Ok, this one is a little hard to follow at first. Borrowing from some ideas I have gotten from Mauro and others I have created a design that uses a LM3886 and a OPA2227 (dual low noise opamp) to create a non inverting amp, but the LM3886 is operated as inverting. Basically a double inversion with a buffer input.
The first part of the OPA2227 is simply a high input impedance buffer, which feeds the signal through the second gate in inverting mode, that signal is input to the LM3886 in inverting mode, so the final output is not inverted(or completely flipped, which ever you prefer
).
Here is the schematic.
Sorry, its a mess.
The first part of the OPA2227 is simply a high input impedance buffer, which feeds the signal through the second gate in inverting mode, that signal is input to the LM3886 in inverting mode, so the final output is not inverted(or completely flipped, which ever you prefer
).Here is the schematic.
Sorry, its a mess.
Attachments
Jocko Homo said:
You make some pretty aweful assumptions...
A good opamp makes an excellent buffer, and the purpose of the opamp is not "only" to invert the signal.
The worst assumption is about the sound. I have built an amp like this (but it was Maruo's design which is slightly different) and it sounds superb.
One of the reasons this works well is the very low output impedance of the opamp, as well as slew rate and other virtues.
Cheers!
Russ
theChris said:
q1
Yes R2,C7 act to nullify DC.
q2 Well, partly to help set gain for some stages, but on the first stage it is to form a low pass filter to filter out RF.
q3 I was just using values I had used in the past for other applications. Some values I used just because they got me the gain I was looking for.
q4 The reason is the the first opamp gate is purely a buffer to aid the inverting opamp stage.
I am using techniques similar to the ones found here:
http://www.diyaudio.com/forums/showthread.php?postid=622225#post622225
Looking over that thread may answer a lot of your questions.
Almost ready to etch...
I have changed the regulators do to some great input from carlmart and others.
I also added the rest of the missing pieces. I think its ready to go.
The resistor at output can either be 10R 5W with a .7uH inductor wound around it, or .3R 7W.
Here is the current schematic (still a mess sorry).
I have changed the regulators do to some great input from carlmart and others.
I also added the rest of the missing pieces. I think its ready to go.
The resistor at output can either be 10R 5W with a .7uH inductor wound around it, or .3R 7W.
Here is the current schematic (still a mess sorry).
Attachments
carlosfm said:
Ahh now you are more clear, at least on one point. You earlier remark made it sound like I was not using the LM3xx regs. Yes, I had seen that arrangement for PSSR rejection, I wouldn't mind adding that.
Your point about the opamp inverting the signal makes no sense. If an opamp(or any amp) inverts a signal does that mean the inversion is the purpose for the component being in the circuit? Carlos, that is silly.
Thats like saying a person only build an IGC simply because they want an inverted signal or because they enjoy reversing speaker wires.
This is not a new concept, look at the thread I reference earlier.
Thanks for reminding me of the data sheet tip for PSSR on the regs though, not a bad idea.
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