GUITAR AMP EVOLUTION by Keenan

{ I found this a long time ago and gained a lot of knowledge from it. I went looking for it again and found another copy, but now I can't find that one! So I found a text copy I had saved, and tried to reformat it back to the original. I tried to find "Keenan" but he apparently has moved on. His links are dead or deleted. Hey, Keenan, if you are out there... let me know if this is correct and if I should even have posted it! - webmaster@tubemodules.com }

Written by Keenan.
Since I'm writing this for Asian guitarists, and most Asian guitarists prefer preamp distortion to power amp distortion, I'm going to focus on how preamp circuits affect tone. I'm going to ignore most of the tonal contribution of power amps. (All combo and head amps have both a preamp and a power amp.)
PREAMP STYLES: There are many factors which influence how an amp sounds. But one major contributor to tone of an amp is its preamp. The main part of a preamp that does the "work" of a preamp is called a "gain stage". A gain stage is like a pump, or miniature amplifier. The more pumps, the greater the potential amount of distortion.
Clean preamps have very few gain stages. High gain preamps [screaming rock distortion] have many gain stages.
2 stages: CLEAN
3 stages: LIGHT DISTORTION ("CRUNCH")
5 stages: HEAVY DISTORTION

Example:
Clean preamp: 2 gain stages
in-----stage1-----volume-----stage2--------------->

High Gain/High Distortion preamp: 5 gain stages
in-----stage1-----Sgain"----stage2-----stage3----stage4-----stage5----master volume------>

Medium gain "crunch" preamp: 3 gain stages
in-----stage1-----"gain"----stage2------stage3-------------------------master volume----->

Here's a list of common guitar amps, and how many gain stages their preamps have:

AMPLIFIER Total Stage Before EQ After EQ
1 Fender "tweeds", 60's Marshalls 2 2 0
2 Fender blackface (normal channel) 2 1 1
3 Fender blackface (reverb channel) 3 1 2
4 Mesa-Boogie (lead channel) 4 1 3
5 Mesa-Boogie (lead channel) 5 1 4
6 1970's Marshall Master Volume 3 3 0
7 Early JCM-800's 3 1 2
8 Later JCM-800's, JCM-900's 3 3 0
9 Bogner FISH (brown channel) 4 4 0
10 Soldano (lead channel) 5 5 0
11 Peavey 5150 6 6 0


If I wrote this another way, it would look like this:

1. 2+0 Fender "tweeds", 60's Marshalls
2. 1+1 Fender blackface (normal channel)
3. 1+2 Fender blackface (reverb channel)
4. 1+3 Mesa-Boogie (lead channel)
5. 1+4 Mesa-Boogie (lead channel)
6. 3+0 1970's Marshall Master Volume
7. "1+2" Early JCM-800's
8. 3+0 Later JCM-800's, JCM-900's
9. 4+0 Bogner FISH (brown channel), Marshall 6100 (lead channel)
10. 5+0 Soldano (lead channel)
11. 6+0 Peavey 5150

So, in this little chart you can see some of the history of tube guitar amps. Guitarists wanted more and more distortion, so amp designers added more gain stages.
NOTE: There were, of course, other changes. Amps in the 1950's were low powered, often 5 to 35 watts. By the 1970's, most guitar amps were 50 or 100 watts. Until very recently, 50 to 100 watt amps were still standard.

What has changed? Guitarists have rediscovered the rich sounds of power amp distortion, and small, low watt amps get power amp distortion at much lower volumes. Today, while there are still a great many 50 to 100 watt guitar amps, there are also many new smaller amps, such as Fender's Pro Junior, the Matchless Lightning, Soldano Atomic 16, Mesa Subway Rocket, Peavey Classic 20, THD Univalve, and Budda Twinmaster.
Now, obviously a Peavey 5150 can create much more distortion than an old Fender amp. 6 gain stages can create more distortion than 2 gain stages.

But what about a Marshall Master Volume and the reverb channel of a Fender Twin? These amps both have 3 gain stages. So, why does a Marshall Master Volume amp produce more distortion than a Fender Twin? The main reason is that a lot of the gain (the amplification of the signal by a gain stage) is thrown away in the Twin. Between stage 1 and stage 2 there's a passive EQ circuits, and these EQ circuits "eat" a tremendous amount of the gain produced by gain stage 1. Also, between stage 2 and stage 3 there is a huge resistor (3,300,000 Ohms) which also "eats" a very large amount of the signal.

STOCK BLACKFACE FENDER (reverb channel):
in----stage1---EQ---volume----stage2--RESISTOR (3,300K)--stage3----->

If we were to eliminate the EQ circuit between stages1 and 2, and reduce the 3,300,000 Ohm resistor to a more common value (say, 500,000 Ohms or 250,000 Ohms), the Fender would suddenly be able to produce much more distortion. The gain wouldn't be "wasted" or "thrown away" by the EQ circuit and the large 3,300 kilo ohm resistor. (3,300,00 Ohms= 3,300 Kilo Ohms= 3.3 Meg Ohms)

Modifications to Increase Gain:
Eliminate EQ circuit. [replace it with a .022uf capacitor.]
Reduce 3,300K resistor to 250K.

MODIFIED BLACKFACE FENDER (reverb channel)
in----stage1--------volume----stage2--resistor(250K)--stage3-----> loud, distorted signal

I don't actually recommend doing this modification on a vintage Fender Twin Reverb. But, if you had your amp tech build you a similar circuit, you could have him first build the stock circuit, then modify it the way I've described. You'd easily be able to hear the big changes in sound. Here's a more detailed look at the preamps of the 11 amps I've mentioned:

PREAMP STYLES:

1. 1950's Fender "tweeds", 1960's Marshalls
in----G1---------volume----G2----EQ-------------------->

That's right, Marshall's 1960's amps were very similar to some of Fender's 1950's amps. Jim Marshall copied the 1959 Bassman (circuit # 5F6-A) when he made his first Marshall amps. Early Marshall amps and Fender Bassmans are virtually the same amps. The biggest difference was that the Bassman used four 10 inch Jensen speakers in an open back cabinet, whereas the Marshall used four 12 inch Celestion speakers in a closed back cabinet. Speaker and speaker cabinets greatly affect tone.

By the late 1960's, Marshall amps had evolved away from being clones of the Bassman, but their basic preamp style remained the same, with only minor modifications.

2. 1960's Fender "blackface" normal channel
in----G1---EQ---volume----G2--------------------------->

Fender repositioned the EQ to just after the first gain stage, where it "ate" a lot of the signal. This made Fender's 1960's amps somewhat cleaner sounding than the 1950's tweed covered Fenders.

3. 1+2: 1960's Fender "blackface" reverb channel
in----G1---EQ---volume----G2--RESISTOR--G3----->

The reverb channel did have an extra gain stage, but most of this gain was lost by having a huge 3.3 Meg Ohm resistor between stages 2 and 3. The end result was that the reverb channel stayed clean unless cranked to very high volume.

4. 1970's and 1980's Mesa-Boogie lead channel
in----G1---EQ---volume----G2--------------G3----G4-----------------------master volume--->
in----G1---EQ---volume----G2--------------G3----G4----G5----------------master volume--->

Mesa's Randall Smith took the 1960's Fender designs, and added more gain stages. No major amp had ever had so many preamp gain stages, and all this extra gain produced thick, heavy distortion. Over time, more and more amp companies began using this approach, with their own special twists (unique innovations).

6. 1970's Marshall Master Volume
in----G1---------volume----G2----------------G3---------------------EQ---master volume--->

Marshall, taking ideas for amp techs who were already modifying their amps, and from Mesa's new Boogies, decided it should manufacture a master volume amp. Guitarists wanted more distortion from their amps, and they wanted it at lower volumes. Marshall's solution was to add one extra gain stage, which gave its 1970's Master Volume amps a lot of crunch. Not the super saturated gain demanded by metal players in the late 1980's, but perfect for crunchy 70's riffing.
Notice that Marshall didn't simply clone the Mesa-Boogies. They kept the EQ at the end of the preamp, not the beginning, like in Boogies. They also didn't use as many gain stages.

7. Early JCM-800's with diode clipping
in----G1---EQ---gain---G2---DIODES---volume--G3--loop--Phase Inverter---master volume--->

This complex circuit was Marshall's first attempt at mixing tube and transitor distortion in its larger amplifiers. The mix of tube gain and diode clipping produced more distortion, but some players thought the sound was too "buzzy" and "thin" and "cold" compared to Marshall's all tube designs.

8. Later JCM-800's, and JCM-900's with diode clipping (diodes in rectifier circuit)
in----G1---------volume----G2---DIODES----G3-------------------------EQ---master volume--->

Marshall refined the concept in its late JCM-800's and JCM-900's. Using solid state diodes is a lot cheaper than adding new tube gain stages, and many of the new hard rock and metal players were beginning to appreciate the harder sound of these amps.

9. Bogner "FISH" preamp (Brown Channel) Marshall 30th Anniversary (Lead Channel)
in----G1---------volume----G2--------------G3----G4----------------EQ---master volume--->

More tube gain, no transistors, not diodes. This style of preamp produced tons of thick, saturated overdrive and distortion. It's more expensive than just adding some diode clipping circuits, but to many using an all tube signal path sounds warmer, fatter, and richer.

10.Soldano lead channel
in---G1---------volume----G2--------------G3----G4----G5---------EQ---master volume--->

The same approach as the 4+0 circuit, with an extra gain stage for truly insane amounts of distortion. Some people would say adding a 5th gain stage was unnecessary, as 4 tube gain stages are usually enough for very saturated distortion.

11.Peavey EVH 5150
in---G1---------volume----G2--------------G3----G4-----G5---G6---EQ---master volume--->

This is perhaps the extreme of tube preamp gain. Six gain stages produces insane amounts of distortion, which seems to be what Eddie Van Halen wanted. This circuit is similar to the Soldano circuit; the third gain stage using a large 39K cathode resistor, which greatly reduces the amount of gain from the third stage. Later in the amp, large resistors also reduce gain to managable levels. Eddie seemed to want an amp that was just on the verge (edge) of being totally out of control, and most players who've used the 5150 agree that this amp is on the edge of being out of control.


Fender's 1950's "Tweed" Amps

Most old Fender amps from the 1950's had a warmer, darker, more compressed sound than many of their later 1960's "blackface" amps. Fender used tube rectifiers in the power supply, which gave the amps a more compressed feel and sound. Fender also used cathode biasing of the power tubes in some amps, which further added to the compression effects. Using tube rectifiers and cathode biasing made the amps "sing" and sustain more when pushed into overdrive. Perfect for bluesy solos.

Not all Fender amps used cathode biasing, the famous 5F6-A Bassman from 1959 used fixed bias on the power tubes, which gave the amp a less compressed sound.

Fender used 6L6 and 6V6 power tubes. Some think of a 6V6 as a smaller version of the larger, more powerful 6L6. 6V6's distort more easily than do 6L6's. Be careful with 6V6's manufactured today, as they cannot withstand the higher voltages used in older Fender amps. 6V6's manufactured then were better able to take the high B+ voltages Fender amp used.

Marshall's 1960's Amps

Marshall's first amps were almost exact clones of the 5F6-A Bassman.
Marshall separated the speakers from the amplifier by using a "head" for the amp, and speaker cabinet to house the speakers. The closed back cabinet with four 12 inch speakers made the Marshalls sounded punchier than the Bassman, with its 4X10 inch speakers. These early Marshalls still used a tube rectifier, and thus still had some of the sweet compression of the Bassman.

Marshall was using 6L6 style power tubes, including 6L6's, 5881's, and the fantastic sounding KT66's. While KT66's are in the 6L6 family of power tubes, they have a more aggressive tone that many players prefer. Genuine KT66's (there have been rumours of low quality 6L6's being relabeled KT66's) haven't been made in many years, and NOS (New Old Stock) KT66's cost hundreds of dollars. NOS tubes are old tubes that have never been used. They are "New" in the sense that they have never been used. They are "old" in the sense that they were manufactured very long ago. Hence the term "New Old Stock". Another great 6L6 equivalent is the EL37, which is also expensive and hard to find. These are also NOS tubes. Again, NOS is NOT a company, it is simply a way to describe old tubes which have never been used.

Marshall shifted to using EL34 power tubes in the mid-1960's. EL34's are a very different power tube than a 6L6. EL34's have a very tough, midrangey sound when overdriven. This is the tube that most people consider to have the classic Marshall tone. Most Marshall amps in the 1960's used Mullard EL34's, which are no longer made. Today, many amp techs think the Svetlana EL34 sounds the closest to the Mullard EL34. The Svetlana seems to be able to withstand higher voltages better than many other companies' EL34's.

Another big change in Marshall amps around the same time was the change from tube rectifiers to rectifiers using solid state IN4007 diodes. This gave Marshall amps less compression, with faster response to transients (sudden changes in volume, like when you pick a string very hard). Like many changes to Marshall amps in the 1960's, the use of solid state diodes in the rectifier gave the amp a more aggressive sound.

At the request of the Who's Pete Townsend, Marshall began making 100 watt amps. The first few prototypes used the excellent KT66 power tubes, but these were quickly changed to EL34's, which were cheaper and more available in England at the time.

Marshall's 100 watt heads used extremely high voltages on the EL34's plates-around 530-560+ volts! Many EL34's manufactured today cannot take such high voltages. By the early 1970's, Marshall had lowered to voltages in their hundred watt heads to well below 500 volts (450-470 volts in some amps). This was still quite strong. The use of higher voltages in the 100 watt heads gave these units a more powerful sound than the 50 watt head, which had the EL34's plates at just under 400 volts.

Tubes run at lower voltages distort more easily, and have a softer sound than tubes run at higher voltages. With preamp tubes the distortion may also change. An individual gain stage will not distort as easily if it has higher voltage on its plate, but it will have more gain than a tube run at lower voltages.

Many players wanting a smoother, more compressed sound prefer the 50 watt Marshalls. Some players who either presently use of have used 50 watt Marshalls: Allan Holdsworth, Jeff Beck, Angus Young, and Yngwie Malmsteen.

Preamp Changes (1960's, early 1970's)

The basic circuit topology (circuit architecture) remained the same: both Fender tweeds and the 1960's Marshall amps used the same 2+0 preamp style (2 gain stages followed by EQ). Marshall's main modification were adding brightness capacitors for more treble, replacing lower gain 12AY7 preamp tubes with higher gain 12AX7's, and greatly increasing the voltages on the tubes plates.

Still, if you look at the schematic for a 5F8-A Fender Twin from the late 1950's and a very early 100 watt Marshall, you'll see they are extremely similar, with almost identical parts in the preamp.

Marshall modified the preamps in their early1970's amps for a little more gain and even more treble. The treble and normal channels were revoiced to have more distinct sounds.

Fender's 1960's Amps

Fender made a gradual transition away from the tweed circuits. Many of the early 60's amps had tube vibrato, which unlike tremelo, actually changed the pitch of the notes, not just the amplitude. These vibrato circuits required many tubes, so Fender eventually replaced them with simpler tremelo circuits, which just modulated the pitch of the notes.

The mid-60's was Fender's famous "blackface" period, named for the black face of the control panels of the amps. The preamp circuitry was markedly different from the 50's tweed era. Instead of having two gain stages before the EQ, the blackface amps positioned the EQ right after the first gain stage and before the volume control.

Another important change was the inclusion of a reverb channel on many of the blackface amps. The reverb channel tapped a tiny portion of the signal just after the second gain stage, fed it to a 12AT7 tube set up as a miniature power tube, which in turn powered a spring reverb tank. The signal was taken from the spring reverb, re-amplified with a gain stage, and fed back into the reverb channel just before the third gain stage.

stage1--EQ--volume---stage2-----RESISTOR-------stage3----->
                            | |             | |
                             > REVERB CIRCUIT^

These blackface amps had a cleaner, brighter sound than many of the earlier tweed Fenders. This was due to many factors. Repositioning the EQ between stages1 and 2 made it harder for the first stage to overdrive the second, as EQ circuits tend to "eat" a lot of signal. The large 3.3. Meg Ohm resistor between stages 2 and 3 also reduced signal strength. The use of higher B+ voltages made for a stronger, cleaner sound in both the preamp and the power amp. The power tubes were fixed biased, so they didn't compress the sound the way cathode biased tubes do. The EQ circuit had a more pronounced midrange "cut" than most of the 1950's tweed amps. Finally, many of the more powerful Fender amps from this period used solid state rectifiers, which make the amp produce a sharper sound with faster tracking of transients (sudden increases in volume, like from plucking a string hard).

The signal path remained all tube, so the sound was still quite warm. The Fender Deluxe Reverb amp from this period, with its slightly lower B+ voltages and tube rectifier, has an excellent rock and blues sound. It has a beautiful, shimmering clean sound at lower volumes, and a wonderfully fat distortion when cranked. (turned up loud). Not quite as rough as a Marshall, but great for blues and blues-rock.

CBS bought Fender in 1967, and within a year or so was making horrible amps. CBS changed the circuitry of many of the tube amps, and musicians did not like the sound of the new Fender amps. CBS also changed the control panel from black to an ugly silver, and as a result these CBS amps became known as silver faced Fenders. CBS did reverse many (but not all) of these circuit changes when they realized musicians hated the new amps.

Changing a silver face Fender back to a blackface circuit usually involves modifying the driver/phase splitter circuit back to blackface specifications, removing two 2,000 pf caps just before the power tubes, and possibly the hardest part, re-routing the wires (they physical placement of wires) to reduce oscillation. This cannot always be done successfully.

An example: the AB763 circuit is a blackface Twin (the one most say sounds better), and the AA769 and AA270 Twin circuits are examples of the "silver face" Twin. One of the differences is that the 12AT7 driver tube of the blackface Twin uses an 82K resistor on one tube plate, and a 100K resistor on the other plate. The silver faced Twin's used 47K plate resistors, which provided less gain.

Mesa Boogie Amps

These evolved out of Randall Smith's experiments with Fender amps. While there were many techs at the time experimenting with increasing the gain of both Marshall and Fender amps, Randall took the concept further than most. He added tube gain stages to the end of Fender preamps; and between the preamp and the power amp, he added a master volume. This allowed players to push the preamp tubes deep into distortion, yet send just a tiny portion of this distorted signal to the power amp. So at low master volume settings, the power amp ran (operated) clean. Previously, a distorted amp had both preamp and power amp distortion, as there had been no master volume to "dam up" all the preamp gain. Master volumes allowed players to get distorted preamp sounds without loud, distorted power amp tones.

A lot of rock and blues players didn't like this sound, as they felt it was too one dimensional and "stiff", compared to the more complex sound of a whole amp (both the preamp and power amp, and the speakers) distorting. Nevertheless, for every player who didn't like this sound, it seemed that there was another who loved the high gain saturation these Mesa Boogie amps got. Another complaint was the Mesa's clean tones, while quite similar to Fender's, didn't sound as natural or rich as the clean sound of say, a 1965 Fender Twin.

Through the 1970's and 1980's, Mesa continued to refine their Boogie amps, from the original Mark I's, to various Mark II's, Mark III's, and finally, the Mark IV, which is a much more complex amp that the original Mark I. These amps are all "Boogie's"-they all share the use of pre-distortion EQ. The EQ is positioned just after the first gain stage. There are subtle and not so subtle differences in the tones of all these amps, but they come from the same general "family" of circuits. Boogie amps are thought to have a smooth, very compressed, "L.A. studio player" tone.

Mesa's newer "Dual Rectifier" amps are not of the classic Boogie design, but instead are much more like Soldano amps. They have the EQ newtork at the *end* of the preamp, just like Marshall, Soldano, Bogner, VHT, and other "British" style amps. These products have a more aggressive tone that's more suited to grunge and metal.

Marshall's 1970's Master Volume amps

Beginning in 1974, Marshall rolled out their new master volume amps. Marshall began making them in part as a response to Mesa's Boogie amps, and in part to give rock players what they were asking for: Marshall crunch at lower volumes. Marshall kept the EQ at the end of the preamp, and simply added a gain stage so that there were 3 stages of gain before the EQ, not 2 as in the previous Marshall amps. [Marshall kept making the old style, non-master volume amps throughout the 1970's.] With the gain set high and the master low, this gave preamp only distortion. For sure, it sounded like a Marshall, but not the same as an old non-master volume head cranked to 10, which had both preamp and power amp distortion, a tonally more complex brew. Nevertheless, it was a reasonable compromise for many guitarists. Early JCM-800's with diode clipping

By the early 1980's, Marshall was producing amps that mixed tube and transistor distortion. The transistor distortion was accomplished by adding "diode clipping" circuits among the tube preamp gain stages, which gave the amps a lot more distortion, but sacrificed warmth. The tubes before the diodes helped to push guitar signal into the diodes, where they were clipped (distorted), and the tubes after the diodes both amplified and "warmed up" the sound somewhat. These and later Marshalls had a bright, buzzy distortion, especially at low volumes. When cranked up loud, the power tubes would begin distorting, thickening up the sound to reduce the harsh, thin, buzzy distortion. Another unsual (for Marshall) feature was that the EQ was positioned early in the preamp, just after the first gain stage. This would be changed on later JCM-800 models: moved to after 3 gain stages, just like on the 2203 amps. And the new 4210/2205 amps sported (had) an effects loop, something new for Marshall. This allowed guitarists to put their delay pedals after the preamp distortion for cleaner delays. Finally, Marshall used a post phase inverter master volume for these amps. Marshall would later change back to a master volume after the EQ (but before the phase inverter) much like the 2203 amps.

Some metal players loved these new Marshalls, whereas many older rock and blues players hated them.

The 1980's marked a confusing period for Marshall, as they were simultaneously still making 1. non-master volume amps: circuits 1987 (50 watt model) and 1959 (100 watt model), 2. 1970's style Master volumes (circuit 2203-all tube signal path), and 3. the new models with tubes and transistor distortion mixed, like the 50 watt 4210.

Many players call all 2203 style master volumes JCM-800's, but these 2203 amps were being made long *before* Marshall began calling their amps JCM-800's. Also, there were JCM-800's being made which used diode clipping, and thus were *not* the older style 2203 circuit.

So, if you hear someone talking about a "JCM-800", he could mean an all tube 2203 master volume circuit (first produced in the 1970's, and which Marshall continued to make in the 1980's). Or he could be talking about one of the newer circuits with diode clipping, first made in the 1980's. You could ask him "What model number are you refering to?". Or "Are you talking about the 2203 circuit with an all tube signal path, or the circuits with the mix of diode clipping and tube distortion?" If he says something stupid like "All JCM-800's are the 2203 circuit! No JCM-800's have diode clipping!", then you can tell him he's full of shit. (i.e. he's either lying or just plain ill-informed) You can say, "Marshall's 50 watt combo (model 4210) and 50 watt head (model 2205) both use diode clipping. Just look in the "History of Marshall" book.

Marshall's later JCM-800's

Marshall modified the new design, and a 1988 schematic for the 2210 (head) and 4211 (combo) amps show an extra tube gain stage after the diode clipping. The diode clipping itself had been altered to a more complex arrangement-more like a diode bridge rectifier, and the EQ was repositioned to after the third gain stage. Much like the 2203 amps.

For Marshall's 25th Anniversary, they came out with the Jubilee amps, favored by Slash or Guns and Roses, and recently reissued as the "Slash" amps. These are among the most popular JCM-800 amps, which is somewhat ironic, as they probably have to greatest use of diode clipping. Which at low volume, to my ears, makes the amps sound too trebley. When cranked, however, they can get an aggressive, yet warm tone. Listen to any Guns and Roses record, or the guitar solo in "My Mama Said" by Lenny Kravitz. You'll notice Lenny's rhythm guitars sound edgy and bright, but when Slash starts his solo, his tone is thicker and meatier with less high end "buzz" and more "throat." It could well be the EL34's being overdriven.

Marshall's JCM-900 amps continued to rely on pretty much the same formula as the later JCM-800's. There were lots of differences (some of which added gain), but the basic style remained the same: two gain stages in series, diode clipping, third gain stage and EQ and master volume. Some JCM-900 amps used IC's (transistor opamps) for additional gain. Some claim that Marshall began using lower quality components in these JCM-900's, which reduced reliabity. I've heard complaints that the output transformer blows up more easily at high volumes than the output transformers used in earlier Marshall amps.

Marshall designed these amps with the late 1980's metal players in mind, so they have a lot of gain and thin, buzzy transistor clipping mixed in with the tubes. Some amp techs find old JCM-900's used for low prices, and peform extensive modifications to these amps to convert them either to the 1960's style circuits (#1959, #1987), or the 1970's #2203 circuit. These mods are not cheap, but they give the amp a warmer all tube sound.

Doug Hoffman makes some point to point wired boards perfect for converting some JCM-900's to an early Marshall/tweed Bassman circuit. It still requires a lot of work, but less so than making the boards yourself.

Bogner "FISH" preamp (Brown Channel) Marshall 30th Anniversary (Lead Channel)

As many rock and metal players' tastes matured, they began realizing that while they loved the *amount* of distortion the new Marshall amps had, they didn't like the *quality* of it. They wanted the aggressive tone of Marshall amps, but with more underlying warmth, much like Eddie Van Halen's sound. Eddie had led people to believe that his Marshall amp had been heavily modified, so that seemed the natural route for other guitarists to take.

Old Marshall heads from the 1960's and early 1970's were used for both their stock sound, and the fact that their construction made them very easy to work on. Newer amps used printed circuit boards, which were hard to modify.

Guitarists and amp techs began adding master volumes and additional gain stages. Some simply changed some of the resistor and capacitor values in 2203 amps to increase the gain of exisitng stages. Others took the more radical approach of adding entirely new gain stages, which greatly increased the amount of distortion. One of the more popular circuit configurations that came out of this "hot modding" phenomenon was the "4+0" circuit: gain stage, gain control, three more gain stages, EQ, master volume, then the power amp.

Not all of the modificiations sounded good. In fact, many great sounding stock amps were butchered into amps which were noisy, unreliable, and bad sounding. Guitarists found that it's not hard adding gain-what is hard is making the gain and resulting distortion sound MUSICAL.

Some of the more talented amp techs with sharp (good) ears were able to create some good sounding circuits. One was a Mr. Reinhold Bogner, whose "FISH" preamp was popular in the early 1990's. Unlike Boogie amps, each channel was almost completely independent. The highest gain "brown" channel used the 4+0 configuration, the two other distortion channels (Strato and Shark) used the lower gain 3+0 circuit. The Brown and Strato channels are very similar to Marshall circuits, with a shared Marshall style EQ after the gain stages. The Shark channel is a lot like a Vox AC30's Top Boost channel with an extra gain stage. Even the EQ on this channel is very Vox like. It doesn't completely capture the Vox AC30 sound, of course, because its lacking the AC30's power amp and speakers, which are a very important part of the Vox sound.

There were also other amp techs who either modified Marshalls to the 4+0 style preamp, or began making their own amps and preamps with this type of circuit.

Marshall eventually decided to use some of these ideas for it's 30th Annivesary amp (model #6100). While the amp does use some solid state devices, most of the preamp uses an all tube signal path. Gone are the diode clipping circuits common to the JCM-900 and many JCM-800 amps.

The lead channel uses a 4+0 circuit. It is unusual in that after the second, third, and fourth stages, there are "cathode followers". Cathode followers are usually one of the two triodes in a 12AX7 set up to lower the impedance of the signal. Some amp techs claim cathode followers add more "crunch" to the sound. It is normal for a Marshall style circuit to use a single cathode follower just before the tone controls, but not after each gain stage.

Soldano lead channel

Michael Soldano is the person who made the super high gain Marshall sound famous. Some of the Marshalls he worked on he modded to the 4+0 circuit, but for his SLO-100 amp, he added a fifth gain stage to make a 5+0 circuit. It is debatable as to whether or not this extra gain stage is really needed, as four gain stages is usually enough for very saturated distortion sounds.

Unlike most Marshall amps, Soldano amps use 6L6/5881 power tubes instead of EL34's. Other makers of high gain British sounding amps, have decided to stick with EL34's, or offer a choice of EL34's or 6L6/5881 power tubes. One reason for this is that in the late 1980's and early 1990's, it was becoming hard to find good EL34's. Luckily, in 1996, we have more choices for this famous tube. Svetlana's new Gold Top EL34's have been getting very positive reviews in the press and on the Internet, and even Marshall, which had switched to 5881's for many of its amps, has decided to go back to EL34's for many models. Svetlana claims their Gold Top EL34's are modeled after the famous Mullard EL34's used in most of Marshall's 1960's amps. They also claim that the Gold Tops are able to withstand higher voltages than the older Mullards, which is good news, as some of the newer EL34's cannot take the higher voltages found in old Marshall amps.

Peavey EVH 5150

As I've already stated, this amp uses 6 gain stages before the EQ. A 6+0 arrangement. Unlike many other high gain Marshall style amps, there is no cathode follower before the tone network, so the EQ is fed high impedance signal from the plate of the 6th gain stage, not a low impedance signal from the cathode of a cathode follower.

This amp's circuitry is very similar to the Soldano SLO-100. Mesa's Dual Rectifier amps (Dual Rectifier, Trem-o-verb, and DC series amps) also have similar lead channels to the SLO-100. These Soldano, Peavey, and Mesa amps don't sound exactly the same for a variety of reasons: the physical layout of components (lead dress), the quality and type of the components used, some circuit differences, etc.

OTHER HIGH GAIN AMPS AND PREAMPS:

There are now many great sounding high gain amps, such as:

VHT Amplification:

VHT's products are like a combination of a hot rodded Marshall (modified for high gain) and a Hiwatt. Some players claim that VHT's high gain sound is the clearest and most focused of any hard rock or metal amp. The name of their most famous amp, the "Pittbull" should give you an indication of the sound. [Pittbulls are very aggressive, vicious dogs.] VHT amps get great reviews in the guitar magazines.

Custom Audio Electronics:

CAE is most famous for their CAE 3+ preamp, which can be found in the racks of a lot of famous guitarists. It is my personal favorite. I love this preamp. It has an outstanding Fendery clean channel and two extremely rich and aggressive Marshall like lead channels. CAE's lead sounds, while definitely aggressive, seem somewhat more refined than the lead sounds of other amps, like VHT, Bogner, and Egnater. CAE also makes a two channel 100 watt head that sounds great.

Bogner:

Bogner has stopped making the FISH preamp, and is now making just amps. Their 100 watt Ecstacy is has been used by a lot of players, including Steve Vai, and Brad Whitford. The Ecstacy is known for having a sound very similar to old Marshall "Plexi" heads from the 1960's, but with more versatility. The amp has a lot of switches, but it can generate both "old" and "new" amps sounds. It also has the benefit of a terrific clean channel, much like a 1965 Fender Twin, but with more headroom.

Egnater:

Wonderful amps made in Michigan. Bruce Egnater, the company president and chief designer, manufactures both super high gain, multi-channel amps and lower gain amps more similar to vintage Marshalls and Fenders. Egnater amps and preamps also get great reviews in the guitar press. I recommend checking out (trying) their TOL 100 head, which has four channels.

Fat Boy:

This company isn't very well known. They make very good sounding amps which are definitely worth trying if you have a chance.

Wizard:

The same story as Fat Boy-very good sounding amps worth listening to.

THE "RETROS" TREND

By the early 1990's, a lot of guitar players in the U.S. were tiring of(becoming tired of/bored with) high gain preamp sounds. They wanted to return to the sound of power amp distortion, which they percieved as sounding more complex and dynamic than "sterile" high gain preamp distortion. They felt high gain amps were 1. too "cluttered" with preamp gain and 2. didn't deliver sounds that were as rich and "organic" sounding. So, instead of adding even more gain stages, they wanted amps with *fewer* gain stages, and no master volumes!

Some manufacturers like Marshall and Fender began reissuing their older, classic non master volume amps. Some small manufacturers began making their own version of older Fender amps, in part because they felt that Fender's reissues used cheaper construction methods (printed circuit boards) that didn't accurately capture the rich sound of the older amps, which were point to point wired. Today, there are several manufacturers making Fender style "tweed" amps, one of the most popular in 1996 being Victoria.

Fender and other companies such as Peavey, Carvin, Crate, and Mesa also began offering new designs which they claimed offered a more "vintage" like sound, with less preamp gain than their 1980's amps.

Some of the newer "vintage" style amp companies and amp designers include: Matchless, (Tony) Bruno, (Cezar) Diaz, Victoria, Holland, Budda, Guy Hendricks (Guy-Tronics), Naylor, (Kim) Hoffman, (Doug) Hoffman, Trainwreck, Hound Dog, Dr. Z, Penn, Top Hat, Matt Wells, and Tone King. There are more companies, and many, many more custom amp builders in the U.S., some of whom do great work, some of whom just *think* they do great work but in reality make overpriced shit. Always: TRY BEFORE YOU BUY!!!

Not all of these companies and people make Fender style amps. Some, such as Matchless, and Bruno, make amps similar to original Vox AC30's. Budda is famous for low watt amps that sound like a great Marshall from the 1960's. Some make amps which are inspired by both Marshall and Vox sounds (Trainwreck, Hound Dog).

KOREA, ASIA and EUROPE:

It is interesting that the trend toward vintage sounding amps is strongest in America. It hasn't become as popular in Europe or Asia. I know an amp tech in Germany and one in Sweden who both still love high gain preamp designs. Nearly all of my guitarist friends in Asia still love high gain sounds, even those who are now interested in vintage guitars.

I know a Korean rock band that bought a used early 1970's Marshall, and couldn't get a sound they liked out of it. They said the sound too clean. I told them they had to crank it up to "10" to get distortion from it, and even then it might still not be distorted enough, they might have to use an Ibanez TS-9 Tubescreamer to push the amp deeper into distortion. I also told them they should get the amp serviced, replacing worn out old parts, like the filter caps and tubes. Eventually, they decided the amp was too much trouble-they couldn't crank it up to "10" because their neighbors would complain, they didn't have enough money to have the amp serviced, and they wanted an amp with more distortion. Vintage amps may be "cool", but they are not for everyone!

I can tell you that an old Marshall, Vox, or Fender amp that has been properly serviced, can sound fantastic, with some great distortion tones. [Eddie Van Halen now claims that the Marshall amp he used for his early albums was a completely stock Marshall, with no additional preamp gain. He claims he simply turned up all the knobs to "10" to get his overdrive.] But it takes some work, and you need to be able to play the amp near full volume to get overdrive. Which not only makes your neighbors angry, it can destroy your hearing!

If you do come to the U.S. to try some of the amps by Budda, Victoria, Bruno, Tone King, Hound Dog, etc. make sure you are in a store that allows you to test the amps at both low and high volumes. Try using a variety of guitars with it. Try the amps with some pedals, too. IMPORTANT: Don't expect the same sounds and "feel" from these amps as you would a JCM-900 or ADA MP-1 preamp! While some of the vintage style amps can get suprizingly thick overdrive, it's a mix of preamp, power amp, and in some cases, speaker distortion. It's a new universe of sound to players used to modern amps. A lot of the "magic" lies in the "in-between" sounds, being just on the edge of distortion. Try varying your pick attack from light to heavy. Try adjusting the volume knob on whatever guitar you are playing to hear all the different "shades" and "colors" of distortion from the amp.

Realize that amps without master volumes may not be what you really need. But you won't know this until you try several non-master volume amps. It takes time for some players to get used to these products-time to adjust your playing techniques and ideas about tone. Luckily, there are some terrific amps with moderate to high gain and master volumes (CAE, Soldano, VHT, Naylor, Egnater, Wizard, etc.).

THE DIYS (Do It Yourself) TREND:

In America, guitarists are becoming increasingly knowledgeble about their amps. It's like the 1970's, when guitarists realized they could modify their guitars, by changing pickups and other parts to get custom sounds. In the 1990's, guitarists are doing similar things with their amps. This doesn't always mean modification. Guitarists' increased sophistication about and knowledge of amps means they are better able to choose among stock (unmodifed) guitar amps. There are many more amps to choose from, and the overall quality of sound and construction have increased in large part due to guitarists learning more about amp sounds and construction.

But there are a growing number of American guitarists who are working on their guitar amps. There are many new books explaining how amps work, the history of famous amp companies and their products, and beginning in 1997, there will be a new magazine published by Audio Amateur Publications, Inc. for people who build, modify, and repair guitar amps and effects. There are new kits for guitar amps and preamps.

Keep this in mind: WORKING ON GUITAR AMPS IS VERY DANGEROUS!! YOU CAN KILL YOURSELF EASILY!! It's hard to kill yourself working on a guitar, but guitar amps contain lethal voltages, some up to 600 volts DC. So think very, very hard before learning how to do this work.

WORKING ON AMPS: THE EASY, SAFE WAY

Instead of working on amps yourself, you could pay a Korean technician familiar with tube electronics to build you some preamps and amps. First, try learning about tube circuitry. You can buy tube guitar amp books, and you can read articles about amps on the World Wide Web. If you have a basic understanding of how guitar amps work, then, when you decide to pay a Korean amp tech to build you a tube preamp or amp, you will be able to communicate with him about the kinds of sounds you want-and the circuits which make these sounds.

It's one thing to say "I want more distortion." That is a very general statement, and your Korean amp tech may not be familiar with modern guitar amp circuits which create distortion. But if you tell him this: "I want more preamp distortion. I want you to add more tube preamp gain stages. Because I know, the more preamp stages, the more gain the amp will have. And more gain leads to more distortion. I want you to make a preamp circuit like this, using 12AX7 tubes: input--gain stage1---volume control--gain stage2--gain stage3--gain stage4--cathode follower--EQ (bass, mid, treble)--master volume---out" Then he will have a much clearer idea of how to help you. This is much more specific information. More specific, detailed info:

An even better idea is to show him some schematics (circuit diagrams) from some guitar preamps and amps. You can get many schematics from tube amp books, and the World Wide Web. I have many high gain schematics at my web page: http://www.Channel1.com/users/monadyne/Keenan/ Print out both the GIF's for the circuits, and the text files which go with each circuit style (1+2, 3+0, 4+0, etc.) You have to look for them, but they are there.

You'll need two kind of voltages, high "B+" voltages and low voltage to heat the tubes. Tell you amp tech you'll need a high voltage power supply for the B+ voltage, which can be anywhere from 200 volts up to 400 volts for a tube preamp (Tell him "at least 3 milliamps per 12AX7S). You'll also need voltage to heat the tube. Tell him you want 6.3 volts DC, rectified, filtered, and regulated. At least 300 milliamps per 12AX7 tube. Tell him you want "bleeder resistors" attached around the filter capacitors to safely discharge the stored energy. 220K resistors will be okay. Tell him you want your amp or preamp to have a "standby" switch that lets the tubes heat up using the 6.3 voltage supply, but keeps the high B+ voltage off. After 2 or 3 minutes, then you can turn the standby switch to the "on" position, which turns on the high voltage B+. Doing this will make your tubes last much, much longer. Tubes should warm up first before any high voltage hits them. Applying high voltage to cold tubes makes them wear out much faster.

And print out some of the articles from the world wide web that deal with this material. Show these articles to him. Let him take them home and read them.

You can then work closely with the engineer, because you'll have enough electronics knowledge that you can "speak your engineer's language". You don't need to know as much as your engineer, you just need to know a moderate amount about tube circuitry. What you'll really need the engineer for is protecting you from the high voltages. Your amp tech can implement the ideas you have, actually building the circuitry in your mind. His hands will be on the amp, your hands will be away from the amp. You'll just be looking at him and the amp while he works. Keep your hands OFF of the amp. Let your tech do the actual work! After a while, you may learn enough from him to begin working on amps yourself. Have him teach you about safety.

Instead of just building a high gain tube preamp, you could have your engineer build you a 5F6-A Fender Bassman. You can get parts for such a kit from Doug Hoffman in Florida. Look for a link to his web page at the "Ampage" web page, under "Manufacturers". Remember, a tube guitar amp ALWAYS needs a speaker [or speakers] to work!! NEVER turn on an amp unless it has a speaker of the correct Ohm rating attached, using speaker cable, NOT guitar cords!!