Welcome
Username or Email:

Password:


Missing Code




[ ]
[ ]
Online
  • Guests: 25
  • Members: 0
  • Newest Member: omjtest
  • Most ever online: 396
    Guests: 396, Members: 0 on 12 Jan : 12:51
Members Birthdays:
All today's birthdays', congrats!
Gagazet (33)
Chris Cristini (36)


Next birthdays
07/22 Reaching (40)
07/22 ryanshow (38)
07/23 Will (38)
Contact
If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.


Special Thanks To:
  • Aaron Holmes
  • Aaron Wheeler
  • Adam Horden
  • Alan Scrimgeour
  • Andre
  • Andrew Haynes
  • Anonymous000
  • asabase
  • Austin Weil
  • barney
  • Barry
  • Bert Hickman
  • Bill Kukowski
  • Blitzorn
  • Brandon Paradelas
  • Bruce Bowling
  • BubeeMike
  • Byong Park
  • Cesiumsponge
  • Chris F.
  • Chris Hooper
  • Corey Worthington
  • Derek Woodroffe
  • Dalus
  • Dan Strother
  • Daniel Davis
  • Daniel Uhrenholt
  • datasheetarchive
  • Dave Billington
  • Dave Marshall
  • David F.
  • Dennis Rogers
  • drelectrix
  • Dr. John Gudenas
  • Dr. Spark
  • E.TexasTesla
  • eastvoltresearch
  • Eirik Taylor
  • Erik Dyakov
  • Erlend^SE
  • Finn Hammer
  • Firebug24k
  • GalliumMan
  • Gary Peterson
  • George Slade
  • GhostNull
  • Gordon Mcknight
  • Graham Armitage
  • Grant
  • GreySoul
  • Henry H
  • IamSmooth
  • In memory of Leo Powning
  • Jacob Cash
  • James Howells
  • James Pawson
  • Jeff Greenfield
  • Jeff Thomas
  • Jesse Frost
  • Jim Mitchell
  • jlr134
  • Joe Mastroianni
  • John Forcina
  • John Oberg
  • John Willcutt
  • Jon Newcomb
  • klugesmith
  • Leslie Wright
  • Lutz Hoffman
  • Mads Barnkob
  • Martin King
  • Mats Karlsson
  • Matt Gibson
  • Matthew Guidry
  • mbd
  • Michael D'Angelo
  • Mikkel
  • mileswaldron
  • mister_rf
  • Neil Foster
  • Nick de Smith
  • Nick Soroka
  • nicklenorp
  • Nik
  • Norman Stanley
  • Patrick Coleman
  • Paul Brodie
  • Paul Jordan
  • Paul Montgomery
  • Ped
  • Peter Krogen
  • Peter Terren
  • PhilGood
  • Richard Feldman
  • Robert Bush
  • Royce Bailey
  • Scott Fusare
  • Scott Newman
  • smiffy
  • Stella
  • Steven Busic
  • Steve Conner
  • Steve Jones
  • Steve Ward
  • Sulaiman
  • Thomas Coyle
  • Thomas A. Wallace
  • Thomas W
  • Timo
  • Torch
  • Ulf Jonsson
  • vasil
  • Vaxian
  • vladi mazzilli
  • wastehl
  • Weston
  • William Kim
  • William N.
  • William Stehl
  • Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Forums
4hv.org :: Forums :: General Science and Electronics
« Previous topic | Next topic »   

Head unit help - DC offset?

Move Thread LAN_403
BlakFyre
Sun May 24 2009, 06:29PM Print
BlakFyre Registered Member #1563 Joined: Wed Jun 25 2008, 03:55AM
Location: Wimer Oregon, Wewt for sticks!
Posts: 30
I replaced my head unit in my car a while back ago with a different model that was stock in the same car. I added my own line in on the old unit as it didn't even have a tape deck in it.
Th DSC01641
As you can see, the signal came in from the bottom brown cable, and then immediately jumped around the amp board. I just patched in through one of the jumpers.
I want to do the same thing with my new (new to me) unit, however things are a little different. The amp is designed differently as it has a 5 channel equalizer ( yes, it has the sliders =D) and a fairly well done bass boost.
Th DSC01637
As you can see, the signal comes in through the red highlighted wires and instead of jumping around, it goes though some filters. I figured this was good because if I was to plug my mp3 player in (I plan on making a dock for charging and line out) I would have to worry about DC offset. Here's the problem, when probing to find the incoming signal, every time I hooked up an external source the audio would pop. I had the source at an extremely low volume so I was expecting a little click or small pop, but this would be devastating if it was to go through a second amp (as it will be). Granted the mp3 player will be in line out mode so its DC offset should be minimal, but if I hook anything else up while the amps on, kaboom.
What I'm wondering is, is there something I can add to the all ready installed filter caps (highlighted in green) so that the difference in voltage when hooking up other devices isn't as drastic. Should I put some metal film resistors in so the caps charge slowly? How will this effect my sound?
Back to top
ConKbot of Doom
Tue May 26 2009, 03:42PM
ConKbot of Doom Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329
If you could find some audio isolation/impedance transformers you could use those. Radio shack sells some but I'm sure the quality of those is lacking.

If you could find a commercial "direct box" meant for hooking high impedance devices (electric guitars) up to a low-z microphone input on profesisonal mixing board. That would certainly be higher in quality, and might not be that costly if you were to find two (stereo ;) ) for cheap from a pawn shop or thrift store who happens to have them.
Back to top
BlakFyre
Tue May 26 2009, 06:33PM
BlakFyre Registered Member #1563 Joined: Wed Jun 25 2008, 03:55AM
Location: Wimer Oregon, Wewt for sticks!
Posts: 30
The problem is a high DC spike during initial connection of an external device, that would still pass though the isolation transformer. I guess I should go look how DC offset is handled in other devices.
Back to top
Nik
Tue May 26 2009, 08:44PM
Nik Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
I had a similar problem with my own home made AUX input, I i just turned the volume way down on the head unit when connecting things.
Back to top
Steve Conner
Wed May 27 2009, 09:20AM
Steve Conner Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
If there are already DC block caps in the signal path, it shouldn't pop. Unless the head unit designer forgot to put resistors to ground, to set the initial conditions on those caps.

So, I suggest you try putting a 100k resistor from each terminal of the aux input jack to ground. Metal film, whatever, doesn't matter, won't affect the sound.

If this doesn't change the pop, or makes it worse, you know the problem is something more involved. Maybe the aux input jack has switch contacts that connect the signal from the head unit through to the power amps when the plug is removed, and maybe that signal has a DC offset. So when the plug is inserted, the DC offset actually goes away.
Back to top
BlakFyre
Sat May 30 2009, 05:31PM
BlakFyre Registered Member #1563 Joined: Wed Jun 25 2008, 03:55AM
Location: Wimer Oregon, Wewt for sticks!
Posts: 30
I'm going to try the resistors. I can't imagine those caps doing anything else, the tuner board must just turn on more gracefully, so they didn't think the resistors were needed. Thanks guys, may be a few days till I get back to it.
Back to top

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob

Go to:

Powered by e107 Forum System
 
Legal Information
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.