Re: >>> Sparkle Face Research Project <<<
Posted: Tue Jun 13, 2017 3:28 pm[quote="mrpicard"]As promised, here is the Bone Bender 1 Schema:
Hi there,
thank you mrpicard,
Here's short tour through the circuit. The first stage in a Mark 1 is a buffer and it was made with a germanium transistors and the first run of Bone Benders were made like this. However as I consider the buffer having little impact on sound while on the look out for ways to reducing noise I decided to try a J-Fet and the adjusted the inputimpedance to be more similar to what could be expected from a germanium transistor and that is seen in the choice of R1 that effectively sets the inputimpedance of the J-Fet as that has an internal impedance of several Mega Ohm's; for a germanium transistor input impedance is roughly calculated as hie+hfe times the emitter load and thus is a little less predictable and varies with setting of Attack control but I set R1 empirically while listening to how volume control on guitar reacted and top treble and decided 300K was about fine.At buffer output comes Attack control that effectively limits gain of circuit by the divider it forms with the input impedance of gain stage 1. Gain stages 1&2 are made similar and both are set up with traditional stabilization networks for a transistor- note though that since germanium transistors have a leakage current from Collector to base known as Icb and that Icb is a variable between the germanium transistors the stabilization network must take this into account ( for silicon transistors of modern kind Ibc is generally so small it can be ignored for all practical purposes- not so with germanium transistors as those can even be turned on into working state by virtue of Ibc) while in the circuit there's a trimmer to each base so linear at very small signals response can be set- how to do this is described above in a Guitarit's Approach to Biasing Fuzzes. There are two caps one for each gain stage between collector and base and those are amplified by the Miller effect so their true value is gain times pF+ ghost Miller cap,that is formed internally to the transistor- Values of those caps were set empirically to limit upper treble just above 'vital' treble as in just above where a loss was perceived. Finally there's a Volume control and the circuit since it uses all NPN and N-channel J-Fet is negatively grounded and the B-tree is supplied with a decoupling capacitor and series filter resistor and also polarity protection and there's an LED connected to show status of fuzz as in activated or not activated and because of this the fuzz can be driven from a standard +9V supply and it is fairly stable to Voltage fluctuations so there is no real benefit from running the circuit from a battery while it certainly can be driven by a battery. However sound will differ with differing Voltage and on some supplies Voltage can be manually set from say 4,5V to 9V and of course at lower voltages sound will saturate sooner.
Difference between the versions are noted in the schematic and notice since there's ample trimming range any typical germanium NPN transistor can be used in the circuit and be biased but biasing must be performed if linear to small signal conditions shall apply.
I am greatly looking forward to hearing thoughts on the Bone Bender 1 design both from those that have a BJF and those that build one themselves and speaking of DIY if anybody would like to do a vero layout et.c I'd much appreciate that.
Have fun
BJ
Hi there,
thank you mrpicard,
Here's short tour through the circuit. The first stage in a Mark 1 is a buffer and it was made with a germanium transistors and the first run of Bone Benders were made like this. However as I consider the buffer having little impact on sound while on the look out for ways to reducing noise I decided to try a J-Fet and the adjusted the inputimpedance to be more similar to what could be expected from a germanium transistor and that is seen in the choice of R1 that effectively sets the inputimpedance of the J-Fet as that has an internal impedance of several Mega Ohm's; for a germanium transistor input impedance is roughly calculated as hie+hfe times the emitter load and thus is a little less predictable and varies with setting of Attack control but I set R1 empirically while listening to how volume control on guitar reacted and top treble and decided 300K was about fine.At buffer output comes Attack control that effectively limits gain of circuit by the divider it forms with the input impedance of gain stage 1. Gain stages 1&2 are made similar and both are set up with traditional stabilization networks for a transistor- note though that since germanium transistors have a leakage current from Collector to base known as Icb and that Icb is a variable between the germanium transistors the stabilization network must take this into account ( for silicon transistors of modern kind Ibc is generally so small it can be ignored for all practical purposes- not so with germanium transistors as those can even be turned on into working state by virtue of Ibc) while in the circuit there's a trimmer to each base so linear at very small signals response can be set- how to do this is described above in a Guitarit's Approach to Biasing Fuzzes. There are two caps one for each gain stage between collector and base and those are amplified by the Miller effect so their true value is gain times pF+ ghost Miller cap,that is formed internally to the transistor- Values of those caps were set empirically to limit upper treble just above 'vital' treble as in just above where a loss was perceived. Finally there's a Volume control and the circuit since it uses all NPN and N-channel J-Fet is negatively grounded and the B-tree is supplied with a decoupling capacitor and series filter resistor and also polarity protection and there's an LED connected to show status of fuzz as in activated or not activated and because of this the fuzz can be driven from a standard +9V supply and it is fairly stable to Voltage fluctuations so there is no real benefit from running the circuit from a battery while it certainly can be driven by a battery. However sound will differ with differing Voltage and on some supplies Voltage can be manually set from say 4,5V to 9V and of course at lower voltages sound will saturate sooner.
Difference between the versions are noted in the schematic and notice since there's ample trimming range any typical germanium NPN transistor can be used in the circuit and be biased but biasing must be performed if linear to small signal conditions shall apply.
I am greatly looking forward to hearing thoughts on the Bone Bender 1 design both from those that have a BJF and those that build one themselves and speaking of DIY if anybody would like to do a vero layout et.c I'd much appreciate that.
Have fun
BJ
