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Old 6th September 2012, 06:38 PM   #2971
mikelm is offline mikelm  England
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I agree 100% LC with all your points but I think Jay was asking if having that 100R in place and not actually grounding the heat sinks & case would cause a problem

I thought you would know because you said you test in that mode before you put the amp into an earthed casing
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Old 6th September 2012, 06:48 PM   #2972
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Quote:
Originally Posted by Lazy Cat View Post
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.
This is one of the reasons to have some impedance in the earth lines going back towards the transformer.

Doesn't have to be a choke Hugh Dean puts little resistors in all legs going back to the supply.

If it is a choke it certainly doesn't have to be anywhere near a big as the chokes I am currently using.

But some impedance in all the power lines makes a big difference to the sound.
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Old 6th September 2012, 08:32 PM   #2973
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Quote:
Originally Posted by Lazy Cat View Post
Similar like the rivers
Funny, when i work with electrons, i always have some sort of hydraulic equivalent in my mind. Where caps are tanks, resistances are tubes of different diameters, voltages are pressure (or level of the water) etc... I have a representation of each active device that way.
It helps to get the feeling.
And you get a very affraying idea of the signal you are supposed to treat, from wavelets to tsunamis.
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Originally Posted by Lazy Cat View Post
...suited to each part of the circuit individually...
Funny too, thinking to PSUs, and unable to find a satisfying solution in my mind, i just began to design a power fet at the current source of the power transistor after the decoupling cap...
Looking to the article pointed by milkem, i had this strange thought too: "Why the hell did i always, by reflex, put caps after PSU regulation transistors ?
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Last edited by Esperado; 6th September 2012 at 08:37 PM.
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Old 6th September 2012, 08:48 PM   #2974
mikelm is offline mikelm  England
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Quote:
Originally Posted by Esperado View Post
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.
Hehe - I think we have almost completely opposite view on this topic. I spent last 18 months systematically going through every aspect of my amps design with the top priority of reducing noise in every area I can possibly think of and am I am very happy with the results this process brought.

But when I say noise I am absolutely not referring to mains hum - rather the big culprit for me is HF noise which amps somehow manage to demodulated into a kind of audio hash that may be very difficult to measure but can really ruin the sound of an amp. I suspect this demodulated noise raises the high order HD noise floor let's say H6 - H20 There are very many potential causes of this noise.

A classic example of increased H6 - H20 HD ruining the sound of an amp ( though not caused by HF noise ) is adding a poorly designed servo to an amp. In spice we can see the higher harmonic noise floor rise by as much as 25dB and subjectively the nice sound of the amp is suddenly lost. I'm sure anyone who has experimented with servos knows what I mean.

Also when I refer to noise I'm not just referring to hiss levels because I have noticed that amps with similar hiss levels can sound very nice or quite horrible.

Quote:
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 !!!!
I think if we consider the o/p of an amp, everything that is present that was not present at the i/p signal can be grouped in 3 main categories.

1) Harmonic Distortion
2) Phase distortion
3) Noise

If there are other categories I am happy to hear about them but I don't see what else there can be.

One way we could talk about this forever and never get anywhere is by not defining our terms so I propose the following

Harmonic Distortion = H2 - H5

For me regardless of it's cause Harmonic Distortion H6 - H20 is undesirable and I regard it as noise ( even though I realise in reality measured H6 - H20 is going to be a mixture of HD, resonances not related to the signal & completely random noise )

Phase distortion = A delay in time of voltage or current or combinations of both

Noise = everything else that is not directly related to the signal

This can be a chaotic mix from very many sources. Sources of noise I am aware of are and have tried to address are:

mains born noise ( Caused by many things including poorly designed power supplies ! )
noise from switching diodes or transistors
HF ringing in secondaries caused by combination of inductance & switching diodes
noise on the domestic earth lead ( Also caused by many things including poorly designed power supplies ! )
noise from micro resonances caused by combination lead / track inductance & capacitance and excited by the signal - often caused by bypass caps.
noise from micro resonance in mosfet input leads
noise from micro resonances caused by combination lead inductance & capacitance and excited by other noise !
noise from slight instabilities caused by poor feedback design
noise from semiconductors.
noise from industry standard resistors.
noise from electrolytic capacitors.
RF noise picked up by speaker leads & casing and injected into the amp via the o/p or the earth line.

there may be other noise sources I have missed !


Given that I am not that concerned about low order HD all that is left according to my definitions above is phase distortion & noise.

I think phase distortion is important that why I like fast CFB amps like SSA that can produce beautifully clear transients

But even with the most wonderful amplifier topology in the world - which some version of SSA may well be - if the above issues are not addressed correctly it can still sound very bad and if they are addressed correctly it can sound very nice indeed

You guys may think I've got noise on the brain and you might be right but having just spent 18 months systematically working on all of the above issues I can testify to what a huge difference it can make when ALL of these issue are addressed.

Anyway - that's my rant for tonight - I hope some of it makes sense !

cheers

mike

p.s. I forgot noise from poor connections

Last edited by mikelm; 6th September 2012 at 08:53 PM.
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Old 6th September 2012, 09:02 PM   #2975
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Thanks Mike, very valuable informations and nice reading. Will apply some answers to the topic tomorrow since tonight I left on reserve Joules so I can just read hehe. Good night to you and Esperado too.
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Old 7th September 2012, 12:57 AM   #2976
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Originally Posted by mikelm View Post
Hehe - I think we have almost completely opposite view on this topic.
Like L.C:i will argue to morrow. But i'm sure we will agree together at the end with a nice cup of tea.. Once we will tune together our definitions of Harmonic distortion and Inter-Modulation distortions.

Just little words about. Let suppose there is no intermodulation distortions ? Who care about high order harmonic distortions that appears outside of our earing frequency window ? We do not ear them. It is the intermodulation product between those upper harmonics distortions and the instruments in the range -they are IN the window, - that we listen and hate.
Harmonic distortion themselves are not so disagreeable. They just change more or less the tonal texture of instruments. Loudspeakers produce lot of them, and we can enjoy them. Led Zepplin produce lot of them, i love Led Zepplin :-)
Lot of audiophile loves old analog records. They are full of noise (tape hiss, vinyl cracks it do not bother.
Intermodulation (both static and dynamic) product artefacts, confuse the message and the separation between instruments and paint everything with mud.

If you love SSA sound, it is not because it produce little harmonic distortion (some tune their sample to add some), it is because it is fast, and so, produce very little IM. and TIM.
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Old 7th September 2012, 02:01 AM   #2977
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Quote:
Originally Posted by Esperado View Post
If you love SSA sound, it is not because it produce little harmonic distortion, it is because it is fast, and so, produce very little IM. and TIM.
Totally agree!
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Old 7th September 2012, 06:11 AM   #2978
mikelm is offline mikelm  England
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Quote:
Originally Posted by Esperado View Post
Who care about high order harmonic distortions that appears outside of our earing frequency window ?
I only complain about H6 - H20 for that very reason - I include up to H20 for our younger friends for me let's say H6 - H15

Quote:
It is the intermodulation product between those upper harmonics distortions and the instruments in the range -they are IN the window, - that we listen and hate . . . Intermodulation (both static and dynamic) product artefacts, confuse the message and the separation between instruments and paint everything with mud.
Agreed - I do hate that sound - could you define static & dynamic IMD please

Quote:
Harmonic distortion themselves are not so disagreeable.
Agreed

Quote:
Lot of audiophile loves old analog records. They are full of noise (tape hiss, vinyl cracks it do not bother.
mmmm - not so fond of those things

Quote:
If you love SSA sound, it is not because it produce little harmonic distortion (some tune their sample to add some), it is because it is fast, and so, produce very little IM. and TIM.
Let's say I love CFB sound if implemented well - didn't get to symmetrical design yet. My development has been with SE CFB design but never the less I absolutely agree about ( low order ) HD, I stated that already.

So I think we agree completely about HD ( not so bad ) & IMD ( very bad ) and I think can put those things to one side ?

But . . . my finished design isn't significantly faster that the design I started with 18 months ago - in fact I slowed it down a little bit by increasing FB impedance from 1000R / 50R to 2200R / 100R ( this gave less ringing on square waves with a capacitive load and sounded better )

But my finished design sounds much better now then my initial design did with the basic circuit topology hardly changed. The main difference is that I worked on the different types of noise that I list in my post above - so according to my definition noise is very important indeed.

I think there are three things we need to clarify

1) Do we believe / accept the HF noise ( let's say 20Khz - 20Mhz ) from whatever source, somehow get's demodulated by the amp and ends up as grundge in the audible H6 - H20 noise floor ?

2) Do we need to revise my definitions to make sure we're arguing about the same thing.

3) Can we define static & dynamic IMD

cheers

mike

Last edited by mikelm; 7th September 2012 at 06:22 AM.
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Old 7th September 2012, 09:38 AM   #2979
shaan is offline shaan  India
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Well, before going for the standard SSA CCS made of SSM, TL and jFETs I was thinking of a last take on a CCS commonly used in many amplifiers. I wonder why I didn't think of it before as I have many many times used it in my previous projects with good results(although not in a similar place as it is now).

I have simulated the CCS with the SSA and this one really shows some hope. I think everybody here understands this CCS more than me and so I am not gonna "describe" it. I will use trimmers there to control the current and measure it around the 100ohm load resistors.

It looks like this CCS is fairly tolerant of temperature variations. Heating the BD bjts to different temperatures seems to affect the offset to +-10mV at most. Also the current looks super stable with signal at 7uA CCS current per 10mA feedback current(1:1400) or per 1000mV of feedback voltage(1:140000), all AC. This is only what I see through the monitor but don't know how to derive the dB value of the CCS variation current. Please educate me. I attached some traces. I am going to build it and will update once tested. I hope this one will be less noisier than the Wilson.
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File Type: png SimpleCCS.PNG (86.6 KB, 318 views)
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Old 7th September 2012, 01:23 PM   #2980
shaan is offline shaan  India
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Thumbs up This will do...

Test done. Results very positive.

1. Very stable current supply, offset drift from cold to warm is less than 15mV.

2. Almost zero noise from speaker(input short to ground).

3. Turn on thump gone(only a little cone excursion). Also both + and - PS capacitors drain equally at turn off.

4. I was worrying as the CCS doesn't use the ground potential, what if it doesn't start. But it did. Something new for me, hasn't played with symmetrical CCS before.

5. Music come alive. Mission accomplished! Clean and Clear. Going nod-nod and tap-tap... WOOHOO!
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File Type: jpg DSC07652.JPG (141.5 KB, 253 views)
File Type: jpg DSC07653.JPG (110.9 KB, 249 views)
File Type: jpg DSC07654.JPG (140.7 KB, 111 views)
File Type: jpg DSC07658.JPG (160.9 KB, 130 views)
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