Ultra linear and phase inverter drive

[Tage]

Yeah shortly after I posted I found a better drawn schematic and realized that that was going on there, I kinda like that design, and I may implement it should just using a 12at7 not work out the way I hope. as far as the UL taps I think I'll just wire them away and try it with screen resistors and then with the taps and see which the customer prefers.

[imaradiostar]

For me the advantage is at the blurred edge between power amp grind and clean preamp distortion. I would argue that both power amp distortion fans and preamp distortion fans would be able to hear and appreciate the difference. You get the ability to avoid grid blocking and bias each output valve independently of the others. That's worth the parts count to me!

jamie

[defaced]

I remember it being proposed here... By you. I thought it was well recieved and valid. The only rub is that it doesn't fit into the ideal of an "all tube" circuit (for marketing) and it has become passe in light of new digital sampling amps (main signal OR effects) and the uber gain preamp into a 100W power amp modern designs that all the wankers use. Better power amp distortion is sort of a tube purist crank kind of thing that MOSFETs don't really fit into. And the metal kids don't crank their amps or they couldn't get that V notch, mid scoop wanker tone. For builders like us it's great. But I don't know if it has a place in any non technically inclined demographic.

You know, I used to read this forum on a daily basis because people had worthwhile stuff to say. To say the least, I learned alot here, but not so much anymore because of the attitudes. You old farts need to get off your high horse. There is life outside of a cranked plexi and strat/tele/LP. Your attitudes suck and it doesn't shine well.

Thanks,
Some wanker

-----

Back on topic. If you searched for MOSFET follies, you probably stumbled upon my schematic of RG's DC coupled source followers. It does work and isn't a difficult build. I encourage trying it. I designed it to be modular so you can build it as is and try it without hacking into the circuit too much.

[Tage]

I don't build my amps for myself, my customer is an AC30 guy who like to run his amp all out. He asked for a bass amp that had "good power tube distortion." As soon as he told me this I knew he was the type of guy who listened to a lot of marketing, but I told him I would do my best to create a bass amp with good crunch. I Have now decided that some preamp distortion and sheer power from the power amp will be more than reasonable crunch, without deterring from the fundamental bass tone.

And FWIW if a customer asked me for an amp that had a V notch and scooped mid tone, that's what I would give them. Most of what I have built and been ask to build has really been the opposite, the Hardcore guys I build and modify for want more and more mids, because they know live they need that to cut through. I'm happy to oblige that pursuit to a point too. I don't think wanting a notched mid range makes some one a wanker though, but then again I'm Canadian so Wanker is just something I hear them say on Top Gear.

Let's stay on topic now...

[exclamationmark]

I don't know if it's been explicitly mentioned in this thread, but using the direct coupled source follower method with low-medium value grid stoppers I find allows a 'rounder' sounding power amp distortion (I mean that both figuratively and literally - on the scope), even if extra power output isn't your goal. If you've ever scoped the output of an amp into a resistive load driven into clipping, the output is usually pretty damn square shaped, with a good amount of crossover distortion. Though in the end, it does sound slightly different; they/you may not like it, although you can return it to it's usual behaviour by sticking larger grid stoppers on the tube (not a good idea with triodes, however, due to the miller capacitance). This bias shift effect will obviously still be missing, although most people tend to try to eliminate that anyway.

If it were me, I'd stick a thimble on top of the fet's and tell people they're nuvistors, haha.

[Chuck H]

I don't think wanting a notched mid range makes some one a wanker though, but then again I'm Canadian so Wanker is just something I hear them say on Top Gear.

Didn't mean any offense. When I say wanker I'm implying any of the following:

A person who's always yanking his locking trem around (which I have been known to do).

A metal player that likes his tone to sound like a booming buzz saw. (which I have also been know to do)

A kid that doesn't know better than to turn the bass and treble up and the midrange to zero trying to get a dynamic sound while trying to play as fast as possible (which I used to do)

Sorry to stay off topic. Done now.

[Steve Conner]

I'll stand up and be counted, I do those things too! Except for the locking trem, I hate them.

And I now know better than to try and get the scooped mid tone at gig volume with a sensibly sized amp. I admire Ken Gilbert's solution, which was to use an insanely sized amp, but I can't be bothered carting a rig that size around.

[Chuck H]

I admire Ken Gilbert's solution, which was to use an insanely sized amp, but I can't be bothered carting a rig that size around.

+1

Sort of an icon here. For those who haven't seen it, it's still up for viewing at his site:

The Big Ass Guitar Amplifier | ken-gilbert.com

[R.G.]

I don't know if it's been explicitly mentioned in this thread, but using the direct coupled source follower method with low-medium value grid stoppers I find allows a 'rounder' sounding power amp distortion (I mean that both figuratively and literally - on the scope), even if extra power output isn't your goal. If you've ever scoped the output of an amp into a resistive load driven into clipping, the output is usually pretty damn square shaped, with a good amount of crossover distortion. Though in the end, it does sound slightly different; they/you may not like it, although you can return it to it's usual behaviour by sticking larger grid stoppers on the tube (not a good idea with triodes, however, due to the miller capacitance). This bias shift effect will obviously still be missing, although most people tend to try to eliminate that anyway.

Good point.

The MOSFET follower idea first occurred to me to replace cathode followers for driving tubes into class AB2, with signal excursions into positive grid voltage. It's not widely appreciated, but practically every tube will go a bit more into conduction if it's grid can be driven positive. It's just difficult to do this with a high impedance drive, like the plate of a preceding tube. The grid impedance goes from near-infinite to a few K over a couple of tenths of a volt, and a high impedance drive will flatline right there. It's easy to see on a scope, as you note. A low-impedance follower drive will push the grid further above the cathode (because it can!) and will not only eke out some more watts on a power stage, but the hard clipping is converted into softer, mushier current/emission clipping; again, rounder and easy to see on a scope.

For the purposes of this thread, a DC coupled follower driving a power tube grid is in capable of doing the grid-current rectification into a coupling cap that causes bias shift and blocking distortion because there is no capacitor to store grid conduction charge into.

If it were me, I'd stick a thimble on top of the fet's and tell people they're nuvistors, haha.

I like this very much. I think what I ought to do is to make up some wacky-looking metal cylinders with wanky wire leads coming out and tell people they're Elbonian power pentodes with cold field-emission cathodes, surplus from the Elbonian space program.

Inside would be an IR832 (or similar) with a resistor from one wire to the "cathode" lead and a diode to the "plate" wire to fake a useless but convincing screen current, a "grid" lead with protection zeners and maybe some small caps to fake a suitable lower frequency response, maybe some other tomfoolery. The positive "grid-cathode" could be explained as a side effect of the cold-cathode construction.

I bet I could come up with some suitably over-the-top hifi tweako language ( aged in flours-of-suphur in used wine-barrel casks then cryogenically tempered to 53 Rockwell hardness... ) and sell these as very high-end replacements.

[R.G.]

+1
Sort of an icon here. For those who haven't seen it, it's still up for viewing at his site:
The Big Ass Guitar Amplifier | ken-gilbert.com

It has many appealing characteristics, including completely solving the equipment theft problem.

[Tage]

MMM, the BAGA... a real feat of tube power.

[Chuck H]

I like this very much. I think what I ought to do is to make up some wacky-looking metal cylinders with wanky wire leads coming out and tell people they're Elbonian power pentodes with cold field-emission cathodes, surplus from the Elbonian space program.

Inside would be an IR832 (or similar) with a resistor from one wire to the "cathode" lead and a diode to the "plate" wire to fake a useless but convincing screen current, a "grid" lead with protection zeners and maybe some small caps to fake a suitable lower frequency response, maybe some other tomfoolery. The positive "grid-cathode" could be explained as a side effect of the cold-cathode construction.

I bet I could come up with some suitably over-the-top hifi tweako language ( aged in flours-of-suphur in used wine-barrel casks then cryogenically tempered to 53 Rockwell hardness... ) and sell these as very high-end replacements.

I met a guy at winter NAMM 2009 who did just this. He built transistor circuits that could retrofit in a tube preamp environment and stuffed them in preamp tube sized cylinders with a male 9 pin on the bottom. He had a couple of amps in his booth using his preamp tube replacements. I couldn't get to his booth once things were under way and we weren't allowed to make any noise prior to opening. So I can't offer a personal evaluation. Nor can I remember the name of his operation.

[Steve Conner]

I've seen quite a few like that. I also designed my own version, based on a LND150 with a resistor and diode network to make the curves more triode-like. I don't think it works properly in every application, for instance I wouldn't trust it in the Marshall cathode follower or the SLO cold clipping stage. But I heard from someone who got good results in less critical places like the FX loop.

[jrfrond]

I met a guy at winter NAMM 2009 who did just this. He built transistor circuits that could retrofit in a tube preamp environment and stuffed them in preamp tube sized cylinders with a male 9 pin on the bottom. He had a couple of amps in his booth using his preamp tube replacements. I couldn't get to his booth once things were under way and we weren't allowed to make any noise prior to opening. So I can't offer a personal evaluation. Nor can I remember the name of his operation.

Jet City sells these. They actually sound pretty good.

[kg]

MMM, the BAGA... a real feat of tube power.

and remarkably still running on the original, and basically no-longer-available, kt90s.