Question on different type of capacitors. - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th December 2014, 10:17 AM   #1
diyAudio Member
 
Join Date: Apr 2014
Location: US
Default Question on different type of capacitors.

I just read Morgan Jones amplifier book. Page 218 to 222 talk about different type of capacitors. He explained about the "d" of the cap which caused by the polar molecules of the dielectrics. That the loss is between upper audio frequency to low RF. It is being regard as a series resistance that cause loss at the frequency band.

My question is for tube circuits. The signal path of tube circuit are usually high impedance circuits. Input impedance usually in >10kohm. What difference does it make if there is a few ohms in series with the cap in the signal path? Why is it important to get caps with low "d" for signal path that a few ohm loss is nothing?

I can see it's important for filter caps, but not for signal caps.

I can see this maybe a little more important in SS amp as the circuit impedance are lower than tube circuits.

I design guitar amps and effect pedals, I actually make it a point to use ceramic caps if all possible. I really don't hear the different in guitar amps.

Last edited by Alan0354; 6th December 2014 at 10:43 AM.
  Reply With Quote
Old 6th December 2014, 12:24 PM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
High-k ceramic caps are fine for use a coupling capacitors in wireless sets and guitar amps, and anywhere else where high-fidelity is not a design aim. For hi-fi they will introduce some distortion due to their non-linear capacitance. Low-k ceramics are fine as they are linear but they tend to be huge if you need serious amounts of capacitance.

Almost any film cap has sufficiently low losses for audio use. The issue is dielectric linearity - and again most are plenty good enough. An exception is polyester/Mylar which is best used only in non-critical points as it is slightly nonlinear.
  Reply With Quote
Old 6th December 2014, 12:33 PM   #3
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
Here is an old classic all about audio caps.Picking Capacitors - Walter G. Jung and Richard Marsh
  Reply With Quote
Old 6th December 2014, 06:37 PM   #4
diyAudio Member
 
Join Date: Apr 2014
Location: US
Thanks

Alan
  Reply With Quote
Old 6th December 2014, 06:40 PM   #5
diyAudio Member
 
Join Date: Mar 2002
Location: Glasgow
Why does dielectric linearity matter in a coupling capacitor that is supposed to have hardly any signal voltage across it?
__________________
"Some of the arguments conjure images of white-coated engineers with putty in their ears, designing audio equipment and not caring how it sounds, only how it measures. I have never met such a person"http://scopeboy.com/amps
  Reply With Quote
Old 7th December 2014, 12:48 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
It doesn't matter, except for the cap which sets the LF rolloff. In some designs this cap is the one which feeds the output stage grid, so signal levels are quite high. Interestingly, some people using some designs can hear that polyester caps sound slightly different but they wrongly ascribe this difference to superiority rather than minor inferiority.
  Reply With Quote
Old 7th December 2014, 06:59 PM   #7
diyAudio Member
 
Join Date: Apr 2014
Location: US
I read the article posted by woody. The testing was done by RC network with R=1K. BUT in tube amp, grid leak resistor for small tubes are usually 1M. That is 1000 times larger than 1K!!! The effect is going to be a lot smaller.

I do see problem with coupling caps, yes the voltage across the cap is very small compare to the grid leak resistor of the following stage at the pass band as it supposed to be. The problem lies with the upper and lower pass band frequency when the impedance of the coupling cap is high. eg, for 0.1uF coupling cap. At 20Hz, the reactance is about 80Kohm. That is not like a short circuit with a 220K grid leak resistor of the power tube.

I don't see there's a problem in the more critical higher frequency, reactance of the coupling cap is much lower at higher frequency, effect of change of capacitance at high frequency is really not that important.

Last edited by Alan0354; 7th December 2014 at 07:01 PM.
  Reply With Quote
Old 7th December 2014, 07:45 PM   #8
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
For many years, people kept using caps that deviated from optimum in at least two ways: non-linear distortion in large amounts like most ceramics and tantalum caps., or high in Dielectric Absorption like Ceramic, electrolytic, or even Mylar.
We measured this and documented it decades ago. Light loading only reduces DA, but it does not completely eliminate it. Just because some people think that virtually all caps sound OK is not necessarily so. My clients use the best caps that they can find. Recently Silmic caps that are silk based electrolytics look like a good compromise, when you need larger values for coupling caps, yet have no space available.
  Reply With Quote
Old 8th December 2014, 09:13 PM   #9
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by john curl
Just because some people think that virtually all caps sound OK is not necessarily so.
Just because some people think that coupling caps do not form part of simple potential dividers does not mean that it is not so.

DA is, I understand, well modelled by a linear array of high value resistors and capacitors so cannot contribute to distortion (but may cause a trivial change in LF frequency response). However, all these issues have been argued over many times in other threads so it might not be helpful to repeat them all here in response to Alan's 'innocent' question.
  Reply With Quote
Old 8th December 2014, 09:51 PM   #10
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
leaving the Jung/Marsh "capacitor tasting" article as the only ref is playing to the nave subjectivist, audiophile nonsense
if you want to know a big part of why all those dielectrics, constructions of caps were there for Marsh to make up his smorgasboard, look to Ma Bell's requirements, engineer's response to objective circuit requirements and realities of materials, fabrication limitations that make for so many different types of capacitors


Bateman's Capacitor Sound series is good -even if he still doesn't "deconstruct" the use of DA to rank capacitors for audio

Pease article on Capacitor Soakage does call that into question
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What type of capacitors are these? Hamman Solid State 6 10th November 2012 07:30 PM
Capacitors type ?? help papanohn Parts 2 9th January 2007 01:05 AM
Capacitors, which type and brand sounds best to you?? John Biles Everything Else 31 16th December 2005 07:13 PM
Continental Capacitors' "Type-A" oil-filled capacitors? radical Parts 0 21st October 2004 09:39 PM
Capacitors - Which type to use marlow Solid State 8 10th January 2002 06:13 PM


New To Site? Need Help?

All times are GMT. The time now is 01:46 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2