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hey, i'm afraid the LM368 IS an opAmp, not a verry "good" one, compared to the LM675 or the LM3875. the fact the gain is fariable via an external system is a practice in verry much old opamps, but has become mostly obsolete because negative feedback works way better (more linear and less frequency responding), but for hobby projects they left it in the LM386
FYI: NO NEED FOR A RESISTORthe internal circuit from the powersupply limits the current within its nature, its kinda hard to explain but the power drawn from the net can't go higher than a certain wattage. also a current limiting resistor for those currents should be of high power capability, more than 10W will be dissipated, since the current neded to heat this up is more than 2A.i should know, being an electrical engeneer
no need for a resistori have read in a few comments that a current limiting should be added, but most if not all powersupplies have a current limitation internal. for this to work there should be more than 2A of current, given that an apple power charger is 5V the resistor should dissipate more than 10W, most resistors are rated 1/4W, also that kind of resistor would be bulky and will become warm, instead of the tip becoming hot making the tool useless
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use the pentode and the triode for the two gain stages, the pentode will sound heavy, since the pentode has a far higher mu (gain) factor than the triodes in this schematic
hey,another way for a gain POT is connecting pin 3 to the tube's pin 9, POT pin 1 to ground and a 100uf cap between POT pins 1 and 2 (see image, srry for the use of MS Paint), this works verry good for me, u used it in a transistor/tube hybrid pedal, but i used a trim pot, and another pot for changeable gain
yes, by turning the gain kob to a lower resistence, the gain gets higer, keep this in mind while making the pedal so you don't have reverse knobs, i've had that a few times and it sucks
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