A Question Of Tone...?

[zozoe]

Greetings, putting speaker & pickup choices aside, in a given amplifier with1-vol 1-tone, with the tone control all the way up, is getting more high-end content more complicated than simply swapping some cap or resistor values on the tone control? OR, with that tone full up, OR is it a case of 'It is what it Is' & the curcuit 'as is' simply cannot produce any more hi-end without the need for more invasive surgery elsewhere in the circuit? Would changing tone pot values do anything? The amp is a Victoria Ivy League 2-10 amp.
Thnx in advance!! ॐ

[xtian]

Surely, a schematic will help us help you. All the common tone stacks we deal with are passive, and attenuate, not boost. We typically get more brightness or high end with: bright cap on volume pots (only works when pot is set lower than fully CW), treble peakers (e.g., JCM 800), presence controls. If your amp is too bassy or flubby, you can cut bass, and this may help your perception of the high end.

[zozoe]

thnx xtian, understood, but basically, as you said, the tone is usually a high-cut,,,, and I suss that any 'brightening' of the signal (aside from a bass cut) would live somewhere deeper & warranting some minor surgery? I don't don't any of this stuff myself, but I'm trying to get a better grasp on things....
I'm aware, there's so, so many variables, but generally asking.....

[WhopperPlate]

thnx xtian,,, understood,but basically, as you said, the tone is usually a high-cut,,,, and I suss that any 'brightening' of the signal (aside from a bass cut) would live somewhere deeper & warranting some minor surgery? I don't don't any of this stuff myself, but I'm trying to get a better grasp on things....
I'm aware, there's so, so many variables, but generally asking.....

https://el34world.com/charts/Schematics ... _schem.pdf

Ivy League is essentially 5F10 Fender Harvard

Easy enough to adjust things in a simple circuit like this. Cathode bypass caps and coupling caps can make big changes in perceived brightness.

Listen to Xtian , take this as an opportunity to learn the basics.

[statorvane]

Check the variation in preamp wiring from these two otherwise identical amplifiers.





One channel of each is emphasizes the bass freqs and the other is brighter (with a 500 pF peaker cap parallel to the 680K mixing resistor).

The change that transforms the 2019 bass amp into the 2022 lead amp is the addition of a 5000 pF treble bleed cap on the lead channel volume pot. This amplifier's "lead" channel is very bright at low volume settings (but also very loud). There is some interaction with the controls on these amplifiers, particularly noticeable on the 2022 (2061X as well).

Great "little" amps BTW.

[Stevem]

Please note that whenever a so called brite cap is placed across a volume pot that cap only performs it tone changing function up until the volume pot is up half way, and from that point up on the volume pot the added top end effect drops off along with the added increase in volume from opening up the volume pot more.

If you want that brite change to stay on then you need to place the same value cap across both ends of the volume pot .

[maxkracht]

thnx xtian, understood, but basically, as you said, the tone is usually a high-cut,,,, and I suss that any 'brightening' of the signal (aside from a bass cut) would live somewhere deeper & warranting some minor surgery?

I understand being uncomfortable with the idea of cutting bass, but it might as well be the same as adding highs. Because this is a technical forum, we are more likely to describe what is literally happening instead of the perception of what is happening. For example: a "brilliant" switch/channel on a vox is a massive bass cut compared to "normal", but "bass cut" is terrible marketing compared to "brilliant". People usually call that chime instead of lacking bass.

Easy solutions that others have mentioned. Lower the first cathode bypass cap, maybe somewhere around 0.5 - 5uf. Smaller caps only boost highs, the bigger the cap the more lows.

If that's not enough, lower the first coupling cap, maybe .0047uf or somewhere around there. Both are relatively easy to put on switches if you want to compare. Your tech should know how to do this safely.

While you're at it, maybe have your tech fix the mains wiring on your Victoria. They tend to copy fender a bit too closely for modern safety standards.

[R.G.]

As a broad generalization, the triodes accurately amplify what they're fed as a voltage difference between their grids and their corresponding cathode. This is generally true for the whole audio range, although 12AX7’s and similar tubes can’t get a whole lot above audio/20kHz for flat response; they start drooping from high frequency effects significantly above that.
Their response is relatively flat; external tinkering is needed to make them make more treble, bass or mids.

The response in terms of tone on a triode stage depends on frequency cuts on what signal comes in at the grid (guitar pickups, guitar controls, cable capacitance, input resistor/jack loading, etc.), cuts on the cathode voltage by shunting signal to ground around cathode bias resistors, and cuts on the signal at the plate by frequency-selective loading of the plate. Without inductors to resonate with the circuit capacitances, you don't get resonance peaking, so the only way to boost treble is to cut bass. You can only boost certain frequencies over others by either resonances or induced resonances by some kind of active filtering setup.

Looking at the lead amplifier schematic:
The input triodes can produce reasonably accurate response through the whole audio range.
Cathode resistors lower the total gain of the triode section; cathode resistor bypass caps raise the gain back up to the "natural" gain of the stage at frequencies above the point where the capacitor has less impedance than the cathode resistor. The cathode capacitor makes the stage a bass-cut stage. In this case the frequency is low: it is (pardon my math)
F = 1/ (2*pi* R * C) = 0.6Hz.
So there's no audible bass or treble cut from this. (I'm doing quick and dirty frequency response calcs; there are other effects, but these will get across the idea.) You can make the stage cut bass by reducing the cathode resistor bypass cap. Changing to a 32uF from the 320uF I see there would change the response where bass begins to be lost by a factor of ten, too – up to 60Hz. Changing it to 20uF (a common value in older amps) moves the bass-cut point to about 90Hz, and to 10uF results in a 180Hz rolloff. The amp will start to sound more mid- and treble-y.
Note that the first triode can only amplify what the input jack feeds it. Any treble loss from the pickups, guitar controls, or cable capacitance will still be there.

The plates feed the plate coupling caps into the tone controls. The bigger the plate coupling cap, the more bass gets coupled to the tone and volume controls.
The plate caps are loaded with the 1M volume controls, the 680K mixer resistors, and the tone network. This network has some complex math involved to get to an exact-ish response, but I'll just do some more Q-n-D estimates to get a feeling for what's happening. As a crude estimate, the frequency response of the plate cap and volume control give flat(ish) reponse down to sub-1-Hz, so no cut there. It's so far below the 82Hz of low E or the 41Hz of bass low E that the crude estimate is justified.
The volume pot itself can have its treble "boosted" by the 0.005 "bright" cap. This shunts treble around the upper end of the volume pot at low volume settings, but becomes more irrelevant as volume gets higher.
The tone pot set to fully bass makes a capacitive divider on the plate signal. The 0.022 plate cap and the 0.01 divide the plate signal down to 0.01/(0.022+0.01) or about 1/3 at this setting. The remaining treble and bass have to go through the full 1M of the tone pot in series with the 500pF treble-side tone cap, then into the 680K mixer resistor to the next stage.
Effectively, all frequencies of the signal are cut.
With the tone pot fully treble, the plate signal is not divided by the plate cap and the bass cap, so the treble frequencies get a variable bypass around the volume control loading and into the 680K mixing resistors. The bass frequencies are relatively cut by the increased low frequency impedance of the 500pf treble cap, so you get more treble and less bass.
One of the 680k mixer resistors is bypassed by a 500pf “bright cap”. This cap bypasses the losses in its 680k mixer resistor starting from F = 1/(2*pi*680k*500pF) = 468Hz and on up. This makes this path decidedly more trebly.
Another place to lose treble or bass is in the speaker. Changing speakers can have a remarkable effect on tone, as can the inherent response of the output transformer.