OTL Asylum OTL, Output Transformerless Amplifier User Group.

---

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

---

[ Alert Moderator ]

---

The MP-1 and MP-3 servo system

Posted by Ralph (M) on December 22, 2023 at 10:49:36

In Reply to: Excessive DC offset on MP1 posted by Lew on December 22, 2023 at 09:57:21:

The LED begins to light up at about 13mV. In normal operation the DC Offset tends to be about 1mV or less.

Its rare to have an IC failure to cause the servo to malfunction. If the preamp does not have a vacuum tube high voltage regulator, then there are no known instances of the servo opamps failing. They have been damaged in older units (Mk1 and some Mk2s) that have the tube regulator due to arcing of the regulator.

Usually the DC Offset LED lights up due to a tube (6SN7) problem. It might be a bad connection on a tube socket too. If the socket is worn, moving the tube while the preamp is on might have the DC Offset LED going on and off due to poor connections in the socket itself.

There have been some updates to the servo system over the years, all with the goal of extending its dynamic range and limiting its bandwidth so as to promote stability of the DC level at the output of the preamp.

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

Sonic Craft

---

[ 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 ]

---