Using 2 chips to boost voltage handling - Page 3 - 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 1st February 2005, 01:02 AM   #21
diyAudio Member
 
Join Date: Sep 2003
Location: Illinois
Quote:
Originally posted by azira
This kind of what you were thinking soundNERD? I scribbled this down a while ago, still a lot of hurdles to clear before it'd be a usable idea though..

good part is that the chip wouldn't have to swing rail to rail, infact only being able to get within .7V of the rail would be ideal.

edit: I remember now, after posting why I scrapped this idea... diodes still don't isolate the outputs from driving eachother... damn...
I think thats exactly it. Did you post it here a few months ago asking the same question as this? If so, then yep, thats what I'm remembering.

Quote:
Originally posted by HDTVman


BANG! Whats that smell?

smoke from chip amps
Don't worry, I'm used to that. OPA541 running at +/-38VDC driving a load under 4 ohms. the chip literally snapped in half and the lights dimmed as the transformer hummed. A little longer and the breaker probably would have popped.
  Reply With Quote
Old 1st February 2005, 02:35 AM   #22
jcx is online now jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
i don't think 2 chips will do it but 3 could, look at the bootstrap amp in the article i pointed to earlier

if transistors are somehow beyond consideration, then the same principle can be employed with 2 chip amps replacing the transistors
Attached Images
File Type: gif boot.gif (8.9 KB, 183 views)
  Reply With Quote
Old 1st February 2005, 03:34 PM   #23
HDTVman is offline HDTVman  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Chicago area
Quote:
Originally posted by azira


Can you explain what is bad about it. It's not down on paper will all values listed... but is the idea really faulty? Is this circuit also a bad idea, it seems like sort of the same thing to me.
--
Danny

Ya Danny, it is a bad idea.

1. the two outputs are at half the dc voltage of the power supply for each chip. This means that the top chips output is at +30 VDC and the bottom chip is at -30 VDC. That's at no signal by the way. Remember the output is from chip output to chip output so now you have 60 VDC at the speaker terminals.

2. You could use output cap coupling but the turn on thump would be something else. Remember that you also need to drive the inputs 180 degrees out of phase and with +- 30 volt offsets.

3. Normal bridge circuit would give the same power output by the way.

The difference that the circuit you posted has is that there is only one output, not two and the load is referenced to ground.

Does that help?

BZ
__________________
What ever makes the tunes flow
  Reply With Quote
Old 1st February 2005, 04:11 PM   #24
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Quote:
Originally posted by HDTVman



Ya Danny, it is a bad idea.

1. the two outputs are at half the dc voltage of the power supply for each chip. This means that the top chips output is at +30 VDC and the bottom chip is at -30 VDC. That's at no signal by the way. Remember the output is from chip output to chip output so now you have 60 VDC at the speaker terminals.


BZ
1. This is not correct, you assume that an opamp by default centers its output on the rails but in truth it does not. The only reason it appears that way in standard circuits is that the - input or lets call it the reference input is set at the midpoint between V+ and V- and the + input varies around that value.
If instead, the reference input was set at the V+ rail and the + input was varied around that, the output would start at the V+ rail and attempt to vary around that as well, however, obviously the chip cannot deliver higher than V+ out.

Quote:
The difference that the circuit you posted has is that there is only one output, not two and the load is referenced to ground.
That is also not correct. The class-B output stage is two seperate current drivers connected at the outputs and inputs just like the opamp circuit I drew. If you black boxed the current drivers in both circuits you would see that they are identical. The key to making them act the same is to configure it so that each current driver is active for only 1/2 the cycle.
--
Danny
  Reply With Quote
Old 1st February 2005, 04:18 PM   #25
azira is offline azira  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Near Seattle
Quote:
I think thats exactly it. Did you post it here a few months ago asking the same question as this? If so, then yep, thats what I'm remembering.
I don't think I posted this idea. I tried simulating it a couple times and ran into some implementation difficulties that I never got around to solving. One of the interesting problems with this configuration is that many opamps don't behave nicely when their + input is drive above (or below) the rails.

Quote:
i don't think 2 chips will do it but 3 could, look at the bootstrap amp in the article i pointed to earlier
Yeah, this circuit is pretty cool... I lost the link to that article about 6 months ago. NP posted a few GC circuits with similar bootstrapping ideas as well.
--
Danny
  Reply With Quote
Old 1st February 2005, 04:53 PM   #26
jcx is online now jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
hardly any chip amps are able to survive any terminal swinging beyond the rails

most devices have a parasitic diodes to one power rail (body-substrate diode) and will conduct large currents when any terminal swings > 0.6 V beyond the substrate rail

on the other rail you may be able to pull some terminals a little beyond the rail without catastrophic short circuit current - but not by enough to be useful - the exception is "Open-Collector" outputs which make really poor linear amps

some devices even form parasitic SCR structures with the substrate, if you exceed the max current limit into some terminals then the chip will try to short the power rails together, and latch up in that condition

in any event exceeding the Vmax will risk avalanche bvreakdown


Spice macro models are really usless for modeling breakdown/reverse bias/crowbar power supply effects, they are simply not designed to model these phenomina
  Reply With Quote
Old 1st February 2005, 09:52 PM   #27
HDTVman is offline HDTVman  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Chicago area
PC modeling software is fun to play with and can be a useful tool, but it needs to be tempered with a dose of the real world.

If you want to build something as an experiment, stacking 2 chip amps like that go for it but don't expect it to sound like much. There will be a big crossover notch during the switch over from one chip conducting to the other. Thats if none of the problems JCX brought up never existed, and they do.

40 years of experence does make a difference. I use modeling software too, but I temper my designs with that experence. It's fun to model stuff as a starting point, but if it can't work in the real world it has no point other than playing at the computer.

BZ
__________________
What ever makes the tunes flow
  Reply With Quote
Old 1st February 2005, 11:15 PM   #28
Stocker is offline Stocker  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Austin
Quote:
Originally posted by HDTVman
If you want to build something as an experiment, stacking 2 chip amps like that go for it but don't expect it to sound like much. There will be a big crossover notch during the switch over from one chip conducting to the other.
BZ
Feedback.
__________________
Jesus loves you.
  Reply With Quote
Old 2nd February 2005, 12:07 AM   #29
simon5 is offline simon5  Canada
diyAudio Member
 
Join Date: Nov 2004
Location: Québec, Québec
Or a small DC offset.
__________________
DIYaudio for President !
  Reply With Quote
Old 2nd February 2005, 04:45 AM   #30
HDTVman is offline HDTVman  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Chicago area
How about the voltage difference from the ps voltage and what the output will do. Check the specs on some power opamps. somewhere from .7v to 2.5v x 2. The power supply is set up as +60 0 -60 in this example correct? One chip powered by the +60 to 0 volt supply and the other from 0 to -60 correct?

If the chip amp we use can swing to 1.5 volts of the rails then there will be a 3 volt step in the output as the input signal crosses 0.

No amout of feedback can help you here.

We haven't started talking about what the recovery of the chip amp looks like after being clipped, which is what is happening at the 0 crossing in this example.

It's still a bad idea.

BZ
__________________
What ever makes the tunes flow
  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
[enquiry] Treble Boost/High frequency Boost circuitry elnino86 Parts 2 18th December 2008 12:33 PM
Name some amp chips that work on a single rail voltage please speaker Chip Amps 13 22nd March 2008 08:23 PM
TL Power handling fortyquid Multi-Way 9 13th October 2003 12:18 AM
Power Handling Myren Multi-Way 1 30th October 2001 07:18 AM


New To Site? Need Help?

All times are GMT. The time now is 04:46 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