![[-]](https://theultimatetone.com/images/collapse.png "[-]")
11-08-2018, 02:41 AM
Hi jmcd
The resistor in series with the diodes is for voltage compliance, making the clipping softer. You can zero that resistor and have a harder distortion and either way is quite useful for different kinds of music.
If the bounding network is placed at the output of a follower, as in a Marshall, a DC blocking cap is an absolute necessity. The cathode sits at 1-200Vdc and were you to add a pair of 10V zeners in anti-series, the cathode would be pulled down to about 11V. Remember that while one diode "zeners" the other is forward biased and acts like a standard diode, otherwise the series connection would not work.
Placing the cap in series with the bounding network DC-isolates the network but retains the connection between the follower and the EQ. This is purely aesthetic and is probably the way to go in a modification. As a new build, the coupling cap between the follower and EQ allows the builder to use lower-voltage caps in the EQ. In this scenario it is a good idea to add a leak resistor to ground on the EQ side of the new cap. This assures a charge path for the cap regardless of how the bounding network is switched (if it is).
You can use BJTs as low-noise zeners, but the clipping is then at about 7V - no freedom to change this.
Placing the MV after the bounding network is logical because there must be significant signal for the diodes to clip it. The EQ works regardless of its position, although being fed directly from the MV is not a great choice as the source impedance into the EQ is variable. It is one thing for it to be dynamic, as with plate-drive, but off the MV it goes from zero to half the MV pot value, to whatever the impedance is driving the pot. The tone versus MV sweep could be very changeable and unpredictable.
The resistor in series with the diodes is for voltage compliance, making the clipping softer. You can zero that resistor and have a harder distortion and either way is quite useful for different kinds of music.
If the bounding network is placed at the output of a follower, as in a Marshall, a DC blocking cap is an absolute necessity. The cathode sits at 1-200Vdc and were you to add a pair of 10V zeners in anti-series, the cathode would be pulled down to about 11V. Remember that while one diode "zeners" the other is forward biased and acts like a standard diode, otherwise the series connection would not work.
Placing the cap in series with the bounding network DC-isolates the network but retains the connection between the follower and the EQ. This is purely aesthetic and is probably the way to go in a modification. As a new build, the coupling cap between the follower and EQ allows the builder to use lower-voltage caps in the EQ. In this scenario it is a good idea to add a leak resistor to ground on the EQ side of the new cap. This assures a charge path for the cap regardless of how the bounding network is switched (if it is).
You can use BJTs as low-noise zeners, but the clipping is then at about 7V - no freedom to change this.
Placing the MV after the bounding network is logical because there must be significant signal for the diodes to clip it. The EQ works regardless of its position, although being fed directly from the MV is not a great choice as the source impedance into the EQ is variable. It is one thing for it to be dynamic, as with plate-drive, but off the MV it goes from zero to half the MV pot value, to whatever the impedance is driving the pot. The tone versus MV sweep could be very changeable and unpredictable.
