LOL Tom thank you for helpful input and taking time to share your knowledge. It is much appreciated.
I feel that I am failing to properly articulate my questions(s) regarding the changes in overall gain from this preamp that might result from eliminating the tone circuits and the latter half of the opamp. I believe you would know the answer(s), if only I could ask the question(s) in the right way 😆
If you replace the tone control with a wire as suggested you won't see any change in overall gain*
*: Assuming tone control pots at centre position.
Tom
*: Assuming tone control pots at centre position.
Tom
That 220k to ground increases the “noise gain” in the op amp to a reasonable value, and sets the maximum gain if it loses feedback altogether. When set to maximum cut the circuit has loss. This R to ground at the inverting input forces a bit of “gain” that’s not seen by the signal to keep the op amp stable. In the case where the bass wiper goes intermittantly open as it rotates, it keeps a maximum closed loop gain of -10 with that 2.2 meg. The circuit would still work if you took those two components out altogether. It would just sound like thunder as the bass control is rotated, and have drastic changes in the amount of hiss as the treble control is rotated, perhaps even going unstable. Maybe not when brand new, but get some years on those pots and you‘ll see. Yeah, the op amp itself may be unity gain stable BUT often stability margins reduce drastically in cases where wires go running off the board to pots, and where pots are in proximity to ground. Stray capacitance. It’s just good practice to mitigate these potential problems.
Of you are leaving that second op amp “disconnected“ those two resistors will operate the op amp with a noise gain of 10x. It’s a good place to leave it to insure it won’t do anything audible.
Of you are leaving that second op amp “disconnected“ those two resistors will operate the op amp with a noise gain of 10x. It’s a good place to leave it to insure it won’t do anything audible.
I'll take a wild guess at the intent of your question.
Intuitively, having resistors in the signal path seems like it should cause loss of signal strength and that removing said "resistance" to the signal should increase strength?
Not in this case. The opamp is responsible for supplying appropriate gain and it is the ratio of resistor values (and capacitor ratios) that control circuit gain/frequency response.
For example, when you change the treble control's wiper position, you're changing the ratio of the resistances on either side of the wiper; this allows you to either reduce or increase signal gain at higher frequency.
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