OP AMPS QUESTION

[daverave]

are there any better op amps than the ne 5534 with better low noise and slew rate ???

[traverso40]

are there any better op amps than the ne 5534 with better low noise and slew rate ???

LT1028 Linear Tchnology
cheers traverso

[daverave]

thanks for that will have to order some.

[Qiaozhi]

are there any better op amps than the ne 5534 with better low noise and slew rate ???

KRinAZ used an LM4562 for increased sensitivity -> http://www.geotech1.com/forums/showt...586#post206586

[Davor]

Hope you know how to configure an op amp for low noise. Most of the designs here can't be improved noise-wise by simple op amp replacement.
Perhaps you should indicate what schematic you intend to improve?

[daverave]

i want to improve my surf pi as i got some jitter on the audio...i scoped the coil waveform coming from the 1st amp and it has noise imposed on it...i took the 1st amp out of circuit and audio was so nice and smooth and without jitter...i really want to improve this detector and make it more stable.

[Davor]

Noise is not the parameter you can fix with low noise op amp in surf PI. It is limited to ~4nV/sqrt(Hz) - exactly the NE5534 figure. Op amps with better slew rate and linearity may do a trick or two, but most probably the noise you experience is due to the avalanche noise of a MOSFET.

[daverave]

so is it better to use a bipolar coil drive instead of a mosfet...the noise i see on the scope looks random....but even with the detector gain turned right down i can still hear jitter on the audio....when i first made my surf pi i did not consider noise but now ive taken it apart and done some tests i can see things are far from perfect and i just want to improve this noise problem.

[Altra]

One thing that can help reduce noise is changing the TX frequency. If
you add a pot that can adjust the TX +/-100Hz in the field you can syncronize
the tx and interference.

[kt315]

http://www.findmall.com/read.php?34,...181#msg-127181

[daverave]

i wonder if the damping resistor might be part of the problem as its only a 1/4 watt metal film and it does run hot and maybe creates noise when hot !!!

[Teleno]

... most probably the noise you experience is due to the avalanche noise of a MOSFET.

As I understand, avalanche noise exists only when the bias voltage is close to the breakdown voltage. Once the flyback is over there should be no such noise, methinks.

[daverave]

not sure what you saying but i have taken the mosfet to its limit of 200v....the coil is drawing about 120 ma

[Qiaozhi]

Does the noise change when you move the coil from a horizontal to a vertical position? If so, it's most likely externally induced noise. Testing PIs in the house is well known to be problematic due to EMI.

[kt315]

in room use a microcoil with short wires connected. this will reduce EMI influence transfering from around.