Matador
Well-known member
The stock 60's Fender Reverb topology has the reverb signal being injected in parallel with the 'dry' signal across a 3M3 || 10pF LPF network that is placed in series with the dry signal. This arrangement works since the dry signal path and the reverb signal path both undergo 360 degrees of phase shift thus can be summed across this network.
It's also pretty noisy: shorting across the 3M3 || 10pF network causes the background hiss to drop considerably (and yes, you lose the reverb), which got me to thinking: if I were building a single channel version of the circuit, the normal and vibrato channel are mixed together at the input to the PI through 220K mix resistors. If there is no dry channel, one just shorts one of the 220K resistors to ground. But what if we were to use it to mix the reverb in with the dry signal?
Schem is here: https://robrobinette.com/images/Guitar/Deluxe_Models/AB763_Deluxe_Reverb_Annotated_Schematic.jpg
One thing I notice is that injecting the reverb at the 220k mix resistor places the reverb signal out of phase with the dry signal, causing cancellation. However since we pass through the reverb transformer, there's an opportunity to add 180 degrees more phase shift by reversing the leads of the reverb transformer, and which point we align back with the polarity of the vibrato channel, and in theory this should work and be far less noisy.
Has anyone tried this? I've attached the 'stock' topology and my 'proposed' topology.
It's also pretty noisy: shorting across the 3M3 || 10pF network causes the background hiss to drop considerably (and yes, you lose the reverb), which got me to thinking: if I were building a single channel version of the circuit, the normal and vibrato channel are mixed together at the input to the PI through 220K mix resistors. If there is no dry channel, one just shorts one of the 220K resistors to ground. But what if we were to use it to mix the reverb in with the dry signal?
Schem is here: https://robrobinette.com/images/Guitar/Deluxe_Models/AB763_Deluxe_Reverb_Annotated_Schematic.jpg
One thing I notice is that injecting the reverb at the 220k mix resistor places the reverb signal out of phase with the dry signal, causing cancellation. However since we pass through the reverb transformer, there's an opportunity to add 180 degrees more phase shift by reversing the leads of the reverb transformer, and which point we align back with the polarity of the vibrato channel, and in theory this should work and be far less noisy.
Has anyone tried this? I've attached the 'stock' topology and my 'proposed' topology.
