10-31-2018, 01:23 AM
(This post was last modified: 10-31-2018, 11:05 AM by jmcd.
Edit Reason: more thoughts came to mind...
)
The Marshall 1987x and a host of other amps (including the Trainer YBA1, Viva Canada!) have dual inputs, each with its own volume. The parallel inputs come together by way of equal-value resistors (470k in the Marshalls; 100k in the YBA1), often with one of the resistors bypassed with a cap. Many people mod the YBA by swapping out the 100k resistors with 470k resistors in order to 'plexi-fy' the Bass Master. I have several questions about these resistors:
1. Why are they there? If they act as grid stoppers, why not have just one?
2. In what way does their value matter?
3. If bypassed with a cap, as on the brighter input of the 1987x, does this form a bright boost or cut? Initially, I assumed that it was a boost, but now I'm thinking that it interacts with the tube's miller capacitance to form a cut.
Thanks in advance for the edification...
1. Why are they there? If they act as grid stoppers, why not have just one?
2. In what way does their value matter?
3. If bypassed with a cap, as on the brighter input of the 1987x, does this form a bright boost or cut? Initially, I assumed that it was a boost, but now I'm thinking that it interacts with the tube's miller capacitance to form a cut.
Thanks in advance for the edification...
