Modded BPA-200 - 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 16th May 2004, 01:50 PM   #1
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
Default Modded BPA-200

Ok guys, i think i'm just gonna go for it here. I want to use 6 lm3886 chips in a bridge parallel design for a sub amp. So basically i'm gonna follow BPA-200 w/ 3 chips in parallel instead of 2 for a total of 6 bridge parallel. I noticed in the bpa-200 schematic that one parallel set of chips uses 20.5k resistors in the feedback and 21.5k for the other set of parallel chips. I assume that I do need to follow this. What if i just use 10k inputs and 220k feedback instead for both sets? Anyone have a more complete schematic of the opamp input stage? If this for some reason doesn't work, i'll just turn it into a 6 channel lm3886 amp...but I'd like to try the bridge parallel design first...for the heck of it. Besides adequate power supply, .1% .1ohm output resistors, adequate heatsinking, any other advice? Thanks!

-Matthew K. Olson


oops, posted this in the wrong spot, moderator, please move this if need be...thanks!
  Reply With Quote
Old 16th May 2004, 01:58 PM   #2
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Default Re: Modded BPA-200

Quote:
Originally posted by Mattyo5
oops, posted this in the wrong spot, moderator, please move this if need be...thanks!

Done!
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 16th May 2004, 06:13 PM   #3
diyAudio Member
 
Join Date: Jan 2004
Location: northern israel
Default 20.5k/21.5k

It has to do with inverted/non-inverted topology gain. In one case it's Rf/Ri, in the other case it's Rf/Ri + 1.

Why would you want to use higher than recommended nominals? More resistance => more noise.
  Reply With Quote
Old 16th May 2004, 08:18 PM   #4
diyAudio Member
 
tlmadsen's Avatar
 
Join Date: Aug 2003
Location: Roskilde - The vikingships
Hi Mattoy5

Have a look at this threads. You might pick up something usefull

200 watts Gäjnklon (Gainclone) - BPA200

I agre with "unitgain". Why do you want to make the gainresistors bigger ?? It will give you more noise and more DC-ofset. Something you DON't need when you are paralleling chips.
(make sure you take care of the DC-ofset some how...)

You don't have to use the same resistors as in the BPA-200, but you most make sure that both your non-invertes and your inverted section have the same gain as explained by "unitgain" otherwise your "bridging" will be running "strange" to say the least

Have fun

Thomas
  Reply With Quote
Old 16th May 2004, 10:36 PM   #5
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
Well, i'll order some chips, and use the same resistors as the BPA-200 recommends, just more chips Same opamp too I guess. I guess I can check dcoffset, before I actually tie the chips together. Keep those ideas comin! Thanks guys!

-Matthew K. Olson
  Reply With Quote
Old 18th May 2004, 02:39 AM   #6
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
What is an acceptable dc offset ...ie what can I live with per chip ? Obviously zero would be best, but would 20mV be ok per chip? Or do I need to use output couple caps or something ridiculous? I'm going to hand match the feedback and input resistors, and I'm not going to bother w/ the dc servo's, but i'm just wondering what an acceptable dc offset is per chip before I tie them together. Thanks!

-Matthew K. Olson
  Reply With Quote
Old 18th May 2004, 03:28 AM   #7
diyAudio Member
 
Join Date: Apr 2004
Location: NSW Australia
Send a message via ICQ to rampage101 Send a message via MSN to rampage101
There's plenty of threads on the dc offset, but 20mv will be fine.
__________________
What's a signiture?
  Reply With Quote
Old 18th May 2004, 07:30 AM   #8
diyAudio Member
 
tlmadsen's Avatar
 
Join Date: Aug 2003
Location: Roskilde - The vikingships
I am sorry, but 20 mV DC off-set is way too much for paralled chips, unless you make the output resistors bigger.

See my replay in

Can you tell me how to beef up PA100?

Have fun

THomas
  Reply With Quote
Old 18th May 2004, 03:00 PM   #9
diyAudio Member
 
Join Date: Aug 2002
Location: Farmington, CT
Send a message via AIM to Mattyo5
What you said in your other post is that if there is a differential of basically >20mV, then that can be trouble. But, if each of the chips are have +20mV offset (say 16mV, 22mV and 25mV), then the differential between chips would be minimal and they would have minimal current flowing between chips. I have a 6 channel lm3875 amp that is pretty darn close to that, so I doubt getting offset that low is difficult if I handmatch all the resistors. Thanks for the thoughts though guys. Helps

-Matthew K. Olson
  Reply With Quote
Old 30th November 2005, 07:50 AM   #10
Will is offline Will  Malaysia
diyAudio Member
 
Join Date: Sep 2001
Location: Kuala Lumpur
Default On a related note

Can the 4 x 22uf caps be omitted ?
If not, what's the best for the job ? Elco 50V non polarised ?
Attached Images
File Type: jpg bpa.jpg (37.2 KB, 370 views)
  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
193L in a Modded DAC-AH.. JandG Digital Source 49 27th December 2011 11:56 PM
Modded ST70 Done Steven-H Tubes / Valves 5 3rd March 2008 01:34 PM
My SI modded amp works! spots25 Class D 4 20th April 2005 11:25 PM
My SI modded amp. TriodeGuy Class D 3 18th April 2005 01:17 PM
wtb a modded psone lcd rahssan Swap Meet 0 10th November 2004 11:29 AM


New To Site? Need Help?

All times are GMT. The time now is 02:36 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