"Bypass caps" and their effect on perceived sound - Page 7 - diyAudio
 "Bypass caps" and their effect on perceived sound
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

 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
diyAudio Member

Join Date: Aug 2009
Location: College Station, TX
Quote:
 Originally Posted by 20to20 1-2 ohms is when the filament is cold. Depending on the tube type, it rises to anywhere from 20 -80 ohms when the filament is hot.
Can you present your calculation of 20-80 Ohms? The figures given by andyjevans support the answer of about 3 ohms when hot.

Chris

 13th October 2012, 04:29 AM #62 diyAudio Member     Join Date: Aug 2009 Location: Johnson City, TN Using the datasheet values of 2.1V at 625mA and 4.2V at 325mA I get: 2.1V - 3.36R 4.2V - 12.923R
diyAudio Member

Join Date: Jun 2010
Location: W-S, NC
Quote:
 Originally Posted by cnpope Can you present your calculation of 20-80 Ohms? The figures given by andyjevans support the answer of about 3 ohms when hot. Chris
Sure, before he specified his 2v DHT's I assumed we were discussing typical 6 or 12v tubes with 150ma to 300ma heaters. 12.6/.15 = 84 or 6.3/.3 = 21 These are the tubes customerily used when doing the "filament" biasing trick.

 14th October 2012, 07:38 AM #64 diyAudio Member     Join Date: Oct 2004 Location: Mazowieckie, Jozefoslaw I have found the document, in Polish, in which some testing of various electrolytic caps was done. See page 13 - old cap (80s I guess) was tested without and with a bypassing caps. Oscilloscope traces are self explanatory. http://www.mrelektronik.pl/032.pdf
diyAudio Member

Join Date: Mar 2007
Location: Canandaigua, NY USA
Quote:
 Originally Posted by disco Above 10KHz electrolytics behave differently, from brand to brand, from type to type. Wouldn't it be a explanation for differences in decoupling a ps?
Sure, but if that difference is affecting anything, it's better to deal with it at the source or destination, rather than fight the inductance of the wireing. There's no benefit to doing it at the main cap, unless there's some physical constraint like lack of space anywhere else or the lure of lugs in plain sight to attach to, IMO not the best reason to do it that way.
__________________
I may be barking up the wrong tree, but at least I'm barking!

diyAudio Member

Join Date: Jan 2004
Location: GRASSE (France)
Quote:
 ... IMO again, if bypassing electrolytics has an effect, the correct design solution is really to bypass someplace else, either at the rectifiers to kill RF, or at the circuit where you're not fighting with the inductance of the wiring from the main caps. The correct return point for the bypass is also important, and it may not be where you think!
I understand that the bypass should positioned at the rectifiers levels, but I do not see what you mean by "The correct return point for the bypass is also important, and it may not be where you think" ??

Thanks for your extra explanation (and sorry for my English),

diyAudio Member

Join Date: Sep 2006
Location: Pleasant Hill, CA
Quote:
 Originally Posted by Conrad Hoffman Sure, but if that difference is affecting anything, it's better to deal with it at the source or destination, rather than fight the inductance of the wireing. There's no benefit to doing it at the main cap, unless there's some physical constraint like lack of space anywhere else or the lure of lugs in plain sight to attach to, IMO not the best reason to do it that way.
It is not just an inductance of wireing. It is combination of spread inductance, capacitance, and non-linear semiconductor layer in aluminium-oxide semiconductor electrolytic capacitors. When (especially class AB) amp draws power from PS with such capacitors phase intermodulation happens. I desctibed what I found, back in the parallel thread about bypassing capacitors. Bypassing did not change neither THD, nor IMD, nor frequency response. But stereo image improved, also cymbals sounded much more natural. I suspected phase intermodulation as the only thing that can affect the sound such a way and indeed found strips of sidebands of slightly different heights.
__________________
The Devil is not so terrible as his math model is!

diyAudio Member

Join Date: Sep 2006
Location: Pleasant Hill, CA
Quote:
 Originally Posted by Nounours18200 I understand that the bypass should positioned at the rectifiers levels, but I do not see what you mean by "The correct return point for the bypass is also important, and it may not be where you think" ??
Think about AC current that flows through the cap and so called "Common Wire". Common Wire is what some people call "Ground", but actually it is not a zero-ohm ground. It is a wire that has resistance and inductance. It is called "Common" because it is common for many currents that flow through it.

Take for example short 10 A peaks of current through diodes that charge a PS filter cap. If say resistance of the ground wire that passes this current is 0.001 Ohm that means already 0.01V peaks on this wire, from minus of a bridge, or a center tap of the transformer, to the filter cap. In relation to 1 V sensitivity of the power amp it is -40 dB of loud buzz. Solder there negative leg of the cap that filters B+ for preamp, and you have this loud buzz as if coming from nowhere.

People often claim that vacuum rectifiers "sound better". Indeed they would cause more forgiving to the wrong layout result because of higher internal resistance and lower level of charging peaks.
__________________
The Devil is not so terrible as his math model is!

Last edited by Wavebourn; 14th October 2012 at 09:04 PM.

 14th October 2012, 09:36 PM #69 diyAudio Member     Join Date: Apr 2006 Location: Holland And for the perceived "sound" of vacuum rectifiers internal resistance and damping of the tank is of importance. __________________ jaap
diyAudio Member

Join Date: Sep 2006
Location: Pleasant Hill, CA
Quote:
 Originally Posted by disco And for the perceived "sound" of vacuum rectifiers internal resistance and damping of the tank is of importance.
Still, carefully designed layout is more important in any case. With proper layout advantages of vacuum rectifiers play no role anymore, while lesser sag under the load leads to preference of SS rectifiers.
__________________
The Devil is not so terrible as his math model is!

 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 OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post bikehorn Multi-Way 10 5th February 2015 11:50 PM gripracer Swap Meet 3 10th December 2009 08:31 PM percy Parts 2 3rd October 2009 06:53 PM ray_moth Tubes / Valves 23 27th April 2005 09:55 AM Two Moons Multi-Way 4 6th January 2002 05:27 PM

 New To Site? Need Help?

All times are GMT. The time now is 01:09 AM.