Emulating tube amps with JFETs? I can't find any link

[Xavier]

OK after 30 minutes using the search function.....

Some posts mention one big thread about JFET amp emulators and how you translate the original schematic with tubes into a jfet amp emulator.

I've done a couple of them but all I've done (incorrectly) is simply drawing jfets instead of tubes. After some reading I realize this is not the right approach, specially after seeing some of the cap values.....

Can anybody help me find the damn "big" thread? it looks to be deleted.....or in any case, any source of information on how to do this.

Thanks

[puretube]

go here:
http://www.runoffgroove.com/articles.html,
find what you like,
and then put the names of the relevant pedals
into the "search"-box...

[KerryF]

i have always wanted to know this too.

[R.G.]

Just keep in mind that even though you emulate tube amps with JFETs, the results are emphatically not identical to the amps being emulated. They may be good sounding in their own right, but they are not a sufficiently good emulation.

If they were, we would not still have tube amps, eh?

[JimRayden]

If they were, we would not still have tube amps, eh?

Actually, we would. There are just too many mojo-driven instrumentalists out there (some in here too) to let those magic glass bottles fade into nothingness. If anyone was to invent a circuit to EXACTLY replicate the tube tone, there'd still be enough people to disregard it and say it has nothing on their 6L6's. And by golly, if people buy tube amps, they are being produced, no matter how good the company engineers think the new technologies are.

---------
Jimbo

[Xavier]

Just keep in mind that even though you emulate tube amps with JFETs, the results are emphatically not identical to the amps being emulated. They may be good sounding in their own right, but they are not a sufficiently good emulation.

If they were, we would not still have tube amps, eh?

Sure RG!. The only thing I want to do is a correct translation, as far as component values is concerned, so that the emulation actually sounds decent by itself.

[mojotron]

I think that it is very problematic to use the term 'emulator(s)' or 'model..' with the process of building/designing pedals related to certain tube amps. ROG uses phrases "...adaptation of tube amp schematics for use as distortion pedals..." and I think it sets a better expectation if we use the term "adaptation" or "relation to"... instead of talking about an analog pedal being an 'emulator' or 'model'.

Essentially, the evaluation of how thoroughly a pedal emulates a given amp is very subjective. Also, when it's more likely that the process of designing a pedal that is based on an amp schematic leads to a similar sound - then really emulation is not the end result; rather, what we end up with is a dang good pedal that gets a great kind-of sound from more general purpose (read: cheap/crappy) equipment. If you look at a design like BSIAB2, Ed took a totally different approach and used sound shaping to design to a sound; compare that to the process our ROG buddies used of swapping triodes with JFETs/trimmers on something like the Thunder Chief to design to an architecture or topology: You end up with two great sounding pedals but they can tend to be very different souding on some/most settings, yet floor you with how close you can get to some sounds.

I think a great deal of what there is to know about this sort of stuff is found in ROG's fetzer valve article:

http://www.runoffgroove.com/fetzervalve.html

And, this is a good background info
http://www.aikenamps.com/MillerCapacitance.html

I have not seen a big thread except for a number of very informative threads with some of use (PaulC and RDV) chatting about the Dr Boogey and Miller Caps and also some discussions on getting good tone from things like the Fetzer Valve, Vibin Champ, Thunder Chief... as well. Perhaps we need a summary thread for some of these ideas?

[David]

Shortly before ROG cornered the market on JFET emulation circuits, a guy here with a handle that resembled "Steve C" was doing it also.  He created several prototypes (which I lost, so don't ask);  more importantly, he described the "algorithm" for adapting a tube circuit for JFET use.

Unfortunately, I have no idea if the information is still around.

[puretube]

http://www.diystompboxes.com/smfforum/index.php?topic=21433

[Xavier]

I think that it is very problematic to use the term 'emulator(s)' or 'model..' with the process of building/designing pedals related to certain tube amps. ROG uses phrases "...adaptation of tube amp schematics for use as distortion pedals..." and I think it sets a better expectation if we use the term "adaptation" or "relation to"... instead of talking about an analog pedal being an 'emulator' or 'model'.

Essentially, the evaluation of how thoroughly a pedal emulates a given amp is very subjective. Also, when it's more likely that the process of designing a pedal that is based on an amp schematic leads to a similar sound - then really emulation is not the end result; rather, what we end up with is a dang good pedal that gets a great kind-of sound from more general purpose (read: cheap/crappy) equipment. If you look at a design like BSIAB2, Ed took a totally different approach and used sound shaping to design to a sound; compare that to the process our ROG buddies used of swapping triodes with JFETs/trimmers on something like the Thunder Chief to design to an architecture or topology: You end up with two great sounding pedals but they can tend to be very different souding on some/most settings, yet floor you with how close you can get to some sounds.

I think a great deal of what there is to know about this sort of stuff is found in ROG's fetzer valve article:

http://www.runoffgroove.com/fetzervalve.html

And, this is a good background info
http://www.aikenamps.com/MillerCapacitance.html

I have not seen a big thread except for a number of very informative threads with some of use (PaulC and RDV) chatting about the Dr Boogey and Miller Caps and also some discussions on getting good tone from things like the Fetzer Valve, Vibin Champ, Thunder Chief... as well. Perhaps we need a summary thread for some of these ideas?

Whoa, the article on the Fetzer valve is EVERYTHING I need to know about JFET "adaptations"

Thanks for pointing up this article

[aron]

See this thread as well - you would do well to send Jack Orman a message or two.

http://www.diystompboxes.com/smfforum/index.php?topic=42045.msg303655#msg303655

The truth is I don't remember anyone else doing an amp emulation before Jack Orman did. Not in the clearly present way he posted his schematic with his mini-boosters. I still have mine in my studio; complete with 3 band EQ, "amp gain stages" etc.... It was ground-breaking at the time.

I knew I wasn't imagining! In 2000, he posted this incredible preamp:

http://www.diystompboxes.com/smfforum/index.php?topic=14906.0

Miller Capacitance? See the Shaka Braddah 3, look at the 33K resistor right on the gate of the Mini-Booster. Uh yes.... Jack Orman....

Here's my tube amps for beginners link:

http://www.diystompboxes.com/pedals/tubedummy.html

It only takes a little while to realize that JFETs do sound good, but they are not tubes and no pedal I have heard can sound just like the real "amp". Certainly not respond like the real thing - at least not the complete amp. No FET emulation is going to sound like a Trainwreck 

I tried!

Aron

[Xavier]

Thanks Aaron

I think I have given you the wrong impression . I am aware about the fact that these emus DON'T sound like the real thing, but they make really good dirt pedals. I know the Boogey doesn't sound like a real rectifier, but it's in the same ballpark tonewise, and to me that's all I need.

I will check all these links right away !!