Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time.

---

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

---

[ Alert Moderator ]

---

RE: DC Voltage and leaving amp on.....24/7

Posted by JonM (A) on February 21, 2022 at 11:21:17

In Reply to: RE: DC Voltage and leaving amp on.....24/7 posted by walkstoslow on February 21, 2022 at 07:23:54:

The au317 Service Manual is available on line - I found it easily (link below). There are actually two potentiometers in each channel for adjusting the output bias voltage (VR03/VR04 for rough adjustment, and VR01/VR02 for fine adjustment - VR01 & 03 are right next to each other in one channel, and VR02 & 04 are next to each other in the other channel).

Each channel also has also a pot - VR05 and VR06 - for adjusting the quiescent bias current in the output stage (measured as a voltage across the emitter resistors on the output transistors). If you know how to read a schematic, it's pretty easy to find the test points where you put your test leads to make the measurements, and the manual tells you what the target voltage is. (If you don't know how to read a schematic, I suggest you leave VR05 and 06 alone.)

Changing the bias current can affect the output bias voltage, so if you adjust the bias current, you will want to go back and recheck the output bias voltage and keep it near 0.

All that said, Story gave good advice. The bias may vary a bit as the amp comes up to temperature, so it's wise to let it run for a few minutes before you adjust, then let the temperature settle again, adjust a second time, wait for a bit, and check a third time. After that, you should be all set.

• au317 Service Manual   (Open in New Window)

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

VH Audio

---

[ 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 ]

---