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In Reply to: RE: Paralleling KSG Silver Mica Caps posted by gusser on July 20, 2017 at 17:04:28
Not being familiar with this term, I looked it up and it made me wonder if lead inductance might be desirable in AF circuits where presumably we don't hear above 20 khz, or far less for many of us.
Which leads to the question. Is it better to go for maximum bandwidth or sufficient bandwidth?
I have no opinion one way or the other. Just curious.
ray
Follow Ups:
If you mean counting on the component lead as a deliberate inductor, I would say that's bad engineering in an audio circuit. If you need a small inductor, then put one in. Of course sometimes component artifacts do work in your favor. And in cheap consumer gear, tricks like this were pulled all the time. Look at an AA5 radio as the king of corner cutting circuit design.In RF circuits, the lead inductance is a design nuisance and often must be worked around. That's why it is often recommended here never to recap tuner circuits. Mica and ceramic capacitors rarely fail and just moving them in old point to point wired circuits can change RF alignment.
A lot of people also think todays high speed digital circuits are the product of superior semiconductor engineering. And that would be only partially true. But another factor is surface mount technology and FPGA's. Here, the lead length is much smaller or even microscopic in an FPGA. This means much higher clock rates can be run without the problems of component lead length and their associated inductance.
Edits: 07/21/17 07/21/17 07/21/17
Exactly, as for my hearing @ 55 above 12K drops off like err, A cliff, the point is exactly the same as the one arguing has on his/her head.
Just opinion here.
The Mind has No Firewall~ U.S. Army War College.
General rule of thumb for measuring equipment is 5x the measured bandwidth. So to accurately measure a 20khz square wave, your scope needs at least 100khz of bandwidth.And I would say today, an audio amplifier that goes out to 100khz is good but also the reasonable limit. Going beyond the 5x rule is just wasting money and additionally inviting stability issues you don't need.
A popular example is the HK Citation power amps with their video pentodes in the driver section. But there was a very good reason for this. Remember that the Citation uses nested feedback loops. Stu Hegman needed video bandwidth to get the gain he required and keep phase shift low at the same time. But as you can see these were somewhat complicated audio amplifier circuits for the day. The complexity is in the math of selecting those component values.
Edits: 07/21/17
My bad.
I was thinking almost exclusively of speakers and the desire to go far beyond 20k. This IS DIY Tube.
Am well aware the 'usefulness' of wide bandwidth in output transformers and agree 100k is excellent and in some cases {yours mentioned} required. Writing of output transformers, Silk and Hashimoto are the equal {better?} of many highly revered ones.
The Mind has No Firewall~ U.S. Army War College.
I think the video pentode was just an easy choice driven by output impedance, gain and the required plate dissipation rating required to get the first two. For gain, gm and load resistance rule, and with output impedance, the load is set...which drives plate dissipation requirements well beyond the usual signal pentodes.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
"General rule of thumb for measuring equipment is 5x the measured bandwidth. So to accurately measure a 20khz square wave, your scope needs at least 100khz of bandwidth."
Not to nitpick your comment, but for accurate visual analysis of square waves, 10X is a better rule. We have scopes where I work with bandwidths of 1.5 gHz, and we make (among other things) devices that output TTL-level square waves to beyond 200 MHz. I've tested 80 MHz square waves (one of our "standard" frequencies) with both a 400 MHz scope and our 1.5 gHz scope. There's a marked improvement with the higher frequency instrument.
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