dpresley58 Posted September 23, 2009 Report Share Posted September 23, 2009 I've built a small transistor-based preamp and powered it with a standard 9v battery. Its using a SPST switch to which the ground is hooked to turn it on. The problem is that there is a substantial thump when the switch is thrown, and I'm looking for a solution with a small component count that would slowly ramp the power to the circuit in hopes that approach would eliminate the pop. Is there a simple approach to this? Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 23, 2009 Report Share Posted September 23, 2009 I've built a small transistor-based preamp and powered it with a standard 9v battery. Its using a SPST switch to which the ground is hooked to turn it on. The problem is that there is a substantial thump when the switch is thrown, and I'm looking for a solution with a small component count that would slowly ramp the power to the circuit in hopes that approach would eliminate the pop. Is there a simple approach to this? Post its schematic for us to see if its biasing can have a slow ramp-up. Quote Link to comment Share on other sites More sharing options...
dpresley58 Posted September 23, 2009 Author Report Share Posted September 23, 2009 Thanks. The schematic is under Topic 9 of this link.http://runoffgroove.com/fetzervalve.htmlAlthough the author used pots for dialing in the source and drain resistors, I've calc'd resistors for the individual transistors. He shows a small breadboard jig for measuring these values. Since my application is stereo, I had to find 2 trannies that were more or less matched. I'm using the J201, by the way. Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 23, 2009 Report Share Posted September 23, 2009 The Jfet is self-biased so its output suddenly jumps up when its power supply voltage is applied.If you slowly ramp up its power supply voltage then it should not make a POP sound. Quote Link to comment Share on other sites More sharing options...
dpresley58 Posted September 23, 2009 Author Report Share Posted September 23, 2009 What would be a good method of doing this while keeping component count down? A decent-sized cap (100uf) with a pull-down resistor to ground on the way from the switch to the board? Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 23, 2009 Report Share Posted September 23, 2009 Since you are switching its ground instead of switching its positive supply to turn it on and off then ramping the power supply voltage must also be done backwards. A PNP emitter-follower transistor can provide the Jfet preamp with a ramping 0V. Quote Link to comment Share on other sites More sharing options...
dpresley58 Posted September 23, 2009 Author Report Share Posted September 23, 2009 I see what you're saying... Not particularly married to the switching situation - the positive could be used just as easily, since it only really amounts to breaking the battery leads with a switch. I'll look into the emitter-follower.And thanks... Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 23, 2009 Report Share Posted September 23, 2009 If you switch its positive supply then an NPN emitter-follower can provide a slowly ramping positive supply to the Jfets. Quote Link to comment Share on other sites More sharing options...
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