5E3 Tone Stack / Volume Control Theory

[jakejoseph]

I am having trouble wrapping my head around how the theory behind how the tone stack on a 5E3 works.

This is what I think I see....

I see the basic high pass filter created by the 0.1 uF bypass cap and the subsequent two volume controls.

The tone control then adds another high pass filter through the 0.0005 uF cap and the tone control pot and 2nd volume pot.

Then, I get kinda lost. There are good articles on the web about how a Baxandall works, is there one on how this seemingly simple circuit works?

[MWJB]

The primary function of the 0.1 is a coupling cap, you could (and people do) use 0.022 or 0.047uf here to tailor frquency response (reduce bass).

The tone control works slightly differently depending on which channel you plug into.

In the Normal/Mic channel it is a simple hi cut pot, with the 0.0047uf cap dictating how much highs are bled off to ground (other amps often use values from 0.003 to 0.01uf here, higher cap value bleeds off more highs). Turning up the tone pot reduces the cap's ability to bleed off the highs. You will notice that this channel sounds much darker & thuddier than the Bright/Inst channel...

You will notice an additional 0.0005uf (500pf) cap that bleeds highs around the Bright/Inst volume pot, to the tone pot. In the Bright/Inst channel, the tone pot works as a compound tone pot, the 0.0047uf cap does the same as before, but at lower volumes especially, the additional 500pf cap allows highs to pass around the Bright/Inst volume, preventing the series resistance of the unused portion of the volume pot from dulling off highs when turned down from fully open (as happens on the Norm/Inst channel).

[jrfrond]

There is no mystery to it really. Towards on side, the tone control straps a 500pF bright cap across the volume control. Toward the other, it rolls-off whatever highs pass through the volume controls through a .005 cap to ground. The mid point of the tone control is essentially neutral. There is no volume control bypass or high-cut. In addition, as with any "bright cap" strapped across a volume control, the caps effectiveness decrease as the volume is raised, and is out-of-circuit with the volume control at maximum.

[MarkusBass]

There is a very good document, which explains both how the tone controls work in 5E3, and shows possible modifications of the amp: http://online.physics.uiuc.edu/cours...5E3_Deluxe.pdf

Mark

[jakejoseph]

At full volume, the tone control does very little, is that right?

Thank you for all of your help on this. I have a much better understanding now.

One more thing, I ran this as a simulation using a spice program (if anyone has a recommendation for an inexpensive spice program, I would greatly appreciate it)- I noticed that at full volume, the tone control doesn't really do anything. Does that seem right? Did I set the simulation up correctly?

I can do a DC analysis using Kirchoff's laws. I have never been taught how to do such an analysis with AC. Is there anywhere on the net that has info on how to this by hand?

[MarkusBass]

I tested only one Spice program; it's SwitcherCAD III by Linear: http://www.linear.com/designtools/software/ . It's very good and it's free .
With full volume the 500p capacitor is shorted bt the Volume pot. You can get good results with the volume pot turned up only by 30%. See the attachment.

Mark

[Bruce / Mission Amps]

Nearby BS alert!

There is a very good document, which explains both how the tone controls work in 5E3, and shows possible modifications of the amp: http://online.physics.uiuc.edu/cours...5E3_Deluxe.pdf

Mark

I hate the article and anyone who reads it ought to know right off the bat it is EXTREMELY biased with severe ass kissing.
Much of that treatise is really bullshit.
Opinions, horribly biased by mis-assumptions from a couple guys who probably don't know squat about guitar amps, guitar tone or real playing, and then written by the techno whizzy kid trying to impress his profs.

And what experience does this weenie or his prof have with tone, playing real amps or anything else that is subjective?
Most of it is based on comparing a very inexpensive, Chinese parts equipped amp kit, produced by webervst ...(not even close to a real one) with what?... one "original" amp of dubious condition?
With respect to his professors Deluxe amp... we have know idea if it is was worth a shit anyhow.
That kit amp doesn't use a correct power or output transformers, and note, his assumption that most people are using a 12AX7.... that is only because his cheap kit came with one. Totally false. What an ass.
Also... all the knuckleheads are doing is modifying and changing the amp design into a completely different amp. I will wager doesn't sound much like a classic tweed Deluxe... which is considered by the hoards, the holly grail of small power amps!
By the way... the black face Princeton amp addressed most all of those issues and you don't see them selling for thousands of dollars. It is a different amp though.
Nope, I don't buy into that ass kissing drivel.
Just build a different amp and call it something else because their version sure as hell is no tweed Deluxe.

[Steve Conner]

The procedure for solving an AC circuit is just the same as for DC, except you use complex arithmetic. Kirchoff's laws still hold for AC circuits, provided you use complex numbers everywhere. http://en.wikipedia.org/wiki/Complex_number

The textbook we used was "Introductory Circuit Analysis" by Boylestad.

[jakejoseph]

Uh, oh

I haven't done that sort of math in years...P-chem I think.

I'll check that book out...but it sounds like I should get my calculus book out first.

J

[Steve A.]

... One more thing, I ran this as a simulation using a spice program (if anyone has a recommendation for an inexpensive spice program, I would greatly appreciate it)- I noticed that at full volume, the tone control doesn't really do anything. Does that seem right? Did I set the simulation up correctly?...

At full volume the treble-cut portion of the tone control should have some effect although the treble-boost portion is bypassed. Then again with the volume set to 12 you might not hear a lot of tonal differences because it is so loud (I don't think that the spice program factors that in- or does it?)

Steve A

[Steve A.]

...That kit amp doesn't use a correct power or output transformers, and note, his assumption that most people are using a 12AX7.... that is only because his cheap kit came with one. Totally false. What an ass...

Bruce:

Weren't they using 12AX7's in the Deluxes in the recording studios in the early 70's for all of those rock recordings- goosed up with a stomp box or two to get mondo distortion?

Wasn't a Tweed Deluxe used on some of the Steely Dan recordings?

I do agree with you that the net result was absolutely nothing like a vintage 5E3 tweed deluxe, and as the 70's turned into the 80's and 90's the roots rock guitarists were pulling the 12AX7's out and putting lower gain tubes back in there for a more authentic vintage sound.

Just wondering (and not disputing your evaluation of that article!)

Thanks

Steve Ahola

[MarkusBass]

A discussion of this and other tone stacks: http://amps.zugster.net/articles/tone-stacks
I hope this time it has nothing to do with AK (ass kissing)

Mark

[jrfrond]

All of the SPICE graphs and FFT analysis is very cool and glitzy, lending some real technical legitimacy to the whole she-bang, but it means nothing until you test it with your ears for tone and fingers for feel. Amp tweaking is 99% empirical.

[MWJB]

Agreed, what makes an amp great is the sound it makes...that's the bottom line. If the software helps you get an angle on it then great, but especially in the case of the 5E3 tone control, you've just got 1 or 2 caps to play with (depending on channel used)...20 minutes with some jumper leads and crocodile clips and you should be sorted, twice that if you want to solder (though a novice may struggle to remember the changes unless done in a quickfire A/B test)...not that playing with the tone caps seems to be a very popular past time (coupling & cathode bypass seem the more usual route to tailoring frequency response)?

[Enzo]

Plus, even if you get some real precise response curve graph, just what does that curve sound like anyway?