PA100 (x2 LM3886) FeedBack Capacitors - 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 23rd November 2011, 06:51 AM   #1
Al1B is offline Al1B  Iran
diyAudio Member
 
Join Date: Mar 2010
Default PA100 (x2 LM3886) FeedBack Capacitors

as you can see there are two Capacitors (C2 & C4) in this Schematic, that better be non-polar version....
Click the image to open in full size.
i put two 220uf 50v in series with negative pins connected to each other and got something around 110uf at last....

can somebody explain me the difference this 10uf can make?

and the other thing,, What is so special about "BlackGate STD" capacitors, i tried to search on google but no results...

thanx Already
  Reply With Quote
Old 23rd November 2011, 07:52 AM   #2
diyAudio Member
 
Join Date: Dec 2010
Location: INDIA
does this LM3886 require a stabilized power supply....i got two of them and just blew up when i tested those
  Reply With Quote
Old 23rd November 2011, 09:48 AM   #3
kimk is offline kimk  China
diyAudio Member
 
Join Date: Apr 2009
Electrolyte capacitor connected in series capacitor nonpolar when after ...

10UF may be too small, is not conducive to the low-frequency extension ..

Large capacity equivalent series inductance and large leakage current, dissipation factor will be big ..
  Reply With Quote
Old 23rd November 2011, 03:02 PM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
polar electrolytic are OK in those locations.
Add protective diode in at least one direction +ve of diode to +ve of electrolytic.

You can also add a protective diode in the opposite direction if the electrolytic voltage rating is at or less than the -ve rail to power ground voltage.
__________________
regards Andrew T.
  Reply With Quote
Old 23rd November 2011, 03:03 PM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by sweetperfume View Post
does this LM3886 require a stabilized power supply....i got two of them and just blew up when i tested those
no.
__________________
regards Andrew T.
  Reply With Quote
Old 23rd November 2011, 04:58 PM   #6
Al1B is offline Al1B  Iran
diyAudio Member
 
Join Date: Mar 2010
Andrew T: so u say i use the ones i made with a little difference in capcitance ? or normal electryicals ? which makes better results ?

im yet wondering what makes those black caps (1000uf 50v) that big they are...


Click the image to open in full size.
  Reply With Quote
Old 23rd November 2011, 06:40 PM   #7
diyAudio Member
 
Join Date: Nov 2004
Location: Germany
Absolute values of C2 and C4 are not too critical, they're only needed to reduce gain to unity at DC and cutoff is plenty low enough for that. Real bipolar ones would be preferred, though with 1k of series R it's not too much of a deal either.

1000 buffer caps seem a little excessive, they're less than an order of magnitude smaller than typical power supply bulk capacitance. Anyway, it doesn't hurt either.
  Reply With Quote
Old 24th November 2011, 06:53 PM   #8
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
C8,9 are a bad idea - don't put C there, you could disconnect them from the -in and gnd those ends of the caps

also from the pic I bet the PCB power layout is the classic wrong +,- PS on opposite edges of the board
  Reply With Quote
Old 1st December 2011, 01:30 PM   #9
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by Al1B View Post
as you can see there are two Capacitors (C2 & C4) in this Schematic, that better be non-polar version....
i put two 220uf 50v in series with negative pins connected to each other and got something around 110uf at last....

can somebody explain me the difference this 10uf can make?

and the other thing,, What is so special about "BlackGate STD" capacitors, i tried to search on google but no results...

thanx Already
A polar cap datasheet may also list its reverse voltage tolerances. For example, a 6.3v cap may have insufficient reverse tolerance. However, a 25v polar cap may have enough reverse tolerance for the job. Check the datasheets.

A larger NFB cap can "allow" louder lowest notes, so what is the percentage difference between 100 and 110 and how much many more notes lower might that be able to play? Two. It can pass about two notes lower pitch.

There are many interesting bass effects possible in the relationship between the input cap versus the NFB cap.

Why not un-series your 220uF and use the 220uF values for NFB cap for half the distortion? Hey, no problem going bigger as long as its clear (a good performing cap). Also potentially helpful to treble is to add a little 10nF inexpensive polyester in parallel to the NFB cap.

Most audiophile capacitors are also know as "Low Impedance" and "Low ESR" which are very useful types to put at predrive and "right next to the chip" as well as useful for signal caps. Many manufacturers make a selection of low impedance cap.

If building without a scope handy, C8, C9 are actually a good idea for Parallel Non-Inverting LM3886. The C8, C9 caps promote stability, and its better to promote stability in some way rather than do without.
  Reply With Quote
Old 3rd December 2011, 07:57 PM   #10
Marc Vi is offline Marc Vi  Netherlands
diyAudio Member
 
Join Date: Feb 2004
Location: The Netherlands
To have a - 3dB cutoff frequency of 4 Hz, C2 and C4 should be 39 microFarad. The nearest by value is 47 microFarad. So you put in serie two capacitors of 100 microFarad, voltage reversed connected.
  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
PA100 (x2 LM3886) 0.1% Resistors Al1B Chip Amps 18 23rd September 2011 06:46 PM
LM3886 PA100 Problem baene123 Chip Amps 53 30th December 2009 04:00 AM
Parallel LM3886 Chipamp layout (PA100) zei Chip Amps 6 11th September 2008 12:12 PM
PA100 Heat Issues...LM3886 Based..Any Ideas? MartyM Chip Amps 10 16th December 2007 11:18 PM
pa100 pcb single sided layout lm3886 dgaxeman Chip Amps 6 24th May 2006 01:45 AM


New To Site? Need Help?

All times are GMT. The time now is 07:18 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