FWIW and leaving power stages aside for the moment, usually *Preamp* tubes have cathode decoupling caps ... and those are usually electrolytics ... smack in the middle of the signal path.
It's a Rogers HG88 Mark III integrated valve amplifier, big brother to the more ubiquitous Rogers Cadet III that you may have heard of. I've owned it from new.
It employs four Brimar ECC807 valves, which are now unobtanium, and four rare Mullard ECL86 valves. Power output is 15W per channel.
HG88 Mk III Ampl/Mixer Rogers, Catford see also Rogers Birmi
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Kind of feel like I'm being nit picked here... but that's fine.
Interstage coupling would have been more correct. However, since we're discussing audio electrolytics vs. standard electrolytics and their effect on the sound of an amplifier, how much of an impact does a bypassed cathode resistor have beyond stage gain and frequency response?
Specifically, would an audio grade electrolytic make any difference over a standard in that application?
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That's certainly true of my Rogers amp - 50uF electrolytics in the circuit attached earlier.
In your experience, does the choice of capacitor type for this function have an important influence on the quality of reproduction?
Cathode bypass. Wouldn't the term decoupling only apply when used in the feedback network for providing 100% DC feedback as in many solid state amplifier and preamplifier designs? Not nit picking, just asking.
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The terms 'cathode bypass' and 'cathode decoupling' are both used in this article which examines 'partial bypassing' and its ability to introduce treble boost.
I got lost at the mention of 'Nyquist plot'!
http://valvewizard.co.uk/ChoosingBypassCaps.pdf
I got lost at the mention of 'Nyquist plot'!
http://valvewizard.co.uk/ChoosingBypassCaps.pdf
Yesterday I discovered over 100 cold solder joints in Nad 306
Now after re-solder there is so much music detail that I feel intoxicated
To much of anything is bad
Now after re-solder there is so much music detail that I feel intoxicated
To much of anything is bad
Thinking ...... it goes deeper than that.
I associate different concepts for the two terms. I bypass a resistor (with a C) to 'short/cancel' its effect - physical action. That decouples/eliminates it from the signal circuit - electronic effect.
(For completeness: One also use bypassing capacitors in the power supply line. Again, of course, 'feedback' is in the mix; this time of the undesired kind.)
The term decoupling has also been used by others to describe power supply bypasses. In some ways this is all semantics.
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How does this prove your theory about audio caps? Basically what you're saying is all the time you spent replacing caps, you never noticed this problem? Do you even know what a cold or defective solder joint looks like?
Are you ever going to post a picture of those speakers?
It doesn't completely eliminate the resistor from the circuit since the reactance of the cap will change with frequency. You've paralleled a reactance with a resistance. It is in effect a filter. At a given frequency, the cap's reactance will equal the resistor value.
The static, DC operation will stay constant while the dynamic, AC operation will change depending on frequency.
But since we're dealing with feedback, I could point out to a specific poster, it is not smack dab in the middle of the signal path, but only determines the circuit AC gain at any given frequency. Resistance on the cathode causes feedback and bypassing increases the gain (reduces feedback) at frequencies above the point where the bypasses reactance is equal to the cathode resistor value.
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...and before anyone jumps on me... I do realise the open loop gain for a single triode is determined by other factors. The decoupling cap in a solid state circuit doesn't function in exactly the same manner.
This is what I've learned and please feel free to correct me if I'm wrong.
This is what I've learned and please feel free to correct me if I'm wrong.
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Sounds like you like to tinker - nothing wrong with that!
I've just replaced the BAF wadding in a pair of my speakers with acoustic grade fibreglass (fiberglass in the USA), just for the sheer joy of it.
I think they sound better, but my wife has just said she can't make out the voices on the radio. Perhaps she's just being mischievous?
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