Ld1014d question about noise

[woody]

In looking at this high power jfet I wonder if it might be suitable for a small low impedance source follower in the 50 to 100ma range. Does anyone know if it would be very noisy when used like that with a 500 ohm source impedance ?

 

[BesPav]

What signal swing are desired?
In the --someVolt range i suppose noise will not be the problem.

 

[woody]

I was thinking about 5v 50 ma at 15v drain to source with a 500 ohm input source resistance at 1k hrz.

 

[BesPav]

For ~100 Ohm headphones?

 

[Presidentovich]

Is this an amplifier for speakers???

 

[BesPav]

Is this an amplifier for speakers???

No.
50 mA idle current follower can't provide enough current to drive speakers.

 

[jackinnj]

Familiar with the Zen8? PassDiy

 

[MarcelvdG]

It has a high transconductance and it must have a large die area, so chances are its equivalent input voltage noise level will be quite low. Current noise will be low(*) as long as you reverse bias the gate, which will happen automatically at 50 mA to 100 mA.

(*): Regarding noise current, a smaller JFET will be even better, but you will only notice that at very high source impedances, like those of condenser microphone capsules without built-in amplifier.

 

[jackinnj]

Here's the Zen9 "noise" -- to get flat frequency response (into a 6 ohm passive load) I had to increase Vds to 2.12, and lower the current to 1.6A. Gain is 21dB.

I've run the LU1014 on its own, not yet satisfied with the results.

 

[jackinnj]

Here's the LU1014D all by itself, powered by Groner's ultra low noise current source (400pA/RtHz), adjusted to 50mA:

 

[woody]

In looking at the old Pass Bride Of Zen preamp it occured to me that it would be incredibly easy to modify it to a cascode using the Ld1014d like was done in the Zen 8. Heck with about 2.5v across the Ld1014d at 40ma it wouldn't even need any heatsink. I was just concerned with the noise. Wonder if it would sound better than the original.

 

[jackinnj]

As it relates to the LU1014D, try as I might I can't get gain over 5x at 50mA in a simple config. Needs more gas, but will leave further analysis to another DIY member. Nonetheless, noise is very good and consistent with the results I wasn't happy with, in the sense that the 1/f corner is roughly the same.