Dual Mono fnshed, but what to do about CHG, and DC offset - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 10th February 2014, 08:44 AM   #1
diyAudio Member
Join Date: Jul 2011
Location: West London UK
Default Dual Mono fnshed, but what to do about CHG, and DC offset

Hi , I'd thought I'd ask two questions before sealing up the amp.
I built the dual mono amp, but have two issues, firstly, what to do with the CHG terminal on the amplifier boards, (I haven't wired them to anything at the moment, and assume they need to go to the earth post on the chassis where the incoming ac power cable is earthed) and secondly, I measured at the speaker terminals, 80mv DC on one and 120mvDC on the other, this seems unacceptably high especially as I have little or no DC going into the amp boards, would this go once they're earthed? Thanks
  Reply With Quote
Old 10th February 2014, 10:03 AM   #2
diyAudio Member
Join Date: Oct 2006
What is the schematic? Is it a kit?
  Reply With Quote
Old 10th February 2014, 11:37 AM   #3
diyAudio Member
Join Date: Jul 2011
Location: West London UK
Hi Mr Wagner, thanks for your reply, it as a dual mono kit from BrianGT @ Chipamp.com.
I have just read about 300 posts from the sticky "understanding star grounding" and have realised that I haven't connected any ground to the chassis earth post (to be made a "star" point).
As I understand it, I have to connect the CHG, the PG+ and PG- (from the psu's, there are two psu's, and two transformers 25v sec's) as well as the speaker grounds and RCA grounds? I should say that the speaker posts and the RCA posts are both insulated from the chassis. Is this correct?
I can post a photograph if it helps.
I was wondering why I had no hum, now I know-nothing grounded so no loops.
Hopefully once it's grounded I'll still have no hum, but doubt it reading these posts, though I was careful to have at least 25mm separation of signal to power cables by buying a largish chassis to put it all in.
If I do, I'll build two of those ground loop isolation circuits (with 35a bridge rectifiers), one for each psu, I'm led to believe.
Still don't know where the Dc offset is coming from.

Last edited by semmyroundel; 10th February 2014 at 11:39 AM. Reason: spealling
  Reply With Quote
Old 10th February 2014, 01:01 PM   #4
diyAudio Member
Join Date: Oct 2006
If it is the 3886 kit, then did you use the optional Ci 47uF?

I don't connect everything to the safety ground, but it is my option. Usually it is suggested through the isolator thing.
Can you make a pic of your amp?
  Reply With Quote
Old 10th February 2014, 01:25 PM   #5
infinia is offline infinia  United States
diyAudio Member
infinia's Avatar
Join Date: May 2005
Location: SoCal
Is your power transformer labeled with Safety Agency markings?, if yes and you built with properly rated fusing and took care with all primary wiring / insulated. Also consider that your power switch, fuse holder, and even wire can be approved for primary circuits. I would just call it Class II and be done (fixed 2 wire AC cord only). The danger is connecting primary circuits to the secondary side or chassis. IMO the biggest danger I see around here , is undersized cheap XFMRs (rare for DIY) together with flammable materials, like wooden boxes etc.
Dual Mono is the most difficult to get right after the fact , once you start adding extra connections to grounds and chassis connections IE creating new ground loops.

DC offset is a feature of minimal design chip amp kits. what does the vendor say about it? around 100mV is borderline for most stuff
like four million tons of hydrogen exploding on the sun
like the whisper of the termites building castles in the dust
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Need a 2W Bipolar DC - DC Converter circuit to make a dual rail power supply elmura Power Supplies 2 27th August 2012 08:30 AM
DH-220 Clone (SMART TA-242) can't adjust DC offset using offset bias pot? beady Solid State 6 17th March 2011 10:53 AM
What causes DC offset in mono Hafler? reiver Solid State 3 16th June 2008 07:22 AM
Single Mono's or Dual Mono? Tazzy Pass Labs 8 3rd October 2002 02:03 PM
Dual Mono - Anti Mono Power Supplies pmkap Everything Else 3 16th February 2002 05:10 AM

New To Site? Need Help?

All times are GMT. The time now is 10:09 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2