers (IMD, Damping, Cross Talk, and Input Impedance) are still important, but unless you're putting a very large system together (I'm talking 10 power amps or more), don't concern yourself too much.  Most folks getting into a system that big are going to hire a geek like me to do it for 'em anyway.  But just for giggles, here's what they are and how the affect what comes out of the speakers.

• IMD - Intermodulation Distortion.  Dang...that hurt.  IMD is one of one of those distortions that is really uncool.  To explain it, you have to have a quick primer on the concept of Intermodulation.  Whenever you mix 2 different frequencies together, you wind up with 4!  Yep...it's magic.  You get the original 2, plus the sum and difference of them.  So..if you mixed 800Hz and 1200Hz, you would also get 400 Hz (1200-800) and 2000Hz (1200+800).  To bad we can't do that with currency.  Anyway, it's an annoying artifact, so the more negative this number is the better.
• Damping Factor - I would tell you how this number is derived, but you would just want to throw something at me.  Let's just go with this...the damping factor is an indicator of how well an amp can physically control a speaker.  Think about what's happening with a speaker...it's travelling one direction and then all of a sudden has to go the opposite way.  If the amp doesn't have enough control to do this, then the first thing you notice is that the low end is muddy and undefined.  The Damping Factor (sometimes written as DF) is one of those "bigger is better" numbers.  There are a lot of other things that affect the system Damping Factor (when you add in the speaker and the wire that hooks it up).  If you see an amp with 200 or better, you're in good shape.  Don't look for this spec on a budget amp...it would reek if they printed it.
• Crosstalk - This one is actually pretty easy to understand.  On a stereo (or multi-channel amp), the crosstalk is a measure of how much of the signal on one channel gets into another one.  Again, the more negative the number the better.  I only pay attention to this spec if the amp is going into a critical listening environment (like a studio).  But live...all the noise coming off the stage is going to mask the minor amount of crosstalk in the PA system.  As long as it's at least -40dB I'm not gonna sweat it for a PA.
• Input Impedance - This is almost useless to spec now unless you plan on hooking up 10 amps in parallel.  Back in the 60's when stuff had real transformers in it for the audio, this mattered.  Now...no so much.  It's just another big number to confuse the average user. 

I realize the last couple of weeks have been really tech-heavy.  Those of you who got through this...kudos.  Regardless of how much of this sank in, I hope this helps those of you buying equipment in the future.  Again, I hate seeing people get ripped off or wind up with less than they thought they were getting.

Next week...I promise no (OK...very, very little) math.  We'll talk about working with sound and lighting companies.  I recently played a show where we hired in the production (and man oh man was it nice to not have to pack a PA at the end of the night).  A lot of what we'll discuss also applies to playing on house systems at a club. 

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

Watts The Meaning Of All This

I'm going to let you in on a little secret about most consumer grade electronics manufacturers. They're counting on most people having absolutely no idea what all of those numbers on a specification sheet mean. They're banking on the fact that most people believe a bigger number is a better number.

Now before you beat yourself up over this, just keep in mind that unless you've got an electronics background and understand how specifications are derived then terms like S/N ratio and Total Harmonic Distortion are just buzzwords.

Furthermore, consumer grade audio manufacturers are really bending the rules nowadays...all in the quest of that all mighty big number. The pro grade guys...not so much. Because the guys that are ready to spend a few thousand dollars on a power amp can spot a B.S. spec in a split second.

So for the next couple of weeks, I'd like to impart a little bit of this inside information to you. We'll talk about what certain specifications are, whether a bigger number is actually better (not always), and how a spec affects how a piece of gear sounds. We'll also talk about the ways that manufacturers "fudge" the numbers...especially wattage.

I had originally planned to cover all of the major specs of a power amp in one article, but after I started writing this I realized that it would wind up being a very long post.  So we're going to split it up.  This week, we'll talk about wattage and power ratings.  Next week, the other specs.

Which Watt?
The output power of an amp is the most manipulated, massaged, and maladjusted spec on a power amp.  After all, that's the first thing people look at.   "Ooooo....2000 watts for just $100...I'll take it".  Yeah, you'll take it all right...but I'm not going to say where you're going to take it.

First, let me clear the air here. A watt is a watt...period. There are no "tube" watts, "solid state" watts, "British" watts, or "American" watts. Anyone who uses these terms falls under the category of "repeats whatever they read on bathroom walls". The formulae for calculating power does not contain a variable for any of these terms (but maybe there should be an "moron" variable). You hear these terms used with guitar amps mostly, but be aware they're out there and they're bunk!

There are several variations of the power formulae, depending on the variables that you know, but at the end of the day it boils down to this:

Power (watts) = Volts * Amps

 

 

Like I said, there are variations of that if you know the load that the amp is operating into.  The most frequently used is:

 

 

Power (watts) = Voltage Squared / Resistance (ohms)

 

 

You'll see that one written as P= E^2/R, and we'll be using that one later.

So with that said, lets look at a good set of wattage numbers, and then some not so good.

In With The Good
I consider Crown and QSC to be amoung the best amp manufacturers out there.  You'll see their amps on a lot of pro touring rigs, and the care they put into those high end products are reflected in their consumer grade stuff.  Since we've been talking about the Crown XLS 802 for the last couple of weeks, we'll give 'em a little more free advertising.

These are the average power numbers and are very conservative.  Most amp manufacturers use RMS (root-mean-square) power (which would result in a slightly higher number). Either measurement is a good indicator of what the amp can pump out all day long without breaking too much of a sweat.  Crown specs the frequency, the distortion level, and the loads they test into.  If it looks simple, it's because it is.  These are honest numbers without any trickery involved.

Taking A Peek At Peak To Peak
Prior to the mid 70's, amp manufacturers had no guidelines on how to spec power.  So how did they do it?  Easy, by using methods that would make for the biggest numbers! So you saw wattage ratings expressed in either Peak Power, or the notorious Peak To Peak Power.

So what are these numbers?  This is definitely one of those cases where a picture is worth a thousand algebra equations, so let's look at a sine wave:

The point at which the waveform crests and reaches it's maximum (or minimum) value is the peak.  Peak to Peak is 2 times that.

So lets say that I'm testing an amp into a 8 ohm load (typical for a loudspeaker), and I measure the peak value at 28.28 volts (there's a reason for that weird number).  OK, so how much power is that?  If you plug in the numbers you'll see:

 

(28.28 * 28.28) / 8

 

800 / 8

 

100 watts

 

 

So, the peak power of this amp is 100 watts.  Any guesses as to the Peak to Peak power?  Anyone?  Yep, 200 watts.  Sound pretty impressive, doesn't it.  But there's a slight problem with this number.

 

 

Not So Peak Performance

The problem with the Peak power numbers is that for most amps they're not sustainable.  What I mean by that is they can produce that power for a very short period of time (a few hundredths of a second).  If you tried to produce that continuously, you would burn the amp out pretty quickly. 

 

Looking at the sine wave above...you can see that the amp actually spends very little time (relative to the rest of the waveform) at the peak value. 

 

At some point in the mid 70's, the Federal Trade Commission finally stepped in and put some rules in place about how manufacturers can specify the power of their amps.  And with that came two new values...RMS and Average. 

 

Sustainable Power

RMS and Average values are what an amp can produce over an extended period of time without destroying itself.  So...what are they and how do they compare to the Peak numbers?  Glad you asked:

 

 OK...so that graph looks a little intimidating, but here's the bottom line.  The RMS (root mean squared) power is about 71% of the peak, and that is by far what most amp manufacturers use.  The average power is even more conservative, and is about 64% of the peak.  Crown uses the average power, but then again they've always been very conservative with their specs.

Hey Man, What Happened
So lets use what we just learned on the example I gave earlier.  Prior to about 1975, a manufacturer could have advertised the amp in my example as a 200 watt amp, and not told you how they came up with that number other than to say it was Peak to Peak.  But what can this amp really do?

First, anytime you see Peak to Peak, divide it in half.  Again...it's a BS number.  Now, take the 100 watts you have left and multiply it by .7, which leaves you with 70 watts.  That's a much more realistic number.  But what's more impressive...70 watts or 200 watts (sounds like one of those phone commercials with the kids, doesn't it)?  So now you know how the game is played.

Full Disclosure
A wattage rating alone is useless without knowing at a bare minimum the load you're operating into and the distortion.  The example from Crown, that's a complete spec.  But that's not so much the case with our next contestant.  And I don't mind calling them out, because Pyle is one of the worst offenders as far as manipulating their numbers and playing off the average consumer's lack of electronics knowledge.

What A Pyle Of...
OK, we saw a good wattage spec.  How's about something from the other end of the scale:

Two things to point out.  First, they are not doing anything illegal.  Second, keep in mind that they are advertising this amp as a 1,400 watt product.

Under the section for "Continuous Output Power", they list the amp as being able to produce 70 watts per channel into an 8 ohm load, and 110 watts into a 4 ohm.  That alone tells me that the power supply for this amp is under designed.  On a decent amp, it would produce about twice the wattage into 4 ohms as 8.  On this amp, the power supply runs out of gas before then.  That's a red flag.

There's another flag on this as well.  In the 8 ohm mode, they spec that the amp can deliver 70 watts over the full audio bandwidth (20Hz to 20kHz).  But, on the 4 ohm ratings, the 110 watt figure is only spec'd at a single frequency.  So that does that mean?  It means that the distortion figure likely goes to hell at frequencies above and/or below this.  That's a bad sign.

Anyway, we have power and load.  The Total Harmonic Distortion (THD) is listed as 0.1% at "rated output power".  So, that infers that it's at the 70 watt / 110 watt figures.  But then they throw out "Maximum Power" for the two loads.  And guess what, there's no definition for "Maximum Power" other than what they define.  Most likely, that wattage is at a higher distortion value...probably 1% (which still isn't terrible).

And then there's that Peak Power....which I'm at a loss on how they came up with.  If you take the 100 watt figure as an RMS value and work the math backwards, the Peak value I come up with is 142 watts.  So how the hell did they come up with 700 watts?

Hey Rocky, Watch Me Pull A Spec Out Of My A$$
Here's how they did it.  If you measure the power supply rail of the amp at idle, it's likely coming in at around 75 volts (a typical value for a 200 watt amp).  Now, if you plug that number into the power formula we used earlier, then you get:

(75 * 75) / 8

5625 / 8

703 watts

 

 

So in effect what they are saying is that the amp has the "potential" to produce a peak output of 700 watts.  However, there's a whole lot wrong with this:

• As soon a you put a signal in the amp, the supply rail is going to drop a bit
• Even if the supply rail didn't drop initially, it will in a few thousaths of a second
• Assuming they've got a really good power supply that maintains it's voltage under load(which they don't), you're going to have switching losses through the output transistors.

So the 700 watt spec is valid...until you actually try to amplify something.  That's real useful...not!

 

You should be on the lookout for other obscure power ratings.  There's no official industry definition for "Music Power".  Some manufacturers will make that 6 or 7 times their RMS and then come up with some tech-speak about non-recurring non-simultaneous power excursions in typical program material.  Screw you guys...you're trying to sell a 200 watt amp (on a good day) as a 1400 watt amp.

Levelling the Playing Field, And Then Not
As I said earlier, the Federal Trade Commission standardized how wattage could be advertised around 1975.  Amp makers either played by the rules or got fined for false advertising.

However, in the last couple of years the FTC appears to be bowing to pressure from electronics manufacturers.  They are now considering no longer requiring the distortion figure in print or radio advertising.  Their "rationale" behind this is a crappy as Pyle's power numbers:

• Most equipment produced today has a low distortion value.
• Most consumers don't understand that number
• Consumers that want to know the figures can find them on the Internet.

As to the first point, it should be noted that most equipment made today is capable of low distortion.  But if you're going to advertise it at a power level that 10x of reality...that goes out the window.  The other two points, I unfortunately can't argue with.

A Dead Give Away...
I've gotta give Behringer the "Most Exaggerated Wattage" award for their new iNuke series amps.  And here's why.

There's a basic law of energy conservation that says you can't get more power out of something than you put into it.  Keeping that in mind, and the fact that a watt is a watt regardless of how it's being used take a look at this spec sheet for what they claim is a 3000 watt amp:

There are a lot of numbers here, but I've highlighted the two of interest.  First is the claim that the amp can produce 1500 watts per channel into 2 ohms (and don't get me started on 2 ohm load measurements).  Then look down at the Power Consumption at 2 ohms...they're stating that it's 350 watts total.

If there's one number you can usually trust on a spec sheet, it's the power consumption number.  You see, if the manufacturer wants to get a UL (Underwriters Laboratories) sticker or equivalent, they have to state the max power the amp can draw under worst case conditions. 

So, what Behringer is saying is that they can put 350 watts into the amp, and get 3000 watts out.  Really?  Where did the other 2,650 watts come from?  OK...here's how they do it.

They're using the same trick as Pyle, and basing that 1500 watt per channel number on the power supply rail voltage (probably about 110 volts) The power supplies used in light weight amps (switching power supplies) can deliver a lot of power instantaneously, but can only do it for maybe a 1/10,000th of a second.  And then that's it...it's out of juice until it recharges on the next power cycle.  So it's a completely useless number other than for marketing.  If someone could make a device that could continuously output more power than it took in, they wouldn't be jacking around with amps.  They would be making trillions of dollars selling cheap energy to the world.

The bottom line here is that you can't have more continuous power out than you take in.  If you read anything to the contrary, it's more marketing BS.  In fact, the true power output of an amp should always be less than the power it draws from the AC outlet.  No amp is 100% efficient.  Some really good (and expensive) ones approach 90%...but most are in the range of 50% to 70%.  So, expect a true 500 watt amp to draw between 700 to 1000 watts.  The difference between the two figures is what's lost as heat.

Oh, and what do our friends from Pyle list as the power consumption for their "1400 watt" amp:

Wow...it's blank! Go figure.  Losers....

I realize we've covered a lot of stuff today, but to me this is important stuff.  I'm really tired of seeing decent working musicians spend their hard earned money with these companies thinking they're getting 3000 watts of power only to find out it's really less than 1/10th of that. 

In fact, it bugs me so much I'll make this offer.  If you're considering buying a power amp and you're not sure of what you're getting, then email me at the address below.  Either tell me the make and model or the amp or send me a PDF of the spec sheet.  I'll read it and tell you what you're really getting, not what the magazine ad wants you to believe.

Next week, we'll wrap up our discussion on specifications and how they impact the way an amp sounds.

Until then, keep the meters out of the red.  Especially if you don't have as much power as you think!


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