Fender, Marshall, and Traynor Tone Stacks

I’ve recently begun recording a second disc with the band I’m in, Shayna and the Bulldog. On our first disc, we were a little unhappy with the guitar tones we got, so over the past year we’ve expanded our amp collection and knowledge. The first disc contained primarily a Fender Blues Junior and Hot Rod Deville (4”x10”) for the rhythm guitars, while the lead was done entirely on a Fender Deluxe Reverb Reissue. With a couple more amps and more knowledge, we are now stuck with the dilemma of options. Recently after band practice, the following conversation took place.

Charles: “We could use the Traynor YBA-1 through a 4x10 cabinet for our rhythm guitar tracks. It has basically the same circuit as a Marshall JTM45 and gives that fat, chunky rhythm guitar sound.”

Joel: “Yeah, but … the Traynor it just ..”

Charles: “It just .. what??”

Joel: “It’s missing that growl .. that feeling. Can you do anything to it?”

And so the search began. The question of the hour, dear readers, is what gives an amp that growl? To approach this vague question, I had to consult the small part of my soul that is not an engineer. We opened at an outdoor gig a couple years ago, where I had the opportunity to play a fully cranked Marshall half-stack, which most certainly had “that growl.” This was before I took the model and serial number of every amp I played or even saw, so I have no idea what the model was unfortunately. Anyhow, since that time, I have associated Marshall amps with that growling, mean, distortion that breaks up at just the right part of the attack and makes bar chords sound like Satan himself is beating a drum in your chest. From this abstract idea, I began just to wonder. What *is* it that makes that sound, opposed to the relatively cleaner, chunkier sound of an overdriven Fender? From there, I wandered into thinking about diametrically opposed ideas about the cultures surrounding the amplifiers, such as monarchy vs. democracy, English vs. metric, the Beatles vs. Zeppelin, Churchill vs. Roosevelt, etc… Quickly, I realized how unprepared I was to answer any of these questions, so I returned to guitar amp terms: is it the tubes, the tone stack, the transformers, the cabinets, etc… There are a lot of differences, and I was at least a little bit prepared to answer these questions.

Returning to the debate about the Hot Rod vs. the Traynor and realizing that a true Marshall really “growls,” I guess the primary question is, what is the Traynor lacking, as far as emulating a Marshall tone? I should preface this discussion by noting that I think the Traynor has an entirely unique sound all its own, which should not be discounted in quality, simply because it is not Marshall-like. However, I think my goal is to give the Traynor a more Marshall-like growl. Sure, I could look at the schematics for the JTM45 and make the mods to create a JTM45 duplicate, but I want to answer a couple questions about this ‘growl’ along the way.

In coming weeks, this investigation will quantitatively run through some of the many facets that make up a final guitar tone, such as tone stack, tube types, closed vs. open-backed speakers, and anything else I can think of that can be measured and might be affecting the tone. I will begin today, with a theory-based discussion using Duncan Amps excellent tone stack calculator.

The Tone Stack

For those unacquainted with the tone stack of a guitar amplifier, this is generally your bass, mid, and treble knob. Some people might argue that the presence knob is part of the tone stack, but those people are wrong and this is not up for discussion. Anyhow, a typical tone circuit consists of a very basic RC filter with 3 potentiometers (knobs). However, it is well known, there is more than one way to skin a cat, and Fender and Marshall amplifiers most certainly go about the tone circuit in separate ways. Classical Fender and Marshall tone circuits are shown below:

Figure 1. (a) Shows a typical Marshall style tone circuit, compared to (b) which shows a typical Fender style tone stack.

Okay, great. But what does this mean to the amplifier tinkering individual? The electronically inclined could solve these circuits and come up with nice equations to show the frequency cut-off points, etc... However, I don’t like math very much, and Duncan’s Amp page has created a wonderful tool for analyzing tone circuits, so I will use that for the sake of efficiency. Below, we have the Fender and Marshall tone stack frequency response. Again, the untrained eye can see the difference between the two. If you are not familiar with frequency response curves, the x-axis is a given frequency, while the y-axis tells how loud that frequency will be reproduced.

Figure 2. (a) Typical Fender tone stack frequency response. (b) Typical Marshall-style frequency response.

To relate these plots to the sound of a guitar, one should note that a typical electric guitar can produce fundamental frequencies between 82 and approximately 1000 Hz. Now, if you look at the plots above, you can see that the large dip in the fender plot over the decade between 100 Hz and 10 kHz certainly must produce a different tone than a Marshall, which has a much less dramatic dip. When one considers higher harmonics and subharmonics of a guitar pluck, you can get the idea about just how much this affects the tone. It’s worth mentioning that no matter how you turn the knobs on a Fender amp or Marshall, the two frequency response plots will basically NEVER match one another. They both provide a range of control over the low, middle, and high frequencies, but as was mentioned earlier, there is more than one way to skin a cat. Here, we have identified one possible source of a lack of “growling-ness” from an amp.

How does the Traynor, the bastard cousin of the Marshall fit into this argument? The results of plugging in the stock values for the Traynor tone circuit into the Tonestack Calculator are shown below.

Figure 3. Traynor YBA-1 Frequency response, using stock capacitor values.

Here, you can see the Traynor circuit has a decidedly Marshall-like response (note the small dip between 100 and 1000 Hz) ; however, the very low frequencies are quite a bit different. At first glance you may think the YBA-1 would give a more ‘bass-y’ response than the Marshall. This is not the case, however, since frequencies between 10-100 Hz are generally inaudible. I hypothesize that this low-end “growl” is probably happening somewhere between 100-400 Hz. The Marshall Frequency response is actually greater in this range.

That is all for the theoretical analysis of tone stacks. Next week, we will compare the tone stacks to some experimental data from the Hot Rod Deville and the Traynor YBA-1. Until then, grab the free Duncan Amps tone stack calculator and see what kind of tone circuit your amp has!