Noob question about Brian May Treble Booster vero.

[stax67]

Hi,

I been trying to learn a bit about circuits before I attempt to build anything and I not sure about the switch in this circuit (attached).

Does the input always run through C1 with either C5 or C6 in paralell?

If so how would I set lay it out if I wanted to bypass C1 so that I have C1 or C5 or C6?

Thanks,
Luke

[antonis]

Hi & Welcome..

If switch is a ON-ON type, yes..
(C1 is always in parallel either with C5 or C6)

If switch is ON-OFF-ON, for ONs like above and for OFF C1 is standing alone..

[stax67]

Thanks antonis, that makes sense. I thought that was the case but started doubting myself.

What effect does adding these caps in paralell have on the audio? More/less treble/bass?

Thanks,
Luke.

[kaycee]

The smaller the capacitor, the less bass signal going through to be boosted. Usually these are set up to give treble boost, a bit more mids and near full boost. Just makes the pedal a bit more versatile.

[Oolooloo]

When capacitors are connected in parallel, their capacitance adds up.
For example, if C1 is in parallel with C5 via the switch, to the circuit it looks like one capacitor of capacitance:
    C1 + C5 = 4.7nF + 22nF = 26.7nF

In this circuit, the larger the capacitance, the more bass it lets through. It shifts the frequency at which low frequencies start to roll off.
Look up RC filters to better understand it.

[stax67]

Thanks everyone. I understand now.

I'll take a look at RC filters.

Really great community on here.

[antonis]

Caps in parallel result into higher equivalent capacitance..
Taking into account that equivalent capacitance is in series with input signal, it lets more bass to come through..
(it actually forms a High pass filter with Q1 impedance and bias configuration.. At point A)



Cap(s) for upper blue part and resistor(s) for lower red part of voltage divider..

[PRR]

> What effect does adding these caps in paralell have on the audio? More/less treble/bass?

The box is a "treble booster". But the transistor is an "everything booster".

The caps, and the input of the transistor, make a Bass Cut. Leaving mostly treble.

More or less capacitor changes how much bass is cut-away; and the apparent treble-boost.

The cap-combinations seem to be like 27u, 10u, and 5u, giving bass-cut below 300Hz to 1500Hz, from alto to tweety-bird.

[stax67]

Ok thanks, it's starting to sink in, I hope.

I have a couple more questions about the circuit.

1. I've read that it should go first in the pedal chain and not after other pedals, especially buffered pedals. Is this correct?

2. I've seen a mention of adding another pot after the one that's already in the circuit for a volume knob. Is the pot that's already there not a volume knob?

Thanks,
Luke.

[Marcos - Munky]

1. well... it usually goes first in the pedal chain. Indeed, some of them were made to plug in directly on the guitar jack, some are even built inside the guitar itself. But that doesn't mean it "should" go first. Imo you should try it before and after each dirt box you have. You may end up liking it at first, or after all dirt boxes, or even somewhere in the middle of them. I only have one boost in my pedalboard, and it isn't really a treble booster, but anyway I put it between two low gain overdrives, so I can get both "boost the overdriven sound" and "overdrive a boosted sound" options.

2. yeah, the pot is a volume knob. It doesn't makes any sense to add another one after the one already in the circuit.

[idy]

The pot is marked "gain" but is an input attenuator. When it is attenuating least, the signal is strong enough that the transistor will clip a bit. If you had a volume knob at the very end of the circuit you would be able to clip and have level that maybe plays better with following circuits, not too hot.

A "real" gain control would change how the transistor operates... usually this is a pot in series (or parallel, with a cap for frequency shaping) to the emitter resistor. (R6, C4). Check out a fuzz face or a Super Hard On (there it is the "source" instead of the emitter.)

So three strategies often (mis)labeled according to the whim of the "marketer:" input attenuation, gain control, volume attenuation. Called boost, hot, pre, more, volume, gain, louder, whatever they think will excite guitarists.

But no, you probably don't need an additional knob on this thing.

[antonis]

The "Gain" pot should be a real gain pot only in case of bias configuration was made with C-B feedback resistor..

As it is, it simply is an attenuator voltage divider (as well said above..) and its impact is only on input signal..
(in the mean of it doesn't vary stage gain..)

There are many versions of Brian May Treble Booster, some of them exhibiting an ouput pot called "Intensity" which isn't nothing else than a conventional Volume pot..