Intro and switch transient question

Rob22315 · 12th October 2010, 04:06 PM

Saying hi since this is my first post. I came here looking for tips on how to add a buffer preamp (vol and tone are still passive) to my bass.

Thanks to the great tips here, I was able to adapt the tillman/Hugsley preamp to my bass guitar and it works great. I added a switch so I could switch between passive and active. The 9v battery switch too (DPDT). I get a wicked pop when I switch from passive to active, any way to cure this? Note, I do not have the .1microfarad cap on the input to the JFET as shown in Hugley's layout, only a 3M resister. Would that fix it?

I'm sure the answer is simple but I haven't done electronics in a while and a quick search didn't help.

Thanks in advance.

DF96 · 12th October 2010, 06:10 PM

I am not familiar with the circuit, but you must always ensure that when switching signals the DC level is the same. This usually requires a DC blocking capacitor and a resistor to ground for each input, if these are not included in the preceding unit. If you have omitted a capacitor then this could be the cause.

Rob22315 · 12th October 2010, 07:04 PM

That would do it. I have one I can add easily enough.

Rob22315 · 12th October 2010, 11:12 PM

The circuit I built looks very similar to the one in post 81 at the link below:

http://www.diyaudio.com/forums/music...project-9.html

My resistor values are tuned to my JFET and I left out the cap on the input.

12th October 2010, 04:06 PM	#1
Rob22315 diyAudio Member Join Date: Oct 2010 Location: Washington DC metro	Intro and switch transient question Saying hi since this is my first post. I came here looking for tips on how to add a buffer preamp (vol and tone are still passive) to my bass. Thanks to the great tips here, I was able to adapt the tillman/Hugsley preamp to my bass guitar and it works great. I added a switch so I could switch between passive and active. The 9v battery switch too (DPDT). I get a wicked pop when I switch from passive to active, any way to cure this? Note, I do not have the .1microfarad cap on the input to the JFET as shown in Hugley's layout, only a 3M resister. Would that fix it? I'm sure the answer is simple but I haven't done electronics in a while and a quick search didn't help. Thanks in advance.

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12th October 2010, 06:10 PM	#2
DF96 diyAudio Member Join Date: May 2007	I am not familiar with the circuit, but you must always ensure that when switching signals the DC level is the same. This usually requires a DC blocking capacitor and a resistor to ground for each input, if these are not included in the preceding unit. If you have omitted a capacitor then this could be the cause.

12th October 2010, 07:04 PM	#3
Rob22315 diyAudio Member Join Date: Oct 2010 Location: Washington DC metro	That would do it. I have one I can add easily enough.

12th October 2010, 11:12 PM	#4
Rob22315 diyAudio Member Join Date: Oct 2010 Location: Washington DC metro	The circuit I built looks very similar to the one in post 81 at the link below: http://www.diyaudio.com/forums/music...project-9.html My resistor values are tuned to my JFET and I left out the cap on the input.

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