The output transformer plays a very large role, but is not everything in shaping an ampās tone. Upgrading it takes what the amp already is, and then enhances it.
I am often asked how upgrading an amplifierās transformers will improve tone. Itās a simple enough question, but the answer is a little complex. First off, letās examine what an output transformer is and why someone would inquire about replacing it. Then weāll get to some things to consider when replacing your ampās transformer.
The output transformer in a push-pull guitar amplifier is the last stage of the audio path before getting to a speakerāitās one of the large blocks of metal mounted to the amp chassis (or speaker, as is sometimes seen in older amps). The transformerās function is to convert the high-voltage/low-current signal from the amplifierās power tubes into a low-voltage/high-current signal to power the speakers at a low impedance. It is responsible for how efficiently the audio power of an amp will transfer to the load of the speakers, and it prevents hundreds of volts (DC) from passing to the speakers.
There are different reasons why a person would want to change their output transformerāthe most obvious being a blown or damaged unit. This can happen when an amp is operated without a proper load, such as not having a speaker plugged into the amp or driving a different speaker impedance than the one the output transformer is looking for. Another reason to replace a transformer is to upgrade quality and tone. Because transformers are the most expensive component of an amplifier, it is common for amp manufacturers to cut costs on the size and quality of them. A large transformer simply has more iron, so not only are the material costs higher, the weight of heavier transformer will affect a manufacturerās shipping costs.
In regards to tone and how an output transformer affects it, itās my opinion that an output transformer does not change an ampās character. A new transformer will not change an ampās DNA or make a Marshall sound like a Vox. After all, an amplifierās tone is the sum of all of its partsātubes, capacitors, wiring, speakers, etc. If you were to run clean water through an old, dirty water filter, you would ruin what the water had to offer before being filtered. It would still be water, but changed in a way that detracted from what it could have been. The output transformer plays a very large role, but is not everything in shaping an ampās tone. Upgrading it takes what the amp already is, and then enhances it. Physically larger output transformers generally sound larger, since they have a larger window for tone to flow through. Tone is usually clearer, fuller and truer.
If upgrading or replacing your ampās output transformer is in your plans, there are a few things to consider. First, and most importantly, the amp should be unplugged, all tubes should be removed, and all voltages in the amp should be fully discharged. There are lethal voltages inside an amplifier, so do not service your amp if you donāt know how to properly discharge all voltage.
Finally, make sure the replacement transformer will physically fit on the chassis and in the cabinet itās going into. It is easy to forget the size of the speaker and its affect on the space left in the cabinet. Measure twice to avoid disappointment!
It is very important to note the wiring of the old output transformer. I often clip the old transformer leads and leave a little bit of the old wire so I can see the color and location of the original. Keep in mind that green or black is not always ground, and that manufacturers often use different colors for the ground. A new replacement transformer should come with a schematic, so pay careful attention to it and note the proper wiring.
With the new transformer installed and all wiring and solder joints double-checked, itās time to turn on the amp. Before doing so, be sure to turn all pots all the way down. If the primary leads on the transformer are reversedāa simple mistake to makeāthe amp will produce a loud squeal. And if the volume were to be up with this squeal, it would scare the life out of anyone. A simple swapping of the leads going to the power tube plates will take care of this issue. It is a good idea to use a variac to ramp the amp's voltage up gradually, going easy on the new output transformerās maiden voyage. When the amp is running at full-voltage, you should then turn the amp off, reinstall the tubes, turn it back on, and double-check the power tube bias. The new output transformer will need to break-in over time, but all thatās left now is enjoying your amplifier's improved tone!
Remember that an amplifierās tone is the sum of all of its parts. The output transformer is one very important part that easily gets overlooked and often suffers from cost-cutting-minded amp builders. So experiment! After all, your amp is your voice, so why not make it the best voice it can be?
Jeff Tweedy''s Fender Princeton is on the bench for a summer tuneup.
Temperatures are warming, music festivals are on the rise, and summer is officially around the corner. Working bands will be hitting the road and taking to the sky, spreading their music across the world. But is their gear up for the task? Gear is the lifeblood for any bandāwithout it, musicians cannot do their job and make a living. And while no piece of gear is completely ābullet-proof,ā there are steps we can take to ensure our gear possesses the most important quality it can have on the roadāreliability.
One band that recently got ready to tour is Wilco. These guys are notorious road dogs and are known to carry a vast array of gear on tour. In this article, we will look at front man Jeff Tweedyās early-ā60s brownface Fender Princeton 6G2-A and getting it ready for their tour.
This amp came to the shop in working order and sounding great, but needed a good cleaning and check over for reliability. At first glance, I noticed that this amp has mostly original components, with the exceptions of the filter capacitors and one of the cathode capacitors in the preamp. Had these capacitors not been replaced, from a reliability standpoint, consideration would have been seriously given toward replacing them. Electrolytic caps, generally speaking, have a life span of around 15 years. After this time, the electrolytic inside the cap can dry up and/or, as is often seen, the capacitor will begin to leak. You will usually see bulges and/or leaks from the positive end of the cap. In the case of this Princeton, only one capacitor in the preamp was original, so it was replaced with a high-quality capacitor of the same value. I always give the original components back to the client, especially in the case of a vintage amp. This way they have all the original partsāgood to have for a possible future sale.
As I progressed further into the amp by checking the resistors, caps, wiring, solder joints, and cleaning/tightening the tube socketsāI considered the tubes. There is a 5Y3 rectifier, two 6V6 power tubes and two 12AX7 preamp tubesāall vintage. The preamp tubes, a vintage Bugle Boy and a vintage Tung-Sol, were left alone after testing output and carefully listening for microphonics and noise. These great sounding and reliable tubes have survived many years and should survive many more. The rectifier tube appeared to be in great shape and was left alone. However, the power tubes were replaced with some known reliable ones because power tubes tend to have a shorter life span than the other tubes in an amplifier. When reliability and the demands of touring are important, itās always a good idea to replace them. It is also a good idea, as a tech, to give the owner of the amplifier an extra set of tubes of the same bias as the ones you are putting in. If the tubes fail on the road, the band can replace them on their own, without worrying about proper tube biasing. I also like to tape an extra fuse or two to the inside of the ampās cabinet, just in case a fuse blows. These simple things can make an amp failure much easier and less expensive to manage when on the road.
It is important to take a close look at the wiring of an amp before it goes out on tour. Old wires can oxidize and become brittle with age. With the amp on and a signal going through it, it is a good idea to nudge the wires to look for signs of wear and listen for changes in output. Any crusty, worn, blackened, or fragile wires should be replaced with new wire. Also worth checking out is the AC power cable. This should be quality three-prong grounded cable. Touring musicians have more important things to worry about than the possibility of a great-sounding amplifier having the potential of causing them electric shock.
The last step with this Princeton is playing it. I inspect the speaker for unreasonable wear and then turn the amp up to listen to the speaker. Like changing summer to winter tires on a vehicle, a musician will occasionally want to save their vintage speaker from the abuse it may take on the road, and opt for a temporary speaker replacement. Itās also a good idea to burn the tubes in by running a signal through the amp and into a dummy load. This will push the tubes as if you were playing the amp loudly, but save your ears. Finally, I check the handle on the amp. Whoever will be transporting it from show to show will certainly appreciate a solid handle, which can be used without a second thought, about the possibility of it giving out.
Every tour is a little different, and the strain on the instruments changes. Itās important to remember the fine line between āroad-readyā and simply sounding good, because both are simultaneously possibleācredence should always be given to both. Some musicians are comfortable sacrificing some overall tone for higher reliability, while to others, tone is of utmost concern. In the end, I am confidant that the amps I work on will be solid and reliable enough to handle the rigors of many shows on the long, winding road.
Pete Thorn talks about various options to control your volume, while still maintaining your tone.
It was 1991, and I was playing a club in Hermosa Beach, California. I was just doing my thing and having fun rocking out when suddenly, my guitar volume dropped dramatically. Itās always a jarring event when something like this happens mid-gig and all kinds of things flashed through my head. What could be wrong? Bad guitar cable? Amp blow a fuse? When I turned around to look behind me, there was the club owner fiddling with my amp to my shock and horror. āHey, what the f#$*?ā I yelled. āYouāre too damn loud!ā he yelled in reply.
This wasnāt the first time someone told me to turn down and it certainly wouldnāt be the last, though it was the first and only time a club owner had done it himself. Itās something we electric guitarists have to deal with constantly. Striking a balance between tone, feel, and stage volume can be challenging for everyone involved (yourself, other band members, soundmen, club owners, etc.). Fortunately, there are more tools available today than ever before to control the volume coming out of your speakers, while still preserving the righteous tone youāve fought hard to create.
The Old Days
In the ā50s and ā60s, rock ānā roll was just coming alive. PA systems, as we know them today, did not exist. Bands relied on the volume coming from their amplifiers to project into the audienceāand quite frankly, the whole thing fascinates me. What would it have been like to see The Beatles in the early ā60s? Could you hear the band at all? Up until the late ā60s, guitar amplifiers were all tube and usually anywhere from 5 to 50 watts. There were no master volume controlsāyou simply turned up the channel volume on the amp you were plugged into, until you achieved the desired volume and tone. As rock music grew in popularityāand crowds and venues grew largerāguitarists like Pete Townsend and Jimi Hendrix demanded bigger and more powerful amplifiers with larger speaker cabinets. The stack was born and 100-watt heads plugged into multiple of 4x12 cabinets quickly became the norm. The tones were awesome, and the volume was deafening!
And Then Came the PA
As the ā70s progressed, so did PA systems and guitar amps. The need for massive stage volume was negated with the advent of high power PA systemsāyou simply needed to throw a microphone in front of a guitar amp and, voilĆ , a 5-watt Fender Champ could now fill an arena. The only problem was that guitarists had grown accustomed to the tones the big 50- and 100-watt amps could createāthese higher power amps created bigger, beefier tones with much more headroom. The challenge now was how to reign in the volume while retaining the magic tone.
Master Volumes
The first Marshall amps with a master volume control were introduced in 1975. These amps allowed the player to crank the preamp to achieve overdrive, but still control the overall volume of the power section via the master volume. These amps sounded great, but not exactly the same as their ānon-master volumeā counterparts. Still, master volumes have become very commonplace on modern amps, and they are an excellent way to control overall output while maintaining your desired tone.
When You Just Have to Crank It
Preamp distortion has its own characteristics, and while it can sound great, there is something truly magical about pushing the entire amplifier into overdrive. Most amps have a sweet spot and the magic is achieved when the preamp, power amp, output transformer, and speakers are all working in harmony to create guitar tone bliss. Unfortunately, your bandmates or soundman might find your sweet spot to be unacceptably loud. Following are some ideas for getting your amp in the zone and controlling the volume ā¦
Load Resistors and Re-Amping
One solution is to āload downā your amp using a dummy load, and then āre-ampā or āslaveā through another power amplifier. This technique has been used since the ā70s, and it can sound really good! You can also add line level effects between the slaved amp and the power amp. In my opinion, the tone and feel of a rig like this is altered by the load resistor. But thatās not necessarily a bad thing since it can create a cool compression and bounce to the feel of the slaved amp. A downside is that you have to deal with the extra weight and bulk of the second amplifier.
Attenuators
An attenuator goes between your amplifier speaker output jack and your speaker cabinet. Its job is to absorb some of the ampās power, thereby reducing the volume coming out of the cabinet. One of the first attenuators was the Tom Scholz Power Soak, first used by Scholz himself with the band Boston in the late ā70s. Many more attenuators appeared on the market such as the THD Hotplate, Komet Airbrake, and Weber MASS. All these devices will allow you to reduce your amplifier volume in steps of a few dBs at a time. Most guitarists agree that these units do an admirable job of shaving off some volume at gig and rehearsal levels, while achieving varying results at higher levels of attenuation.
In the last few years, some new attenuators have hit the market that feature a new design. Units such as the Faustine Phantom, Alex Attenuator, and Aracom feature a āreactiveā design, meaning they respond to an amplifier much like a speaker does. This translates into improved tone across the whole range of attenuation, allowing guitarists to turn their beloved 100-watt heads into ābedroom volumeā amps. These attenuators have been a godsend for manyāturning amps that were previously rendered almost unusable by sheer volume, into reasonable gigging, recording, and practicing machines.
Power Scaling
Power Scaling is a technology developed by Kevin OāConnor at London Power. Power Scaling allows you to reduce the voltage delivered to the output section of your amp, with the result being reduced volume and quicker breakup. Itās a relatively new and promising technology, and you can find it in amplifiers from Suhr, Reinhardt, Soultone, and others. A huge advantage of Power Scaling is that itās completely contained within the amplifier itself.
Whatās Right for You?
You really have to try all these approaches to see what works with your setup. I use all of them to varying degrees, and in the case of my Suhr Badger amps, I use three of these methods together. The Badger has Power Scaling and a master volume, and I use it through the Faustine Phantom attenuator when recording, employing all three methods of attenuation in small degrees, to achieve the perfect tone and volume. Good luck on your quest for tone and the perfect volume level for your situation!