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previous: ChrisW I did have the same idee as Reverb ... -- 6/30/2000 9:19 AM

Re: disconnecting the tone stack

6/30/2000 3:06 PM
dgiust	Re: disconnecting the tone stack I'd like to offer my suggestion, kind of a combination of ideas, along the lines of the idea I had in the first place. You've got the 6.8k in there. Disconnect it and put a resistor in series to ground, whatever value you decide on, say 10k just to put a value on it.The idea is to switch so the 10k is "bypassed" , so that the 10k is not in the circuit, so the "bottom" of the 6.8k goes to ground. That'd be normal mode. Mid Boost mode would be both in series. So what you want to do is somehow connect the "top" of the 10k (the side connected to the 6.8k) to ground (for normal mode) , and for mid boost mode, open that connection to ground. My solution would be to use simple BJT switching. Any low power generic transistor will do. You can rectify and filter the 6.3VAC heater voltage to get around 4-5 DC (depending on the actual 6.3VAC voltage, and how it's set up)to use as your VCC for the transistor. Put a cap (say 0.1uF) at the junction of the 6.8k and the 10k. Connect the collector of the BJT to the other side of the cap. The BJT emmitter connects to ground. Connect one side of a 10k resistor to the base of the BJT, the other side to the DC.This will provide bias to turn the BJT ona and off. The footswitch will connect to the base of the BJT. When the switch is closed, the base of the BJT is at 0V, ground, the transistor is "off", it's essentially doing nothing. So the 6.8k and 10k are connected in series, mid boost mode. Click the footswitch,the bias voltage gets applied to the base, "turns on" the BJT, creating a path to ground. Signal at the junction of the 6.8k and 10k gets shunted to ground thru the cap. Normal mode. Three things....Some people may say, hey, a BJT in a tube amp?..ok.I say, the function is what's important. Also, I have tried similiar things with a master volume control with good results, but I haven't tried this yet, so experimentation with values is , of course, encouraged. Third, my favorite reason to do it this way...cheap and easy, and easy to undo if it doesn't work for you. I like the idea of using the unused input for the f/s jack, that's what I did on my homebrew. Good luck with whatever you decide to try.

6/30/2000 3:06 PM

dgiust

Re: disconnecting the tone stack

I'd like to offer my suggestion, kind of a combination of ideas, along the lines of the idea I had in the first place.
You've got the 6.8k in there. Disconnect it and put a resistor in series to ground, whatever value you decide on, say 10k just to put a value on it.The idea is to switch so the 10k is "bypassed" , so that the 10k is not in the circuit, so the "bottom" of the 6.8k goes to ground. That'd be normal mode. Mid Boost mode would be both in series. So what you want to do is somehow connect the "top" of the 10k (the side connected to the 6.8k) to ground (for normal mode) , and for mid boost mode, open that connection to ground.
My solution would be to use simple BJT switching. Any low power generic transistor will do. You can rectify and filter the 6.3VAC heater voltage to get around 4-5 DC (depending on the actual 6.3VAC voltage, and how it's set up)to use as your VCC for the transistor. Put a cap (say 0.1uF) at the junction of the 6.8k and the 10k. Connect the collector of the BJT to the other side of the cap. The BJT emmitter connects to ground. Connect one side of a 10k resistor to the base of the BJT, the other side to the DC.This will provide bias to turn the BJT ona and off. The footswitch will connect to the base of the BJT. When the switch is closed, the base of the BJT is at 0V, ground, the transistor is "off", it's essentially doing nothing. So the 6.8k and 10k are connected in series, mid boost mode.
Click the footswitch,the bias voltage gets applied to the base, "turns on" the BJT, creating a path to ground. Signal at the junction of the 6.8k and 10k gets shunted to ground thru the cap. Normal mode.

Three things....Some people may say, hey, a BJT in a tube amp?..ok.I say, the function is what's important.
Also, I have tried similiar things with a master volume control with good results, but I haven't tried this yet, so experimentation with values is , of course, encouraged.
Third, my favorite reason to do it this way...cheap and easy, and easy to undo if it doesn't work for you.
I like the idea of using the unused input for the f/s jack, that's what I did on my homebrew. Good luck with whatever you decide to try.

Replies:

JCS Today I used the A/B box to switch ... -- 7/1/2000 12:18 AM