Thanks Richard this is setting me on the right track, but I have more questions...
On 05/10/2024 22:04, Richard Lee via groups.io wrote:
Dunno about piezo amps @ about 10M but for a LN condensor mike over 1G, the diodes must have VERY low leakage.
1n4148 far too leaky and noisy.
yes, I think it is degrading my noise levels even at the <5M input impedance of the circuit I linked to.
Guru Scott Wurcer liked a smoke alarm FET used as a diode. Another 'diode' for this is the BE junction of an old fashioned LN BJT like BC214 or 2n5087.
no space for this in my piezo circuit but I'll keep it in mind for future higher impedance pluggable setups.
Schottkys have very poor leakage which gets worse with time. The latest THAT 1510/12 datasheets for microphone preamps recommend cheapo 1n4003GP (Glass Passivated).
Why 4003 rather than say 4007?
and what is the advantage of the glass passivated? does it reduce the leakage?
I've seen BAV199 (dual low leakage surface mount) mentioned in some searching for fet input protection. The small size, though hard to solder, would actually suit me for my current application.
any comments on BAV199?
is overall beefiness a consideration? ie max forward current, max reverse voltage? BAV199 are small diodes with low voltage and current specs.
