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In Reply to: RE: "homemade dual opamps." posted by sailor321 on December 21, 2016 at 16:38:31
He's not really making a "homemade opamp". That would require a couple billion dollar investment in a semiconductor fab. He's not even making a discrete opamp from a handful of transistors.
He is simply incorporating a minor tweak to another opamp and placing it on a header adapting it to fit into his existing opamp IC socket. More specifically he is using an opamp with an offset adjustment to null out any DC offset at the output of the opamp. This is typically done with a multi-turn trimpot.
Also, I'm not sure what he means when he says "it's easier if you have an opamp tester". Personally, I've never heard of such a thing. Try Googling it. You -might- find an oddball classroom gadget or hobby toy that fits that description . A good digital multi-meter (DMM) is what most professionals would use.
A representative op-amp block diagram with 100K-Ohm offset adjustment trimpot.
Follow Ups:
That would require a couple billion dollar investment in a semiconductor fab.and so, by definition, wouldn't be home made. I at least took fmak's "homemade" to mean "homebrew" (aka "tweaked") esp after he described the circuit.
Whatever, configuring op-amps so they don't need an output cap is definitely not new. For many years, I used an I/V circuit discussed by Audio Synthesis in HiFi News way back in 1987. It used a voltage reference chip to adjust the -IN of an AD42 op amp and thereby cancel DC offset on its output. IIRC, similar circuits were discussed by Walt Jung and others.
The device did me for ~25 years until I replaced it with a Lampizator SRPP circuit that sounds much better even though the tubes it uses are even older than the AD42 and definitely need output caps. (The TDA1541A chip that has happily driven both devices is now 30-odd years old but is soon to be reconfigured to use "simultaneous" mode courtesy of a spanking new USB board from Audial. Or so I hope.)
D
Edits: 12/22/16
This is another ignorant statement. I have just bought two discrete dual opamp replacements for $90. Add another 30 or so, and another circuit board layer can be added to cancel out any offset dc as you alluded to.It is quite sad that self styled computer geeks simply don't know what they are on about wrt simple electronics, and yet they seem to want to establish web credibility by slighting others.
Edits: 12/22/16
Welcome back, Fred.
We missed you!
This demonstrates all too well your ignorance
Please show me an "opamp tester". I have never seen one, really. I've always used a quality bench DMM and oscilloscope. What brands of "opamp testers" are out there and how much do they cost?
If you'd asked nicely, I would have explained.
The nature of your posts is such that I won't have a conversation with you.
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