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Weird preamp behavior
Hello everyone,
I've been modifying Minipulse plus. And while I was swapping some op-amps with the NE5532, all seemed normal until I replaced it with JRC2904D (LM2904D) because it gave me abnormal wave. So I thought of sharing it with you guys hoping that someone can clarify what might be going on.
It's strange enough that this particular amplifier gives the detector a very noticeable detection range when compared to NE5532. 3-5 more inches for most coins and an inch or two for a gram nugget.
Here is some info about my setup:
coil is mono, 30 CM in diameter, about 310 uH, and 1.7 ohm
TX pulse width about 57.5 uS and rate is 1000 pps
Damping resistor is about 311 ohms (please see photo when I lowered the resistance)
Main sample pulse width is adjustable 10 - 64 uS
Yellow is preamp output & Blue is TX Pulse:
Yellow is preamp output & Blue is Flyback:
Yellow is preamp output & Blue is Main sample pulse:
Yellow is preamp output (while damping resistor is too low at 145 ohms. Also it's about same wave when coil is perfectly damped but a coin is presented to the coil) & Blue is Main sample pulse:
Yellow is preamp output (while a cola can is presented and coil is perfectly damped at 311 ohms)& Blue is Main sample pulse:
This is a normal output of NE5532 with its noise:
I should mention that the waveform at pin 1 (first stage) is the same at pin 7 except saturation takes less time. Finally, the LM2904 is frequently considered an immediate replacement for LM358, but when I tried it out it, I didn't get any response mostly because it didn't fit with my timings although its output signal is similar to LM2904.
Thanks
I've been modifying Minipulse plus. And while I was swapping some op-amps with the NE5532, all seemed normal until I replaced it with JRC2904D (LM2904D) because it gave me abnormal wave. So I thought of sharing it with you guys hoping that someone can clarify what might be going on.
It's strange enough that this particular amplifier gives the detector a very noticeable detection range when compared to NE5532. 3-5 more inches for most coins and an inch or two for a gram nugget.
Here is some info about my setup:
coil is mono, 30 CM in diameter, about 310 uH, and 1.7 ohm
TX pulse width about 57.5 uS and rate is 1000 pps
Damping resistor is about 311 ohms (please see photo when I lowered the resistance)
Main sample pulse width is adjustable 10 - 64 uS
Yellow is preamp output & Blue is TX Pulse:
Yellow is preamp output & Blue is Flyback:
Yellow is preamp output & Blue is Main sample pulse:
Yellow is preamp output (while damping resistor is too low at 145 ohms. Also it's about same wave when coil is perfectly damped but a coin is presented to the coil) & Blue is Main sample pulse:
Yellow is preamp output (while a cola can is presented and coil is perfectly damped at 311 ohms)& Blue is Main sample pulse:
This is a normal output of NE5532 with its noise:
I should mention that the waveform at pin 1 (first stage) is the same at pin 7 except saturation takes less time. Finally, the LM2904 is frequently considered an immediate replacement for LM358, but when I tried it out it, I didn't get any response mostly because it didn't fit with my timings although its output signal is similar to LM2904.
Thanks