Virtual Center Tap Resistor Value

[jrfrond]

I had a field service tech once who needed a 15A fuse for a piece of gear, and had none in his kit, so - honest to God - he wired a 5 and a 10 in parallel.

Fuzz Logic!

[R.G.]

My credentials are not the issue here. Like many amp builders/techs or whatever, my opinions are the result of 30+ years of experience, and amp design/debugging is as much empirical and black art as it is science. Your mileage, however, may vary.

I should be very clear - no, it's not your credentials that are at issue, by any means. However, I was very amused at the comments that you were an amplifier designer/technician/builder and others were not. It struck as so funny that someone would say that, that it made me invent the wholly fictitious NACATDAB ("National Association of Certified Amplifier Technicians, Designers And Builders").

However, I have deep suspicions about the credentials of some other commenters, particularly those who can't figure out fuses, or even that they don't know about fuses when it's pointed out to them.

Nope, wasn't you I was talking about. 8-)

[Tom Phillips]

Runaway!

[Merlinb]

d amp design/debugging is as much empirical and black art as it is science.

It may be empirical, but it's not a black art. It's just science you haven't learnt yet! :P

[Chuck H]

It may be empirical, but it's not a black art. It's just science you haven't learnt yet! :P

True enough. But sometimes it's so convoluted that only guys with bushy grey eyebrows in lab coats with no particular tastes or references for guitar amp tone are the ones who have learnt as much as we know about what's happening in an overdriving, transformer coupled tube amplifier. So this is what makes it seem like black art when emphirical know how is employed for design. Not many have both an appreciation for guitar amp tone and enough learnt science to dispell the myth and lore that perpetuates on line about guitar amp design. I think most of them post HERE.

[jrfrond]

Chuck, I didn't think you were talking about me. No problems here dude. No problems with anyone at all.

The "black art" portion of amp design that I refer to is that sometimes, things work (or not) for no apparent reason. OK, I'm educated in the field, and I DO realize that there IS a scientific explanation for everything, but I reserve the term "black art" for the ones that are not readily apparent, and force me to go back to the books to figure it out!

There are more than a few self-proclaimed "amp designers/techs/builders" that do not really know much about electronics at all, don't even own a 'scope, or anything beyond a Simpson 260, and their approach is almost TOTALLY black-art. It is my feeling that, to do a proper job, you need to arm yourself with the proper tools, test equipment and knowledge base. THAT is what essentially translates the "black art" into science.

I'd like to point out that, after 30+ years, I am still learning every day. It's most likely what keeps me in this business. Even if you work solely on tube amps (which I don't), you still occasionally find things that trip you up.

Hey, I DO like "NACATDAB (National Association of Certified Amplifier Technicians, Designers And Builders)"! Perhaps we need to charter such an organization, hmmmm?

[Chuck H]

I wasn't actually talking about anyone directly, just the nature of what we do here. My point is that if we all had lab gear that could do things like spectro imaging of EMF inside a chassis under operating conditions or if we didn't have day jobs and took the time to map every frequency curve due to impedances and subsequent effects then what we do wouldn't seem like "black art". But we sort of languish in a position where, although much is known, most of us don't have the time or tools to fully understand it. It's a mixed blessing that for what we do exacting finite tolerances aren't needed but because so much about the design of guitar amps is emphirical I think it perpetuates myth and lore. That's also why I mention that I think this particular forum is one of the best places to gather info. I think the group here as a whole is as far that mentality as it gets on line. Elsewhere on the net, even the hi fi forums where exacting tolerances for the circuits are so much less emphirical, you can find people buying special glitter tape that makes music sound better by altering the listeners perception to stick on the door casing of their listening room, CD's and amplifiers (true) or $200 wall plugs.

[Enzo]

If we all had all the space science diagnostic gear and multidimensional phase displays and what not, that wouldn't mean we all knew what to tweak to get where and indeed where "where" ought to even be.

SOmehow I am reminded of my days in the tavern. I shot pool every night for several hours, in a local bar that was not very far from the University. I got to be a reasonable shooter. I beat more than I lost to, I'll say that. There were guys who were hard to beat. And then there were the engineers. These were guys who came in, decided they knew how to shoot pool because they understood vectors and momentum and stuff. Lots of lining up and checking from many angles. I am quite sure they understood all the physics of the table. But the guys who just went with the black art of shooting billiards blew them off the table every time. The students understood vectors, but didn;t get the pool table. KNowing why English on a ball works is not the same thing as using it. Understanding a masse shot is not the same as pulling one off.

SO I am all for all the theoretical knowledge and analysis, but I also have room to respect someone who gets results using the black arts approach. "I don;t know why, but 120k always sounds better than 100k in this spot."

[R.G.]

read Gladwell's "Blink"

[Chuck H]

As a pool player (what "real" players would call a five baller) I get the reference. That was my point about guys with bushy grey eyebrows and lab coats being the ones who understand, but don't care. And the guys who care being the ones who don't understand. Well, except by rote experimentation, emphirical as it were.

[cminor9]

That's also why I mention that I think this particular forum is one of the best places to gather info. I think the group here as a whole is as far that mentality as it gets on line. Elsewhere on the net, even the hi fi forums where exacting tolerances for the circuits are so much less emphirical, you can find people buying special glitter tape that makes music sound better by altering the listeners perception to stick on the door casing of their listening room, CD's and amplifiers (true) or $200 wall plugs.

I agree. It has been said that most people have but 4-8 sites that they visit on a daily basis. This seems to be one of those sites for many folks. My browser lists the top eight sites I visit. This site is in that list. Even when I have nothing on my bench, it's fun to come here and see what everyone else is up to. I certainly enjoy the "company" of the people who post here more than I do at most other sites.

That said, at the risk of people pissing a few of you off...this whole beef between a few of you is getting really old. There are several threads now where someone is asking a question, and then the question and answers get swamped by a pissing contest between a few people. Where there used to be good clean debate based on technical merit, there is now a bunch of d!ck waving and pedantry that revolves around a few personalities who don't like one another (which is NOT debating technical merit). Sure, there are a few good points that come out in the arguments, but largely it's just argument. It was kinda funny at first, but now it's crapflooding a several threads.

Couldn't you guys just like go to a pub, get a beer, and shake hands? Shooting paintballs at each other might be a great stress reliever. Or just have a straight up pub brawl. I don't care. To most of us here, you guys are all experts and we can learn from you. Stop trying to be the alpha guru. There is plenty of room at the top and there is room for multiple opinions (not multiple facts; opinions).

Why am I posting this here when it's not really my fight? Because as an outsider to this whole thing, I can objectively tell you it makes all of you look bad. Or, as the old saying goes "when you throw mud all you do is lose ground."

Sorry in advance if I ruffle anyone's feathers.

[Chuck H]

Well we used to have a saying here... "Don't feed the trolls" ("trolls" has no specific definition). It worked for the most part but sometimes you get a pseudo troll. A guy who's not quite a troll. Just enough not a troll to avoid being tarred and feathered and marched to the edge of town by torch light. So this guy/girl eventually gets under the skin of someone or someones and by this time there's already history between them. So they bicker and poke like an old married couple that long ago stopped enjoying the relationship. How much easier to ignore someone that annoys you when you don't have a history.

It usually doesn't last long (in relative time). I've seen it a few times here in almost two decades.

[Tom Phillips]

Good points.

... Where there used to be good clean debate based on technical merit, there is now a bunch of d!ck waving ..

"...d!ck waving..." First time I heard that expression. Made me laugh out loud.

I'm off to a New Years Day brunch.
Happy 2011 to all.

Tom

[Chuck H]

I had heard it. But it still makes me laugh. It always occurs to me that this kind of activity requires warm weather. In cold weather we'd have to call it dick wiggling.

[cminor9]

Well we used to have a saying here... "Don't feed the trolls" ("trolls" has no specific definition). It worked for the most part but sometimes you get a pseudo troll. A guy who's not quite a troll. Just enough not a troll to avoid being tarred and feathered and marched to the edge of town by torch light.

Yup. I know what you mean. But that's the thing: I can see that and I am sure others can too. If everyone feels like a person is trolling, then treat that person like you'd treat the guy at timecube.com. That guy yells and rants and raves, and guess what? Nobody even takes him seriously enough to debate him. Well, there was that one time he was invited to MIT to debate, but that was clearly tongue-in-cheek.

If that person is trolling, he wants a response. If he doesn't think he's trolling, then maybe the lack of interest in debate with him will get the point across. Or maybe not. Then he's the crazy guy on the street downtown who yells back at the voices.

Like I have to tell myself when my young children want to argue with me about something: "What does it take to argue with a fool? Another fool."