ATTENUATING

FEATURING THE WEBER MASS 100 AND SOME CHOICE COMMENTS ON USING EFFECTS

 

Turn That Damned Thing Down!

WARNING! A few days after I posted this article I managed to burn-out my attenuator by cranking-up my amp without using the “Bypass” switch. If you are going to use an attenuator you should get one rated for TWICE the wattage of your amp. It will still work just fine and you have some safety margin. No amplifiers were harmed in the writing of this article.

UPDATE TO THE WARNING: I took the top off the Weber MASS 100 that had smoke pouring out of the top of it because I drove it ‘way too hard for its 100 watt rating – and PRESTO! no damage that I could see. So I plugged it in and damn if it doesn’t still work, and not a sign of smoke or flame! Still I recommend getting a higher wattage attenuator than your amp’s rating: for a 100 watt Twin at least 150 – 200 watts.

If like me you spent a long time playing through solid-state amps you shrug-off numbers like 50 watts and 100 watts: just everyday stuff, a power range for solid small-venue performance but that can be played clean in your bedroom. But once you cross-over into the tube world you see that those are really big numbers.

I don’t know if anyone has ever calculated the actual ratio of tube watts to solid-state watts as far as perceived volume goes, but I’ve read claims that range from 1:3 to 1:10. My personal experience would cause me to estimate it at 1:4 if there were some generic amps that could be used for comparison. It doesn’t really matter, except you really need to look into the wattage rating for your situation. If you are playing at home then maybe a Fender Princeton at 15 watts or a Vox AC10 would be the best choice. If you are playing in a band and at small gigs then maybe a Fender Deluxe at 22 watts or a Marshall DSL40 at 40 watts would be a good choice. If you play larger gigs then there will be a PA system to mic through. If you play football stadiums then you might need 100 watts. Maybe.

If like me you, through whatever chance and misfortune, find yourself the owner of an archaic high-wattage tube amp, and in particular the dreaded and vilified Red Twin, then you will at some point become interested in attenuation. I had to look it up so I thought I’d save you the time. The Merriam-Webster.com dictionary says of the word:

transitive verb

1 :  to make thin or slender

2 :  to make thin in consistency :  rarefy

3 :  to lessen the amount, force, magnitude, or value of :  weaken

4 :  to reduce the severity, virulence, or vitality of <an attenuated virus>

intransitive verb

5 :  to become thin, fine, or less

— at·ten·u·a·tion \-ˌten-yə-ˈwā-shən, -yü-ˈā-\ noun

First Known Use of ATTENUATE: 1530

 

And about 440 years later guitar players began indulging in wanton acts of signal attenuation in order to tame their 100 watt Marshall and HiWatt and Sunn stage rigs. Actually maybe the proper way to say it is they “attenuated” their amps. Early amp attenuators were crude, often just a commercial-grade rheostat with in/out jacks. Eddie van Halen famously used a Variax voltage regulator on the power cable of his stadium-buster, and dialed the amount of “house current” going to the amp to 90 volts instead of 110. Today they come in three basic flavors: effects loop volume controls, solid-state speaker signal “drains”, and speaker motors.

 

The Cheap and Easy Way

There are a couple of cheap and easy ways to at least reduce the incredible force unleashed by the likes of a Fender Twin so you can play it without causing panic in the streets. You can remove one set of power tubes on dual push-pull power amps like the Red Twin – just make sure you know which tubes (if any) can be safely removed. On the Red Twin it’s the two center power tubes, leaving the outside pair to go on alone and generate about 60 watts (pretty-sure that’s RMS, so before breakup into distortion). Using low-power mode gets you down to about 15 pretty-muddy-sounding watts. Check the usual Internet resources for information about your own unwieldy dinosaur of an amp.

If pulling tubes just isn’t an option for you then you can spend about twenty bucks on a series loop volume control. This only works if your amp has effects send/return or pre amp-out/power amp-in connections. YOU SHOULD NOT CONNECT A SERIES LOOP VOLUME CONTROL BETWEEN THE AMP AND SPEAKERS! REALLY SWEAR-TO-GOD ACTUALLY! There will be casualties if you do.

But anyway, the volume box causes your signal to be routed through your amp’s series loop.  By making the volume box the last “effect” in the chain it can be used to turn-down the signal being fed to the power amp. The advantage here is the loop uses a low-voltage and low-noise line signal that is easily attenuated with an inexpensive potentiometer. The disadvantage is you aren’t really using your power amp; you are only getting amplification from the pre amp. Passive volume boxes like this are safe to use because, again, they only handle low-voltage signals in the effects loop – they can’t hurt your amp.

They also don’t do a great job, and you end-up with very little dynamic content in your tone.

 

The Engineers’ Way

An electrical engineer would look at this problem and think: “Obviously we want to terminate the signal as late as possible in the instrument to pre amp to power amp to speaker chain” and so would take the well-known and well-understood “signal drain” circuit off the shelf and dust it off. Drains (or “dumps”) are essentially a butt-load of large-scale resistors that can be used to simply drain-away your signal to ground. Kind of like what anti-depressants do for our stressful cares and worries: just shunt that crap to the biggest chunk of metal around – oh, look, it’s the amp chassis….

The resulting ugly metal box is inserted between the amplifier and your speakers via the usual ¼-inch unbalanced Tip-Sleeve-type jacks. Most amps that you are going to do this with will have a two-strand speaker wire that pokes-up from the amp’s innards and is plugged-in to the amp speaker output. You unplug that speaker wire and plug it into the attenuator’s “To Speaker” or whatever output jack. Then you use another short, two-strand speaker wire (not a shielded guitar cable) to connect the amp’s speaker output to the attenuator’s input connection.

Is this didactic insistence on the use of regular speaker-grade cable important? Well, think of it this way: the plug that comes out of the guts of your amp is at the end of a two-strand speaker wire. It makes sense that when you hijack this connection with an attenuator that you plug into the amp what its makers intended, and on the vast number of tube amps today that’s speaker cable and ¼-inch unbalanced TS plugs.

The emphasis on short wires is to avoid noise in the form of interference with the speaker wire. But anything up to three-or-four feet would probably be fine.

So, you’ve got your black-box in the line from the amp to the speakers. And it’s got a big rheostat knob on it and by gum, when you turn it your amp gets quieter and louder just like having a master volume control (really). And then an audio engineer comes along and says “Of course we obviously want to terminate the signal as late as possible in the instrument to pre amp to power amp to speaker chain” and adds “you’ve got the right idea but you are missing the point. We don’t want to just implement a fairly expensive variable resistor, when we’ll lose all the detail and nuance that the player has put into shaping the signal up to this point”. And so the “speaker motor” speaker simulator was thought-up by I don’t know who and it works pretty-well. Well enough that even though it’s ‘way more expensive than all those other ways to attenuate an over-powered amp, it’s the best way to go. This doesn’t include such solutions as using adapters to install lower-powered tubes, a la Yellow Jackets – but that’s not attenuating, that’s what I would call “re-voicing”, and sometimes that’s just what one of these old monsters needs.

 

Speakers 101 for People Who Distrust Science

A speaker makes sound by physically pushing the air around it out of shape. The unit of work agreed upon by some elitist cult of 19th century “scientists” is the watt. A watt is defined as 1 joule/second.

The joule (/ˈdʒuːl/ or sometimes /ˈdʒaʊl/), symbol J, is a derived unit of energy, work, or amount of heat in the International System of Units.

And that’s all you need to know about it, fellow non-scientist skeptic (who nonetheless is willing to benefit from the science of electronics in your guitar-playing life). For some mysterious and wondrous reason it is God’s will that a joule is a measure of energy or work that starts with 1 so we can measure that. Think of the joules as the gallons of gas in your gas tank, and the watts as the tiny robot squirrels that drink the gas when you step on it, and they run like crazy in the wheels of your car. Or don’t.  No, wait – yeah, go ahead; let’s say the watts are tiny robot squirrels that run in the wheels of your car. How many of them you have determines how fast you can go and how many joules (remember they’re like gallons of gas) it takes to maintain a given constant rate of speed, and how many gallons of gas (joules) it takes to accelerate (put load on) the…squirrels.

A guitar amplifier speaker works the same way. It takes energy to do the work of moving the speaker coil inside its magnetic shell. It’s this motion that is transferred to the speaker cone, itself a shell of paper or some similar “brittle” material. The movement of the speaker cone disturbs the air near the speaker and these disturbances travel from air molecule to air molecule, but quickly fall-off in volume (essentially amplitude), and are attenuated by loss of energy as the speaker-generated disturbance dissipates throughout a space. Sometimes a disturbance will contact a surface and this will cause it to “bubble” back into the space, now interacting with later disturbances of air sent out by the speaker.

Moving all this air takes watts (robot squirrels) being fed joules (gallons of squirrel-gas), and that’s the business of the amplifier’s power stage. Guitar power amplifiers are not generally designed to be transparent amplitude-increasers. The tubes and the circuitry and even the transformers contribute to the final signal, or sound for all intents-and-purposes: the high-voltage-for-humans-and-other-living-things signal that is presented-to and accepted (or maybe not)-by the speaker(s). Let me put that another way: the signal that leaves the amplifier and goes through that two-strand speaker wire is where the watts are used that that amp is rated for, and are dangerous. Tube amp wattage ratings are usually RMS, or “root, mean, and square” – it’s an average of watts used. An actual amp is operating far below this wattage and only reaching into the headroom for creating complex tones through dynamics. Or an actual tube amp is nickeled-and-dimed and constantly exceeding the RMS rating and clipping like scissors. Both ways there are times when an amp pushes-up past its breakup point, and while you do have all the squirrels (watts) running, they are really sucking-down the gas (joules) and things are not “efficient”.

When you have a lot of watts (robot squirrels) you are usually driving large speakers with large magnets and big-old coils, so you have a lot of load. “Load”, for our purposes, is like where watts go to finally fulfill their destiny and accomplish their work and…nah, just kidding it’s just like real life and your robot minions have to go back around and keep pushing the speaker coil as long as you keep feeding them the joules. Remember: watts are not a consumable quantity; watts are a measurement of work being done by expending joules (energy).

So if there’s no load – meaning no speaker – then tubes and resistors and transformers are all in danger of being over-loaded – there’s nowhere to get rid of all the work energy the squirrels get from the joules, and so it backs-up on them like a bad pot-roast and blooey there’s a smell.

 

Introducing the Weber MASS 100

This is not an advertisement for Weber attenuators – except if they want to send me samples to review please do, fine folks at www.tedweber.com – I think their speaker motor designs are very complete and are a good representation of the field as a whole. Weber also makes solid-state attenuators, but I don’t personally have any experience with them. I do have a MASS 100, though, so I can talk about it specifically as an example of these devices in general.

MASS stands for Mobile…Ass-something I don’t know. I’m pretty-sure the “SS” is for “Speaker Simulator”, and that’s the key point about this speaker motor attenuator. Inside the black metal box (about the size of a toaster for long, thin bread) is an actual speaker coil and magnet. It’s a sort-of dry humping version of a full guitar amplifier speaker. It doesn’t make any sound, and the box doesn’t vibrate off the top of the amp or anything, but it allows you to get close to the full awesome sound of the amp but without the awesome neighbor-alienating volume. And unlike a simple drain the sound that does survive the attenuation retains more of the character of the amp.

Obviously you can’t throttle a 100 watt amp without affecting the tone that emerges from it, but the interesting thing about using the speaker motor device is how good the tone is. A change in emphasis comes about, trading epic scale for more dynamic range in your playing. And even with it cranked all the way down (and on the Red Twin, anyway, you can still just hear the speakers as if they were very small) the signal from the line out jack sounds like a monster amp – just one that has been tamed a bit, and that has no identifiable speaker characteristics, which is where the tone controls on the line out can come in handy.

WeberMASSFront

Front of the unit

Rear of the unit

Rear of the unit

The Weber MASS 100 is a good example of modern speaker motor attenuators. On the front panel it has the main attenuation volume level knob. This is actually a heavy-duty rheostat so it has that “zipper” feeling when you turn it. Next you can select between 2, 4, 8, and 16Ω impedance to match the expected load. Above that is a large bypass toggle that you should be very careful with. The small toggle switch to the left of the bypass switch is for 3 db, 6 db, or no treble boost. Below that is another large toggle switch that adjusts the “sweep” range of the volume knob, selecting between high/low variants. The rest of the knobs and the last small toggle switch control the volume, tone, and bypass for the line-out circuit.

The MASS 100 is fairly representative of the speaker motor class of attenuators, with an emphasis on compatibility with your rig via the 2, 4, 8, and 16Ω output impedance selector, and some basic helper features like the 3 and 6 db boost to bring back some of the high end lost to attenuation, and the selectable high/low range for the sweep of the attenuation rheostat. Also a high-rated unit like the MASS 100 can be used with a lower-wattage amp with no problem – at least according to that previously mentioned Weber Company Web presence at www.tedweber.com , if you can believe stuff you see on the Internet.

Also if you can believe things like this you see on the Internet, the selfsame company Web site claims that when you have the attenuator turned all the way “down”, and the amp sound in the speakers is just a whisper, you can disconnect the speakers. As long as the attenuation knob stays all the way to the left, and no one bumps the bypass switch, your output amp should be safe because it “sees” the load it expects, “behaving” the way it expects (like a speaker).

Maybe. I haven’t gone that far yet. With the knob all the way over the sound coming from the amp is so quiet I can just turn it toward the wall or put some sort of improvised gobo in front of it, and use the line signal. More often I’m using it to “restrain” the beast, and play at tolerable daytime levels. I plan to be very conservative in my use of something that seems well designed and well-built, but that my amp was never designed to have in the high-wattage speaker line.

So How Does It Do?

Not bad. It’s not the miracle cure that will make the Red Twin sound like a Deluxe Reverb, and it does change the tone of the amp somewhat. But overall you can get a good loud-cranked Red Twin tone at a bearable level for everyday playing. Personally I have no idea what my Red Twin “really” sounds like when the volume is cranked-up because I like living in this town. I know with the gain channel volume up around three or four it’s loud enough to terrify pets and old people, and do serious harm to your hearing if you’re standing right next to it.

So now I have what sounds like a pretty-great Fender amp that can actually be played. It has the spanky attack and clean chime on the clean channel. Over on the gain channel you finally get to actually hear what the Red Twin is capable of in terms of distortion. With help from a Tube Screamer it’s creamy and sensitive to dynamics. Yes I know I’m probably shortening the life of my power amplifier, or at least its tubes, by driving it into a single simulated speaker that’s only moving to avoid becoming a heat sink. But it sounds good and plays great.

There are downsides. The box gets warm. It doesn’t seem dangerous or anything, but unlike tubes this heat is being generated by friction. There are plenty of ventilation holes in the box – don’t cover them with anything.

The other downside is you aren’t really hearing the speaker’s contribution to the overall sound of the amp. Very little air is being disturbed when you have the attenuator cranked ‘way down like for playing in an apartment or in the evening – what they call “bedroom level”. So there is little or no speaker distortion, the final kind of distortion in the sound chain. And other speaker characteristics are radically subdued or, well, attenuated.

So it’s different. The attenuator “changes” the sound of your amp, in some ways like a change of speakers might do. But mainly for a high-wattage amp like a Twin Reverb it scales the sound down, and in the process it loses the tactile “whoa” factor when playing the Twin loud and it makes your body vibrate. And it loses treble, because that’s where the watts do the most work providing headroom for high frequencies. So features like treble boost aren’t just nice to have, they’re necessary unless you’re going to boost the treble somewhere further down the line.

The biggest change is how you use effects pedals in the chain between guitar and amp. If your pedals provide any amplification, i.e. has a “Level” knob, this has a huge affect on the quality of the attenuated signal. So I’m going to add yet another section here about that.

Using Effects Pedals with an Attenuator

I’ve seen posts in online forums where people say you can’t use effect pedals with an attenuator and that the effects will sound like crap. That’s partly true. You can’t use effect pedals with a speaker motor attenuator the same way you use them without one.

People tend follow the old rule about how you break-up the effects chain into three general categories: first there are signal-making gain effects like compressor, Wah-wah pedal (if Word says you capitalize then damn it you capitalize it!), overdrive/distortion/fuzz, pretty-much anything with a Level knob that makes the pedal output louder (not just a mixing level knob that adds or subtracts effect signal with “dry” input from the previous source).

After these noisy pedals you would have a noise suppressor of some kind if you’re worried about the noise that’s been added to your signal. Then come modulation and pitch effects like tremolo, phase-shift, pitch-shift, vibrato, etc.

Finally there come the ambience/time effects like chorus, delay (echo), and reverb. Notice chorus is not amongst the pitch-changers because it’s really a form of delay. Also some people mate flangers with choruses, but they almost never get any little phase-shifters out of the match. Flanging is supposedly a simulation of running two tapes of a signal and using the thumb to slow the supply reels to get them in and out of sync with each other. I used to do something similar using the eraser-end of a pencil and the little reel hubs on cassette tapes.

When it comes to the ambience/time effects you have the option of putting those effects in the amplifier’s effect send/return loop. If your amp has that, or similar jacks for preamp signal out and power amp signal in (not always exactly the same as an effects send/return loop in that the signal level may be different).

It’s not a bad rule, and if you stick to re-arranging the order of effects within their category things can sound interesting and different without sounding too awful. Just remember put the noisy signal amplifiers first after the guitar, maybe followed by a noise suppressor, then the “fun” effects after that and then the “playing space” effects last. But you can completely get away with putting the chorus in among the fun effects, and putting a delay in with the noisy signal amplifiers. Some combinations will sound like bovine butt-gravy, while others will have promise and will improve your sound. There really are no rules, and the main big non-rule is you want the noisy signal amplifiers as close to the guitar-end of things as possible because they actually shape its tone. Everything else is going to be personal choice.

Now, finally, after that general rant about the great dilemma of signal chain topologies, we come to the deal with using effect pedals with an attenuator: gain-staging – a term over-used here to mean getting the same amplitude across all effects down the chain. The signal coming off the first pedal should have the same amplitude as the signal coming off the last pedal in the chain. Also the level of the signal should be as close as possible the same when pedals are switched-out (bypassed). That one is a bit harder to accomplish. And you may find there are relationships between the levels that come through two pedals far-removed from each other in the chain. Some fanatic anal-retentive might make lists of settings to accomplish this unity gain with different pedals active for different sounds.

If your input (or effects loop) signal is uneven as it passes from effect to effect some of its subtleties and upper frequencies are lost. If it continually drops and then is re-amplified it will become either “mushy” or “harsh” depending on who is winning: the boxes that drop the signal or the ones that over-amplify it. If you can even-out the gain to the signal between the boxes (especially the ones of the signal-making, gain-changing, noisy amplifiers at the front of the chain), keeping the gain in the spot where it’s high enough to be well above the noise floor, but not so high it’s clipping, then you are not adding to the upper-frequency loss that the attenuator (remember that thing?) inherently suffers. If you’re running a bunch of effects and you’re really crushing the attenuation, then the 3 db / 6 db make-up circuit in box like the MASS 100 is really handy and does a good job of getting the treble back up where it should be – as long as your effect chain isn’t the actual problem.

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