Attila
We have had a lot of postings lately about tone, amps etc ....all in search of the holy grail of sound, you may find this article interesting ....enjoy
Tone Controls: Tone and Gain Sucking Leeches? - by Don Mackrill
Guitar amps have tone controls. Always have, always will... maybe.
More tone controls are better – treble, middle, bass – a tone stack for every channel! Always has been, always will be... maybe not!
WHY?
Tradition is a powerful thing and change is hard to make. But, if you consider how tone controls affect an amp's signal chain, investigate what a guitar and amp sound like with minimal tone controls (or none!) and then decide if you REALLY need them, you might be surprised at your conclusion.
Tone controls change or modify the tone of an electric guitar signal as it passes through an amp. However, the primary determinant of how your electric guitar sounds is the instrument itself, the amp’s overall design (gain stages, pre vs. power tube overdrive, etc.), its tubes, the speaker(s) and YOU the player. Tone controls are but one in a long line of factors strung between your brain, your gear and your ears.
We all have used tone controls to change the sound that our amp produces. Roll off the bass for a humbucker equipped guitar; trim the treble when you plug in that ice-pick Tele; peg the bass when playing your Strat; boost the mids to cut through the mix. All useful stuff. But, what would you sound like if you didn’t have tone controls at all?
In my opinion, despite their tone tweaking usefulness, traditional tone controls can detract from the quality of the tone... if you consider what your amp would sound like without them. Let’s dive into the nature of tone controls to find out why I hold this wacky belief!
Virtually every tone control you’ll run across, at least in a typical tube amp, is a ‘passive’ device. That means that it cuts or reduces the volume of certain frequencies. A passive tone control cannot boost frequencies.
Terminology check: tone controls are often referred to as ‘tone stacks’. The passive components that comprise tone controls – resistors, capacitors and potentiometers – are connected in such a way that when they are drawn on a piece of paper - a schematic - the treble, middle and bass controls look like they are ‘stacked’ on each other. That’s where the term tone stack comes from.
Because tone stacks are constructed from passive components, even if you turn the knobs up to 10, each tone control still reduces certain frequencies.
Yes, that’s right. With passive tone controls there is no such thing as a TRUE 'flat' setting where the signal is not affected in any way there is always some signal loss.
What the heck does all that mean?
Below is a graph that shows the frequency response of a typical treble, middle, bass (TMB) tone control often used by an amp company originally located in southern California. The graph depicts the level of frequencies with all the tone controls set to 10. As you can see the signal level at all frequencies is well below 0 dB -- that means that the signal level is being attenuated or reduced as it goes through the tone stack - even at a 10 setting (yes Nigel, the same would hold true at 11 too!).
What does this mean? Two things.
First, a tone stack reduces the overall level of your signal. That’s why amps with traditional tone stacks need an extra gain stage to return the signal to its level before it got hosed down by the tone stack - more components, more cost, more complexity.
Second, even when all the knobs are on 10 the stack is changing the tone profile of your signal. The tone stack’s frequency response as shown in the graph has a big dip centered on 300 Hz. That means that the volume level of those frequencies around 300 Hz is a lot less than the rest of the frequencies – a cut in the low mids.
Here’s our tone stack’s frequency response set to provide a flat frequency response. Note that although the tone controls are not shaping the tone - all frequencies are being passed at an equal level -the signal has been severely attenuated across the board.
10Hz
100 Hz
1000 Hz
10000 Hz
You’ll likely be surprised to learn that to produce this ‘flat’ response the controls have to be set as follows:
Bass = 1
Middle = 8
Treble = 0
I bet that’s not where you set your tone controls!
There are a few things at play here. First, at this flat response point you have to really boost the volume to compensate for the gain loss through the tone stack. Second, it shows how much the typical tone stack scoops mids - bass and treble have to be severely attenuated to match the low mid-frequency response of the stack. Finally, this shows that the tone controls are highly interactive and changes in one dramatically affect the other - you have to dial in crazy settings to get a flat response.
So, if it takes this dramatic an alteration of your tone controls to get a true representation of what your guitar sounds like why bother?
Is all this ‘bad’? Not necessarily. The tone stack in question has been used in dozens of amp designs that produce great tone. Maybe you won’t like the true sound of your guitar!
However, I want to plant a crazy idea in your brain: what would happen if you didn’t have a tone stack or you had a very simple tone control that could make subtle tone changes, but would not suck nearly as much gain and would not dramatically alter the frequency response of your guitar?
Well, in my experience you can really ‘hear’ your guitar (!) … you’ll hear a more balanced tone coming from your rig. Your tone will have more presence and, with an amp that has been designed with minimal or no tone controls, you will experience a more responsive, dynamic feel. If you like that sort of thing it’s VERY cool!
Of course, it’s impossible to properly convey the sound of a ‘tone-stacklessR17; amp on a piece of paper … you have to hear the difference!
So, when you see amps with minimal tone controls don’t dismiss them. Play through them when you get the opportunity so you can see for yourself. You may be surprised at what you hear and feel!
Send me an EMAIL (Don Mackrill) if you would like to discuss this further!
PS: Crystal ball time! I predict you’ll see an increasing number of amps with ‘lift’ switches that take the tone stack completely out of the circuit. A few big name amps have had this feature for years labeled as a “solo” switch. Why call it a solo switch? Because eliminating the tone stack increases gain and midrange response - both perfect for bringing your sound front and center! Wouldn’t that boost in tonality be a good thing all the time?
Consider having your local amp tech add a lift switch to your favorite box so you can experiment for yourself … the stack might get lifted and never put back!
MikeM
I guess that you are not Don, right?
I have discussed this with Karel a little, and online quite a bit. I believe in the idea of no tone stack. Hence me going for a modified 5F1 (Champ - volume control only) with a switchable tone control, not even a stack as I will be using one tone control only.
I however have no first hand experience. Although on my Vox (Modelling) I usually have the tone stack around; B: 2, M:6, T:4. Maybe that's cause I used to live on a tele ?
I am not sure about other people but I read that you should set your eq, treble first, then bass, then mids, and only set it until each one blooms (Opens up - wait that still says the same thing - tough to explain that one)
Interested to see other people's view on this.
(Waits for Alan's sage reply ? - WOOT @ 22 days 22 hours and 22 minutes online)
Manfred-Klose
I am a electronic noob so bare with me.
He mentions that a passive circuit cant boost eq, so what about making it an active circuit then?
FenderBender
Active tone circuits work well in a solid state environment due to the high gains attributable to transistors and op-amps.
It is very difficult to produce a tube based active tone stack, due to the relatively low gain of a tube. A typical triode has a gain of 50, which is relatively low compared with a tranny or op-amp. Using pentodes could increase gain, but also bring in undesired distortion, so it is very rare to find active tone stacks in tube amps, unless they have modelling type preamps that contain semiconductors.
Gearhead
Active/passive imho is not an issue: there is plenty of gain in only one preamp tube to have tone stack and still drive the output tube(s) into clip.
Call me stupid (you'd probably not be far off) but I really don't understand why this bloke makes such a fuss about gain loss. Nothing like a whole series of gain stages to 'tube up' even a clean guitar sound.
If you look up the frequency response of your typical pickup (see also www.gitarrenelektronik.de) you will find that an electric guitar produces way more mids than anything else. Of course, this is partly due to the range of notes that are on the instrument. But the other thing is that the pickups do not pick up all the lower and higher frequencies due to the way they work. The 'amp company originally located in southern California' did make guitars as well - and they really understood exactly what was going on. I believe Leo intentionally made the tone stack imbalanced to get the whole system to sound right.
Mr. Don M. should just multiply the frequency response of a couple of pickups with the frequency response of the tone stack in the setting one would use with those particular pickups - I bet they work out a lot flatter than he thinks.
matta
Manny,
Remember the other day when you were at the shop I took you through the Fender Bassman I was working on? You saw the preamplifier stage, but as I pointed out the 12ax7 is actually a dual triode, 2 valves in one, one half is the preamplifier, the other is used to make up for the insertion loss of running it through the passive tonestack.
A 12ax7 has a max gain of 100, more than enough to make up for the insertion loss.
That said I do believe, as with most things, the more you add, the worse it sounds... You can, as Gearhead pointed out just add more gain stages to accomodate the insertion loss, but I do believe that it takes away from the sound... It has to...
Here is a terrible analogy I just thought of, if you cut a cake up into slices, you can put the slices together, but you will never have a whole cake again, part of it goes everytime you make a cut, a small sliver disappers... Few cuts mean there is more cake to go around.
I believe some of the best sounding tones come from fewer components. You can totally change the voicing of an amp just by changing the size of the cathode cap, want more bass? Use a 25uF cap like Fender did, want a brighter tone? Use a .68uF like Marshall did... That SINGLE change will have a huge change on your tone without the need for your typical TMB stack.
Gearhead, also remember that Leo made the Tweed Champ with no Tonestack, the variable tone, and single knob to boot only came with the later 5F2, Tweed Princeton.
Heck even Classics like the Vox AC30 came with a single Tone cut control, the TB option only came a few years later, the idea taken by Dick Denny from Gibson of all people.
Matt
Attila
Tell you what ...... I am going to ask Don to share his views on your comments
His website is
http://www.mackamps.com/ maker of well ...er....AMPS
MikeM
Interesting Matt, makes me consider putting a switch in to swap caps...
I think the analogy is effective ?
Manfred-Klose
I believe some of the best sounding tones come from fewer components. You can totally change the voicing of an amp just by changing the size of the cathode cap, want more bass? Use a 25uF cap like Fender did, want a brighter tone? Use a .68uF like Marshall did... That SINGLE change will have a huge change on your tone without the need for your typical TMB stack.
Interesting Matt, makes me consider putting a switch in to swap caps...
Mike M has beaten me to it ?
Is it possible to mod a valve amp and put in a few switches that can switch between the caps?
P.S: this is like a really cool crash course to understanding valve amps, thanks guys i like the info.
matta
To both Mike & Manny, you can indeed, in fact I'd use 3 way switch, with center off, have a 25uF cap which Fender used (and a zillion other guys from Boogie to Vox), a smaller .68 like Marshall and the last, well NO bypass cap, 3 very different voicing, without the need for a TMB stack...
Matt
MikeM
Yea I love chatting to these guys in the know ? You learn so much so quick!!!
Man I remember Karel saying you can change any/everything when you DIY but now I am getting so many options!!! Think I will set it up temporarily being able to change caps and then settle on one!!
Matta, what would the effect of a no bypass be? More bassy? Yows... Hahaha man this is awful! So much for a simple little amp!!
Gearhead
Still. If you want flat response just buy a R100000 hifi amp - no tone controls on any of them. Betcha they won't sound very nice as guitar amp though. Less parts like Matta suggests? Buy a Pass Labs - still no guitar amp.
In the Triaxis patent Randall Smith makes an interesting observation: none of the guitar amps ever to be released without non-flat tone controls with channels that influence each other, was as succesfull as those that did have them. I do not pretend to know all the history of all those amps back in the day, but I do suppose there are good reasons for having tone stacks or tone shaping in the amp. Apart from the pickup response I mentioned earlier, the frequency response of guitar speakers also comes to mind.
The downside to cap switching seems to be to me that (unless you make a >10 step setup) there are little steps in between and many different guitars to match to. If the tone of the guitars calls for slightly different settings and the amp has only big steps, your only option left is to use the tone knob on the guitar itself.
matta
Gearhead,
I didn't say I'm looking for a flat freqency response amp... Not at all! Ever played through a vintage, or even reissue Champ or GA5? Hell you couldn't get less unflat if you tried! It is dirty, gritty, but amazingly musical, with a suprisingly low parts count... Much of that influenced by the input, the midrange guitar pick up, and the high pass speaker, ESP. with the older, more ineffcient, smaller speaker.
RE cathode bypass caps, actually you don't have many options, the change, at least audibly would need to be HALF the value up or down, 3 shades still offer more than onle fixed one.
Couple that with two inputs on the guitar amp, most Channel 2's use a voltage divider to take the incoming singnal down 3dB, in essense raking the output of a humbucker down to a single coil, driving Channel 1 with the humbucker with hit the grid harder resulting in yet another sonic shade.
Let us not forget the tone controls on one's guitar as well and the impact this has on the shades you can coax out of an amp without touching it.
RE amps selling better more units because of a tonestack? Sure, but I think much of that comes from the need for the crutch, like guys buying 15 or 30 Watters for bedroom playing...
Matt
matta
Mike, no cap will give you a rawer, more in your face tone with less bass, think 50's/60's rock and roll. The bigger the cap the more bass will pass, it is part of the reactive capacitance phenomina.
Matt
Attila
Gearhead wrote:
The downside to cap switching seems to be to me that (unless you make a >10 step setup) there are little steps in between and many different guitars to match to. If the tone of the guitars calls for slightly different settings and the amp has only big steps, your only option left is to use the tone knob on the guitar itself.
I did this to my Ibanez LP Pro under advice from the good Dr. Helmuth Lemme, from Gitarrenelektronik's A preamp, 10 position rotary tone switch (Linear tone filter) and active base and treble circuits ....I calculated something like 50 odd settings including in and out phasing ...phew to many settings 8) the active base and treble circuit, alleviates the need to adjust the volume after making changes on the rotary tone filter on the fly
Lethe
Gearhead wrote:
Active/passive imho is not an issue: there is plenty of gain in only one preamp tube to have tone stack and still drive the output tube(s) into clip.
Call me stupid (you'd probably not be far off) but I really don't understand why this bloke makes such a fuss about gain loss. Nothing like a whole series of gain stages to 'tube up' even a clean guitar sound.
If you look up the frequency response of your typical pickup (see also www.gitarrenelektronik.de) you will find that an electric guitar produces way more mids than anything else. Of course, this is partly due to the range of notes that are on the instrument. But the other thing is that the pickups do not pick up all the lower and higher frequencies due to the way they work. The 'amp company originally located in southern California' did make guitars as well - and they really understood exactly what was going on. I believe Leo intentionally made the tone stack imbalanced to get the whole system to sound right.
Mr. Don M. should just multiply the frequency response of a couple of pickups with the frequency response of the tone stack in the setting one would use with those particular pickups - I bet they work out a lot flatter than he thinks.
Nicht alle koennen Deutsch sprechen...
Attila
Feedback from Don
Hi Attila,
I appreciate that you found my article interesting enough to post. It appears to have generated a lively discussion and I am pleased to participate.
Having now re-read my article, I realize that I should have been more clear about the reference to flat frequency response. I included the Fender tone stack example to show how much it affects the gain and tone of the signal passing through the amp. However, I recognize that the main point of the article can easily be interpreted as being: guitars sound best when their response is flat. That's not what I intended!
As Gearhead points out, the signal coming from a guitar is anything but flat - the bumps and dips across the guitar's frequency spectrum are what makes different guitars and pickups sound the way they do - and it's why we love them!
My main point was supposed to be that messing with the signal coming from your guitar as little as possible provides a wonderful and compelling - and different - listening/playing experience.
Gearhead is correct that for every gain reducing tone stack there can be a tube recovery stage. However, in my opinion - from a design concept perspective - fewer gain stages and fewer passive circuits that alter tone and reduce gain (regardless of the following extra gain stage) make for a very dynamic, touch responsive, and toneful amp. If you ever get a chance to play a quality amp with a simple signal path you may be surprised at the depth of tone and its responsiveness.
Messing with the guitar signal as little as possible produces beautiful tone and, I believe, a different tonality than if an amp has a complex signal path and multiple tone shaping capabilities. I am not saying that amps with many gain stages and tone stacks sound bad. That's obviously not true. But, I do believe that hearing your guitar through a 'minimalist' amp is a different experience and one that many prefer once they've experienced it. I'll bet that hearing your guitar through an amp that burnishes the tone with only a few tube stages will reveal nuances and tone that you've never heard before. IMO, that's a cool thing!
Regards,
Don Mackrill
Mack Guitar Amps
Don@MackAmps.com
Virtuoso Tone without the Prima Donna Price!
416.705.9620
www.MackAmps.com
Valie
In answer to Manfred, if you go to the ampage website I think there is a circuit that is called "The son of Boogie". They do a lot of cathode switching on a single switch. As I recall the Marshall circuits of the 80's use to have a slope resistance cotrol as well. That is the resistor in the tone stack which would give you a little brighter sound if you wish.
Gearhead
Thanks Don for clarifying the 'flat' point.
I have built a minimalist tube amp, intended for use with separate preamp. It was intended to have as little tone affecting circuitry and parts as practically possible. When I was too lazy to carry the preamp with me to a lesson, Keira pointed out to me that the guitar plugged straight into the poweramp sounds rather mid-heavy. The more I compared with/without tone controls, the more I realise that some scooping of mids adds balance to the signal. The whole point then becomes, how much scooping is cool.
Vick
Question:
Duz a guitar's tone pot affect ur signal in the same way?
and If yes...is this why sum guitars dont have tone pots?
