[NEWBIE] Slew Rates and smearing of audio
« on: October 12, 2004, 05:06:09 AM »
After reading a lot of info on the web I am starting to get very interested in this

In particular this article on the John Hardy web site...
http://www.johnhardyco.com/pdf/OutboardMicPreamps.pdf

Where he talks about the problems of transformerless preamps and the use of Capacitors to block the 48v going to the rest of the circuit
The absorption of part of the audio by the caps and then the release of it a slight time afterwards tends to make the sound smeared
This I can understand (well written for us newbies)

Can anybody else expand on this.. particularily with reference to the best way of monitoring the signal coming of tape to get a non coloured view...


[NEWBIE] Slew Rates and smearing of audio
« Reply #1 on: October 12, 2004, 05:36:05 AM »
Thats the stuff - dielectric absoption
http://www.audience-av.com/on_capacitor_dielectric_material.htm

Because Audio flows through the capacitor it retains the HF and then release it causing the signal to become smeared
Articles talk about phase and delay in the same sentence...
Is this junk?

Gus

[NEWBIE] Slew Rates and smearing of audio
« Reply #2 on: October 12, 2004, 10:20:15 AM »
DA does make a difference.  One place you can hear it well is in guitar amps.  Build one with PET and one with polypro.   Change the treble cap in a marshall tone stack to something different than ceramic.

  when I build or work on a guitar amp I use polypros and micas if I don't want to add anything.  For some "warmth"  use  PETs for the grid drive of the ouput tube(s) add them going to the pre to taste.  Like Carbon Comp resistor the higher the signal level the more nolinear.  I even use PETs on the cathodes of the preamp stages.

  The ceramic cap in a marshal tone stack is part of its sound IMO.

  Does anyone know if the early marshalls use M9  grain instead of M19 in the transformers I think I read that somewhere.  That might be whay some people like the early ones better again its energy starage with a time delayed release.

  There is a science to the sound of parts.  I mearure what I can when I find a cap etc I like or dislike as well as other parts.

NewYorkDave

[NEWBIE] Slew Rates and smearing of audio
« Reply #3 on: October 12, 2004, 12:55:05 PM »
Here's some interesting reading from a respected engineer who has no vested interest in the audio biz:
http://www.national.com/rap/Application/0,1570,28,00.html
http://www.elecdesign.com/Globals/PlanetEE/Content/2461.html

Peter Simonsen

[NEWBIE] Slew Rates and smearing of audio
« Reply #4 on: October 13, 2004, 01:56:47 PM »
Quote from: "NewYorkDave"
Here's some interesting reading from a respected engineer who has no vested interest in the audio biz:
http://www.national.com/rap/Application/0,1570,28,00.html
http://www.elecdesign.com/Globals/PlanetEE/Content/2461.html


In my book and to the very best of my knowledge...and then again regarding all the double blind testing I have done..I agree greatly with him..*S*

Thanks for the link NewYorkDave..good reading indeed..;-)

Kind regards

Peter

volki

[NEWBIE] Slew Rates and smearing of audio
« Reply #5 on: October 14, 2004, 03:14:54 AM »
veeery interesting indeed - so dielectric absorption (DA) is the s**t! or rather, it's to be avoided? =O)

but that also arouses some further questions. maybe you guys have any thoughts?

1. so DA introduces a kind of subtle slewing that results mainly in even-order harmonic distortion. i wonder if the amount is somehow proportional to voltage or power applied, or if it follows a different law? i suspect the former., because pease said, the effect remains approx. the same for a given ratio of charge/decharge time. this would mean that also low-level signals receive the same relative distortion as high level, whereas e.g. in active stages, high level signals are more prone to distortion (at least in class A).

2. when it comes to vintage devices - i wonder how good the quality of the cap's was decades ago, when they were made? plus, maybe DA gets worse with a cap's age? so maybe a part of the sound in a vintage unit is actually DA?

3. comparing tube and transistor units - for impedance matters,  the transistor circuits have capacitances in the order of one or two magnitudes higher. since DA rises with capacitance, this would mean that these are much more prone to unpleasand DA induced distortion than tubes...? - or, in other words: just like it's often said that not only is tube or transistor topology what matters, but also the interaction with the associated transformer (let alone overall circuit design), this could even be extendetd to different amounts of effects due to DA?

Gus

[NEWBIE] Slew Rates and smearing of audio
« Reply #6 on: October 14, 2004, 09:49:59 AM »
Think of using DA as a spice to your circuit design, the same way you would use a transformer with different lams andor winding style.

IMO ESR is different you alway want the lowest ESR in an Electro ESR seems to be related to chemistry(the better the chemisty the lower the ESR) size and price.

Take a very good look at the cap graphs in the links different Mylar(dupont name for PET film they make) have different curves.  People tend to like the mallory 150 wound films better than the orange drop PET  in guitar amps not all orange drops are polypro.  Also the voltage rating seems to have an effect because the higher voltage films are thicker and I think the DA goes up some more because there is more volume of dielectric to get "lost" in.

I think of ceramic as the grit adder, good in effects high ouput guitar pickup tone caps and amps A little goes a long way

PETs as the warmth adder more bass but less clartiy PETs have this to different amouts one of my fav PET caps is close to polypro lack of sound.

polypros add little to nothing

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
[NEWBIE] Slew Rates and smearing of audio
« Reply #7 on: January 02, 2005, 02:45:42 AM »
Was thinking about audibility of DA and found this thread...

Quote
so DA introduces a kind of subtle slewing that results mainly in even-order harmonic distortion.


DA does not cause any nonlinear distortion, right? It can be sucessfully modelled by adding parallel RC-circuits, so it must have some EQish effect (if loaded), no?

Samuel

volki

[NEWBIE] Slew Rates and smearing of audio
« Reply #8 on: January 02, 2005, 04:23:12 PM »
Quote from: "Samuel Groner"
Was thinking about audibility of DA and found this thread...

Quote
so DA introduces a kind of subtle slewing that results mainly in even-order harmonic distortion.


DA does not cause any nonlinear distortion, right? It can be sucessfully modelled by adding parallel RC-circuits, so it must have some EQish effect (if loaded), no?

Samuel

well, after checking out the two links posted by new york dave and especially taking a look at the graphs displayed there, i came to the conclusion that DA actually does cause nonlinear distortion. actually, you can think of it as "dielectric remanence". if you will, you can draw a parallel to the magnetic remanence effect in transformers, which is known to cause distortion, too.

for additional info, you might want to google for the article "picking capacitors" by richard marsh et al,  it covers DA and other parasitic fx on capacitors.

 

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