In post #15 I suggest removing R3 and R4 and then connect pin 3 directly to pin 1 (and/or) 4 of the HT9170 (as I have in my circuit sketch in post #92). This will let you use the internal 'half rail' voltage reference (2.5V) within the HT9170 to provide the bias for your opamp, rather than the resistors.rogs
Im going to try the circuit you suggested in post #15 where you stated
keep it simple by using the LM358 circuit.And subsituting it with the
LMV358 part.R3 and R4 would need to stay in the circuit
to bias the IC with a single power supply as stated in the datesheet.
But you suggest removing them. Why? The circuit my not function
correctly with out those resistors in the circuit.
If this circuit dose not give me the results i need. Maybe you got a completed circuit schematic that you
used and build for a Preamp.With these parts.
This is a much lower impedance reference than the resistors provide, and should help with any noise or hum problems that may come form either the supply rail itself, or from the high value of the resistors R3 and R4.
Not saying that will occur, but it may
As I mention in several of my previous posts, a recording of the DTMF you have manged to pick up so far would give a much better idea of what's actually happening, and hopefully give some pointers as to why you're not getting the results you need.....