Suggestions on Balanced Bridge circuit

Mambo · 9th January 2007, 01:08 PM

Hi All!

I'm simulating a Full Balanced Bridge, circuit and on the simulation program it seems to work very well: it recalls to the Ampzilla III but without all the auxiliary circuits around it, the only additional trimmer which is present, excluding the 2 that set the idle condition, is that on the base to ground connection of one of the input bias generator transistor. Chaning the current which flows in the Zener it allows a precise adjustment of the output DC level on both the halves.

I already done the layout for this and I'd like to get some comments and suggestions from You before putting it under the UV lamp

Thank You Very Much

Elvee · 10th January 2007, 07:13 AM

Hi

It looks like a pretty good classical circuit, I see no obvious flaw.
I'd just make some "economic" improvements: the three bias strings of each rail could be merged without inconvenient (perhaps adjust R5/7 to the new voltage, or add two diodes to the string). I'd also add a decoupling cap across the strings.
Note that you could retain your adjustment principle, as a minor voltage alteration of the cascode bias would have no effect.
LV

darkfenriz · 10th January 2007, 10:50 AM

nice

AndrewT · 12th January 2007, 10:17 AM

Hi,
a red LED could replace each of the three diodes strings.

I, personally, don't like Miller compensation caps across the VAS. I suggest you reduce or remove the 22pF caps and add other compensation to adjust stability. Stability cap from VAS collector to inverting input (base) does the job and arguably sounds nicer.
I note your global feedback returns to the LTP emitters. Does this simulate well? I have no experience of this.
Do the junctions of r35 r36 and r45 r52 need to connect to ground? a single 13k would do the job.

The mpsa at the front end are relatively low gain and this will increase the input offset current. Consider high gain or even very high gain in these locations.
The closer the gain of the NPN and PNP the less the offset current. There is an argument that the NPN/PNP should not be equal so that the offset is always "one way" rather than moving either side of zero as junction temps (and gains) change under loading.

thanh · 12th January 2007, 01:08 PM

Hi Mambo!
I also love balance. I hoped that it can cancel distortion but I haven't had any good result.
Mambo! How distortion is it ?

Mambo · 12th January 2007, 04:05 PM

AndrewT,
I agree with You about the use of different components, Led and High gain Transistors and especially about the last ones, but I have many of them in house and prototyped with them

Also the use of a common resistor for the VAS cascode bias generator is a good choice: i'l do that.

From he simulation point of view (circuit maker) i see no issues, and the feedback going to the LTP is not an issue: this is how the true balanced bridge should work, look ad the Ampzilla III schema and on some books.

Thanh,
from what I remember the primary objective of a balanced equipment is not to lower the level of the harmonics but to have a better noise performance: however it seems to be in the simulation a little reduction in the 2nd and the other even harmonics if compared to the single ended version from which i started over to get this

12th January 2007, 01:08 PM	#5
thanh diyAudio Member Join Date: Jan 2004 Location: ho chi minh city	Hi Mambo! I also love balance. I hoped that it can cancel distortion but I haven't had any good result. Mambo! How distortion is it ? __________________ Justice for Victims of Agent Orange http://www.petitiononline.com/AOVN/Thank all of you!

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
Bridge-balanced amplifiers	lndm	Tubes / Valves	2	17th February 2011 05:20 PM
Integrated DAC + Bridge LM3875 (Balanced)	Yoshy	Chip Amps	21	28th April 2009 04:40 AM
Bridge/Parallel with balanced input	sangram	Chip Amps	6	7th January 2006 05:50 AM
full or half bridge balanced or not?	oldroborg	Class D	3	18th December 2005 10:08 PM
Balanced -> Bridge?	Nappylady	Chip Amps	1	12th December 2003 03:57 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

10th January 2007, 07:13 AM	#2
Elvee diyAudio Member Join Date: Sep 2006	Hi It looks like a pretty good classical circuit, I see no obvious flaw. I'd just make some "economic" improvements: the three bias strings of each rail could be merged without inconvenient (perhaps adjust R5/7 to the new voltage, or add two diodes to the string). I'd also add a decoupling cap across the strings. Note that you could retain your adjustment principle, as a minor voltage alteration of the cascode bias would have no effect. LV

10th January 2007, 10:50 AM	#3
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	nice

12th January 2007, 10:17 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, a red LED could replace each of the three diodes strings. I, personally, don't like Miller compensation caps across the VAS. I suggest you reduce or remove the 22pF caps and add other compensation to adjust stability. Stability cap from VAS collector to inverting input (base) does the job and arguably sounds nicer. I note your global feedback returns to the LTP emitters. Does this simulate well? I have no experience of this. Do the junctions of r35 r36 and r45 r52 need to connect to ground? a single 13k would do the job. The mpsa at the front end are relatively low gain and this will increase the input offset current. Consider high gain or even very high gain in these locations. The closer the gain of the NPN and PNP the less the offset current. There is an argument that the NPN/PNP should not be equal so that the offset is always "one way" rather than moving either side of zero as junction temps (and gains) change under loading.

12th January 2007, 04:05 PM	#6
Mambo diyAudio Member Join Date: Feb 2002 Location: Italy	AndrewT, I agree with You about the use of different components, Led and High gain Transistors and especially about the last ones, but I have many of them in house and prototyped with them Also the use of a common resistor for the VAS cascode bias generator is a good choice: i'l do that. From he simulation point of view (circuit maker) i see no issues, and the feedback going to the LTP is not an issue: this is how the true balanced bridge should work, look ad the Ampzilla III schema and on some books. Thanh, from what I remember the primary objective of a balanced equipment is not to lower the level of the harmonics but to have a better noise performance: however it seems to be in the simulation a little reduction in the 2nd and the other even harmonics if compared to the single ended version from which i started over to get this