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In Reply to: RE: Small IDHT tube cathode bypassing posted by cpotl on July 07, 2015 at 05:45:08
" but with a competent design it should be so minimal that the difference between one type of capacitor and another should be inaudible."
Sorry, WRONG, wildly wrong, as often you are. Oh well, at least you are consistent.
1994, Sound practices, Marzio and Jelasi authored :
" When constructing equipment capable of attaining high peaks of musicality, the quality of the passive components assumes critical importance. This is particularly true for capacitors. Note that in the list of components, electrolytic capacitors are not recommended, not even as power supply filters. We bypassed the high value capacitors (with exception of Cl which is placed in a non-critical position) with others of small capacity in silvered mica and/or paper and oil. This practice is common among extremist experimenters who know how much the quality of these components can influence the final result ".
Marzio and Jelasi used THREE carefully-selected capacitors in 1994 on their driver and finals stages' Rks, as shown in their schematic and parts list.
Jeff Medwin
Follow Ups:
If different bypass capacitors lead to different sounds, then this will necessarily correlate with different levels of audio signal appearing across them. I take it this is not being disputed?
My definition of a "competent design" was one where the bypass capacitor was chosen so that the audio signal developed across it is negligible. There will then, more or less by definition of "negligible," be no audible difference between one such choice and another. If a given choice of capacitor fails to achieve the goal, then I would not call that a competent choice, since it will lead to some colouration of the sound.
Chris
What you write is a pile of baloney. You obviously are a theorist and you must NEVER build good revealing amps and actually LISTEN to the parts. Every film cap you buy sounds different than another brand, of the same exact specified value.
There are people who will spend up to and over $2,500 for a single film cap. Think its "perfect sounding" versus a 60 cent WIMA MKP series caps? Likely not. Think it sounds different? Of course it does !!
What you theorize and post has no relationship to reality. Reality is what you HEAR, the end-result when you play a good amp through a good audio system.
Audio performance, "how it sounds to you", is ALL that really matters. I am done discussing this with you. Post on, as much as you feel compelled to do so.
Jeff Medwin
"There are people who will spend up to and over $2,500 for a single film cap."They are fools.
If they want to understand what is going on, they could put an oscilloscope across the capacitor, and look at the audio signal. If it is not negligible, they could either bypass the capacitor with another one that corrects the deficiencies, or they could chuck out the original one and get another. Any way it is done, the solution costs a few dollars, not thousands.
Chris
Edits: 07/09/15 07/09/15 07/09/15 07/09/15 07/09/15
Based on you response, I think you do not understand the basic principles involved. You surely cannot dispute that the different sounds, if they are real, are the result of different audio signals appearing across the bypass capacitor? If the cathode resistor is bypassed properly, there will be a negligible audio signal across the capacitor. If it is not done properly, because of a bad choice of capacitor, or insufficient capcacitance, there will be an audio signal, almost certainly frequency dependent, and that will imply a colouration of the sound from the amplifier. Now, you may like that sound, and there is nothing wrong with that, but it does then mean that you like to achieve a "sound effect" via a non-ideal bypassing of the cathode resistor.
It is as simple as that.Chris
Edits: 07/09/15
If I was rich I would pay my minions to stack up silver foil oil caps with bipasses on my cathodes.
And I would only use one eye minions because well you know why!
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