OTL Asylum OTL, Output Transformerless Amplifier User Group.

---

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

---

[ Alert Moderator ]

---

RE: Tim Mellow 25W OTL amp.

Posted by Klarskov (A) on June 9, 2022 at 05:51:15

In Reply to: RE: Tim Mellow 25W OTL amp. posted by cpotl on August 13, 2018 at 07:17:57:

I have built this amplifier and in general I am very pleased with it, but perhaps there is room for improvement?

Tim Mellow mentions in his article that one can increase the input impedance by grounding C1 and connecting the input to C2. However, this will, as he says, "tend to unbalance the input stage slightly unless you use an "ideal" solid-state current source in place of R7". I tested the arrangement briefly and quite superficially (with a LM317 wired as a current source - the "cold" end of the current source connected to ground not to -430V). It seemed to work - but I did not test it very thoroughly.

One of the reasons I am interested in this modification is that this would make the amp non-inverting (as it is published it inverts the absolute phase - which, in most cases, in not problem since the remedy is to invert the loudspeaker connections, but for aesthetic reasons...). Yet, there would be a couple of other small advantages: The neon bulb N1 would not be needed and the burden on RV2 during warm-up would also be reduced.

Has anybody experimented with this approach.....?

In my version the DC at the output does not really stay as low as Mellow says - would a DC-servo be a good idea?

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

Kimber Kable

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

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

---