on my modular preamp pcb theres a considerable length of track from the output of the circuit to the output jack.
my question is where is the optimal location for the output resistor in this situation? should it be nearest the output transistor or the output jack(rca)?
what i wonder in detail is how the feedback will behave with these variables. with the output resistor far away from the circuit the trace leading up to it is included in the feedback. will it then happily cancel the distortion to where the overall distortion is lower than with the alternative scenario where the excessive trace length is isolated from the circuit by having the output resistor right at the transistor?
my question is where is the optimal location for the output resistor in this situation? should it be nearest the output transistor or the output jack(rca)?
what i wonder in detail is how the feedback will behave with these variables. with the output resistor far away from the circuit the trace leading up to it is included in the feedback. will it then happily cancel the distortion to where the overall distortion is lower than with the alternative scenario where the excessive trace length is isolated from the circuit by having the output resistor right at the transistor?
At audio frequencies it won't make a difference. I presume "considerable length" doesn't mean >1km.
Wire is linear(*), so you don't have to worry about distortion happening along a length of wire.
(*) Like all metal conductors and resistors.
Wire is linear(*), so you don't have to worry about distortion happening along a length of wire.
(*) Like all metal conductors and resistors.
The output resistor isolates a negative feedback loop from the outside world at high frequencies and help keep the amplifier stable. In my opinion, that resistor should be placed next to the output stage transistors to minimize the size of the Vout node. Although the signal we are dealing with is of mere audio frequency range, the characteristics at higher frequencies, into many MHz, of a feedback loop is important to the amplifier's performance and stability. So the size and extension of the Vout node might matter. Length of PCB trace leading to an RCA jack on the other hand is usually not an issue. I'd see it as a small extension of the interconnect cable that follows it.
If all the resistors are placed close to the active device (transistor or op amp), then long traces won't affect audio.
If the long traces go directly to the op amp inputs or output, then they can pick up stray signals or introduce stability issues.
So that 100 ohm resistor in series with the output should be placed as close as possible to the output of the op amp. The output is an input too and if you're careless about layout then some day you'll discover this for yourself.
A good design is impervious to long cables, external EM fields, and power supply noise.
If the long traces go directly to the op amp inputs or output, then they can pick up stray signals or introduce stability issues.
So that 100 ohm resistor in series with the output should be placed as close as possible to the output of the op amp. The output is an input too and if you're careless about layout then some day you'll discover this for yourself.
A good design is impervious to long cables, external EM fields, and power supply noise.