John Curl's Blowtorch preamplifier part III

Status
Not open for further replies.
Jump to Latest
#621
Hi John,
The BT threads were moved into the Lounge area due to the highly speculative assertions made by many members including yourself. It was felt that the thread, as it was developing, would benefit from lighter moderation to allow all the excesses members were taking. This actually turned out to be the right decision. Don't forget all the baiting you were doing for information. So this thread developed as it did with everyone taking part. I only have to say one thing before people begin to object.

No one single snowflake ever feels responsible for an avalanche.

By this time, if you feel as though you would participate in an honest and open discussion about audio design, we would welcome a new thread so everyone can start fresh. We'll leave this one open if it continues to generate posts. Keep in mind that the new thread will be subject to normal moderation. That means that OT posts disappear and warnings or action is taken when people step over the line. Here the team has allowed a more lax enforcement, so keep that in mind people.

So John, we would be delighted to see a new thread, probably in the Line level forum. Either start one yourself, or just ask any moderator and we would be happy to set one up for you.

-Chris
 
#625
PMA said:
This is a good idea and it would separate those who are really interested in analog design from those who just take an opportunity to chat about anything not related.
Click to expand...
An accompanying thread with JC as lecturer explaining his methodologies and experiences would be a great chance to spread the knowledge without interruption.
Intelligent questions without back chat and argument would be appreciated by all I am sure.
In the meantime I am fine with this thread temporarily veering OT.....indeed this is how diverse knowledge gets shared.
The personal jibes are unwarranted and only serve to demean the author of such unnecessary quips.....there are several here who are regularly guilty of this.

Dan.
 
#626
 
#630
dadod said:
If one wants to use jfets in preamps or I/V converters it means for sure that is going to be expensive exoteric equipment. Unobtainable complementary jfets and need for meticulous matching it's main obstacle to get cheap (moneywise) equipment.
Why not to use bjts only and the matching problem solve by using low noise matched quads as THAT340 .
Here is one example of the current to voltage converter suitable for a DAC outputs. It’s non balanced configuration but easily upgraded to balanced one.
The main source of noise are those current to voltage resistors, in this case R19 and R1. Lower the resistor value les nose, but increase in distortion.
And yes, this is non GNFB circuit.
Damir
Click to expand...

Sometime I intrude in this high audio society and get a comments only about my spelling errors.
Here is LTspice file if someone wants to plays with it.
Damir
 

Attachments

#632
traderbam said:
Thank you George. That's very interesting.
I wonder if Scott Wurcer can comment on their characteristics, such as DA?
Click to expand...

DA does matter for a sample and hold, I would think the existence and dominance of all the switched cap audio converters would answer this question. As I mentioned in the past the DA of a bond wire parasitic going through the packaging epoxy was easily measured compared to an internal/external hold capacitor.

DA is also a loss mechanism and as such has noise. Switched cap circuits at the theoretical noise floor of KT/C have been demonstrated.
 
#633
scott wurcer said:
DA does matter for a sample and hold, I would think the existence and dominance of all the switched cap audio converters would answer this question. As I mentioned in the past the DA of a bond wire parasitic going through the packaging epoxy was easily measured compared to an internal/external hold capacitor.

DA is also a loss mechanism and as such has noise. Switched cap circuits at the theoretical noise floor of KT/C have been demonstrated.
Click to expand...
How would a Cdom cap in a analogue op-amp compare to a discrete polystyrene of same value, for instance?
Those articles seem to suggest silicon caps have higher leakage. No mention of DA that I noticed.
 
#634
DF96 said:
What has DA got to do with audio? Dielectric linearity is what we should be concerned about, not DA.
Click to expand...
Is not dielectric non linearity the driver of DA ?.
Introduction
Dielectric absorption describes an intrinsic property of dielectric materials
wherein the charge on a capacitor returns to a certain degree after briefly shorting the
terminals. Dielectric theory suggests that this behavior stems from a gradual polarization
of the molecules of the dielectric material in the presence of an electric field [1]. After
the removal of the externally applied electric field (shorting), the remaining dipoles set up
in the dielectric still have an electric field of their own. This field in turn restores some
charge to the capacitive plates as the induced dipoles decay over time in the absence of
the initial electric field placed on the capacitor. The rate and final value of the returning
charge is dependent mainly on the molecular structure of the dielectric material involved.

The dielectric absorption effect is significant in modern-day capacitors, leading to
important non-linear behavior referred to in the electronics literature as “soakage.” This
non-linear effect on capacitance has been a thorn in the side of circuit designers since the
invention of capacitors over 100 years ago [1-2]. Soakage must be considered when
working with systems that rely heavily on precision analog signals that are stored as a
voltage in a capacitor because errors are often introduced over time as charge “soaks”
into and is released from the dielectric material. This behavior can cause very large
errors in many common analog signal conditioning and filtering circuits, including but
not limited to the ubiquitous sample-and-hold components found in virtually all analogto-digital
conversion circuits. In addition to measurement accuracy and precision, safety
is another major concern related to charge soakage in capacitors. In the case of high voltage/high power systems, capacitors must often be discharged several times before they can be safely handled.

To better understand this phenomenon, an absorption-compensating mathematical
model of a capacitor has been described using a succession of RC circuits connected in
parallel with the original capacitor [3]. The RC circuits mimic dielectric absorption
behavior by representing delayed release energy storage elements. The number of RC
components and the R and C values of each must be experimentally estimated in each
case
Click to expand...
Exploring Dielectric Absorption: Data Collection System Development

What Causes Dielectric Absorption?
Theory tells us that all the potential energy
of a charged capacitor is held in an
electrostatic field which causes the dipoles
in the dielectric to orient themselves along
the lines of force. In real life, however, all
dielectrics have some degree of chemical
polarity, so some energy is also stored
as chemical changes in the dielectric
molecules.
After this first polarizing process, the
dielectric contains two types of electrons:
bound and free. The bound electrons
saturate the negative plate and the surface
of the dielectric. The free electrons move
through the dielectric. Free electrons
which travel from one plate to the other
cause leakage. But, some free electrons

only move part way through the dielectric,
and store energy chemically, similar to the
way a storage battery holds energy. These
are the electrons responsible for D/A.
D/A is often called “soakage” because
the capacitor acts like a sponge. When
discharged through an external path, this
soakage charge releases very slowly,
taking minutes or even weeks in some
cases.
Fig. 8: The free electrons passing through
the dielectric cause leakage. The ones
which cause dielectric molecules to change
state cause D/A.
Click to expand...
Sencore - Understanding Dielectric Absorption

So what is the overall time behaviour and the detailed noise/spectral/stepping behaviour of this lossy charge and discharge parasitic energy storage mechanism.....that might be the key to why different dielectrics sound different apart from the readily observed THD and IMD behaviours.

Dan.
 
#635
traderbam said:
How would a Cdom cap in a analogue op-amp compare to a discrete polystyrene of same value, for instance?
Those articles seem to suggest silicon caps have higher leakage. No mention of DA that I noticed.
Click to expand...
I wonder why the technology of film capacitors do not seem to improve so much with years, while nano technology is growing more and more and electronic invade all domains.
The main issue with electrolytic caps is their wear.
Would I say a nonsense comparing the technology of these capacitors with that of batteries? The technology of batteries progress at a frantic pace, not those of capacitors Why?
About audibility, everyone is free to make his own opinion, and no need for DBT for this. Some people think that other things are more urgent to improve. Others each and every detail matters.
On my opinion, the most important thing is that the short life of electrolytics is the weak point of all the electronic components we use.
 
Last edited:
#637
dadod said:
Sometime I intrude in this high audio society and get a comments only about my spelling errors.
Here is LTspice file if someone wants to plays with it.
Damir
Click to expand...

Hi Damir, I know why it goes so, but would have to be "politically incorrect" if I explained that in open English.

Okay, at least I was the one who opened your file. Just let me know if the result is the same as you get.
 

Attachments

  • Damir_I_V.PNG
    Damir_I_V.PNG
    137.5 KB · Views: 245
#638
Tournesol said:
The main issue with electrolytic caps is their wear.
Would I say a nonsense comparing the technology of these capacitors with that of batteries? The technology of batteries progress at a frantic pace, not those of capacitors Why?

On my opinion, the most important thing is that the short life of electrolytics is the weak point of all the electronic components we use.
Click to expand...

Very true.
The reality is a bit tough.
As long as the short life of electrolytics is just a bit longer than the warranty period of consumer products, there will be no drive from that market for longer living and more reliable capacitors. Modern customers are tuned to short time usage of their toys. They don’t mind if these products are short-lived.
It is even convenient if gadgets and consumer products would have a few components inside that would predictably degrade or even fail after say twice the warranty time.
Only this behavior pattern has to be adopted by all brands.

The batteries capacity and size on the other hand are at the very front of a product’s public acceptance criteria.

George
 
Status
Not open for further replies.
Top Bottom