AndrewT said:
I think that this grounding discussion has proven that my analogy to religion here is accurate.🙂.
I am sure there are just as many different approaches to where to connect the RCA input "ground". Here's what I usually try to do. It is not unusual, and many others do it. I connect the RCA amplifier input shield to the analog (quiet) ground of my amplifier through a 4.7 ohm "ground stopper" resistor. I also reference the negative feedback circuit to that shield node. I like to prevent much ground current from flowing in the shield.
Indeed, I like to view the center conductor and shield largely as a differential pair of signals. If you want to go a step further, you can actually configure the differential input stage of your power amplifier, along with the power amplifier's negative feedback, as a differential (instrumentation) amplifier. This allows you to use the voltage on the shield as the true reference for the voltage in the center conductor. The shield, of course, still sees only 4.7 ohms to the amplifier quiet ground. Notice also that this prevents the pair of shields in a stereo pair from forming a ground loop.
Bob
Bob Cordell said:
Bob,
Thanks for this. I need to make some last minute changes to my amp board ... 😀
Jan Didden
Hi Bob,
thanks for the info.
just in case I have misunderstood, I shall rephrase:
RCA pin to coax centre to PCB input.
RCA barrel to coax shield to 4r7 to PCB signal ground to NFB ground.
Do you connect RCA barrels to either central ground or to safety earth or to each other?
thanks for the info.
just in case I have misunderstood, I shall rephrase:
RCA pin to coax centre to PCB input.
RCA barrel to coax shield to 4r7 to PCB signal ground to NFB ground.
Do you connect RCA barrels to either central ground or to safety earth or to each other?
Wavebourn said:
Experimenting is why my viewpoint is what it is, even if my way of describing it is in a different language. My bad, but you should hear what I hear. This is the sole reason for my insistance.
AndrewT said:
Hi Andrew,
I expect it to show only the current being delivered from the supply to the amplifier circuitry/load. Anything availible to the load resistor (amp output) should be reflected in the drop across the .1 ohm. If I watch both the amplitude and phase, the output might just show a difference between the speed at which the supply can service the amp and how wide the bandwidth is. Or I could be proven wrong.
I don't really care about the charging currents and glitches since I'm bypassing the whole mess right at the rectifiers back to my main ground (good filters). I'm not going to guess what the more correct way of doing this might look like. Once again, ICBW...
Regards, Mike.
jacco vermeulen said:Mr Bettinger,
in this Bob Cordell interview you've become on par with Mr Cordell by posting the 26th time.
Unfortunately you're still three posts behind the clear leader in this rallye, Mr AT&T.
Let's all hope Mr Cordell doesn't feel like posting.
I'm not sure who Mr AT&T is so I'm not suitably affected and I'm not sure why I'm continuing on anyway, from the sounds of this this is all well covered ground. Anything I say is summararilly dismissed based on sematics. It's not like it's the elephant in the room and I'm blind. It's turned into more like watching a accident unfold and not wanting to look but being drawn to it.
The funny thing is, the complete lack of any interest in the possibility of things being different than we were all told. It's human nature to compartmentalize things and move on to the next big thing. Open minded experimentation is not the persona exuded by the site. But that's cool.
Luckily for me I have been forced into thinking a bit before spouting my gibberish; it still gibberish, just not to me.
I see Bob's returned to the conversation now so I'll bow out if there's not much I can add. Although I will make one more postulation concerning the grounding of the amplifier input ). There is another way to look at it. (not to mention a much more comprehensive system view).
Regards, Mike.
MikeBettinger said:
Have we really?
Yes, and the reason for my entrance into the discussion was that you seemed to have something to say that was worth listening to, but the argument you presented had a problem that had already been pointed out by several others and which was still not satisfactorily answered. Since this problem, although perhaps a detail, seemed central to your argument, which you seem to confirm, I thought this really had to be sorted out before analysing your argument further.
Yes, I thought that was what you were doing, but I must say it didn't seem you did understand what was asked since your answers did not even make any clear reference to the question, even less answering it. Hence, I do think there was still a communication problem between us. I do however think the question asked several times by myself, and before that by several others, was perfectly brief, clear and simple and related directly and concretely to a particular detail of your argument. It did thus surprise me that you seemingly failed to address the question at all in your answers and instead flooded us with lots of seemingly irrelated or unimportant details.
Yes, I understand that is one of the things you have been saying all the time, and was not what I had problems with (although I do find your view somewhat unusual). However, I do not see how and if this relates to what I did ask about.
Good. A simple answer to a simple question. I really do wonder why it took sooooooooooo long to get the answer.
And then you immediate seem to contradict the answer you just gave!!! However, you say that you "feel" it is this way. Are we to understand that the claim was meant as some kind of philosophical standpoint rathern than a physical fact? The question remains to be answered what you really meant, since you seem to agree with me on the electrical reality. Or maybe you didn't really mean much with this statement after all, and maybe it isn't really important to the rest of your argument after all? However, you have repeatedly said it is important to the argument, which is why the question what you mean is also important.
A nice way to think of the ideal ground. Of course we can never do better than to approximate it, so the quest is for the best approximation.
Christer wrote:I do however think the question asked several times by myself, and bef
Maybe a drawing or schematic now and then will give a clearer view for this topic?
At least for me...
Loek
Maybe a drawing or schematic now and then will give a clearer view for this topic?
At least for me...
Loek
MikeBettinger said:
Mr Bettinger,
the comment was not really directed to you.
I've read most of your posts, wholeheartedly agreed with the ones you placed at the CTC thread in particular.
You obviously have a lot of professional experience, and a different view based on experience is a welcome catalyst for a cerebral massage.
AT&T is a company that has often made a mess because of lacking expertise, but nowadays has internet lines everywhere. Overhere, AT&T just reached the No-10 ranking of the ones with most lines in most threads. Number 1 to 8 are all mods/ex-mods, Nelson Pass ranks 9th.
At this rate, Mr. NP will be surpassed around Januari 1st.
Common courtesy is letting the one being interviewed do most of the talking, not the one with little to no experience/expertise who should be doing most of the listening.
I seem to have been raised in a different environment, my bad.
Good thing i'm always able to put on a funny nose.
AndrewT said:
Hi Andrew,
In the simple version of what I described, you are correct. However, the RCA barrels are not connected together and they are not connected to any ground (other than at the source from which they originated). Each RCA barrel makes it way to ground in the power amplifier through its own 4.7 ohm ground stopper resistor.
Hope this helps.
Bob
MikeBettinger said:
Mike,
Your posts are always welcome on this thread, even if I or someone else doesn't always see things the same way. We all come from different backgrounds and different experiences that shape our questions and our understandings and our ways of explaining things and the analogies we use. That diversity makes us all work harder to understand things, and forces all of us to question some of our own understandings. That is a healthy thing. Don't forget, this thread got started by me raising a question on something I did not understand.
Cheers,
Bob
Bob Cordell said:
All,
I appreciate that, but I also realize that on this topic there is a fundamental difference in my viewpoint that leads to nowhere.
Rather than attempting to continue the discussion, I made time to go back through the thread to see where the disconnect lies and to attempt to sort it out, at least for my own edification.
I guess that, once past the semantics and differing experiences, the fundamental "question that I failed to answer” was not so much a question but a difference in perspective. My comments concerning the return currents from the speaker circulating back into the transformer instead of through the filter caps could not even be entertained as part of the discussion. But then, this is what I presume to be the main point of contention (Andrew seemed on line with this, although later comments seemed to muddy this water). This point, by the way, is what dragged me into the discussion. I realize there were various splinter discussions concerning the location of the main ground, the charging currents that came in to the (my) big picture as well. But these just served to confuse the whole.
I don't want to beat this to death anymore because it is more of a put-up or shut-up debate and there is little in place to effectively pit one's understanding against another’s in any meaningful way - and because the difference is fundamental and would require a change in a fundamental belief (by me or others), which I seriously doubt is going to occur. This is not a problem, or anything that hasn't occurred many times on many topics. The thing is to let it go, although I can't help feeling that a discussion over coffee with a few napkins' worth of figures would bring the discussion into a balance, (I can't respond to a look of confusion over the internet).
I don't believe, as Andrew speculated, that the correct way to implement a main ground will surface from more discussion, primarily because, after re-reading the thread, I stand behind everything I wrote and it all makes sense to me; at the same time, though, my comments create some big disconnect that my way of describing things will not bridge.
I for one do not have the time or energy to fully flesh-out this topic, and all of the side concepts that are part of the bigger fundamental picture. This I might add is responsible for my lack of fully understanding and properly responding, at times, to the thread as it was unfolding. There is a lot of effort being expended by all that requires a similar commitment on my part if one wants to play.🙂
I have learned a lot, while hopefully shaken a tree or two in the process.
And now back to your regularly scheduled programming...
Regards, Mike.
Dear all,
I tend to support what Mike is saying. Let us assume for one moment that the amplifier is required to operate at 100 Hz (the European line frequency) and it so happens that it was in sync with the supply frequency and we had full wave rectification. Does one need capacitors at all - obviously the ground return is to the transformer centre.
Kind regards
I tend to support what Mike is saying. Let us assume for one moment that the amplifier is required to operate at 100 Hz (the European line frequency) and it so happens that it was in sync with the supply frequency and we had full wave rectification. Does one need capacitors at all - obviously the ground return is to the transformer centre.
Kind regards
Early in this thread a question was posed regarding how large should the power supply cap be. In the yonder years these were called resevoir caps and that is exactly their purpose.
The size of the cap can be calulated based on the minimum terminal voltage required to sustain the necessary current flow at maximum power through the load between charging cycles.
On the other hand the transformer should be rated to supply the necessary current to sustain maximum power through the load as well as recharging the capacitor during the charging cycle.
If the reservoir capacitance is less than optimum, then low frequency reproduction will suffer or be distorted. On the other hand if it is larger than optimum then money is wasted without any improvement in signal reproduction.
A practical consideration is to connect a wire wound resistor of 4 or 8 ohms to the amplifier output and apply a 20 Hz square wave signal to the input of the amp.
Turn the level up until the power generated in the resistance is what you require. Compare the output waveform to the input waveform and you will immediately see if your power supply is up to the task at hand.
The size of the cap can be calulated based on the minimum terminal voltage required to sustain the necessary current flow at maximum power through the load between charging cycles.
On the other hand the transformer should be rated to supply the necessary current to sustain maximum power through the load as well as recharging the capacitor during the charging cycle.
If the reservoir capacitance is less than optimum, then low frequency reproduction will suffer or be distorted. On the other hand if it is larger than optimum then money is wasted without any improvement in signal reproduction.
A practical consideration is to connect a wire wound resistor of 4 or 8 ohms to the amplifier output and apply a 20 Hz square wave signal to the input of the amp.
Turn the level up until the power generated in the resistance is what you require. Compare the output waveform to the input waveform and you will immediately see if your power supply is up to the task at hand.
MikeBettinger said:
MIke
I have been silently following this thread and must admit to a bit of confussion.
You are an experienced and knowledgable person, so it should not be wise to dismiss your position and go ahead.
It is trully a fundamental fact that energy comes from the transformer secondary. It is equally fundamental that once the filter caps are inserted, there are basically two different circuits operating sequentially, one when the diodes are conducting and another when they are blocking, which happens most of the time in a reasonable design.
In this second scenario, the secondary winding circuit is effectivelly open, meaning the only currents flowing through the center tap can be only those derived from stray capacitive couplings.
So I must asume your point concerns mainly with the charging cycle.
While I can relate whith your feeling of frustration, kindly, I must solicit you to press on. Note I am closer to the capacitor common as reference ground idea, but really want to be sure I am not missing something you learned worth taking into account, rather than trying to convince you out of your position.
Rodolfo
Rodent said:
I think that there is a lot more to it than this. If I understand your point, you are essentially saying that if the reservoir capacitors are big enough to avoid clipping on the largest bass signals to be handled, the power supply is as good as it can get and as good as it needs to be. I wish it were this simple. I think you would find that in most cases, where people have upgraded the supply with much larger capacitance and hear a substantial improvement in sonics, that a before-and-after measurement of that amplifier would reveal only a very small increase in low-frequency clipping power. Not enough to explain the improved sonics. I am assuming that these people who have upgraded their supplies are hearing an improvement under conditions where they are NOT clipping the amplifier.
I think it is hard to make generalizations here. I think it has a lot to do with the amplifier's power supply rejection, both in the input/driver stages and in the output stage. It is undeniable that bigger caps with smaller ESR will reduce power supply ripple and, to some extent, power supply modulation. Power supply ripple can be pretty nasty, it being a sawtooth wave with harmonics extending pretty far out. Hopefully this ripple is well-filtered out in the rails used for the input/driver, but in many designs it is pretty raw as it is applied to the output stage. How well do we think the output stage will reject this nastiness?
Note that a second level of main power supply RC filtering, say 10,000 uF and 0.22 ohms, will have a corner frequency of 60 Hz, meaning that the nasty fundamental and harmonics of the sawtooth will be attenuated by 6 dB starting at 120 Hz and rolling off at 6 dB/octave after that if the 10,000 uF cap has a good ESR. This will really round off the sawtooth wave. Note, that any kind of power supply rejection tends to decrease at high frequencies, so the increased rolloff of the RC filter can really help. We'll have 20 dB of attenuation from this additional filtering stage at 600 Hz. This is also the capacitor that likes to be right near the output stage power transistors to close the current supply loop locally. The presence of the 0.22 ohm resistor will cause only a fairly negligible reduction in available supply voltage.
The power supply rails go up and down with the average current draw of the output stage. Although most amplifiers run the rails through at least an RC filter network before use by the input/driver circuits, that doesn't do a lot for this slower variation of voltage as a function of program material. Some input/driver circuits will be more affected by this, and some will be pretty darned immune.
Just some food for thought.
Bob
Note that I use a square wave. Ever tried running your X watt amp at X watt square wave. Now observe the square wave on a scope and see what rubbish you get if the cap is too small.
If your X watt amp produces anything triangular in shape, then you need to beef up your supply somewhat - regardless of PSRR. If the amp where so good to reject short commings in the power supply why use caps at all?
Rodent said:
This is obvious. Passing this test is necessary but apparently not sufficient for good sonics. That's all I was saying.
Your assertion in your earlier post would appear to be equivalent to saying that all amplifiers sound the same as long as they are not clipping.
Bob
Bob, I never said amplifiers sound the same, the actual question was how large should a capacitor be and what is the raiting of the transformer for a given power and load.
At the least I am providing the reader with a possible solution and a practical implemetation.
You on the other hand offer nothing exept that whomever offers some solution must obviously be wrong..
So how about it then, offer this forum your rule of thumb for discussion
At the least I am providing the reader with a possible solution and a practical implemetation.
You on the other hand offer nothing exept that whomever offers some solution must obviously be wrong..
So how about it then, offer this forum your rule of thumb for discussion
- Status
- Not open for further replies.