Lack of bass with LM3886 - 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 27th April 2011, 06:38 AM   #11
diyAudio Member
 
digits's Avatar
 
Join Date: Apr 2011
What is the size of the input cap?
  Reply With Quote
Old 27th April 2011, 07:22 AM   #12
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
What digits said + what is the size of the NFB cap (if fitted). and also as gootee said please post a schematic (which should answer both those questions).

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 27th April 2011, 08:24 AM   #13
Vix is offline Vix  Yugoslavia
diyAudio Member
 
Vix's Avatar
 
Join Date: Nov 2003
Location: Somewhere on Planet Earth
Hi,

I don't know if I can really help, but I had the same problem with my GC, compared to NAD 3020 amp. LM3886 sounded anemic compared to NAD. The schematic was a non-inverted one, almost identical to the one as presented in the datasheet. NAD always sounded better with a more fuller sound. Note that I never used the loudness and the tone controls were set to neutral.

Long story short, LM 3886 sounds good until you compare it to something better. I played with it for a while, and now it is collecting dust. I would be also interested if someone comes up with a solution for this problem, but I am afraid that it comes down to topology and the limitation of the chip itself.
  Reply With Quote
Old 27th April 2011, 08:46 AM   #14
diyAudio Member
 
digits's Avatar
 
Join Date: Apr 2011
the way I see it, the best way to apply the national chips is in a 3 way active system. LM1875 for tweeter duty, LM3875 (or again 1875 for efficient speakers) for mids and the lm3886 for subwoofer duty. I do agree just about any decent discrete topology will beat the standard datasheet or gainclone topology with chipamps.

I have a softspot for Carlos' old discretes the original DX amp, not so refined but it was steel balls, or the HRII. I have not realy been keeping up with developments these last 4 years or so, call me Rip van Winkel.
  Reply With Quote
Old 27th April 2011, 12:56 PM   #15
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Quote:
Originally Posted by Vix View Post


Long story short, LM 3886 sounds good until you compare it to something better.


Goodness. And the "something better" is the godawful, as Mr Kessler used to call it, 3020??? And it feels it was only yesterday that chipamps were simply the best amps in existence and people in their droves were busy junking their 300B SETs for a 3875 ultra-platinum kit. Were they all deaf? Or just hated bass?
  Reply With Quote
Old 27th April 2011, 01:44 PM   #16
Vix is offline Vix  Yugoslavia
diyAudio Member
 
Vix's Avatar
 
Join Date: Nov 2003
Location: Somewhere on Planet Earth
Quote:
Originally Posted by analog_sa View Post
Goodness. And the "something better" is the godawful, as Mr Kessler used to call it, 3020???

I don't want to start any flames here, but, imho, NAD just sounds better.
  Reply With Quote
Old 27th April 2011, 01:59 PM   #17
UrSv is offline UrSv  Sweden
diyAudio Member
 
UrSv's Avatar
 
Join Date: Jan 2002
Location: Sweden
Quote:
Originally Posted by Vix View Post
I don't want to start any flames here, but, imho, NAD just sounds better.
And obviously, under extreme circumstances and with a faulty LM3886 based amp, there is no reason why it couldn't.
__________________
UrSv
Those who say it can't be done should not stop those who are doing it.
  Reply With Quote
Old 27th April 2011, 08:00 PM   #18
diyAudio Member
 
Join Date: Sep 2008
Thank You for your interest,

(Sorry about the English)

I am talking about a double mono Brian GT kit, schematic and bom can be found at www.chipamp.com/docs/lm3886-manual.pdf.
It's a non inverted type, I have used the components of the kit (no change).
The transfos are 2X24v AC which gives +/- 35 V DC. After one hour, the heatsinks became a little hot (I will says 40 C max).
There is no input cap (direct coupling).
I have measured about 45 mv offset at the output, that's all I can do, I do not have a scope.
I use the variable RCA output of a Sony CDP 559 ES (no pre-amp).

(a picture will follow tomorrow).

Bye.
  Reply With Quote
Old 28th April 2011, 09:14 AM   #19
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
is the optional Ci=47uF fitted?

I would recommend you convert this amp to AC coupled, until you learn a lot more about how amplifiers operate.
__________________
regards Andrew T.
  Reply With Quote
Old 28th April 2011, 09:48 AM   #20
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
My chipamp is based on the BrianGT schematic and has the optional 47uF feedback capacitor fitted. Attached is the RMAA test of the frequency response. I'd have to look up the datasheet to see what the calc is for determining the -3db frequency (due to the feedback cap) is, but as can be seen the FR is down around 0.6db at 20Hz. Whether this is enough to be noticeable or not I don't know.

When I did power tests I did get quite significant droop in the PS at frequencies below 30Hz. I'm running a single 300VA dual 20V toroid, giving around 28V rails unloaded.

edit: ok for 680 ohm Ri and 47uF ci forumla is fc = 1/(2πRi Ci) which works out at about 5Hz. Increasing the size of Ci will lower the -3db point.

Tony.
Attached Images
File Type: png lm3886_FR.png (21.6 KB, 531 views)
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos

Last edited by wintermute; 28th April 2011 at 09:59 AM.
  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
LM3886 bass amp thomasst Chip Amps 14 17th August 2012 10:22 AM
Active RIAA lack off BASS wabun Analogue Source 1 5th October 2010 07:33 PM
Class-D lack of sustained bass Myth Zero Cool Class D 15 9th July 2009 05:41 AM
lack of bass in a 6h30 design SunRa Tubes / Valves 3 31st January 2007 09:54 PM
Flat bass of paralleled LM3886 manuruthen Chip Amps 7 26th August 2005 08:59 AM


New To Site? Need Help?

All times are GMT. The time now is 11:05 PM.


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