Treble booster questions

[RaistMagus]

I want to get a treble booster, one with selectable range. I see this gets implemented either by a switch (I assume switching between capacitors, e.g. Fulltone Ranger) or with a potentiomeneter (RC filter? e.g. Naga Viper). Any recommendation on what is the best way to select the boosted range? How does the pot thing work?

Also, is the low-freq cut-off the only parameter I should watch for? There are endless clones, do they have different mid and high frequnecy EQ as well (different character?), or just the low-freq rolloff?

I'm considering building some clones by fuzzdog, they offer clones "inspired by" naga viper, range master, Beavis Audio's Brian May Boost, and other treble boosters. Will I be missing anything it I build the clone (30 euros) instead of getting a boutique treble booster that goes for 200+ euros? Is there any tears-of-the-unicorn components, or components that need fine tuning that I will be missing out on?

Do the various treble boosters (range master, naga, brian may boost) sound very different or is it just a matter of the EQ shape they offer?

(If I was to buy new I'd go for a Fulltone Ranger or a Naga Viper or a Colombo Ingot)

[Lino22]

I put a BD 140 power transistor in mine (they have low gain and people say they have a rounder knee) and did the pot variant. It sounds superb.

This is the type of input i have in mine.

[FiveseveN]

It's a CE amplifier, arguably the most basic transistor gain stage you can build. There's no reason it should cost 30 EUR, let alone 200.

Is there any tears-of-the-unicorn components

The original Rangemaster used a Germanium transistor and they haven't been manufactured for a while. Not unobtainable but significantly more rare and thus expensive, though you can say that about many things when comparing to a 50 cent part. The differences in performance between Ge and modern Si BJTs can be important depending on how you use the booster and the details of the circuit.

just a matter of the EQ shape they offer

The shape is the same, a 1st order high-pass filter. The transistor used can have an impact as mentioned before, in terms of available gain, headroom and harmonic content as it transitions into saturation.

[GibsonGM]

I recommend choosing 2 or 3 builds, like a Rangemaster (get the Ge transistor!), and a Brian May, maybe some Wampler or fuzzdog thing...DIY.  To the designer's specs.   Compare what's going on, find what sound you like.  Try some mods, breadboard makes this especially easy!

Lino shows a neat way to send your signal thru a 'variable input cap network', you can play with that with most any of them.  Moving the wiper toward the smaller cap cuts more bass as you go.  Think of caps as frequency-dependent resistors (they are).

I like a Rangemaster for some things, I find it a little nasally, reminds me of c(**d wah.  For other tones, I might use a modified LPB that has a fuller range.   As a guitarist, I want as many different options as I can get, and it's fun to build them and try them!  he he he   IMO, you just don't know til you make one and try it with YOUR rig.  After a few builds, you might hit on a Holy Grail you just can't do without!

[antonis]

just a matter of the EQ shape they offer

The shape is the same, a 1st order high-pass filter.

In fact, a typical CE amp (with bypassed Emitter resistor) has three 1st order HPFs..
The one of lower corner frequency has a slope of 18dB/octave (like a single 3rd order one..)


(simplified enough.. )

Or did I get your answer wrong..??

[FiveseveN]

three 1st order HPFs

But two of those have a cutoff frequency under 20 Hz. There's probably some HF rolloff in the MHz range, is that also relevant?
RaistMagus is clearly not familiar with the math so a simplified explanation is more likely to get the point across.

[antonis]

But two of those have a cutoff frequency under 20 Hz.

I'm not responsible for that!

[mozz]

The original rangemaster was not a pedal, it was meant to be on all the time. You then adjust your amp settings to your liking. A lot of people get that wrong because they do not adjust the amp to the pedal.

[Lino22]

Yeah, i've got it on all the time and use just the volume knob on my guitar. After 20 years of doing this, i may stick with it for the rest of my days. The best pedal out there. I just had to remove the Ge tranny, it was too hissy. BD139/140 does the job and they are quiet.

[Gus]

two sims I have built TBs with tip29 etc.

[Rob Strand]

put a BD 140 power transistor in mine (they have low gain and people say they have a rounder knee) and did the pot variant. It sounds superb.

Modern BD139/BD140's appear to have a higher base to collector capacitance than the old/original Motorola and Philips units.   IIRC, the base to collector capacitance of the OC44's is somewhere in between the two.

It may well be the case that 2N2222 with the 47pF isn't too far off the mark.   IIRC, good BD139/BD140s have gains up around 100, or just under.

[RaistMagus]

How important would you say is an external bias control? Most available treble boosters don't have one.

three 1st order HPFs

But two of those have a cutoff frequency under 20 Hz. There's probably some HF rolloff in the MHz range, is that also relevant?
RaistMagus is clearly not familiar with the math so a simplified explanation is more likely to get the point across.

Thank you for your consideration : )  I can calculate the cut-off frequency of a simple 1st-order high pass filter but  it has to be super obviously presented in the schematic. E.g. in the naga viper schematic above I have no idea which resistors and caps to consider at the input stage for the calculations.

So the significant EQ-shaping part is the 1st-order HPF at the input. How about the breakup and harmonics of the transistor? Can this result in EQ shaping? Some have commented that certain treble boosters can sound like c0cked wah, then it would seem that there is a very pronounced peak, not just a HPF.

two sims I have built TBs with tip29 etc.
...

Nice! I am familiar with spice simulations but only with frequency sweeps of small-voltage models (linear behaviour of all components). If we want to see distortion effects and nonlinearities then this would be a time-based simulation?

... For other tones, I might use a modified LPB that has a fuller range.   As a guitarist, I want as many different options as I can get, and it's fun to build them and try them!  ...

On that note, I do have an LPB-1 that I find too dark and would like to mod. It has two HPFs, one at the input and one further down IIRC. I plan to add a three-way switch to switch between caps, should I only do it at the input HPF, at the later one, or at both?

[FiveseveN]

in the naga viper schematic above I have no idea which resistors and caps to consider at the input stage for the calculations

That would be the 1st box in antonis' annotated schematic. It gets complicated because transistor input impedance is involved. ElectroSmash has all the numbers: https://electrosmash.com/dallas-rangemaster
And then there's the "range" control that further muddles things. You can think of it as a "blend" between the two input cap values, works more or less like a shelving filter.

certain treble boosters can sound like c0cked wah

That's because of the interaction between passive pickups and the input impedance, which is why the SPICE sims above include the guitar circuit. A low-Z source (active pickups or a buffer) would remove this interaction, but you probably don't want that.

How about the breakup and harmonics of the transistor? Can this result in EQ shaping?

It doesn't really influence the input high-pass but harmonic distortion changes the frequency content of the signal, of course.

[antonis]

Lost poist again..!!! 

It's getting silly now..

[GibsonGM]

On that note, I do have an LPB-1 that I find too dark and would like to mod. It has two HPFs, one at the input and one further down IIRC. I plan to add a three-way switch to switch between caps, should I only do it at the input HPF, at the later one, or at both?

That circuit is so simple, the easiest way to change its response is to adjust the input cap, and the output cap would also be 'fair game'.   One could try that cap blend shown above at the input!   

I would make one on breadboard and see what differences the changes make, then incorporate it into your existing build...that's just me   I think you'll find lowering the input cap makes a big difference!   The circuit wasn't designed to be 'treble boosting'; all I wanted from mine is a bit less darkness, as you noted...

[Lino22]

Lost poist again..!!! 

It's getting silly now..

Antonis, when you write a longer text do occasional CTRL+A + CTRL+C.

[amptramp]

One of the considerations for the design of a treble booster is the input impedance of the amplifier connected to the guitar forms a lowpass filter with the inductance of the pickup.  You have a voltage divider between the guitar inductance and the input of the amplifier which causes the apparent gain to go down as the frequency goes up which is not going in the direction of treble boost.

What happens here is the "harmonics" from the guitar which are generally slightly higher than exact multiples of the fundamental due to string stiffness are suppressed and replaced by the harmonics that are exact multiples of the guitar fundamental frequency caused by non-linearity in the amplifier.  When the volume control on the guitar is reduced from maximum, there is a series resistance that is included that changes the filtering on the input so the cleanup when you reduce the guitar pot comes from the interaction of the added resistance of the guitar output with the input impedance of the amplifier.

That gives you a whole bunch of new calculations to do if you want to get an exact characterization of the guitar + amplifier output.

[mozz]

Wasn't the OC44/45 a rf transistor? I would think the capacitance would be less than 47pf. Maybe they were buying rejected parts as you wouldn't pay more for a rf transistor if it wasn't needed.  I may have some here, will have to measure. 

[antonis]

I think OP should be totally confused by also taking into account LPF created of C-B capacitance (multiplied with stage gain + 1, due to Miller effect..) of widely varied corner frequency (dependent on HEAT pot setting..)

@RaistMagus: Better breadboard any treble booster of your taste and tweak ONE AT A TIME item (preferably capacitor)..

[GibsonGM]

Yes; the calculations are strange, and are like a secret language.  I find it much easier to build the thing on breadboard and then PLAY it.   Try it with other pedals before and after, see how or if they interact with changes to the original design.

This is 'tuning by ear'.  Even commercial pedals can sound great with one guitar/amp, and give poor or just not-exciting performance with others...