Tag: MOSFET follower

SiC MOSFET Follower Driver

How many more times

Led Zeppelin wrote a fantastic song on their first album: how many more times. You may not be a rock fan, but hey: what a great song. How many more times do I want to get back to this “slew rate” theme? I don’t know, as much as I have to. Plenty of comments out there of bad designs with wimpy drivers attempting to take the 300B/2A3 or even 45 valves to full tilt with disappointing results. Either way, they always blame the valves.

I came back to revisit the driving of capacitive loads effectively as I’m working on a new 4P1L PSE amplifier. Slowly, but getting there. Previously I looked at adding a buffer to the 01a preamp as a result of slew rate limitations found in Tony’s implementation of this preamp.

buffer

 

 

The circuit design

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Slew Rate (Part IV) and the Tale of the three Source Followers

Some of you may be a bit fed up already with these slew rate posts, however I find this fascinating as is taking me through different routes of experimentation.

On my last tests, I abused the DN2540 to an extent which meant the dead of it. So I ended up adding the appropriate back to back protection zeners on the gate:

Depletion FEET with protection zeners
Depletion FET with protection zeners

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Slew Rate (Part III)

Introduction

Are you writing again about the “Slew” thing? There is a lot to be said about the slew rate still. In fact, this post is about some real life measurements and experiences had in the past few days.

This week I went to my friend’s (Tony) place to listen to his 01a with the additional follower discussed previously. Tony complained about that the addition of the follower changed the sound of the 01a. Something was lost, detail on the treble, airiness. I brought up again my test gear and surprisingly we found some H3 level which wasn’t there on the previous preamp. Odd, could that be the FET follower? In the end after several tests, I checked the operating point (you should never assume they should be as expected) and found that the follower wasn’t operating at the optimal level, source current was low and also the 01a was running out of place. I recalibrated the gyrator and voila. The sound of the 01a, came back!

Unfortunately we ran out of time and I did not take any measurements again after re-calibration.

The H3 bug

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