How's did it go yesterday? Get it working?
I don't see how you'd use an optocoupler or even why in this case. The fundamental problem when combining the two circuits is that the transistor is using ground as it's positive voltage reference and the opamp circuit is using is using +9V (or +4.5V with respect to ground). Ground, V+ and V- are different things to the circuits, but they need to be the same things to work together.
I tried to draw a schematic for you to better explain what is going on and why it's not working but I couldn't draw anything that seemed like it would help (and besides, I'd prolly get flamed for the "errors" in the schematic).
Let's see if I can explain. Transistor circuits generally use a single supply, so 9V and GND in this case. When used as an amplifier, they need a positive base bias voltage but note, this bias voltage is not generally 1/2 the supply like it is in opamps. The bias voltage essentially sets the water level, or the midpoint for our signal to swing up and down.
In your circuit, you grounded the + terminal of the battery and the emitter was tied to the - terminal. Since you said you are getting a signal out with gain, I assume that you have a bias voltage of some sort, eventhough it may not look like the picture in the link i posted.
Opamps can use a single or dual supply, in your case, since you didn't show a ground connection on the power pins, you are making the 9V look like a dual supply to the opamp or +/-4.5V with respect to ground. Again, since you said the circuit works on its own, I assume the supply is referenced somehow to ground (this would be two equal high value resistors, one from + to gnd, one from - to gnd (this is what Ron was talking about).
So our transistor's collector is referenced to gnd, it's emitter is referenced to -9V and it's base must be some - value between (check with a DMM). Our opamp's + pin is at +4.5V, it's - pin is at -4.5V and I assume it's pin3 input is at 0V or gnd.
When we combine the two circuits, our opamp gets it's + pin grounded (by the transistor's supply connection but our voltage reference is also grounded, which means we bypassed the reference resistor from V+ to gnd, which means our input to the opamp is now at V+ or ground in this case. Because the opamp no longer has a half supply reference, it won't work. Does that make sense?
So again, your options are:
If your would like to use the transistor circuit, then the opamp needs to be run as a single supply. For convention's sake, rewire the transistor to a positive supply and ground the negative portion of the supply. The opamp will then have a +9V + and a GND -, so you need to generate a half supply voltage for pin3 with 2 simple resistors (or see the recent post about the guitar preamp).
If you want to keep the opamp as a dual supply config, then use a second opamp in place of the transistor.
Hope this helps!
I don't see how you'd use an optocoupler or even why in this case. The fundamental problem when combining the two circuits is that the transistor is using ground as it's positive voltage reference and the opamp circuit is using is using +9V (or +4.5V with respect to ground). Ground, V+ and V- are different things to the circuits, but they need to be the same things to work together.
I tried to draw a schematic for you to better explain what is going on and why it's not working but I couldn't draw anything that seemed like it would help (and besides, I'd prolly get flamed for the "errors" in the schematic).
Let's see if I can explain. Transistor circuits generally use a single supply, so 9V and GND in this case. When used as an amplifier, they need a positive base bias voltage but note, this bias voltage is not generally 1/2 the supply like it is in opamps. The bias voltage essentially sets the water level, or the midpoint for our signal to swing up and down.
In your circuit, you grounded the + terminal of the battery and the emitter was tied to the - terminal. Since you said you are getting a signal out with gain, I assume that you have a bias voltage of some sort, eventhough it may not look like the picture in the link i posted.
Opamps can use a single or dual supply, in your case, since you didn't show a ground connection on the power pins, you are making the 9V look like a dual supply to the opamp or +/-4.5V with respect to ground. Again, since you said the circuit works on its own, I assume the supply is referenced somehow to ground (this would be two equal high value resistors, one from + to gnd, one from - to gnd (this is what Ron was talking about).
So our transistor's collector is referenced to gnd, it's emitter is referenced to -9V and it's base must be some - value between (check with a DMM). Our opamp's + pin is at +4.5V, it's - pin is at -4.5V and I assume it's pin3 input is at 0V or gnd.
When we combine the two circuits, our opamp gets it's + pin grounded (by the transistor's supply connection but our voltage reference is also grounded, which means we bypassed the reference resistor from V+ to gnd, which means our input to the opamp is now at V+ or ground in this case. Because the opamp no longer has a half supply reference, it won't work. Does that make sense?
So again, your options are:
If your would like to use the transistor circuit, then the opamp needs to be run as a single supply. For convention's sake, rewire the transistor to a positive supply and ground the negative portion of the supply. The opamp will then have a +9V + and a GND -, so you need to generate a half supply voltage for pin3 with 2 simple resistors (or see the recent post about the guitar preamp).
If you want to keep the opamp as a dual supply config, then use a second opamp in place of the transistor.
Hope this helps!