Rock Dog Amp Repairs - Amplifier Myths and Facts

The guitarist cannot begin to make intelligent gear decisions without a basic understanding of tone, power, and volume. Many experienced guitarists still nurse and cherish "facts" that are so incorrect as to be pure fantasy. Some of these guitarists have achieved great tone - but only after years of very expensive trial and error and without ever really understanding what they did to finally get the killer tone they were looking for.

Knowing the facts about amplification can help guitarists take the fast track to their ideal rig and save them thousands of dollars along the way.

Each of the following paragraphs debunks a popular myth and tells the real story. Since most readers are probably more interested in playing than becoming technicians and engineers, I've intentionally simplified some of these subjects a great deal.

You'll find a lot less bias against solid-state amps here than in most articles. So much so that you might think I'm a fan of solid-state amps. That is not the case at all - I strongly prefer tube amps and suspect I always will (I just love glowing lights and shiny things). However, this article is about facts and it is a fact that solid-state amps have come a long way and are an appropriate choice for some players and some situations.

Power Myths

Several common myths about amplifier power are debunked below. The bottom line is that you should select an amplifier for its features and tone, and consider power level as the least important criteria in your selection.

1) My 100-watt amp is twice as loud as your 50-watt amp. This is one of those really sad myths that just won't go away in spite of volumes of empirically and mathematically proven, unambiguous, clear, undisputed, scientific knowledge to the contrary - knowledge that every tech worthy of a soldering iron learned very early in their training. Music store sales persons on commission love this myth because it's sold thousands of 100-watt stacks (not to mention the follow-on sales of expensive replacement tube sets). Here are the facts:

All other things being equal, a 100-watt amp will only be just perceptibly louder than a 50-watt amp. It takes about a ten-fold increase in power to double perceived volume. That's right, you'd need a 500-watt amp to be "twice as loud" as your buddy's 50-watt amp. Even more thought-provoking is the fact that a 50-watt amp will only be perceived as a little bit louder than a 15-watt amp driving the same cabinet!
All other things are almost never equal. There are so many variables controlling sound pressure level (SPL) and perceived volume that it is quite common for a small amp to sound louder than a much more powerful amp.
Cab design, speaker size and efficiency, signal compression, and several other factors have far greater impact on perceived volume than does power level.
The initial purchase price of a 100-watt amp will be significantly higher than a 30-watt amp with similar features.
It will cost you significantly more to re-tube a 100-watt amp.
If you are driving a 30- or 50-watt amp hard enough to require frequent re-tubing, chances are very good that you will also drive the 100-watt amp hard enough to require frequent retubing (at significantly higher cost).

Am I saying 100-watt stacks are evil? No. No one really needs one (see below) but if you want one, be my guest. All I'm saying is that you should be aware that you are spending a lot of money to purchase a miniscule increase in volume.

2) I need a 100-watt amp 'cause my band has started gigging in clubs. This is a myth that I believe originates with hormonally imbalanced teens who have more experience watching movies about teen bands than they have playing real gigs. Unfortunately, it's a self-perpetuating myth because the rhythm player is going to get a big amp 'cause he's being drowned out by the lead player, then the bass has to get a 400 watt amp to be heard at all, then they need a 1200 watt PA system so that the vocals have some chance of being heard over the cacophony from the guitars and bass, and finally they end up having to mic the drummer even in a small club because the drummer is breaking sticks and skins and still can't be heard over the racket. Within a few years their hearing has been permanently damaged and they all decide that they need bigger amps! Three-quarters deaf, they finally make the big time and the guitar magazines write about the three 100-watt stacks that the guitar hero uses on stage and all the wannabees have just got to have the same rig. . . As you can imagine, this is another myth that sales people on commission are in no hurry to debunk! Well, here are the facts.

There is absolutely no venue that requires a larger amp and cabinet than one suitable for use as a stage monitor - provided that the members of the band don't get into a juvenile competition to outdo each other. Need more feedback? Fine, move closer to the amp. Typically, a really good 30-watt rig with a suitable cab is ample! Depending on the composition of your band and the variety of venues you play, an even smaller rig miked to the PA and then pumped to stage monitors may be even better. Note that while a good 30-watt rig has ample volume you may end up having to buy a more powerful rig to get other desired features.
- At a small venue, a 15 to 30 watt amp can be placed behind the band in a traditional position and used without a mic. In this position the rig serves as a monitor for the guitarist and as the primary amplification for the guitar.
- At a medium venue, the small rig can be placed in front of and facing the guitarist as a monitor, and be miked and run through the band's PA. The band's PA speakers are placed along the front of the stage and facing out. This arrangement allows the sound to be balanced at the mixer and allows the band to flood a medium to large venue without damaging their hearing.
- At a large to giant venue, that same small rig can be arranged much as described above but now the band's mixer feeds the house PA. This is the only way to reach the back of the room without dangerous SPL's near the stage at a large venue and would be required no matter how powerful a rig the guitarist has.
Smaller equipment takes up less space on cramped stages.
The money you save by purchasing a smaller amp can fund a nice power conditioner to protect your equipment and clean up power line noise - the conditioner will cost less too since now you don't need one that will handle a billion watts.
If the band members will agree not to compete, all of them can recognize significant savings by not having to purchase unnecessary equipment.
Your band is far more likely to be called back for a repeat engagement if you provide a well-balanced, easily managed performance than if you are just obnoxiously and uncontrollably loud.
Many guitarists already have the monster amp - it isn't necessary to get rid of it. You can use an attenuator (see the attenuator myth) and perhaps a smaller cab.

3) I need a small combo because I live in an apartment. This is sort of the opposite of myth two, above, and is closely related to myth one, above. While a small combo will certainly take up less room, it may or may not be easier to get good cranked tone out of it at apartment levels. First, read myth one again. If it's true that we have to increase power ten times to double perceived volume, then it is also true that we have to reduce power ten times to cut the perceived volume in half. Thus, even a tiny 5-watt single ended tube amp is going to sound about half as loud as a fifty-watt stack (actually, it will be a bit quieter than that because it is probably driving an eight or ten inch speaker instead of a 4X12 cab). Even that five-watt amp will be way to loud to run cranked in an apartment unless your neighbours are very tolerant. Here are some facts you should consider:

Even a 5-watt tube amp with an eight inch speaker is very loud by the time you crank it into distortion.
You can use an attenuator with either a large amp or a small combo. Keep in mind, however, that attenuating below about 1 watt per speaker starts to adversely affect tone - it seems that a certain amount of speaker drive is required to round out distortion (see recent articles on 3-stage amplification architecture tests at amptone.com).

Even one watt into an 8" or 10" guitar speaker is likely to get you evicted.

Many small combos do not offer a master volume, thus making it impossible to even get preamp saturation at acceptable volume levels.
To get true "cranked tube tone" in an apartment at lease-safe levels you are almost certainly going to have to use a combination of attenuation and a sound-proof speaker isolation box with a microphone running to a mixer or stereo. This is true whether you are running a 5-watt, single-ended, class A combo with an eight-inch speaker or a 100-watt stack with a 4X12 cab.
It's not a good idea to run an amp inside of a sound-proof box, so even with a small combo you will need an extension speaker.
It's not much fun to try to enclose a 4X12 cab, so you'll also need an extension speaker with that kind of rig.

The lesson here, once again, is to select amplifiers based on features, not on power level. A tiny five-watt class-A amp with an eight-inch speaker and no features may not be very satisfying after a while, and will be wholly inadequate for gigging, and still isn't quiet enough to run cranked in your apartment! Add a few features such as footswitchable channels, master volume, and an effects loop and that 5-watt amp starts to become pretty attractive!

4) My tube amp has a master volume control that lets me get power-amp distortion at low volume levels. Yet another myth that sales people love.... (seems like there are quite a few of these, hey!). The facts are:

With the possible exception of some very rare and expensive "boutique" amps, a so-called master volume does not reduce power output after the power-amplification stage as the name would seem to imply.
The master volume controls found on popular amps cut the power between the final preamp stage and the power amp.
In all popular tube amps, when you turn down the master volume, then turn up the gain controls to achieve overdrive, you are overdriving the preamp stages, not the power stage.

I firmly believe that manufacturers deliberately misnamed the "master volume" control to deceive consumers - but that does not mean that the control is useless. Quite the contrary, I regard a "master volume" control as an essential part of a good amplifier. The "master volume" control permits running the preamp at full saturation or beyond at reasonable volume levels and allows one to balance preamp and power amp saturation for a wide variety of sounds. I love "master volume" controls, I just think they should be named less deceptively!

5) Power attenuators damage amplifiers. There is some truth to this myth. But, attenuators can be safely and successfully used – and every guitarist should know how and when they can be safely used. Here are the facts:

A properly designed power attenuator does not apply any more stress to the amplifier than does a speaker cab - in fact a good attenuator will usually apply slightly less stress than a cab alone. However...
...when using an attenuator, guitarists typically drive their amplifier much harder than they ever would when driving a cabinet directly. Driving the amp this hard will significantly reduce tube life regardless of whether the amp is driving an attenuator or a cab. As a consequence, it seems like the "attenuator wore out the tubes." In reality, the guitarist was just enjoying much more overdrive than he/she ever would have without the attenuator and is paying the piper.
Some amplifiers are simply not built to be driven hard. When the guitarist uses an attenuator and then runs the amp harder than he would have into a cabinet, very bad things happen and then the guitarist says, "that attenuator ruined my amp." No, driving the amp at "10" ruined it – the attenuator is only incidental in that you never cranked the amp to 10 because it was just way too loud! This problem is particularly common with low-power combos. I had a little 15-watt class A Ampeg Jet J-12T. It's a great sounding little amp that I never cranked higher than about about "4." One day I decided to see if it would do "metal." Using a guitar with hot humbuckers I cranked the little Ampeg to "10" and played for about 2 minutes before the volume just became too painful (I was not using an attenuator, this was directly into the built-in 12" speaker). When I turned the amp back down to reasonable levels I could hear a crackling sound. In two minutes or so I'd blown both of the screen resistors and ruined the tubes. I fixed the amp but never turned it up to 10 again! This amp was just not designed to be driven at these levels.
Attenuators can be used safely if you follow these rules:
- Make sure that the attenuator contains some inductance. This will help maintain natural tone and causes the impedance to increase with frequency.
- The attenuator should either have approximately the same inductance as a speaker or should be of slightly higher resistance than a speaker. It is better to reflect a slightly higher than normal impedance through the output transformer than too low of an impedance.
- Have a reputable tech "cool off" your amp. Explain to the tech that you are going to be driving the amp very hard into an attenuator and you want it biased a bit cold to save the tubes. This will cost a bit in tone (chances are you won't notice this because you probably never drove the amp so hard anyway) but will make the tubes last a lot longer and reduce the chances of damage to other components such as the expensive output transformer. A knowledgeable tech can also tell you if the model of amp you are using is known for blowing transformers and what have you (many guitar amps have output transformers that are not rated anywhere near the amp's max output).

6) Power attenuators kill tone. Actually, it seems that well-designed power attenuators with inductive elements have little effect on tone until you attenuate to below about one watt per speaker. I suspect that the real issue is not so much the power level as the excursion of the speaker coil. At very low power levels the coil has very slow linear movement for a given frequency and thus has very little momentum accumulated when it reverses direction. At higher power levels the linear movement rate is much higher and the speaker tends to overshoot much more, rounding out sharp corners in the input signal. That's just a hypothesis on my part but, whatever the cause, the effect has been tested and measured by 'cybermonk' at amptone.com.

Distortion Myths and Solid-State vs. Tube

There are so many myths, many of them conflicting, that it is hard to know where to begin. Probably the most important thing to realize is that distortion can be broadly characterized as "hard" and "soft." "Soft" distortion is the Holy Grail for most but it's important to realize that both types of distortion are useful.

1) Preamp distortion is bad. Preamp (even tube preamp) distortion is much harder than tube power-amp distortion but the fact is that most rock-distortion uses both preamp and power amp distortion.

2) You can get great tube tone using tubes only in the preamp. The fact is that the "creamy" soft distortion most of us desire occurs only in a saturated power tube section. Tubes in the preamp do warm up the signal by introducing small impurities not typically present in a solid-state circuit, however.

3) Tube and solid-state preamps sound the same. The facts are:

Tubes "warm up" the signal by introducing impurities not present in most solid-state circuits.
Tubes, even preamp tubes, go into clipping more gently than most solid-state circuits resulting in a slightly smoother transition to distortion. Running preamp tubes just at full saturation gives a very full tone that simply isn't found in solid-state preamp circuits.
Amp and effects manufacturers have been fairly successful in modelling tube preamp sounds using digital (DSP) and analogue solid-state techniques.

4) Solid state amps suck. This is only half true. The facts are:

Many solid-state amps do suck, especially older models and entry-level models.
Some newer solid state amps actually sound pretty good, especially for clean tones. None have truly "nailed" power tube distortion but modelling amps are getting close.
Many guitarists and most non-musicians can't tell the difference between the best of the solid-state amps and a tube amp except in a side-by-side A/B test - and some can't tell even then.
A good tube circuit anywhere in the amplification chain can "warm up" a sterile clean signal.
Solid-state amps are much lighter, more rugged, and more reliable than tube amps.
Solid-state amps typically deliver a much more consistent sound over a wider range of output volumes.
Many, many, guitarists who absolutely swear by tube amps and won't even test drive a solid-state amp, never push their tube amps into power-stage distortion - and power stage distortion is about the only thing that a good solid-state amp can't do well!

Solid-state amps have come a long way but are still not quite "there," in my opinion. Some of them do a pretty good job of modelling preamp distortion but they aren't quite over the top modelling the power amp with its complex interaction between power tube, output transformer, and speaker. Even so, nine out of ten people in the audience at a typical live gig aren't going to know or care whether you are using a good solid-state amp or a tube amp. If you do the weekend warrior thing and either play mostly clean or mostly with very heavy "metal" distortion then your best choice of gear might well be a multi-effects unit with a tube preamp driving a good solid-state amp!

5) The entire signal path must be tube; there mustn't be any solid state circuitry in the signal path. This is so silly it would be funny if not for the thousands who make inappropriate and expensive gear choices based solely on the presence or absence of an "all tube" decal on the front panel. The facts are:

We like what tubes do to tone because of colouring they add to the tone. This is true both of clean and overdriven signals.
Clean (non-overdriven) solid-state circuitry of even mediocre quality reproduces a signal extremely faithfully. It will not "sterilize" a signal that has been "warmed up" in a tube stage.
At least one tube stage should be present in the preamp chain to warm up clean tones. This can be a tube preamp in a tube or hybrid amp or it can be a tube pedal or tube preamp in a multi-effects unit such as the GSP-2101 or RP20.
Until modelling is perfected, tube power amp sections provide the most "liquid" distortion. But remember, this is only important if you are looking for liquid distortion! If you're playing mostly traditional country then you want an almost painfully clean signal anyway. Similarly, if you are playing in a shock-rock band you probably want mostly "hard" distortion anyway.
For clean tones there is little practical difference between a solid-state power amp and a tube power amp provided that the signal has been suitably "warmed up" in a tube preamp.

I've seen people pass up a good deal on a great-sounding tube amp because it had a solid-state reverb driver or tremolo circuit and then stick a half-dozen cheap solid-state pedals in the effects loop of the less-capable amp that they purchased because it was "all tube." Maybe P.T. Barnum was right!