Guitar Amps

Well, at some point you’ll want to learn about your amp and you’ll have plenty of questions. So lets take a look at amps from a technical point of view.

Usually you’ll have two major divisions – Tube/Valve or Solid State.

The first type uses vacuum tubes/valves to house the old style transistors. The real up side of Class A/B operation is its inherent efficiency. The simple fact that each tube has a res Tube amps were later replaced by Solid-state transistors, and the need for tubes were gone. tube amps still exist, and are made day in and day out. The difference in how the amps work is pretty much a function of application. Both will provide ample distortion, and can sound remarkably similar.

Tube amps generally have a warmer sound and a more punchy attack than solid-state amps and pickup the players personal style a little better than solid-state ones because the vacuum pressure directly effects how well a tube will perform, thus the harder you push your amp with your playing style, the more dynamic it’ll sound, where as a solid state amp won’t pick up as much of that same articulation.

Most amps, be they combo or head style will have two or 3 channels, an fx loop, a gain control, a 3 band parametric EQ and reverb. Most of them will come with a foot switch but not always.

As for the specifics on how amps work and such – the information below was found on the official VHT amplification site.

 

What’s the difference between tube and solid state rectifiers?

The rectifier circuit in an amplifier converts the Alternating Current (AC) from the wall outlet to Direct Current (DC) required for operating the various circuits inside the amp. Originally, this conversion or “rectification” was accomplished using a vacuum tube rectifier, also known as a dual diode. Later with the advent of solid state technology, the rectification process was accomplished much more efficiently and less costly with silicon diodes.

Besides the cost, one of the primary advantages of the silicon diode is its low voltage drop. Because of this characteristic, the solid state rectifier supply responds much more quickly to the increased current demand created when the amplifier is driven to full output. This gives the amplifier a tight , crisp and dynamic response. The tube rectifier exhibits a much higher internal voltage drop, which in turn causes the power supply voltage to sag when the amplifier is driven hard. We experience this sag as a natural sounding compression, which seems to give the amp a breathing, bouncy quality. In addition the tone will appear to sound softer or more rounded with increased sustain.

Today we find that both the tube and solid state rectifiers have a valid application in helping to enhance the personality of a given amplifier design.

 

What’s the difference between Class A and Class A/B operation?

There are from a technical standpoint, many things that distinguish Class A operation from Class A/B. For our purposes we’ll be discussing only those characteristics which pertain to guitar amps in general and VHT amps in particular.

Generally speaking, the power tubes in a Class A amp are operating at pretty close to full power whether or not a signal is being amplified. As long as the tubes are being operated at reasonable voltage and bias range we’re OK. The beauty of this type of operation is that there is no significant difference between the tubes work interval and its rest interval. The distortion products created by this method of operation are very musical sounding and the overall tone has a pure quality.

When combined with the right output transformer, the harmonic blend created by the tube distortion characteristic and transformer saturation ( that is to say, just past the point of maximum linear operation), is rich, full and fat sounding. It sounds pretty much like an amp turned up loud even when it isn’t because it’s operating nearly full out in a sense.

In class A/B operation the tubes are getting a big break. When no signal is present the tube is essentially at rest. When you begin to play, there occurs a transition from “off” state to “on” state between the push-pull pairs of tubes. This transition, known as the crossover region, produces a noticeably different type of behavior typically referred to as crossover distortion. Crossover distortion contributes a harshness to the sound which can give the amp an aggressive personality. This can be interpreted as a good thing depending on what you are trying to accomplish musically.

The real up side of Class A/B operation is its inherent efficiency. The simple fact that each tube has a rest interval in its duty cycle allows the tube to operate at higher output during its work interval or “on” state. Thus, a power amp operating in Class A/B will typically produce about 30% more power than a comparable Class A amp. Since the typical output transformer in a Class A/B amp will not be required to operate at high continuous current, it will spend less time in saturation mode. This contributes to the clarity and detail of the power amp sound. An additional advantage of Class A/B is that because they tend to run cooler, tube life can be extended somewhat. For strictly comparative purposes however, the essence of the debate is sound quality.

We are attracted to the Class A sound because of its warmth, sonic complexity and rich harmonic content. The Class A/B sound is more articulate, dynamic and gives us the sensation of immediacy.

 

What’s the difference between Series and Parallel effects processing?

The effects loop design in all current VHT Heads and Combos, allow either Series or Parallel operation. In the Series mode 100% of the signal from the preamp section of the amp is routed through the send jack to be modified through the effects device. The modified signal is then returned to the effects return jack and sent to the power amp section for final amplification. Effects such as equalizers, compressors and multi-effects processors with fixed or programmable mix controls are typically operated in Series mode.

In Parallel mode only a portion of the preamp signal is routed to the effects send jack for processing. In this case the original signal path inside the amp is protected from the sometimes undesirable side effects of external devices such as signal loss, impedance mis-matching, coloration of the sound and distortion. Effects such as reverbs, delays, and pitch shifting devices which can be set for 100% “wet” output are typically operated in Parallel mode. The processed signal is returned to the amp to be blended with the internal dry signal and then sent to the power amp section for final amplification.

 

What is Gain Stacking?

Gain Stacking is a new feature on our high gain preamp channels that allows you to pre-select the number of gain stages utilized in a selected channel to achieve the desired amount and type of gain you are looking for. You may set up a crunch sound with 3 stages of gain and a solo sound with 4 stages. Or vice versa. Or you may want 2 high gain lead sounds or 2 medium gain rhythm modes with slightly different tonal balance or volume. This can all be accomplished easily and quickly with Gain Stacking.

The Gain Stacking circuit utilizes a “flying” 4th stage that can be assigned wherever it is needed without the waste of unused or over-compensated tube stages in the preamp section of the amp. This is one of the reasons the Pit Bull preamp design produces as much or more gain than other designs with a lot less noise, hum and microphonics.

 

What are the advantages of printed circuit technology over point to point wiring?

For the record, all VHT amplifiers are primarily hand built PCB assemblies. No automated board stuffing or flow solder processes are used. Honestly, if we felt that the sound quality or execution of our products would be improved by the exclusive use of point to point assembly, we’d be doing it. On the other hand, hard wired assemblies are utilized wherever it is determined that sound quality, reliability and consumer safety is best achieved.

AC mains, main power supply, board to board interface, long, high impedance audio signals and rectifier tube sockets are areas where hand wiring is clearly the superior method. All other components such as resistors, capacitors, pots, switches, tube sockets (that’s right…Tube sockets…pre and power) and various other items are properly and confidently PCB mounted.

We use top quality double-sided glass epoxy boards with heavy copper plating and plated through holes for maximum reliability and signal integrity. Boards are mounted on heavy-duty tubular aluminum supports attached to the chassis with machine screws. You won’t find any floating preamp boards or pop rivets here. Small tube sockets have large diameter solder pads and a center support pin, also soldered to a large plated through pad.

Large tube sockets are attached to the board with heavy tubular aluminum supports and chassis mounted with machine screws to form a solid and bulletproof board to chassis assembly. We know of no other amplifier manufacturer that uses this rugged and costly method of construction. In fact, most other PCB mounted preamp tube sockets we’ve seen don’t even have a center support pin!

There are a lot of misconceptions and misinformation surrounding the debate over printed circuit board versus point to point assembly. The problem we see is that many times information gets taken out of context, leading to the creation of fresh manure.

We will discuss the issues as they relate specifically to the manufacture of our products. Sure, we’re probably going to hit a nerve or two somewhere along the way, “but” as Stuart Smalley reminds us, “that’s…sigh, OK”.

Since we’re all pretty much in agreement about the origin of point to point wiring and PCB’s, we’ll skip the history lesson and get right to the pros and cons.

 

Sound Quality

Contrary to what you may have heard, great tone is not the exclusive domain of point to point wired amps. Even the use of top quality components and meticulous assembly methods do not guarantee good tone.

There are plenty of examples of great and lousy sounding products in both point to point and PCB categories.

There are well built, mediocre sounding amps and sloppily thrown together, great sounding amps. In fact, undesirable sonic characteristics frequently attributed to circuit boards are much more likely to occur in point to point wired amps. Stray capacitance, phase cancellation, signal degradation, and cross talk between stages are common problems in point to point designs. Most of these conditions are easily minimized or eliminated in a well executed PCB design.

One interesting and often overlooked side benefit of PCB design is the ability to precisely control the way the board will “sound” by experimenting with placement of sensitive components. We frequently use this technique of “tuning the board” to tweak various parameters of a circuit which might normally be accomplished with the relatively “brute force” use of added capacitance or tone robbing bundled wire harnesses.

 

Consistency

One of the most attractive benefits of PCB construction is the inherent consistency of the process. Once the design is complete, it can be easily reproduced with a very high degree of accuracy. In our particular case, the object is to produce an amplifier that meets a set of predefined sonic and functional criteria. These criteria are built into the board design and are not subject to the wide variations in tolerances normally found in the point to point assembly process.

In the late fifties, state of the art point to point construction ( i.e. military and recording/broadcast electronics) incorporated “turret boards” that supported most of the small components on Nickel/Silver plated posts staked into thick Fiber or Glass/Epoxy strips. The bulky components (pots, jacks, switches, filter caps, meters and transformers) were chassis mounted and meticulously hand wired to these boards. Some of today’s more popular (and more expensive) point to point amps utilize low cost phenolic “terminal strips” with thin Tin plated lugs instead of the much more rugged turret boards (and while we’re at it…get real with those filter caps bundled together with electrical tape!!!).

The terminal strip method usually requires much more extensive use of wire, solder and wiring harnesses, resulting in a circuit layout that is subject to wide variations in circuit behavior. Two identical amplifiers built this way are very likely to, and often do sound completely different!

 

Reliability and Serviceability

Needless to say, there is a right way and a wrong way to do everything. We could be a little bit more generous and say that there are an infinite number of interpretations of the term “cost effective”. I have to admit that there are legitimate reasons for peoples seemingly genetic aversion to printed circuit boards. Every time I look into the guts of a PCB amp that falls into the “cheaper to replace than repair” category, I think “here’s another one I’m going to have to defend myself against”.

It’s a fact however, that circuit boards dominate the electronics industry. Therefore it is important to remember that for every department store consumer electronics product that’s on sale this week, there’s an Internet connection bouncing off of a satellite orbiting our fair planet that will probably operate flawlessly far into the next century…utilizing printed circuit boards.

How do we account for this large technology gap? Simply stated, printed circuit boards pretty much do exactly what the designer intended for them to do. Nothing more, nothing less. If top notch performance and long term reliability are the design objectives, then the end product will perform and last provided that it is correctly engineered.

In this context then, it is logical to conclude that a well designed, high quality PCB based amplifier is more than likely to perform as well or better and last easily as long or longer than a point to point wired amp.

 

Cost

All things considered, we feel that the point to point method of amplifier construction is unnecessarily time consuming and excessively costly. When you pay a premium price for a quality point to point amplifier, it is pretty much understood and taken for granted that you’re not necessarily paying for performance and flexibility.

A fat price tag on a boutique amplifier frequently indicates nothing more than what the builder thinks the market will bear. On the other hand, if you understand that you are literally paying homage to the idea of Old World Craftsmanship and appreciate the time and effort that goes into a nicely made piece of modern nostalgia, then you are probably making a justifiable purchase.

A well designed, PCB based amplifier sacrifices nothing to sound quality, construction quality or long term reliability and value merely as an automatic consequence of the use of printed circuit boards. The labor saving aspect of PCB amplifier construction makes it possible to offer a wide variety of features and functions which translate to a higher “Bang for the Buck” ratio. It is important to understand this important distinction before plunking down your hard earned plastic.

 

What is slaving?

This is a method for using amp heads or combos as a signal source in amp/power amp systems or multiple amp systems. The term simply refers to the practice of using one amp (typically a head or combo) as the “Master” amp or primary tone source, and another (typically a power amp) as the “Slave” amp which does the work of driving the speakers. Slaving allows you to generate just the right blend of preamp and power amp distortion in your Master amp.

The resulting output is then attenuated down to a practical signal or line level which can then be routed to a switching system, mixer, effects processor, stereo power amp, recording console or any combination of the above. These kinds of applications are especially useful in live situations where it is desirable to reproduce a variety of different amplifier and distortion characteristics that may have been originally produced in a studio environment with multiple amps and speakers.

It usually involves running the Master amplifier “full out” into an enclosed speaker or “Dummy Load” such as a high power resistor or power attenuator. A low level signal is then taken from the Master amp output using the “line output”, an external signal attenuator (pad), or some type of speaker emulation device, which is then sent to an effects system, power amp and then to a pair of speaker cabinets.

This is not generally considered to be the most practical of systems, but when done right, it’s pretty hard to beat. Anyway, who cares about practical when your main objective is ultimate sonic satisfaction?

 

When should I have my amp biased?

Generally we recommend having the amp biased whenever the power tubes are being replaced. Even if you stay with a particular brand or type, the transconductance of tubes vary even within similarly matched sets. Biasing at replacement time is the best insurance for consistency and reliability.

 

What’s the difference between KT88, 6550, EL34, 6L6, EL84 tube types?

In order to keep the subject matter concise and relevant to VHT amplifier models, we’ll break these tube types down into 3 basic categories:

High power output: KT88, KT90, 6550

Although not widely used in the guitar amp industry, we find them to be ideally suited to players who want power punch and articulation. They are used in a variety of configurations, mostly in pairs and quartets and in some cases, sextets.

They are capable of delivering 100 watts per pair and this is the typical application in which they are applied at VHT in the Two/Ninety/Two and Twenty One Fifty power amps. Quartets of 6550’s are used in the Pittbull Ultra-Lead and are more conservatively operated at about 60 watts per pair. Because of the high output capability and efficiency of these tubes, amplifiers that use them exhibit a wide dynamic range, lots of low end power, crisp attack and to quote Guitar Player Magazine “miles of headroom”.

 

Medium power output: EL34, 6L6

These are the standard bearers of the majority of the tube guitar amp industry for the last 30 years or so. Typical output for a pair is 50 watts. We use EL34’s in the Twenty One Hundred power amp, Two/Fifty/Two power amp, Hundred CLX head, Hundred/CL head, Fifty/CL head, Fifty/ST head and Fifty/Twelve combo. EL34’s are harmonically rich sounding tubes with a strong upper midrange which complements guitar voicing very nicely. When driven hard they exhibit a smooth transition into distortion while maintaining clarity and good tone quality.

All VHT amps that use EL34’s can be switched over to 6L6 operation. 6L6’s generally sound a little cleaner than EL34’s and tend to have a bit more beef in the low end as well as more bite on the top. Some players prefer the extra clarity and punch of these tubes. Others just like them because they are used to the 6L6 sound. We will ship any of the above models with 6L6’s installed by special request.

However, we prefer the sound of EL34’s in our amps and these are what the above models are shipped with as standard equipment.

 

Low power output: EL84

This great sounding and economical tube, has had quite resurgence in popularity in recent years due to its increased availability. Typically used in quartets and run in Class A mode, they are good for about 30 watts or 40 to 45 watts in Class A/B. They basically sound like a small screaming EL34 with a rich fat midrange voice and great distortion tone. We use this tube in the Pit Bull Forty-Five series heads and combos.

 

Do you plan to make a simple plug & play type amp?

For months I have been pondering the debate over whether or not to develop a simple straight ahead amp model that is stripped of the bells and whistles normally found on VHT amplifiers. After recently exploring the concept, I believe we have been on the right track all along. I have owned feature laden guitars and I discovered that all of the knobs and switches that you can throw on it won’t enhance the essence of the instrument one iota.

There are those who feel the same way about amplifiers. I’m not one of them. I believe that an amplifier is an integral part of the instrument. An amplifier extends and fleshes out the boundaries of the instruments capability. A well conceived amplifier accomplishes this task in a variety of ways that are constantly subject to experimentation and new settings possibilities.

Is it possible to go overboard with this idea? Like anything, there is always a point of diminishing returns. The trick is to keep a firm grip on the object. The object being “Make the dog gone thing scream!”

Given that amount of information you should have a good background from which to make decisions on your future amp needs and purchases.