Tube Driver with FETs

[mudmen]

Does anyobody tried to build a Chandler/BK Butler Tube Driver using FETs instead of tube ? Stock unit produces really nice OD tones and I'm really curious if FET 'emulation' will recreate those tones...

[PharaohAmps]

Hmm...  That's an interesting idea.  The Tube Driver and its offspring and relatives use a funny kind of fixed bias setup on the tubes to get a decent output voltage swing on the limited PSU voltage, but with FETs you wouldn't necessarily have to do that.

I would think that two FET stages (or possibly three, with the third used as a source follower) would do the trick.  Also remember that the stock Tube Driver uses a couple of op-amps to drive the tube stages, and a lot of the sound of that unit comes from that interaction.  AFAIK a lot of the "bad" parts of the sound come from it...

But a simple test on your breadboard would tell you what you needed to know.  I'd start with some kind of variable-gain opamp setup, followed by one or two FET stages, like the Fetzer or Marsha Valve, followed by a tone stack.  Maybe some recovery from the tone stack would be in order?  If your first stage is a non-inverting op-amp setup like a TS clip / gain stage, then you follow it up with two inverting FET stages, you'd want a non-inverting op-amp recovery stage with a gain of perhaps 4 or 5.  All that would probably fit in a 1590B if you don't need 5 knobs on it, or a 1590BB if you do.  Gain, Treb, Bass, Volume would do for controls, just like a "real" Tube Driver, and I bet it would actually sound BETTER than the real thing.  Call it a hunch.

Matt Farrow

[Doug_H]

You're going in a circle, dude...

Check out Aron's "Shaka HV" and "Shaka Express" for opamp-driving-fets circuits that sound real good.

The whole novelty of the tube driver stuff *is* the tube.

EDIT: Oh and btw, these have been around for quite some time. (Since when do we call a simple CS jfet stage a "fetzer valve" anyway?!? )

Doug

[wampcat1]

EDIT: Oh and btw, these have been around for quite some time. (Since when do we call a simple CS jfet stage a "fetzer valve" anyway?!? )

Doug

Out of respect for these certain fellers who popularized it around here!!

Brian

[aron]

Whenever I think of JFET use, I think of Jack Orman. Many of you new guys may not know this, but lets get this right. The plain old fact is that most of the JFET use in our DIY pedals came from Jack's early work. AMPAGE has a documented history of Jack's great work with JFETs and the people that subsequently benefited from his work. At various points R.G. and others would kid Jack about his JFET circuits in a kind manner.

In addition, AFAIK Jack was one of the first to post in a clear manner, the use of JFETs to simulate tube amplifier circuits. I can't remember the exact name but I believe it was something like the Marshmallow preamp (I know, sounds funny). It was simply ground-breaking to me when it came out and I still have mine boxed up. 3 band EQ, JFET Mu stages, tone shaping, gain, it was all there.

In addition, BEFORE all of this, he also pioneered the JFET big muff, using single JFET stages and tone shaping.

Jack was largely responsible for the use of the J201,MPF102 and other FETs.

Jack also (from my use of the web) was one of the pioneers that published easy-to-build circuits on the web that sounded great. He also ran a nice forum and helped people on the web for free.

In addition to Jack's great work, for a simple single stage boost, I think of Don Tillman who's circuit has been on the web for a long, long time.

http://www.till.com/articles/GuitarPreamp/index.html

[aron]

Oh one last thing, our old circuits still sound great even if they need a tweak here or there. Just because they are old, don't dismiss them. 

[Doug_H]

Out of respect for these certain fellers who popularized it around here!!

Brian

Hmmmm... Funny, I don't remember Aron calling it a "Fetzer Valve" back in 2001: http://www.diystompboxes.com/pedals/ShakaExpress.pdf

Or Siliconix (vishay) in 1997: http://www.vishay.com/docs/70595/70595.pdf

Or Jack with his Fet muff  (don't remember the date)

Or Horowitz & Hill in the "Art of Electronics" (ISBN 0-521-37095-7) in 1980

And so on... 

Just trying to keep the record straight...

Doug

[PharaohAmps]

You guys are all absolutely right - I think the first thing I ever built for guitar with FETs (other than my first Phase 90 clone) was Jack's FET Muff.

The reason I posted using the terms "Fetzer Valve" and "Marsha Valve" is because the original poster was specifically asking about using JFETS to clone tube stages in the same manner as the guys over at ROG do.

And Aron is right, too - the Shaka FET pedals are great designs and are well worth building.  My real point was that the original poster might get better results from a Shaka-type design than he would by cloning a "starved plate" tube design.  The "starved plate" setup in the Tube Driver isn't always a great-sounding one, whatever Eric Johnson might say.

Matt Farrow

[aron]

Oh, I forgot, he also introduced to me the use of the "grid/gate" miller capacitance effect using JFETs. No doubt he got if from tubes, but my point is no one was thinking of that at the time - at least not publicly.

Also the use of an LED to bias a JFET and many more "secrets" yet to be discovered but documented in some of my early circuits.

[aron]

The "starved plate" setup in the Tube Driver isn't always a great-sounding one, whatever Eric Johnson might say.

Good point. Here's the sorry truth.... Tubes are great... VERY GREAT, but I would argue that they sound best in a guitar amp. With the exception of a very, very few overdrive pedals, I haven't really heard any tube in a pedal sound significantly better than a solid-state pedal. In fact, most pedals with a "tube" are run in starved-mode.

Add to the fact that there are only a very small amount of models that are pure tube pedals anyway and this whole idea starts looking murky.

I'm waiting for someone to really make a killer tube pedal that will blow away all of our solid state pedals. If you have one, send it to me for review and I post my honest opinion. 

[Doug_H]

Also the use of an LED to bias a JFET and many more "secrets" yet to be discovered but documented in some of my early circuits.

I remember that! It sounded great! IIRC though it only worked well in certain circumstances...which I can't remember anymore!

Anyway, there were a lot of cool tricks we played with back then for sure.

Like I told you before, Aron- I'm loving my Shaka IV right now. If I could just have a little more touch-sensitivity it would be there. Funny, everything goes in a big circle, and I end up where I started. And with a slight tweak it becomes the new "ultimate". Weird... Life is funny like that...

Doug

[PharaohAmps]

Funny, everything goes in a big circle, and I end up where I started. And with a slight tweak it becomes the new "ultimate". Weird... Life is funny like that...

Doug

Yeah, it is funny.  I've been building pedals since I got the first Anderton book back in probably '93?  '92?  Must have been in '92 - I built the Tube Sound Fuzz and the Dual Filter Voicing Unit!  I actually had a stash of RC4739's in the R&D drawers of the place I worked at the time

And I run in circles, too.  The only pedal I ever even use anymore is basically an LPB-2.  You old geezers (just like me) MUST remember the old EH Boosters  .GIF file, with the Hog's Foot, Screaming Bird, EGO, and LPB on it?  Muff Fuzz too!  I must have printed 20 copies of that thing over the years.  But it all does go in circles.

BTW Aron's right again.  All those tube pedals sound like poo to me.  That said, the lower the mu / gain of the tube you put in there, the better they tend to sound.  I have a real nice all-tube pedal I built with a 7-pin miniature socket, and I can run about 50 different types of pentodes in it.  Plate voltage is around 140V though, so it's not quite as "starved" as some.

The only commercial tube stuff that I know about that doesn't suck are the EH tube pedals.  The English Muff'N is friggin' amazing if you like Marshall stuff.  And the Black Finger is the bomb, too.

Matt Farrow

[puretube]

http://www.national.com/an/AN/AN-32.pdf

[EDIT]: posted here for the newcomers... 

[aron]

yeah, Jack has posted that PDF multiple times, but like anything else, there are tons of data sheets. It's the person that makes it work and work well that counts.

The only commercial tube stuff that I know about that doesn't suck are the EH tube pedals.  The English Muff'N is friggin' amazing if you like Marshall stuff.  And the Black Finger is the bomb, too.

OK, the English Mff'N is that good? Hmmmmm.......

[puretube]

btw.: I love simulation software - a couple of years ago, using microsim 5 with
2N3819 models, just for fun and education, I drew my tube-pedal circuits,
ran them with a B+ of 320V, and the analysis worked perfect...   .

(got a few crazy future ideas in the drawer, that have been tested fine in the sim...)

[vanhansen]

aron, Seymour Duncan just released the SFX-03 which is a tube based overdrive, not starved plate either.  The tubes run at high voltage.  From what I've heard about it and a couple clips, it's impressive, very impressive.

I'm learning more reading this post about some of our regular senior members than I even knew.  I like that discrete preamp too.

[PharaohAmps]

OK, the English Mff'N is that good? Hmmmmm.......

Yup.  Sure is.

If you're feeling real adventurous, you could build your own tube pedal using the pedal chassis and toroidal transformers that EH sells.  I used that box to build a tube reverb (dwell, mix, tone controls, 12AT7 to drive a BF-style tank, 12AX7 for preamp and mixer) for my THD Univalve, and it works fine.  I stash the reverb tank itself inside the bottom of my speaker cabinet, and just plug it all in when I get to the gig.  I know a Holy Grail or something DSP makes more sense, but I bought that pedal chassis and I had to do SOMETHING with it!  Anyway, it sounds good.

But yes, the English Muff'n sounds real nice.  I think there are some sound clips on the EHX site.

And I HAVE to get a HOG.  Totally.

Matt Farrow

[aron]

The tubes run at high voltage.  From what I've heard about it and a couple clips, it's impressive, very impressive.

OK, I will believe it when I hear it. It will have to sound "significantly better" than solid-state to impress me.

Here's the part I can never get around... have you ever heard the tone of the 12AX7 tubes in a guitar preamp? If you know how to do it, try it one day. Tap the end of a preamp and listen to that tube overdriven sound before it hits the phase inverter and you might be surprised.

[aron]

If you're feeling real adventurous, you could build your own tube pedal using the pedal chassis and toroidal transformers that EH sells.

hehehehe, you mean the ones in my house? 

[vanhansen]

The tubes run at high voltage.  From what I've heard about it and a couple clips, it's impressive, very impressive.

OK, I will believe it when I hear it. It will have to sound "significantly better" than solid-state to impress me.

Here's the part I can never get around... have you ever heard the tone of the 12AX7 tubes in a guitar preamp? If you know how to do it, try it one day. Tap the end of a preamp and listen to that tube overdriven sound before it hits the phase inverter and you might be surprised.

Yes, I've heard a pre-amp before the invertor.  Sounds horrible actually.  The tubes in the SFX-03 Twin Tube Classic are 6021 dual triode tubes instead of 12AX7's.  It's claimed to be a 100% tube signal path with high plate voltage.  Those who were involved in the beta testing of it on the Duncan forum are just raving over it.  I want to try one myself.

The Tillman pre-amp looks like a buffer of sorts.  Am I right?  Or does his pre-amp have more gain than a buffer?