Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Tweakers' Asylum ]

---

[ Alert Moderator ]

---

Re: Stepped Attenuator Pre & Stray DC; BUF634

Posted by Steve Eddy on October 20, 2006 at 12:48:59

In Reply to: Re: Stepped Attenuator Pre & Stray DC; BUF634 posted by Dave Garretson on October 20, 2006 at 03:56:27:

Hey Dave. A couple of questions.

First, when you say the DC is reduced when you run some 10k resistors from signal to ground, are the resistors being placed between the transformer and the intput to the buffers or are they being placed at the outputs of the buffers?

Second, I went to Audio Consulting's website but couldn't find any wiring diagrams there for the CD output transformers. Do the transformers you're using have a center tap on the secondary? And if they do, is the center tap tied to ground?

I'm thinking perhaps the reason you're getting such high DC offset from the output of the buffers is because they're essentially wired like this:

If that's the case, then there's no DC path to ground for the input bias currents and that could be giving you your high DC offset on the output.

If the transformers do have center taps, then simply wire the center taps to ground like this:

This would be the preferred solution as the winding resistance of the transformer secondaries will be rather low and help keep your output offset DC as low as possible.

If not, then create a virtual center tap with a pair of 10k resistors like this (which may be what you were already doing):

se

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 © 2025, Audio Asylum, all rights reserved ]

---

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

---