I've never heard on in person, but I like what I hear on youtube.

I've heard that 12au7's are suitable for supply voltages this low.

Quote from: J M Fahey on February 02, 2011, 07:37:00 AM
Sorry, didn't want to hurt anybody, all the contrary
Beyond that, we are on a technical forum here, and if somebody says 2+2=5, hurt feelings or not, I'll state the result is 4.

As of ROG projects, seeing a typical one gives me headache, the same kind I get when I hear somebody singing absolutely out of tune or playing very fast, missing 80% of the notes.
Let me explain that:
The Fetzer itself is the only serious part, and I was not referring to it.
Its designers know the triode curves they wish to approach, know what they actually have (pentode-like Fets), know all the theory, how things work, do whatever's needed to bend one into the other, brilliant !! :tu:

*But* cloning a tube design , and finding there a typical 1/2 12AX7 with 1K5 on cathode, 100K on plate, 260V B+ , 160V on plate, and substituting it with a Fet, using 1K5 on source ..... (why 1k5 ?).

There's 3 possible answers I can hear:

1) "because I decided I want that FET to pass 1mA and, look at the curves, this particular one passes 1 mA with any drain voltage between 3 and 30V and 1.5 Vgs , so [1.5V/0.001A]=1500 ohms".
*That* is the "serious" answer and the one I expect  :tu:

2) "Duh?? "
Even this one is somewhat acceptable, sort of. 
Nobody was born knowing, but studying or experimenting anybody can learn and advance.With some care it may end up good, in a near future

3) "Because Fender uses it"  :duh
C'mon, you are kidding, right? This is magical thinking of the worst kind.
Why the worst? Because to the uninitiated it "sounds" logical, even powerful (Mojo) , pure pseudoscience.
Add this to the power of internet, and another impossible to erradicate myth is born and spread. :duh
I repeat, I find *good* design work the Fetzer approach and the work of all others who took it seriously, such as KMG, Lab Series, Mensur, Trace Elliott, Yamaha, Roland, Univox (Westbury) and the granddaddy of them all: Randall.
1K5? 9V? Forget it !! (unless you buy 100 fets to farm the 5 to 10 amongst them which might be happy with that value)
*None* of the above mentioned established manufacturers uses anything even approaching that Fet-unfriendly combination.

....

No doubt your criticism of their typical biasing scheme is well founded.

I've actually got 5 of these from Mouser a while back but never got arround to playing with them.

Well, I think the gain-to-headspace ratio is more important than the gain itself. I see a need for designing circuits arround a 9v supply for stomp boxes. But if your supply voltage is that low, your gain needs to be low to have the same gain-to-headspace ratio as the emulated circuit. Frequency response is important, too, and having a lower value drain resistor will reduce the output impedance of the gain stage, which might have a noticeable effect on the frequency response. I would rather have  a trimpot for the source resistor, and, if possible, select fets that bias well for the drain resistor used. I agree that when it makes sense, a higher voltage supply is best.

I wouldn't be too hard on ROG, JM. A big part of their goal is to keep it simple, and I think they do a pretty good job. Obviously, a more complex circuit topology will do a better job of triode emulation than ROG's fetzer valve concept. I do agree, though, that having the trimpot on the load side doesn't make a lot of sense.

His user profile says New Zealand.

I don't know if there is anything to it or not, but I've heard that 12AU7's don't sound too well with anything less than a 48V supply. I haven't tried to find out, though. I've got a 12au7, but I might save that for a firefly amp. The real magic with the ruby type amps is the way the LM386's sound when overdriven. Probably might as well stick with fets or op-amps. Of course, there is one way to find out for sure. 

For FET circuits, I think the reason for using a high voltage supply is simply to use FETs with a higher Idss, which I suppose, are less noisey. My own FET preamp (overly simple, flat response) is not noisey at all using an 18V supply and 2n5457's. A similar 9V FET preamp I built that has one J201 is noisey as hell. I love my Dr. Boogey build, but it is noisey. Then again, with that much gain, maybe it has no choice but to be noisey. Maybe one day, I'll breadboard Mensur's version for comparison.

Based on my limited experience and listening to the sound samples on ROG, Professor Tweed isn't the only good ROG FET circuit.

The Dr. Boogie works quite well at 9V, but Mensur has a higher voltage version that perhaps works better. I think part of the reason some of these might sound different is that they are biased by using a trimpot for the drain resistor. I believe this will have an effect on the output impedance of each stage and effect the frequency response to some degree. I think it might be better to use trim pots for source resistors. In the case of the schematic for this JFETified 5150, it looks like the resistor values are fixed. This is ok, so long as you order several j201's and handpick the ones that bias well with these resistor values.

Also, in automation as well. I think the largest maker of PLCs is Rockwell Automation, which owns the Allen Bradley name. Japan does have a more automated industry, but I think the U.S. still has plenty of opportunity to catch up. Also, when we get to the point where most manufacturing is mostly automated, Chinese manufacturing isn't going to be any cheaper, especially when they have to ship across the pacific.

BTW, I've got an Indonesion Ibanez and a Japanese Jackson. On my budget, I can't stick to buying stuff made here. I do have an old American made Gibson Hummingbird accoustic, but I had to inherit that.

QuoteFrom joecool85: And lastly the items I can't get as mentioned above I try to get from (in this order) the UK, Japan, Taiwan, Korea.  This is primarily for electronics.

Maybe in February or March, you can add Argentina to that list. 

Things could turn around. From what I hear, wages in China are slowly increasing. Also, robot labor is even cheaper than Chinese labor. I think the U.S. also still exports a lot of industrial equipment. Can't remember where I've heard that, though.

I think the term impedance includes resistance and reactance. AC resistance is reactance. You've got inductive reactance and capacitive reactance. All are measured in ohms. Both types of reactance and resistance must be considered to figure total impedance.

Does anyone else think this thread is cool enough to be pinned?

Or even maybe ship with a complete head minus the transformer. Omitting the transformer would lighten things up a bit.