janneman said:
One way to avoid ground loops (ground currents through the screen, in this case) is to separate the mains power ground from the signal ground.
Joshua_G said:
That goes without saying, but what if the preamp signal ground and the power amp signal ground are physically separated? Do you use the screen to interconnect these two signal grounds? Or ground the screen only at one side (which side?), and make some other arrangements to centralise the signal ground?
I believe these types are issues will dwarf any concern about the type of cable.
Jan Didden
janneman said:
When the pre amp and the power amp are two separate units, and when mains power ground is separated from the signal ground in both – in Single Ended Output/Input, the screen must be connected at both ends, or, alternatively, a separate ground wire should connect the signal ground of both – in which case the screen can be connected at one end only – usually the sending end. In balanced Output/Input, the screen would better be connected at one end only – usually the sending end.
All the above assumes that there is zero constant DC on neither the signal output nor the signal input – which is the way it should be. In such a case, there should be no ground current through the screen, even in SE when the screen is connected at both ends.
Hi, 1audio,
I read in JBL Vintage website that capacitor can be subjected to "zero crossing distortion", analogy with x-over distorton at classB power amp output stage. Distortion occurs around area which the signal changes polarity, from (+) to (-), vice versa. JBL use 2 capacitor in series which the joint is biased to +15V. I also saw this in Walt Jung's "Picking Capacitor" paper, fig 1b.
Is this the same with dielectric of output capacitor condition when using a single supply for preamp? In Naim or FM Accoustic preamp, they keep using single supply rail for preamp (only 0 and +rail). Output always capacitor coupled. I see 1 advantage with this approach, that is the output capacitor is always polarized for all signal output. The (-) of the capacitor always more negative than the (+) at all output voltage. There are nowhere which (-) lead is more positive than (+) lead of the capacitor.
I read in JBL Vintage website that capacitor can be subjected to "zero crossing distortion", analogy with x-over distorton at classB power amp output stage. Distortion occurs around area which the signal changes polarity, from (+) to (-), vice versa. JBL use 2 capacitor in series which the joint is biased to +15V. I also saw this in Walt Jung's "Picking Capacitor" paper, fig 1b.
Like RG59 has about 40-60pf. Am I right that the shielding, besides protect from EMI, it will also corrupt analog data? The shielding don't know which one is to be absorbed, which one is the signal, it will be low impedance to all signal within it's impedance property.
Very clever. Is this has been done somewhere?
I see now. Thanks for the information 😀
First time I saw it, it was in National's app-notes back in the 70s. Horowitz and Hill show a very elaborate version in their text.
The whole "linearizing a dielectric" has more than a whiff of pseudoscience. The patent's complete lack of backup data and the frank confession that the explanation for the effect that's not demonstrated could be total BS is something of a clue.
It is a standard technique in instrumentation systems.
Known as a "driven guard" it can minimise shield capacitance and therefore reduce settling time for high impedance measurements.
Known as a "driven guard" it can minimise shield capacitance and therefore reduce settling time for high impedance measurements.
Hi, Janneman,
I think that for inverting input power amp, it is impossible that the ground (junction of decoupling caps of the inverting amp) not connected to the signal sender's (upstream preamp) ground. These 2 ground points should be always connected in least impedance method. If we trace signal current from preamp's output going to inverting amp's input, it will go to amp's rail and should be back to the preamp's ground return. Non-inverting amp is more forgiving for ground return.
If we float the cable's shielding, then the ground return will travel very long PCB track, going back to transformer's or elko bank's CT (or any point which the preamp and power amp's ground are connected) first.
I think that for inverting input power amp, it is impossible that the ground (junction of decoupling caps of the inverting amp) not connected to the signal sender's (upstream preamp) ground. These 2 ground points should be always connected in least impedance method. If we trace signal current from preamp's output going to inverting amp's input, it will go to amp's rail and should be back to the preamp's ground return. Non-inverting amp is more forgiving for ground return.
If we float the cable's shielding, then the ground return will travel very long PCB track, going back to transformer's or elko bank's CT (or any point which the preamp and power amp's ground are connected) first.
The important thing is to avoid ground currents in the screen with a se cable as that would induce hum and noise. That is why in a balanced connection you ALWAYS use the screen as the ground connection between two units (contrary to what Joshua stated), and also you ALWAYS balance the impedances of the two signal lines in the balanced connection.
The result is that a) you have connected the signal grounds of the two units, and b) any signal-line induced hum or noise is cancelled in the balanced receiver.
Note that, contrary to popular belief, it is NOT necessary, nor advantageous for hum & noise supression, to have balanced signal levels.
The ONLY reason to have balanced signal levels is to be able to get twice the signal amplitude from a given supply voltage(s).
Jan Didden
The result is that a) you have connected the signal grounds of the two units, and b) any signal-line induced hum or noise is cancelled in the balanced receiver.
Note that, contrary to popular belief, it is NOT necessary, nor advantageous for hum & noise supression, to have balanced signal levels.
The ONLY reason to have balanced signal levels is to be able to get twice the signal amplitude from a given supply voltage(s).
Jan Didden
I think that this internal wiring discussion depends on a number of factors that have been left out. It is really an inappropriate topic, because of this, not that we have not all learned something.
First, the REAL problem is putting EVERYTHING in the same box. This means that the AC mains, rectifier noise, xover distortion thrown back on the DC power supplies, transformer radiation, etc. is all there. etc. This usually demands electrostatic shielding at the very least. Magnetic shielding and careful wire dressing might be just as important, as well as transformer orientation. What a hassle!
DC on the wires makes a small, but sometimes important, difference. I usually just go for Teflon or a near equivalent and avoid the complexity and compromise of cap coupling.
On the low noise front, IF any of you can and will download the book linked here by Courage, then you will have achieved just about everything that you need to know about low noise audio design, except perhaps, for certain parts that are the best for audio.
The early book M&F, was first published in 1973. It was a wonderful reference at the time, but time marches on. NOW, we have much better parts, at least if you can still find them. The later book, M&C, is an updated version of the early text, and that is good, but I am not sure if it is truly up-to-date about fets. I will have to look at a copy, BUT if you can get it for free (I can't for some reason) then go for it.
Low noise design at an engineers level is mostly formula and experience. An experienced technician should not be intimidated by it. Only obscure definitions and equation notation might throw a tech, but just ask someone at work about some obscure notation. It is just what we learn in school as a formalism, rather than really difficult math.
Just like how doctors use their obscure terms amongst themselves, and leave the rest of us out.
First, the REAL problem is putting EVERYTHING in the same box. This means that the AC mains, rectifier noise, xover distortion thrown back on the DC power supplies, transformer radiation, etc. is all there. etc. This usually demands electrostatic shielding at the very least. Magnetic shielding and careful wire dressing might be just as important, as well as transformer orientation. What a hassle!
DC on the wires makes a small, but sometimes important, difference. I usually just go for Teflon or a near equivalent and avoid the complexity and compromise of cap coupling.
On the low noise front, IF any of you can and will download the book linked here by Courage, then you will have achieved just about everything that you need to know about low noise audio design, except perhaps, for certain parts that are the best for audio.
The early book M&F, was first published in 1973. It was a wonderful reference at the time, but time marches on. NOW, we have much better parts, at least if you can still find them. The later book, M&C, is an updated version of the early text, and that is good, but I am not sure if it is truly up-to-date about fets. I will have to look at a copy, BUT if you can get it for free (I can't for some reason) then go for it.
Low noise design at an engineers level is mostly formula and experience. An experienced technician should not be intimidated by it. Only obscure definitions and equation notation might throw a tech, but just ask someone at work about some obscure notation. It is just what we learn in school as a formalism, rather than really difficult math.
Just like how doctors use their obscure terms amongst themselves, and leave the rest of us out.
Hi, Janneman,
Right. There is "ground" and "ground return path". Ground return path has the same importance as signal path, they are carrying the same current. The later is usually not getting appropriate attention.
Right. There is "ground" and "ground return path". Ground return path has the same importance as signal path, they are carrying the same current. The later is usually not getting appropriate attention.
Hi Lumanaw,
---I read in JBL Vintage website that capacitor can be subjected to "zero crossing distortion", analogy with x-over distorton at classB power amp output stage. Distortion occurs around area which the signal changes polarity, from (+) to (-), vice versa. JBL use 2 capacitor in series which the joint is biased to +15V.---
This seems to have been dismissed by Cyril Bateman :
http://uk.geocities.com/cyrilb2@btinternet.com/index.html
---I read in JBL Vintage website that capacitor can be subjected to "zero crossing distortion", analogy with x-over distorton at classB power amp output stage. Distortion occurs around area which the signal changes polarity, from (+) to (-), vice versa. JBL use 2 capacitor in series which the joint is biased to +15V.---
This seems to have been dismissed by Cyril Bateman :
http://uk.geocities.com/cyrilb2@btinternet.com/index.html
For the record, my associate owns the updated copy of M&C, which is M&O. I have seen that specific book, but over a decade ago. I will have to ask him about the jfet info in the book, before I can give it my complete blessing. That is why I recommend Yishay Netzer's article so strongly. He DOES note the noise characteristics of most of the best low noise parts and is reasonably up to date.
I tried to download the book, but I can't open it with my MAC. It has .rar on the end. Perhaps someone can update me as to what it is and how I might work around the problem
I tried to download the book, but I can't open it with my MAC. It has .rar on the end. Perhaps someone can update me as to what it is and how I might work around the problem
John,
.rar is a variation of .zip. You probably need to download and install an application that can 'un-rar' a .rar...
Jan Didden
.rar is a variation of .zip. You probably need to download and install an application that can 'un-rar' a .rar...
Jan Didden
.rar is the extension for compressd files (just like .zip)
Go to
http://www.bestsoftware4download.com/software/t-free-rar-for-mac-os-x-download-eecirezo.html
for example to find a Mac opener (or google ".rar for the Mac")
Go to
http://www.bestsoftware4download.com/software/t-free-rar-for-mac-os-x-download-eecirezo.html
for example to find a Mac opener (or google ".rar for the Mac")
The linked-to site is a known copyright violator. I killed the link; if someone wants to contact the authors to see if they have given permission for free distribution, I can put it back. The last time I saw a link there, it was for Self's book, for which he had decidedly NOT given permission.
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