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Old 6th September 2012, 12:27 PM   #2961
mikelm is offline mikelm  England
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Quote:
Originally Posted by Jay View Post
In your grounding case with 100R, my question was, will there any chance that shorting the resistor will be much better when there is no earth connection to the chassis? This is not my environment/situation of course.
Not sure about the answer to your hypothetical question - LC would probably know as he mentions this scenario above when he is in testing phase before sinks are earthed.

However, I have two almost identical amps - one with this grounding scheme and the other with the 100R shorted. There is one other variable I have to eliminate but so far the amp with the 100R sounds considerably better.

I'm pretty busy right now but in a few days I'll do some experimentation to establish exactly what is causing what. Also I will add this 100R to every element in my system - I think only then will the full benefit of this mod be realised. As you say, we have to consider earthing in terms of the whole system.

I'll report my findings when I have them

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Old 6th September 2012, 02:30 PM   #2962
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It can be solved only with some thermal independent Vref like TL431 etc. That's why mine CCS are like sch on the pic.
We always start with good resolutions. "Simple is beautiful". Then we always end with the same kind of solutions, a little bit more complicated. ;-)

I have general questions about PSUs.
Why shunt regulation is supposed to sound better. Noise ? Regulation response time ?
Why battery powered system are supposed to sound better ? PSU impedance ? Current Noise in the grounds wires between equipments ?
(I have my own partial opinion , but i'll like to know yours)
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Last edited by Esperado; 6th September 2012 at 02:38 PM.
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Old 6th September 2012, 03:33 PM   #2963
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If you have not yet seen these articles - they are very informative about regulation, noise & batteries



Simple Voltage Regulators Part 1: Noise - [English]

Simple Voltage Regulators Part 2: Output Impedance
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Old 6th September 2012, 03:38 PM   #2964
mikelm is offline mikelm  England
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this index page may be useful for accessing all sections

DIY: solid state
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Old 6th September 2012, 05:11 PM   #2965
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Most of the measurements are noise measurements of PSUs made "as-it", rail side. If we cannot hear noise in our equipment, i believe the problem is not mainly here .

The problem behave, on my opinion, on two sides. The first one (main on the musical perception) is how react PSUs during transients, and the second how ground currents pollute the signals. More precisely what kind of IM is produced by this pollution. This, of course, for analog.
We all know what kind of errors noise can produce in DA converters.

I believe a (so called) fast amp is less sensitive to PSU or ground problems, because it produce less TIM and less IM.
I believe we can improve things on 3 ways.
First, boards side, using two layers, one dedicated to ground connections (star or plate ?).
Second, on power supplies (low impedance, less noise, less HF currents in the ground wires): C trasfos, or shielded toroidal etc).
Third, on the wirings (Symmetrical lines etc).

The only thing i know for sure is, designing audio, we have DEFINITIVELY to forget to think "voltage" and concentrate our minds on "CURRENTS". And keep thinking each wire or track is a F... coil !

I have no idea of how experiment all that together in order to make our mind and find general "Laws" instead of a compilation of cook recipes. If we believe LC on the musical improvement brought by a good CS on only one stage, we can have an idea of the improvement that can be done if such a work is done everywhere !!!!
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Last edited by Esperado; 6th September 2012 at 05:17 PM.
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Old 6th September 2012, 05:15 PM   #2966
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Originally Posted by mikelm View Post
However, I have two almost identical amps - one with this grounding scheme and the other with the 100R shorted. There is one other variable I have to eliminate but so far the amp with the 100R sounds considerably better.

I'm pretty busy right now but in a few days I'll do some experimentation to establish exactly what is causing what.
Thanks. I mentioned about environment variations (when you find no improvement, where for example you use power conditioner, it doesn't mean that there is no improvement with different environment), also my difficulty with solving interference or coupling issues. Those have inter-relationship.

You may believe that an amp will sound good without casing, and may sound terrible when put in enclosure. Then you may not believe that it is not a simple grounding problem. Theoretically we don't want a ground loop so theoretical (but often doesn't work in practice) approach is to ground at one point. But metal casing is not a perfect inductor. The casing also functions as "ground" to shield sensitive circuits. But they also seem to function as antenna, that reflect and radiate interference or so (especially in "dirty" environments).

In old stuffs, any metal even if small are grounded (tape machine is a classic example). The casing of potentiometers must also be grounded. The classics worst case is the use of metal casing of bad quality EI transformer.

It might also not be a secret that when you open the top metal casing, the sound will be improved than when the casing was in position. Also when power supply (aka transformer) is separated in different (or far away) enclosure.

The latest find that I couldn't believe was the effect of nearby switching power supply. I didn't understand how it could manage to interfere with my system (which I believe has no grounding issue).

The fact is that ground (planes) are often used (intentionally or not) as a shield. But the quality of the shield unfortunately depends on... the quality of ground?
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Old 6th September 2012, 05:21 PM   #2967
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Not to forget we listen sources recorded on very bad equipments :-)
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Old 6th September 2012, 05:56 PM   #2968
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Quote:
Originally Posted by Esperado View Post
The only thing i know for sure is, designing audio, we have DEFINITIVELY to forget to think "voltage" and concentrate our minds on "CURRENTS". And keep thinking each wire or track is a F... coil !
Exactly, voltage is just a potential, causing potential, unrealistic problems, but currents when started to flow, they do all the messy stuff in circuits: inductions, interferences, voltage drops, heat, noise, ...
If we concentrate more to correct current "regulation", we'll always gain in quality. Similar like the rivers, who cares about the hight or the nature of their source, local current nature is all what it matters. Is it wild? Smooth? Fast? That's what interests us, when we look at certain point of the river, asking ourselves how to cross it, make a dam, ... so path where the water flows matters. Similar in electric circuits, we have to ensure fast paths to the electrons, not causing to much negative effect to the neighburing parts, circuits.
Regarding amp's PSU, low source impedance and charge [A/s] is all what it matters. Filtrations, referencing, decoupling etc, can all be done locally, suited to each part of the circuit individually. Same as the upper case of CCS, where +/- 15 V potential quality is really not critical at all.
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Old 6th September 2012, 06:07 PM   #2969
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Originally Posted by Lazy Cat View Post
Same as the upper case of CCS, where +/- 15 V potential quality is really not critical at all.
No doubt that for this topology, the input stage is very very very critical. But to think that the +/-15V is really not critical at all, I will think twice he he.
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Old 6th September 2012, 06:13 PM   #2970
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Originally Posted by mikelm View Post
Not sure about the answer to your hypothetical question - LC would probably know as he mentions this scenario above when he is in testing phase before sinks are earthed.
Of course I know, from my experiments experiences I learned that direct grounding (zero ohm) is not always good, since it means that you practically connected one plate of the "capacitor" directly to GND, causing new problems that didn't exist before. Direct capacitor to GND coupling in other words means opening the gate to all kinds of AC currents to flow where they should not. To some currents at resonance frequencies we even enables oscillations etc. So to certain metal parts it is much better to connect them to GND via resistor, thus controling maximum current level and resonance. One example is VAS cascode BJT heatsink connection to GND via 47 ohm resistor. If not, that's same as you would connect 1 nF cap from collector directly to GND. One can just imagine what that causes to VAS's high impedance to GND.
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