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I just wanted to breadboard a Brian May treble booster. Now here I am over half a year later with my own treble booster design while still not having breadboarded a Brian May booster. Oh well.
At its heart this is still just a Rangemaster. There's an aggressive bass cut followed by a single transistor gain stage. Input impedance is very low and the pedal deliberately loads down the guitar pickups in order to take some of the top end shrillness out of the tone. The low input impedance also makes the pedal clean up very nicely by just turning down the volume on the guitar.
Some of my modifications include a "noiseless biasing" network, improved power filtering, as well as feedback resistors and capacitors around the transistor to tailor the tone to my own liking. The transistor - a ZTX651 - was chosen after auditioning around 30 silicon transistors. It's a medium gain (around 200 hFE) power transistor with pretty high parasitic capacitances compared to other more popular silicon transistors. From my listening tests these parasitic capacitances were a deciding factor in how smooth or harsh a transistor sounds in circuit.
While the final circuit design was specifically tweaked around the ZTX651, the following transistors also had something unique about them that I liked: 2N5550, 2N5551, SS8050, KSC1008, KTD718, TIP41C, BD139 and 2N5088.
To get a little more mileage out of the circuit I experimented with a variety of tone controls and whittled it down to the following:
Level - Classic Rangemaster post-gain volume control. Linear taper pot because I found the sweep range more useful than log taper.
Edge - Variable emitter resistor to change the collector bias from roughly 7V to 3V. Lower bias gives a more compressed, modern tone.
Body - Naga Viper style Range control but reversed and with tweaked values. Essentially a pre-gain bass control. I much prefer this over downright switching the input capacitor value.
Texture (Brash/Smooth) - Somewhat of a pre-gain treble control. Switches between three different base-emitter capacitors. Affects mostly pick attack as well as hiss.
I designed the PCB in DipTrace and had it manufactured by JLCPCB. The enclosure design was done in Illustrator and printed by Tayda on a matte white sand 1590B enclosure.
At its heart this is still just a Rangemaster. There's an aggressive bass cut followed by a single transistor gain stage. Input impedance is very low and the pedal deliberately loads down the guitar pickups in order to take some of the top end shrillness out of the tone. The low input impedance also makes the pedal clean up very nicely by just turning down the volume on the guitar.
Some of my modifications include a "noiseless biasing" network, improved power filtering, as well as feedback resistors and capacitors around the transistor to tailor the tone to my own liking. The transistor - a ZTX651 - was chosen after auditioning around 30 silicon transistors. It's a medium gain (around 200 hFE) power transistor with pretty high parasitic capacitances compared to other more popular silicon transistors. From my listening tests these parasitic capacitances were a deciding factor in how smooth or harsh a transistor sounds in circuit.
While the final circuit design was specifically tweaked around the ZTX651, the following transistors also had something unique about them that I liked: 2N5550, 2N5551, SS8050, KSC1008, KTD718, TIP41C, BD139 and 2N5088.
To get a little more mileage out of the circuit I experimented with a variety of tone controls and whittled it down to the following:
Level - Classic Rangemaster post-gain volume control. Linear taper pot because I found the sweep range more useful than log taper.
Edge - Variable emitter resistor to change the collector bias from roughly 7V to 3V. Lower bias gives a more compressed, modern tone.
Body - Naga Viper style Range control but reversed and with tweaked values. Essentially a pre-gain bass control. I much prefer this over downright switching the input capacitor value.
Texture (Brash/Smooth) - Somewhat of a pre-gain treble control. Switches between three different base-emitter capacitors. Affects mostly pick attack as well as hiss.
I designed the PCB in DipTrace and had it manufactured by JLCPCB. The enclosure design was done in Illustrator and printed by Tayda on a matte white sand 1590B enclosure.
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Initially I was looking specifically for lower gain transistors though, as well as models which are available in different hFE ranges, like BC549A/B/C.
