| soundNERD |
If I remember correctly, isn't there some way to hook two chips together to allow double the power supply voltage? What I want to do is power an OPA549 above +/-30 to allow higher voltage output and therefor higher wattage output.
Thanks!
-Mike |
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| loong |
| Do you mean the bridge config? If so, you can see the AN-1192 App Note for some detail. |
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| pinkmouse |
| Bridging will increase the voltage seen by the speaker, but not allow you to increase the psu rails, so you will still need the same transformer. |
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| richie00boy |
| Also bear in mind that bridging causes the load seen by the amp to halve, thus you will be limited to 8 ohm speakers with most chips. |
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| demogorgon |
how about runing one chip on +60v and a nother at -60v, and running them as bridged?
just a quick thought from the top of my head.. |
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| richie00boy |
| Then you will have a nice 60 volt DC offset going though your voice coil and a nasty smell in the room, if not flames ;) |
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| azira |
| quote: | Originally posted by demogorgon
how about runing one chip on +60v and a nother at -60v, and running them as bridged?
just a quick thought from the top of my head.. |
not bridged, parallel... I had an idea like this more than once. Probably need diodes in the output of each amp to prevent them from driving eachother... also would have to deal with crossover distortion. |
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| ErikdeBest |
| quote: | Originally posted by azira
not bridged, parallel... I had an idea like this more than once. Probably need diodes in the output of each amp to prevent them from driving eachother... also would have to deal with crossover distortion. |
As Loong said: you can see the AN-1192 App Note for some detail.
It has been discussed, builded and tested through people from this forum...and...you can find AN-1192 at the website of national, I think it is www.national.com |
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| AudioFreak |
| quote: | Originally posted by ErikdeBest
As Loong said: you can see the AN-1192 App Note for some detail.
It has been discussed, builded and tested through people from this forum...and...you can find AN-1192 at the website of national, I think it is www.national.com |
AN-1192 isn't going to help much is this situation. |
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| jcx |
yes, repeating a ref to something without stating that it had no new info beyond how to bridge was annoying
but http://www.edn.com/contents/images/45890.pdf might help
"Bootstrapping your op amp yields wide voltage swings" shows how to use transistors to increase V handling |
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| loong |
I don't know exactly what you looking for.
My friend made a brdiged amp using the DRV134 (as the diff driver) to drive 2 op amps (OPA54x) with very compact PCB, it produces very good result. With direct drive by the NAD521i and our taste, it clearly beats the NAD 320BEE. |
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| soundNERD |
| i think it was something like this: sorry about the schematic i don't have schematic programs installed on this computer. would this work? |
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| richie00boy |
| quote: | Originally posted by soundNERD
would this work? |
As a voicecoil burner, it would be great. As an amplifier, nope. See my last :) |
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| azira |
| quote: | Originally posted by richie00boy
As a voicecoil burner, it would be great. As an amplifier, nope. See my last :) |
I think you are assuming that each chip's quiescent output is centered on it's rails and not at GND. |
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| richie00boy |
| Show me a chipamp that can swing right to a rail and I'll give you a dollar ;) |
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| 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... |
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| HDTVman |
| quote: | Originally posted by soundNERD
i think it was something like this: sorry about the schematic i don't have schematic programs installed on this computer. would this work? |
Sound heard if this is built.
BANG! Whats that smell?
Source of smell, Speaker, smoke from chip amps, any resistors connected to the circuit, power supply transformer if your not fast or the fuse didn't save you.
This is a bad idea, sorry.
BZ |
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| azira |
| quote: | Originally posted by HDTVman
This is a bad idea, sorry.
BZ |
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.
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Danny |
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| soundNERD |
| 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. :D:D 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. |
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| jcx |
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 |
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| HDTVman |
| 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.
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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 |
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| azira |
| 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.
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Danny |
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| azira |
| 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.
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Danny |
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| jcx |
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 |
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| HDTVman |
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 |
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| Stocker |
| 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. |
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| simon5 |
| Or a small DC offset. |
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| HDTVman |
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.:smash: :smash: :smash:
It's still a bad idea.
BZ |
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| simon5 |
You couldn't bias each OPamp with some DC offset of like 1,5 V ?
Like in a class AB? |
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| Stocker |
HDTVman, I am not saying you are wrong, as I suspect you are right. I recall however one webpage explaining opamp use fundamentals; there was a class-B output stage on the opamp the fellow was using... the output went from horrible crossover distortion to <0.1% with a wire (follower) for feedback.
If you could avoid clipping, or exploding chips, it could work eh?! |
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| HDTVman |
| quote: | Originally posted by Stocker
HDTVman, I am not saying you are wrong, as I suspect you are right. I recall however one webpage explaining opamp use fundamentals; there was a class-B output stage on the opamp the fellow was using... the output went from horrible crossover distortion to <0.1% with a wire (follower) for feedback.
If you could avoid clipping, or exploding chips, it could work eh?! |
The problem is you are clipping as part of the design here. This is not at all like a discrete output stage. The design is being forced to be nonlinear at the 0 crossing because the + chip output can't go below some voltage greater than 0 volts, 1.5 v for example and the - chip can't go more + than -1.5 v. A 3 volt notch you can't avoid and the output can never be 0 volts.
With a class B amp stage at the 0 crossing no current flows and output voltage is 0 but as you start to turn on one of the transistors the voltage starts to increase. Yes you can help the nonlinearity of this type of output with feedback.
I would guess the page you refer to in the quote was using a single opamp in a more normal mode, and yes feedback could help a " Class B " output stage. The basic problem with the described circuit is that in reality it is not " Class B " but a push/pull "Class C " amp near "Class B".
BZ |
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