Has anyone tried servo-less BPA 200?

goldyrathore · 30th March 2005, 02:28 PM

Hi,

Has anyone tried the basic bridge/parallel circuit for LM3886 as shown in Figure 17 at http://www.national.com/an/AN/AN-1192.pdf (page 15). I need at least 175W RMS of clean power for a sub. I intend to use 4 ICs or maybe 6 for a 4 ohm 12" driver.
What should be the supply voltage?

Thanks in advance,
Goldy

Cobra2 · 30th March 2005, 02:35 PM

Bridgeclone

(where I used Zobel & snubbers & plenty more tricks...)

Arne K

macboy · 30th March 2005, 04:59 PM

Quote:

I need at least 175W RMS of clean power for a sub. I intend to use 4 ICs or maybe 6 for a 4 ohm 12" driver.
What should be the supply voltage?

For a bridge-parallel design (with 4 amps) the equivalent load that each amp sees is equal to the real load impedance, or 4 ohms. For a 4 ohm load, the "sweet spot" in power supply voltage is about +/- 28V. Go any lower, and the power output decreases. Go any higher, and the power dissipation increases too high.

goldyrathore · 2nd April 2005, 04:28 AM

Hi,

I intend to use only a pot at non inverting input to reduce the offset. But as I read in other threads, it will not reduce it beyond a point. How much of offset voltage is safe if I use 0.22 ohm at the output of each LM3886? The number of chips per side of the speaker is 3 (total of 6). The supply is 28-0-28.

Thanks in advance,
Goldy

skyraider · 3rd April 2005, 11:35 AM

I built mine without servo, and just to share what i learned:

1. Resistor matching is important. Be friendly with the store owner and they will let you spend a day in the store selecting your resistors.

2. Chips has 'internal offset', so build a few to select the ones with the least offset.

My sub amp has dc offset of about 200mV (I didnt observe rule #2) But for a 200-watter, I dont really care. There is more than enough power to dispense and my sub can take that.

jaudio · 3rd April 2005, 07:10 PM

I agree with skyraider"s two points.

I used trim pot on the non inverted inputs.

I built 20 indepentent modules. I picked 16 modules with the closest dc offset,then I broke that group into four group all with dc matched as close as possible. I ended up with four nearly matched parallel groups. I used two parallel groups(8 modules in total) with a drv134,to make two monoblocks. The dc offset in .0003 on one and .0001 on the other.

One thing I would add make sure all connection are proper and solid or you will get hiss.

30th March 2005, 02:28 PM	#1
goldyrathore diyAudio Member Join Date: Nov 2002 Location: Bangalore, India	Has anyone tried servo-less BPA 200? Hi, Has anyone tried the basic bridge/parallel circuit for LM3886 as shown in Figure 17 at http://www.national.com/an/AN/AN-1192.pdf (page 15). I need at least 175W RMS of clean power for a sub. I intend to use 4 ICs or maybe 6 for a 4 ohm 12" driver. What should be the supply voltage? Thanks in advance, Goldy __________________ Audio enthusiast/hobbyist

2nd April 2005, 04:28 AM	#4
goldyrathore diyAudio Member Join Date: Nov 2002 Location: Bangalore, India	How much offset is safe? Hi, I intend to use only a pot at non inverting input to reduce the offset. But as I read in other threads, it will not reduce it beyond a point. How much of offset voltage is safe if I use 0.22 ohm at the output of each LM3886? The number of chips per side of the speaker is 3 (total of 6). The supply is 28-0-28. Thanks in advance, Goldy __________________ Audio enthusiast/hobbyist

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
To use DC servo or not?	jaycee	Solid State	40	17th September 2007 02:04 PM
Servo add-on PCB	Nicks	Chip Amps	3	21st February 2006 05:36 AM
To servo or not to Servo..	ReSiStAnCe	Chip Amps	10	7th February 2004 01:06 AM
DC servo	Bensen	Solid State	0	23rd May 2003 11:34 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

30th March 2005, 02:35 PM	#2
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	Go here : Bridgeclone (where I used Zobel & snubbers & plenty more tricks...) Arne K __________________ Ars longa, vita brevis

3rd April 2005, 11:35 AM	#5
skyraider diyAudio Member Join Date: Jan 2004 Location: malaysia	I built mine without servo, and just to share what i learned: 1. Resistor matching is important. Be friendly with the store owner and they will let you spend a day in the store selecting your resistors. 2. Chips has 'internal offset', so build a few to select the ones with the least offset. My sub amp has dc offset of about 200mV (I didnt observe rule #2) But for a 200-watter, I dont really care. There is more than enough power to dispense and my sub can take that.

3rd April 2005, 07:10 PM	#6
jaudio diyAudio Member Join Date: Oct 2004	I agree with skyraider"s two points. I used trim pot on the non inverted inputs. I built 20 indepentent modules. I picked 16 modules with the closest dc offset,then I broke that group into four group all with dc matched as close as possible. I ended up with four nearly matched parallel groups. I used two parallel groups(8 modules in total) with a drv134,to make two monoblocks. The dc offset in .0003 on one and .0001 on the other. One thing I would add make sure all connection are proper and solid or you will get hiss.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)