OTL Asylum OTL, Output Transformerless Amplifier User Group.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ OTL Asylum ]

---

[ Alert Moderator ]

---

Re: Thanks, Al.....

Posted by Al Sekela (A) on April 25, 2002 at 16:08:59

In Reply to: Thanks, Al..... posted by Lew on April 24, 2002 at 14:59:38:

Lew,

You're welcome. Did you receive a circuit diagram with your amps?

The 100 uF capacitor in Paul's circuit for the grid of V2 is to remove power supply noise. The left end of the horizontal 100K resistor in Paul's sketch of his circuit is at a-c ground because of the 100 uF capacitor. This causes almost all the noise present at the +300V node to drop across the 499K resistor. The grids are fed through another R-C filter comprising the horizontal 100K resistor and the 0.47 uF capacitor, presumably to remove residual noise the electrolytic cap cannot filter due to its internal inductance and effective series resistance.

The stock circuit uses the 'fixed' voltage drop across the Zener diode to accomplish the same thing. Zener diodes have a residual dynamic resistance, so some small amount of noise will survive at its cathode, and the 0.47 uF cap is meant to deal with it. Mark's circuit adds the additional filter of the 100K resistor and another 0.47 uF cap to further reduce both the power supply and Zener diode noise.

Please see Ralph's comments regarding the effects of bypassing the voltage divider stack in the current source grid circuits.

-Al

This post is made possible by the generous support of people like you and our sponsors:

Atma-Sphere Music Systems, Inc.

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---