GRollins said:
Well sure, if you change the reference point from which you're measuring the voltage. Also, you don't even have to attach your +30 volt rail to anything. Just simply move your reference to the +30 rail. You'll get the same result.
se
john curl said:
What designs would those be? The ones without power supply caps? Can't say I've seen any of those.
But even if it's going entirely into the center tap, the return path isn't back to the power line, which was the point.
se
Tony said:
I'm having trouble reconciling this with your earlier posts.
There's not much being said here at DIY (Which has only been around for something like six or seven years [Has it really been that long? Whoa!]) that wasn't already recognized thirty years ago. When was Picking Capacitors published? 1977? Not that audiophiles hadn't been saying that capacitors mattered for years, but suddenly it became acceptable for those who had previously argued against the audibility of parts to say, "It's scientific, you see!" even though they'd denied it just the day before.
To say or imply it's all new...well, I guess it is to some people. There came the day when my sons took their first steps. The fact that gazillions of babies had taken their first steps earlier didn't matter. When they first walked, it was a first for them. By the same token, the audio world has by slow degrees learned things that matter in audio. Some of those same things, like low noise design, for example, are of equal importance to people who design radio telescopes. Back when there were still such things as big disk drives for mainframes, audio used much of the same technology that was of interest to the designers of those disk drives. Audio overlaps many other electronic endeavors, but isn't an exact match with any other field (think of Venn diagrams overlapping slightly). To attempt to map audio onto something like the design of traffic signals will only create frustration. It won't work. Yes, audio needs switching capability, but it's on a much finer scale than routing traffic.
A number of EEs have been members here. So far, I've yet to hear of a school that really gives a good grounding in the things that matter in audio. Yes, there's Leach over in Georgia, but it's not a complete curriculum the last I heard. There may be others as well, that I'm not remembering, but it appears that most EEs approach the audio field as...let's say, generalists. In medicine, you might think in terms of a GP family doctor sort of guy, a separate and distinct creature from a specialist in cancer, or heart disease, or endocrine disorders. To progress beyond a certain level in audio, you have to become a specialist.
In my case, I took a number of courses in electronics when I was in school. Nearly useless, the lot of them. It took me a long time to unravel the stuff that was of use and the things that didn't work for audio.
Grey
For those who don't find a cyclotron schematic, see attachment.GRollins said:
I find this the most "natural" way to construct a bridge / push-pull amplifier, the most basic differential follower.
It clearly shows the series current path through the supplies. Imperfections there wouldn't hurt if there were no parasitic effects of a fluctuating supply voltage for the current gain devices.
The circuit I linked to in a previous post in this thread shows the same series path for a conventional amp topology.
EDIT: I will never learn that it's called Circlotron, not Cyclotron ;-/
- Klaus
Attachments
I'd say the low level measurement/instrumentation folks have got it all, already. I see all topics addressed in the corresponding app notes of ADI, Linear, National, TI etc.GRollins said:
- Klaus
Steve,
I know this make come as a bit of a shock, but what happens to the AC on the primary side has an effect on the secondary side. Reflected impedance, for instance. If there's a problem with the neutral line, as far as the transformer (and the rest of the circuit) is concerned, it's a problem with the AC overall. As a result, the AC coming off the secondary will have effectively higher impedance, noise, RF, whatever problem you've got on the primary side. It's no mystery--or shouldn't be--that a good return line (i.e. neutral) will lower noise and so forth. So why all this harping other than the well known fact that you just dislike John?
Grey
I know this make come as a bit of a shock, but what happens to the AC on the primary side has an effect on the secondary side. Reflected impedance, for instance. If there's a problem with the neutral line, as far as the transformer (and the rest of the circuit) is concerned, it's a problem with the AC overall. As a result, the AC coming off the secondary will have effectively higher impedance, noise, RF, whatever problem you've got on the primary side. It's no mystery--or shouldn't be--that a good return line (i.e. neutral) will lower noise and so forth. So why all this harping other than the well known fact that you just dislike John?
Grey
It is hard to get a loudspeaker return path through a 10uf cap. AND some amps had only 10uf of power supply capacitance. I owned one, once.
GRollins said:
No shock at all. And I never said otherwise.
What I was addressing was John's notion that the amplifier's ground return extends back to the power line.
Sure. But the power line's neutral is not the power amp's ground return line. It's the power line's return line. Well, at least half the time. The other half it's the power line's hot that's the return.
Because everything John said added up to his saying that the amplifier's ground return went back to the power line. It doesn't. At best it extends only as far as the power transformer's secondary, and most of the time it only extends to the power supply caps.
se
john curl said:
Great. That still doesn't extend the amplifier's return path back to the power line.
se
KSTR said:
Perhaps this will make it a little more clear that pretty much all of the current delivered to the load comes from the power supply capacitors.
An externally hosted image should be here but it was not working when we last tested it.
se
That doesn't look like a 1938 Gibson guitar amp like I used to own. It had LESS than 10uf in the power supply. It worked, however. I wonder how?
john curl said:
Simple. Tubes and transformers.
You can't directly equate simple power supply capacitance between a typical low power tube amp to higher power solid state amps without taking other factors into consideration.
In the tube amp, even though the cap's just 10uF, it's likely to have several hundred volts across it. The energy stored in a 10uF cap with 350 volts across it is much more than a 10uF cap with 25 volts across it. Also, because of the output transformer, the tube's driving a load impedance more like several thousand ohms than eight ohms.
So when you take these factors into account, a tube amp with a 10uF power supply cap will equate more closely to a solid state amp with lower rail voltages, lower load impedance and greater power supply capacitance.
And besides, what's any of this to do with an amp's return path extending back to the power line?
se
Steve Eddy said:
If you believe 'pretty much all' of the current delivered to the load comes from the power supply capacitors, then I suggest you completely remove the transformer from your amplifier and see how long your amplifier continues to play.
If you're right, then we're finally free of all petro-politics in the Middle East and you are rich beyond the dreams of avarice. If I'm right, you need to rethink how your amplifier's power supply works and you might want to consider putting more of those little zig-zags that indicate that you've left things out on the right side of your schematic...right about where the transformer and rectifier would be, in fact.
Grey
GRollins said:
Sure, all of the energy is being supplied at the transformer's secondary. But what I said was "Most all of the current being delivered to the loudspeakers is drawn from the plates of the supply caps which are tied to the voltage rails."
So let's examine that statement.
First, given an amplifier with a reasonably well-designed power supply sized appropriately for the job, for the majority of the time, the power transformer's not even in the circuit. This is during the time which the voltage at the transformer's secondaries is below the voltage across the supply caps and the rectifier diodes are off.
Yet during this time, which on average is the majority of the time, current is being delivered to the loudspeakers. Where's it coming from? The supply caps.
Second, even during the refresh period when the diodes are conducting, most of the current from the transformer's secondaries should be going toward charging the supply caps rather than supplying current to the load. Otherwise you'd never be able to top off the caps.
And this is why I said "Most all of the current being delivered to the loudspeakers is drawn from the plates of the supply caps which are tied to the voltage rails" and why I drew the illustration that I did showing how things looked the majority of the time.
And this goes back to something John said, which was "The return path of the amps output has to go somewhere as we do not usually plant a stake in the ground for it to go there." I was stating that the primary return path was to the plates of the supply caps tied to ground and to a considerably lesser degree to the transformer's secondary center tap.
And this goes back further to John's notion that the amplifier's ground return path extends back to the power line, something which no one has yet been able to substantiate.
se
lumanauw said:
Sort of. It's about having a bank of high capacity "super capacitors" that are dynamically switched in to provide more juice during high current transients.
se
I think I have it now! SE is talking about energy, and I am talking about current. You might think of the ground return current as depleted, because it has lost its original voltage potential that was given it by the DC power supply. Of course, energy is used to make the amp go, and to drive the loudspeaker, motor, lightbulb, or whatever else you might want to control with it. Still, the 'depleted' current' has to be returned to the power supply so that current in some form may continue back to the 'neutral' in the AC line. No current flow back through the neutral line, no amp operation, after a tiny pause for the caps to give up their stored energy. .
- Status
- Not open for further replies.