My First Build - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

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
Reply
 
Thread Tools Search this Thread
Old 7th November 2011, 04:03 PM   #11
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
An AC coupled amplifier using a single polarity supply and DC blocking cap in the output should have ZERO mVdc into the speaker/terminal.

What have you connected in error?
__________________
regards Andrew T.
  Reply With Quote
Old 7th November 2011, 06:20 PM   #12
benb is offline benb  United States
diyAudio Member
 
Join Date: Apr 2010
Perhaps it's a leaky C7?
  Reply With Quote
Old 7th November 2011, 06:39 PM   #13
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
1uA across 6r5 results in 6u5V.
I can't measure that. It is essentially zero mVdc.
__________________
regards Andrew T.
  Reply With Quote
Old 7th November 2011, 06:47 PM   #14
benb is offline benb  United States
diyAudio Member
 
Join Date: Apr 2010
I mean a REALLY leaky C7.
  Reply With Quote
Old 7th November 2011, 08:41 PM   #15
diyAudio Member
 
Join Date: Oct 2011
Location: UK
Quote:
Originally Posted by AndrewT View Post
An AC coupled amplifier using a single polarity supply and DC blocking cap in the output should have ZERO mVdc into the speaker/terminal.
I'm sorry, I really am quite thick, please excuse my ignorance but what do you mean by that?

I have the amp powered from an AC transformer but then it's rectified into DC before being fed into the amp.

.....or am I missing the point here?

On a positive note, when the amps are working, they sound absolutly brilliant. Even to the point that I've been going round listening to several other systems in my house and have found that they don't seem to sound quite as good.
I suppose the speakers make a difference but I'm only using some old ones I found

I've even started planning to case it up soon
  Reply With Quote
Old 7th November 2011, 08:51 PM   #16
diyAudio Member
 
Join Date: Oct 2011
Location: UK
I've done some googling.

Am I correct in thinking that it's AC coupling bit relates to the input source?
i.e we're inputting an analogue source so it needs to be AC.
If we were inputting a digital source, it would be DC coupled ????

Or have I missed the point again?
  Reply With Quote
Old 8th November 2011, 07:38 AM   #17
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by Nurbit View Post
I've done some googling.

Am I correct in thinking that it's AC coupling bit relates to the input source?
i.e we're inputting an analogue source so it needs to be AC.
If we were inputting a digital source, it would be DC coupled ????

Or have I missed the point again?
The MP3 player, CD and PC all have onboard DAC and are all analog at the headphone jack. However, an actually digital source fed into an audio amp sounds like a fax machine except louder and even worse. Please use the analog output jack, not the digital output jack.

DC is 0Hz, no signal on clean DC, although there may be plenty of current. Basically, you're doing AC coupling to avoid melting the speaker's voice coil. C7 is blocking the speaker fire, blocking DC offset. Apparently, C7 is a bit shorted and needs replaced.

That DC offset can happen from flopping about with all that duct tape or it can happen with voltage overrun (overcharge damage). Here's an example of a 63v 2200uF Nichicon: Nichicon PW Series 63V 2200UF Low lmpedance Capacitor
  Reply With Quote
Old 8th November 2011, 01:35 PM   #18
diyAudio Member
 
Join Date: Sep 2006
Location: Wirral UK
Hi Nurbit.

You may find this a little more understandable.

Capacitors

Your "perfect" audio signal is only AC but we all know things aren't always perfect. If any DC is passed into the amplifier input it will be amplified along with the signal. Once you push the DC into your speaker coils they will be held away from their normal resting point upsetting your sound and possibly burning the speakers.

You see the line on the linked page that says "They (capacitors) are also used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals"

So, if you pass your signal through a capacitor only the AC signal will pass through. The DC will be blocked preventing it from being amplified and keeping the magic smoke inside your speaker coils, always a good thing. If no capacitor (or other means of dc removal) is present the amp is considered to be DC coupled.

John
  Reply With Quote
Old 8th November 2011, 04:49 PM   #19
Boscoe is offline Boscoe  United Kingdom
diyAudio Member
 
Join Date: Feb 2010
Location: England
Try using a new cap with a higher voltage rating for C7 just to be sure?
__________________
I thought about it once, but then thought again.
  Reply With Quote
Old 8th November 2011, 07:41 PM   #20
diyAudio Member
 
Join Date: Oct 2011
Location: UK
AH-HA

I get it now Thanks Daniel and John.

I can't re-test the circuit at the minute because they're both getting measured up for their shiny new heatsinks.

I've got some different caps to try too but sadly none of them are new and I don't have an ESR meter to test them.

I will be using brand new parts for the next amp. I'm going to build a true gainclone next time using LM3875s and point to point soldering.... perhaps

Thanks for the help though guys, it's easy to get disheartened when learning this stuff, I appreciate all your answers
  Reply With Quote

Reply


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
What sub to build jasons Subwoofers 1 29th November 2009 09:05 AM
build my first full ranger,let's build another one:a small fullrange high end pc-spea then_dude Full Range 2 30th November 2005 07:54 AM
Do i need to build main supply (240v) filter?Or build power distribution? thomgun_lc Chip Amps 9 16th September 2005 09:52 AM
What should I build first? chipco3434 Multi-Way 1 18th August 2004 10:45 AM
What I build rossco Multi-Way 9 6th August 2003 12:45 PM


New To Site? Need Help?

All times are GMT. The time now is 12:10 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2