full jfet amp simulation of a PP tube amp.

[morcey2]

I don't know if this has been discussed here.  I'm sure it has, but here goes...

I have been toying with the idea of trying to make a full amp simulator, similar to ROG's thunderchief, but with a complete Phase Inverter and 2 jfets pushing a "Output transformer" with the secondary hooked up to a mini reactive load of some sort.  maybe a 8omh resistor and a maybe an inductor of some sort.  Not sure yet. 

This is what I know so far.  I need 2 sets of somewhat matched jfets for the PI and the "power amp".  I've found a couple of transformers that would probably work that have CT primaries and a 2 or 3:1 winding. 

The reason that I want to try this is mostly because I've built a thunderchief, professor tweed, a couple of little Gems, and a real hi-octane.  I've got everything I think I need to do it and just want to see if it's possible.  I've got J201s, MPF102s, and NTE458 that I could use for the different parts.   

Any ideas?  or am I just running on not nearly enough sleep.

thanks,

morcey2.

[JimRayden]

Here's a link somewhat related to this topic. Not push-pull but includes an OT, so it might of come in handy.

http://www.diystompboxes.com/analogalchemy/amps/microamp.html

-----------
Jimbo

[R.G.]

Is it possible? Sure. It's simple to just glom in JFETs for triodes in any amp schematic, then diddle things to try and get it to bias up.

Will it sound similar? Possible. But chances are, no. It will sound like itself, not necessarily like any tube amp.

It's very attractive to think that all's you gots to do to do a tube amp simulator is to plunk in JFETs and make a few tweaks. However, if it was that easy, we would have no tubes today, would we? No one would bother.

[George Giblet]

If you want some advice start with at least 15V.  There's a lot of variables in the equation.

[morcey2]

If you want some advice start with at least 15V.  There's a lot of variables in the equation.

I was probably going to do either 18 or 24 volts.  I've already got a 24v power supply that I can use for it. This is more of an "I'm bored and want to see if this will blow up" than an Einstein moment of any kind.  I'm sure someone else has tried it before and it didn't work for them.   maybe I'll have better luck with my bucket of hi-mojo electrons. Oh well.  I'll see what happens.  Wish me luck!



morcey2

[morcey2]

Is it possible? Sure. It's simple to just glom in JFETs for triodes in any amp schematic, then diddle things to try and get it to bias up.

Will it sound similar? Possible. But chances are, no. It will sound like itself, not necessarily like any tube amp.

It's very attractive to think that all's you gots to do to do a tube amp simulator is to plunk in JFETs and make a few tweaks. However, if it was that easy, we would have no tubes today, would we? No one would bother.

I know that it won't sound like a tube amp, that's what the hi-octane is for!    it sounds real good with a 12at7 as V2.  Anyhow,  you say it will sound like itself and that's exactly what I want to know.  How will it sound.  It's more of a curiosity thing than a scientific effort.  If the character is even similar, I'll be pleasantly suprised. 

It's more just more goofing off trying to find something to do with an excess of jfets while saving money for more projects. 

Thanks

morcey2

[zachary vex]

...I have been toying with the idea of trying to make a full amp simulator...
morcey2.

are you going to use this as a line-driving device, for recording?  or is it supposed to be a pedal that drives an amp?

[MartyMart]

All the recent "Jfet clones" that I have done, as far as the pre-amp section goes, sound
very similar .... a total replacement no, but the character was there for sure.
As for replacing the "power tube section" ....?
I was thinking of using a 19inch rack, and installing perhaps 5 "wish list" pre amp
sections, then you can plug that into either a power amp or a speaker sim etc for
live/recording use.

MM.

[JimRayden]

This is more of an "I'm bored and want to see if this will blow up" than an Einstein moment of any kind.  I'm sure someone else has tried it before and it didn't work for them.

Wasn't Brian May's Deacy amp push-pull? I remember it had a transformer as a PI and an output trafo after the power section...

---------
Jimbo

[petemoore]

  Here's a way to say this about that.

  Tube output Needs to be connected through 'something' resistive, they do nothing and maybe burn out otherwise.
  For those like me, for whome speakers simply werent' the percieved 'correct answer', other items have been fiddled with to replace the speaker as resistive load, once I got back to the speaker as resistive load  I become happy again, for a time...right sized tube amp.
  in an effort to quiet down tube amps or get 'tube amp in a box goin'
  * = 'Somebody' or 'company[s'
  *Have Connected them to resistors in an effort to 'calm them down', but again that 'flattenned' the sound, some report this is good.
  *Have combined 'flat' resistive loads [ie fixed resistances] combined with speaker
  *Made 'quiet' speakers [dampening device replacing tradition speaker cone]..I think they're called 'Power Break or Mass Attenuator'.
  A big part of the sound I purport to percieve that you're looking for is that 'tube output loaded by speaker' sound. This sound can be very illusive to attain without exactly that.
  The speaker is not a 'flat' load, once inertia enters into it...I don't know if there is a 'video explaining' of it...it's a 'mind thing' to grasp...but the movement of the speaker cone 'adds' voltage...and resistance is certainly not constant, it can fluctuate wildly "At Frequencies"...producing a complex sound and need for attempted complex explanation of 'how-why'.
  There's a way to do it, but it'd be rediculously task oriented, require much more than I have to work with here, early models would be less satisfying/more time consuming to me than my tube amps 'n speakers...and I'm not into the compete thing...+ I like that tubes are being produced, and have become available, I ordered a matched set this morning AAMOF.
  Even if my little hatchling tube amp in a box idea could be gotten into a rather large stompbox size, I believe that, even wIth all our vast reservoirs of infinite, encyclopedic "Electromechani-accoustic" abstract and hands on thinking, experimenting, and building...we'd still find out that air, and solid surfaces, though WAY TOO OFT [like last night...Dohhh] are taken for granted by humans, this race is so accostumed to having 'surfaces', that they go completely "Consciously" unnoticed..
  Play the tube amp w/speaker [of course, yeah I know I'm ranting, speaker you'll need, get better one and A/B...]...outside for a time, then try Jfetting one sim of one 'room effect'.
 
 

[petemoore]

  I'd like to see something in this area with a transformer and all, but without the varying resistive load [coil/cone inertia 'thang' varying the load on the output], and the 'play' [complexities happening thereof, and tones produced by tube output and speaker] that happens when these characters get together and work out 'skits' for various input responses...you're back to clipping/not clipping, voicing/prevoicing...which is part of the tube amp/speaker 'thing'.
  I think I've given it away...who's going to do it then?
  Tho'se that know's don't sayso's, sept me...and I'm not makin' the darn hard to make experimental, gonna take some serious effort, time, money, machines, electromechanical prototyping SOB...not into all that when I got a fine guitar, Jfet ampsims, and a FF with lotsa other cools stuff going On Big Time...I simply don't have the means to do so if I would so be inclined to...besides, my tube amps and a decent room would still beat it every time.
  [might be cool to have the "TRUTUBE Amp and speaker [w/tapped output] in a box going INTO my tube amp though...
  I really doubt anyone has tried it, that's why 'they' just went to Fuzz Box for effect in the 'first' place.
                       PETEMOORE"S: "TRUTUBE SLIDEHAMMER"
  THIS BOX TRULY SIMULATES TUBE AMP WITH SPEAKER LOAD DISTORTION>Using patented technologies, an amp, driving a 'Slidehammer' [speaker and microphone inertial simulator electromachanical machine].
  It produces...everything a tube amp produces...EXCEPT...the volume, by itself, the TRUTUBE SLIDEHAMMER makes almost no perceptible sound [a wooden 'resonator' box accessory may be added for a 'small' amount of volume], but EXACTLY replicates to scale, a cranked tube amp and speaker system.
  Because it actually HAS a Tube amp with tube rectifier [optional] AND a PT and an OT [transformers], as well as a choke [for lower noise], full power supply, all the characteristics available with any tube amp type can be replicated.
  The voice coil/cone/microphone got turned into a Voice coil driving a 'suspended, 'sprung weight', which also has a microphone element attached. This puts a variable load on the output section of the tube amp [the same as a speaker does, but to scale], producing the complexities that 'variable resistive loads on tube output' [tube amp and speaker] s are known for, down to the last *nuance.
  What is still missing from the 'Cranked tube amp into speaker into air being reflected .... 'room with surfaces'?
  ...the influence of air near the speaker cone, 'out' in the room...and surfaces like speaker cabinetry, laquer, Swamp Ash guitar body, stainless steel string...and all the synergystic effects thereof, these are smaller influences, some minor 'nuances' have not yet produced the abstract technology to replicate them to scale...that will come in the next phase of this technology, and will be marketed as PETEMOORE"S
"LIQUID AIR/WOOD--TRUTUBE SLIDEHAMMER"

[MartyMart]

..... well I guess that's all been done .......






It's called a "Line6 PodXT" slotted into the new "Power amp" cabinet, that gives you proper
"amp" volume  !!   

MM   

[lovric]

continuing the suggestion by rayden: davisson had aschem of a kathode micro-amp on the previous version of his site. it was a push pull solution. i can send you a scem if you wish.

[JimRayden]

Send one away at my direction too, will you?

---------
Jimbo

[morcey2]

Would you be so kind as sending it my way also?  Anyhow, Here is a PROOMA* schematic kind of based on the thunderchief. 



I did it up in LTSpice and It looks like it may have too much gain.  that or the transformer is doing some wierd things to the signal.  The only thing I'm not sure on is what kind of specs the transformer should have. 

matt

*(Pulled Right Out Of My ___)

[morcey2]

Bumping. 
in LTspice, I can't seem to get the phase splitter balanced very well.  Anybody have any ideas?

matt

[TELEFUNKON]

"long tail" too short? (R15)
increase?
replace by constant current source?

[johngreene]

I built a JFET clone, so to speak, of a 50W marshall (with the EL84s). Used an audio transformer at the output, basically just replaced tubes with FETs and adjusted values to get the thing to bias up right. I built it on a vero board around 10 years ago and it is still sitting in a box. I didn't have the tone control pots at the time to finish wiring it up and since then I guess I just forgot about it. Guess I should dig it out. I ran audio through the various stages and tested it with some pots I dug up at work at the time and checked the response on the scope so I know it works, just never 'heard' it yet.

--john

[morcey2]

I built a JFET clone, so to speak, of a 50W marshall (with the EL84s). Used an audio transformer at the output, basically just replaced tubes with FETs and adjusted values to get the thing to bias up right. I built it on a vero board around 10 years ago and it is still sitting in a box. I didn't have the tone control pots at the time to finish wiring it up and since then I guess I just forgot about it. Guess I should dig it out. I ran audio through the various stages and tested it with some pots I dug up at work at the time and checked the response on the scope so I know it works, just never 'heard' it yet.

--john

Do you have any idea what values you used for the phase inverter?   That's the only part I'm having issues with.  If I get it setup so it is functioning correctly, it converts a 6volt signal to a 0.25Volt signal.  AAAAAAAaarrrrrrrrrgh.   Maybe I'm just smoking crack on this one.  I know that it can be done, just gotta figure it out. 

matt

[johngreene]

I'll have to check when I get home, it's been 10 years. I may even still have the schematic for it near it. I do know that I had everything working including the phase splitter.

I will say that all my previous attempts at this, and there were many, ended up with the guitar (set clean) sounding like it had 'hair'. Not really fuzz, but not very 'amp-like', like the notes had peach-fuzz on them. Not sure how else to explain it.

Which is why I did it with the output transformer, I was thinking that had something to do with it.

--john