dsavitsk

Hey, I grew up at Purdue -- dad was a prof there. Home of McCord Candies -- try the olive and nut sandwich. Indianapolis airport is a lot closer, but has the downside of not being in Chicago

The HD-800 is a very well damped headphone. If you drive them with an amplifier with a very low output impedance, they will be over damped and sound bright and a bit thin. On the other hand, if you drive them with an amplifier that has some output impedance, the damping factor will be less, and they will sound fuller, warmer, and bloomier. Contrarilly, something like the HD-650 is less well damped and thus does much better with an amplifier with a very low impedance. This, however, has little to do with tubes vs. solid state. It is true that most tube amplifiers have a higher output impedanace than most solid state amplifiers. There are a variety of semi-inherent reasons for this -- for instance, tubes generally have lower transconductance. But, when comparing something like the Eddie Current amps vs. say a B22, it has more to do with amplifier topology than anything else. However, it is not the case that tubes amplify different frequencies, or sound much different than transistors, or anything like that. Indeed, the differences are really overblown by many people. Instead, it is that tubes tend to be used in certain ways, and transistors tend to be used in different ways, leading to many gross generalizations about how tubes sound like this, and transistors sound like that. So, what I am trying to say is that I think you are ascribing traits to tubes and transistors that are actually traits of topologies, and not the devices themselves.

This ^^^

Happy Birthday, John! Have a great day in the snow.

Wow! I bet it sounds awesome.

It's a thing in as much as things my brother invented* are things -- he is a psychology professor if that gives him any authority (it probably shouldn't) *Looking around, I don't think the term is unique to him.

Post Christmas Letdown (PCD). Happy Birthday!

NYE and Halloween are my least favorites for the above reason, and for the enforced fun aspect ... ... and from the year that a kid, after eating too much candy, vomited all over our front porch. Then his mother, after getting some candy from us, showed us the vomit but didn't stick around to help clean it up.

In the U.S., too http://en.wikipedia.org/wiki/Implied_warranty

Happy Birthday!

Happy Birthday, and Happy New Year!

Happy Birthday!

There's no IP protection for circuit designs unless they are patented. PCB layout and schematic art is protected by copyright, but otherwise, all the "For DIY use only" scribbling on schematics is nonsense.

A cathode follower, which is what the 12B4 is, has a gain of slightly less than 1, and an output impedance (Zout) of 1/gm. The 12B4 has a gm of around 0.006 S. This means that the Zout from that stage is ~170 Ohms (the white paper you uploaded says 500 Ohms, but this is incorrect). A transformer is an impedance and voltage conversion device. The transformer used has an impedance ratio of 600:8 or 600:4 depending on the tap used. Since the 4 Ohm tap is used for Grados, this is equivalent to a 4800:32 impedance (or 150:1). This means that a 32 Ohm load on the secondary will appear as a 4800 Ohm load on the primary, and that the 170 Ohm output from the tube will appear as a 170/150 or just over an Ohm. Additionally, because transformers are not perfect devices, the impedance of the copper adds to this, which makes the Zout somewhat higher -- by at least a few Ohms. To know how much higher, one would need to measure the transformer. However, the quoted 7 Ohm number is based on the incorrectly calculated 500 Ohm Zout of the 12B4 stage and the 8 Ohm tap. It also fails to account for the losses in the transformer. So, the fact that the actual Zout is probably pretty close to that is a bit of a coincidence. Transformers also transform voltages, and they do this as the square root of the impedance ratio. So, the 150:1 impedance ratio means a ~12.25:1 voltage ratio. Thus, a 12V signal on the grid of the 12B4 will result in less than 1V at the amplifier's output. The driver stage has a lot of gain. A tube's mu is the gain, and the 12AX7 has a mu of 100. However, inefficiencies in the circuit keep this down -- let's say to 60 or so. This means that a 1V signal on the amplifier's input will be an estimated 60V signal at the grid of the 12B4 and close to 5V on the output. Thus an overall gain of ~5. Additionally, the input will clip at 2Vp-p which is 10Vp-p on the output, or 3.5Vrms (which is what is stated in the document as the power limit). Sound like the sort of thing I might say. I would doubt Blackgate caps would be better in this regard, but I really have no idea. 20 years is probably pretty optimistic for any electrolytic caps. There was a pretty nice post a few days ago from Tangent in the DIY section at HF regarding capacitor life expectancy. http://www.head-fi.org/t/583878/capacitor-lifespan

The last page of the file you uploaded has a pretty thorough description of how the circuit works.

I've not heard the combination, so I can't even give a biased opinion. There is a 300R tap on the transformer, so it is designed to pair well. There are also technical things I do not like about the Bottlehead, which I have voiced elsewhere. However, everyone has a different opinion as to what sounds good, and there are certainly people who like what the BH offers. So, there is my bland, noncommittal response.

I can't find where I wrote down the measured values, but gain is approximately 2 into the 32 Ohm tap and 5 into the 300 Ohm tap. I'll see if I can get a more precise value later tonight.

This is how it starts, isn't it? I'll throw in a Frosty.

For the record, I am willing to trade french fries for shilling ...

This one's pretty good, too http://gawker.com/5868761/christopher-hitchens-unforgivable-mistake

I used to like his stuff in The Nation. I saw him speak in Chicago in early 2001. He showed up very late, appeared to be very drunk, and was pretty incoherent. I found most of his post 9/11 commentary to be pretty repellent, and I largely stopped paying any attention to him. A not so nice writeup, http://www.salon.com..._figure_deaths/ And an apropos and ironic quote from Orwell (from the article), "The people who write that kind of stuff never fight; possibly they believe that to write it is a substitute for fighting. It is the same in all wars; the soldiers do the fighting, the journalists do the shouting, and no true patriot ever gets near a front-line trench, except on the briefest of propaganda-tours."

Probably too many factors to predict. Older well made rectifiers can handle a lot more abuse than some of the new cheapies. If you search around, there are tons of stories of cheap modern 5AR4's failing where old tubes worked fine (seems especially common in guitar amps -- partly because a lot of relabeling goes on). In the most extreme cases, you'll see a flash in the rectifier where they arc. This can kill a tube instantly. Assuming this has not happened, then either measuring for voltage changes over time, or putting the tube in a tester is probably the best bet.

The fact that a different rectifier tube changes how your amplifier sounds does not imply that rectifier tubes have some inherent sound to them. Understanding why this is the case is actually of some importance. As KG noted, different rectifier tubes will drop different voltages. Some may also change the impedance of the power supply. This, in turn, changes the operating point of the amplifier itself. Thus, the rectifier simply changes the parameters at which the other active components are operating. Sometimes this may lead to one sound, sometimes to another. But it is not sound imparted by the rectifier. While a particular rectifier may warm up one amp, this does not mean it will have the same effect on another. If you are just swapping out rectifier tubes, there is nothing systematic and no predictability. A variable regulator with a variable output impedance can accomplish much the same thing. For instance, in this circuit, one can change both the voltage, and the power supply’s output impedance. By doing so, one can adjust an amplifier for lowest distortion, or whatever parameters one is interested in. This is much the same thing that is accomplished with the changing rectifier, except that in this case the designer knows what is going on rather than haphazardly changing things, and it is repeatable so that a customer hears what the designer heard and can thus actually judge the merit of the design. To me, an amp that is excessively responsive to tube rolling, particularly one that is responsive to rectifier rolling, is simply a sloppy design. Tube rectifiers do have some real use. They provide an easy slow start circuit. They have lower switching noise than many solid state parts, they dissipate heat above the chassis (heat, of course, that might not exist in a sand rectifier), and they can drop excess voltage which is useful if one is using an off the shelf power transformer. But, if you are using them to tune your circuit, you have an underdeveloped circuit. In that there is not a single person on the planet who can hear a difference in a double blind test? Could be.

I think you mean prophet, but the mistake is funny.