john curl said:
No, John. Please go back and re-read. I was speaking of current as well. Specifically the current delivered to the loudspeaker which is the subject of discussion. Grey confused the issue by bringing up the power transformer which was irrelevant to the point I was making.
You know, I read this, and about all I can do is just sit shake my head.
But I'll try anyway.
John, the amplifier's ground return path does not extend back to neutral on the AC line.
With all your formal education and years of experience with electronics did you not pick up somewhere along the way the fact that current flows in loops? That's where we get the notions of "send" and "return." The current has to flow back to the point from whence it came.
The AC line's neutral is not the return path for the amplifier. The AC line's neutral is the return path for the AC line's hot. Though that's only half the time since we're talking about AC. The other half of the time, the AC line's hot is the return for the AC line's neutral.
On the AC line side of it, what you have is a current loop formed by the secondary of the power transformer up on the pole and the primary of the amplifier's power transformer. And the current that flows in this loop is not the current that's flowing in the amplifier/loudspeaker. That's a separate loop and hence the amplifier's "ground return path" does not return to the AC line's neutral.
Think, John. What are those big heavy things that sit between the AC power line and the the amplifier proper?
That's right, transformers!
And why is it that transformers are so effective at breaking ground loops?
Bingo! Because they provide galvanic isolation!
So now tell me, John, given that, how do you manage to have the amplifier's ground return path returning to the AC line's netural?
se
This is pointless. It does not help to make better designs. It only makes even more unclear some of the real design problems. It is like discussing philosophy.
For the record, I have designed working transformerless power amps in the past. The biggest problem was safety, followed by a tendency to hum. I gave up and went back to using power transformers when AC powering my power amps. Transformers are useful, but sometimes they even inhibit maximum current flow. The trick is to use power transformers so that they become less inhibiting to max current flow (in power amps) yet provide good RFI rejection (toroids are bad at this). The galvanic isolation is useful in reducing hum, and provides a margin of safety. For most other applications, transformers are usually a compromise to get something to work properly. In other words, transformers generally are a step away from good sound, rather than a sound improver. Your opinion may vary from this, but that is not my problem or responsibility, and I would prefer not to debate it.
For the record, I have designed working transformerless power amps in the past. The biggest problem was safety, followed by a tendency to hum. I gave up and went back to using power transformers when AC powering my power amps. Transformers are useful, but sometimes they even inhibit maximum current flow. The trick is to use power transformers so that they become less inhibiting to max current flow (in power amps) yet provide good RFI rejection (toroids are bad at this). The galvanic isolation is useful in reducing hum, and provides a margin of safety. For most other applications, transformers are usually a compromise to get something to work properly. In other words, transformers generally are a step away from good sound, rather than a sound improver. Your opinion may vary from this, but that is not my problem or responsibility, and I would prefer not to debate it.
john curl said:
No, it's not pointless and yes it does help to make better designs.
You can't hope to make better designs if you don't at least have an understanding of some of the most basic concepts. Which you didn't have when you were trying to help make better designs by saying "Unfortunately, many here think only of the forward filtering and not so much about the return path back to the power line."
Now, hopefully, you do have a better understanding, and with that better understanding, you're better able to see what may help or know what won't help.
I fail to see how learning or understanding something you didn't know or understand before can be considered pointless and not helpful with regard to making better designs.
se
OK, fellow engineers! I have designed amps and preamps for more than 40 years, but I can't help much more. What little that I do seem to know and understand has served me fairly well, but I can't offer much more. Maybe we should get Steve Eddy to lead us, but I hope on another thread, as this is the 'Blowtorch' thread and I would prefer it to be for 'Blowtorch' related issues. Is this too much to ask?
FYI Someone asked me within the last few weeks if I would consider working on an audio design project with SE. I politely declined at the time, and I do now, once again. However, Bob Cordell might be available. Dick Marsh is always game for new designs, and he is probably fairly local to you, SE. Never know until you ask.
FYI Someone asked me within the last few weeks if I would consider working on an audio design project with SE. I politely declined at the time, and I do now, once again. However, Bob Cordell might be available. Dick Marsh is always game for new designs, and he is probably fairly local to you, SE. Never know until you ask.
Assuming we are all grown ups, lets get back on topic.
All else, like personal disputes can be handled by mail, phone, fax or SMS.
/Hugo
All else, like personal disputes can be handled by mail, phone, fax or SMS.
/Hugo
Steve,
A transformer is not a brick wall filter. Trying to play semantic games by saying that the transformer provides some mystical isolation doesn't work--the 'barrier' is far too porous for that. Within the bandwidth limitations of the transformer (i.e. no DC will pass, and very little if any GHz will get through) the transformer is no barrier at all...something that digital designers sometimes seem to forget when they spray nasties back up the line to pollute the AC for other components.
Grey
A transformer is not a brick wall filter. Trying to play semantic games by saying that the transformer provides some mystical isolation doesn't work--the 'barrier' is far too porous for that. Within the bandwidth limitations of the transformer (i.e. no DC will pass, and very little if any GHz will get through) the transformer is no barrier at all...something that digital designers sometimes seem to forget when they spray nasties back up the line to pollute the AC for other components.
Grey
😀
eventuallly john curl will be judged not by what he posted here, but by the products that he dished out to the market....
eventuallly john curl will be judged not by what he posted here, but by the products that he dished out to the market....
Steve Eddy said:
If you were to finish the schematic drawing, you'd see diodes and a transformer wired in parallel with the caps.
They are doing something
For that matter, so is the house breaker panel, the next 3+ transformers, all the way back to the mains generator.
The questions then are:
-how much effect?
-what can I control?
certainly I can control the last transformer, diodes , supply caps, etc.
We live in an imperfect world. To the extent that the AC line voltage for stuff here in the US is 60Hz and something in the vicinity of 120V, then you can take steps--some crude, some elegant--to try to make up for the fact that the AC power is of questionable quality.
--A low pass filter is easy and can be done cheaply. It can be as simple as a series inductor or parallel capacitor.
--Here in the US the line voltage isn't as fixed as you might wish, even if it's better than some other countries. I get something on the order of 122Vac at my house, but that's not the case for everyone. If you want to remove voltage as a variable, it's no problem to use a transformer that gives you a slightly higher than necessary rail, then regulate it down to whatever you intend to use. As long as the line voltage doesn't fall so low that the regulator drops out or rise so high that you start getting component failure, you've removed variable rail voltage as a potential problem.
--Rewiring your house, or at least your listening room, is another possibility. If you've got a dedicated line to the mains, you're not going to be at the mercy of resistive voltage drops when something else draws current from the same line your stereo is on.
There are all sorts of things you can do to help fight deteriorating AC line quality. A lot of electronics come with stickers on the back that say something to the effect that "This device must accept all interference" coming from other devices. I beg to differ! It doesn't have to accept interference...it can defend itself to the best of its ability.
Grey
--A low pass filter is easy and can be done cheaply. It can be as simple as a series inductor or parallel capacitor.
--Here in the US the line voltage isn't as fixed as you might wish, even if it's better than some other countries. I get something on the order of 122Vac at my house, but that's not the case for everyone. If you want to remove voltage as a variable, it's no problem to use a transformer that gives you a slightly higher than necessary rail, then regulate it down to whatever you intend to use. As long as the line voltage doesn't fall so low that the regulator drops out or rise so high that you start getting component failure, you've removed variable rail voltage as a potential problem.
--Rewiring your house, or at least your listening room, is another possibility. If you've got a dedicated line to the mains, you're not going to be at the mercy of resistive voltage drops when something else draws current from the same line your stereo is on.
There are all sorts of things you can do to help fight deteriorating AC line quality. A lot of electronics come with stickers on the back that say something to the effect that "This device must accept all interference" coming from other devices. I beg to differ! It doesn't have to accept interference...it can defend itself to the best of its ability.
Grey
GRollins said:
That's nice. I never said otherwise. So what's your point?
No semantic games at all. The issues of noise you bring up here aren't even on the same page.
What was being discussed was John's claim that the amplifier's ground return path goes back to the power line, i.e. the AC line's neutral.
In other words, John claimed that the amplifier's output current (and we're talking about signal current here, not noise) flows out of the amp's output, through the speaker, and is then returned back to the AC line's neutral.
So now if you'd care to argue that this is the case, then I'm all ears. Otherwise, you're barking up the wrong tree.
se
Tony said:
It's not about judging John. It's about incorrect information. It doesn't serve anyone to believe that an amplifier's output current returns back to the AC's neutral line. It not only leaves one misinformed, but can also lead them to erroneous conclusions based on that misinformation.
se
myhrrhleine said:
Sure.
But it's not germane to the issue I've been addressing.
The issue can be summarized in these remarks made by John:
Unfortunately, many here think of the forward filtering and not so much about the return path back to the power line.
What is 'ground'? How is it formed? How does the ground current that is sent there, return to the power line? I am series with my questions. Hint: 'Ground' is not the earth.
Now what does this have to do with amps? Well, amps generate external power and so they require a 'ground' return, where 'ground' in this case is really a common point that is often associated with the chassis in some way.
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.
In other words, John is saying that the amp's output current returns to the AC line's neutral and that this return path needs to be looked at.
Well, the amp's output current doesn't return to the AC line's neutral. As I'd said in previous posts, most all of the amp's output current is sourced from the power supply caps. And it's back to the power supply caps that this current returns, not to the AC line's neutral. And that concept is what my drawing is intended to illustrate.
se
GRollins said:
But ultimately everything is all tied across the same line and anything that draws a significant amount of current from the main line can result in voltage drops on all other branches. Like when my neighbor's air conditioner cycles on any my lights here dim. So a dedicated line doesn't provide complete immunity.
se
- Status
- Not open for further replies.