Baja Triode Emulator Boost Plus

bajaman · Post by **bajaman** » 28 Jan 2008, 23:32

Is that scale on the side of the PCB inches?

Yes

bajaman

seniorLoco · Post by **seniorLoco** » 29 Jan 2008, 07:58

bajaman wrote:I do not do samples - you will just have to build it and do your own
cheers
bajaman

Seriously Baja...please put that on your sig ...permanently

Thanks for yet another great project...this i got to try.
Cheers mate !!

KippeKiller · Post by **KippeKiller** » 29 Jan 2008, 10:25

Hello,

great Design, i'll give it a try.

regards

Mathias

minor7th · Post by **minor7th** » 29 Jan 2008, 11:35

embarassing question time...

On a recommendation, I'm breadbording up the triode. I've noticed a little ol' thing on the schem saying "buffer out".

What's more, having breadboarded up the limiter, I've notices that it has one as well. And what's more, it's there on the breadboard.

Since I feel incredibly silly and wondering where my attention to, well, anything has gone, I thought I'd better check. This is an alternate buffered output?

Oh dear... It must be the drugs.

bajaman · Post by **bajaman** » 29 Jan 2008, 21:07

The buffered output option is there for the bypass operation. You can choose to use it with a single pole double throw switch ( or dpdt if switching an indicating led on/off) on the output of the circuit or buffer, OR just ignore the buffer output connection if you are intending to use a double or triple throw switch and switch the input as well as the output for true bypass operation

cheers
bajaman

minor7th · Post by **minor7th** » 29 Jan 2008, 23:45

bajaman wrote:The buffered output option is there for the bypass operation. You can choose to use it with a single pole double throw switch ( or dpdt if switching an indicating led on/off) on the output of the circuit or buffer, OR just ignore the buffer output connection if you are intending to use a double or triple throw switch and switch the input as well as the output for true bypass operation
cheers
bajaman

Thank you sir. The scary thing is that makes sense!

Cheers

m7th

bajaman · Post by **bajaman** » 30 Jan 2008, 01:56

I am always happy to help

Good luck with the build

cheers
Steve

bool · Post by **bool** » 01 Feb 2008, 23:05

I'd like to have the Dimitri Danyuk AES paper as well - if still possible!

TIA

Edit: while re-reading what was posted here, would it be possible f.e. to swap the fet for a mosfet (maybe with some small circuit changes)?

I remember reading on the internet that mosfets are the closest match for tubes in the solidstate form? Any opinion on that? Just curious... ?

bajaman · Post by **bajaman** » 01 Feb 2008, 23:59

Edit: while re-reading what was posted here, would it be possible f.e. to swap the fet for a mosfet (maybe with some small circuit changes)?

I remember reading on the internet that mosfets are the closest match for tubes in the solidstate form? Any opinion on that? Just curious... ?

The n channel jfet specified - 2SK117 has a sufficiently high input impedance for this application as a slightly less than unity gain transparent buffer - if you use a mosfet it will not improve the sound, it will probably be noisier though

bajaman

bajaman · Post by **bajaman** » 02 Feb 2008, 00:03

Edit: while re-reading what was posted here, would it be possible f.e. to swap the fet for a mosfet (maybe with some small circuit changes)?

I remember reading on the internet that mosfets are the closest match for tubes in the solidstate form? Any opinion on that? Just curious... ?

If you mean the non linear element in the inverting gain stage inverting input circuit, then it will not work correctly without a major rethink in the biasing on of the mosfet - I would stick with the specified jfet for a first build - you are most welcome to experiment though - let us know if you find anything useful out.

cheers
bajaman

bool · Post by **bool** » 02 Feb 2008, 01:05

Thanks for the paper - phew, this stuff is rather deep on first reading ...

Not really sure if I'm up to the task of playing with the circuit by myself. It surely does have a certain "misterious" vibe.

OTOH, I was merely asking if swapping for a mosfet would be doable in one way or another, surely with some fiddling around the circuit; maybe somebody with more experience and know-how could tinker with that idea? Or not... Because everywhere I was able to read the solidstate and tube comparisons etc. it was said that the closest match would be a mosfet but in "guitar" circuits there are mostly fets used ... when "fets" are used.

bajaman · Post by **bajaman** » 02 Feb 2008, 01:59

only a tube sounds exactly like a tube

a mosfet has similar characteristics to a pentode tube.
The purpose of this circuit is to more closely emulate the 2nd ad 3rd harmonic charater of a triode tube, which has a completely different characteristic to the pentode.
The major problem with using jfets to emulate triodes as in the ROG series circuits is that the jfet has a natural square law ratio when driven into clipping, whereas a triode has a 1.5 times law instead.
The purpose of this design adapted from Dimitri Danyuk's paper is to force the jfet into a 1.5 times law clipping characteristic to more closely emulate the triode tube character and sound. A mosfet simply will not work in this circuit as it has a very different characteristic again.

This is why, although the ROG emulators sound okay, they will never emulate the true harmonic content of a triode tube - too much 2nd harmonic and not enough 3rd harmonic content

Perhaps a multi stage tube amp emulation based on the core design principle in this project may be a closer match - food for thought???

bajaman

bool · Post by **bool** » 02 Feb 2008, 10:59

Hmm ... I'm by no means an expert, but aren't pentodes used in output stages of a tube amp?

If as you said fets are mostly used for triode emulation and mosfet are like pentodes, then if somebody would combine that in a circuit then you'd get a better approximation of a real tube amp?

The last time I did -real-ish- tinkering with electronics was over 15 years ago and I'm not quite in shape now for such - let's say advanced - tinkering procedures.

Nevertheless, it's a very interesting read, that.

vanessa · Post by **vanessa** » 02 Feb 2008, 17:56

bool wrote:Hmm ... I'm by no means an expert, but aren't pentodes used in output stages of a tube amp?

Pentode's can and have been used in preamp sections (Gibson, Ampeg and others).

http://www.drtube.com/schematics/gibson/ga-5lpj.gif

bool · Post by **bool** » 02 Feb 2008, 19:37

I see. But aren't the most common ("classic") tube amp sounds comming from the triode-pre and pentode-out configuratons? I mean fenders, marshals etc?

I mean these are those which usually listeners/players etc. associate with the "tube" sound? Not meaning to troll the thread, it's just that this circuit got me thinking.

bajaman · Post by **bajaman** » 02 Feb 2008, 20:02

OKAY - you could use multiple triode emulator core sections and run them into a mosfet push pull output stage and then transformer couple them through an appropriate filter to simulate the speaker frequency response, BUT, that is another project for another day. Best to build this first and evaluate it's merits for yourself

. It was never intended to be a tube amplifier and speaker simulator, just a booster with triode tube harmonic charateristics.

bajaman

Hotrats · Post by **Hotrats** » 05 Apr 2008, 21:23

just to be clear, what made Pentodes and Tetrodes different than Triodes is the tapering (flattening) of their transfer characteristics - essentially providing a higher AC resistance in that area. in this sense MOSFETs and jFETs and Bipolar transistors are all 'more" similar to a pentode/tetrode than a triode. what makes a tube amp sound the way it does has also lots to do with the fact that we generally are not dealing with only one tube element - it's one driving/loading the other where the tube sound starts happening. that's where the expo input current (all tubes have this in common) starts playing a major role - which is ignored here.

thanks for the Dannyuk paper Bajaman - I was doing a few similar things like this last year and took a look at what he's doing in his paper. the first question is really about Noise - the noise in jFET stages is related to Source resistance, the smaller it is the greater the noise (see data sheets). since the curvature of the DC-Transfer response, what gives rise to the harmonics profile (and not clipping), depends on using little to no source resistance to achieve it you're gonna get MAX noise the circuit can put out.

there's another problem that is not immediately apparent in the Dannyuk paper - it has to do with where the DC (idling) operating point lies within the curvature region. When the source resistance is low what happens is the cutoff point moves to the left and the limit point where Id is limited by Idss gets closer and closer to Vin=0. the more curvature we try to produce (reducing source resistance) the more the response gets shifted. this means that the whole region of curvature is not available as it is in a triode circuit - where the DC operating point naturally falls inside the triode stage's transfer region. with source resistance equal to zero (max curvature) the Vin=0 point coincides with Vgs=0 unless there is something additional in the source circuit to shift the response. pretty obvious what that can be.

I built several cascaded versions using my way of shifting and I get wicked compression from the circuit - to do this you also need to up the voltage gain with and extra stage in each element (similar to Dannyuk's op-amp) making sure the range of curvature is allowed to happen within the range of the output device - this means biasing the stage so it's idling close to the rail and allowed to down expand far enough to get a good cross-section of the parabola. When you get enough of the parabola happening and you cascade to such stages the exagerated lobe will act to shut off the following stage - hence the compression effect.

main problem for me at the moment is the noise.
thx!

dimitri · Post by **dimitri** » 09 Jun 2008, 00:36

Great Job, bajaman

Now time to make a next step - tube amplifier/speaker simulator.

Hotrats, I'm not quiet understanding your noise problem

dimitri · Post by **dimitri** » 09 Jun 2008, 00:46

although it does have a fairly high current drain, that could possibly be reduced by using a TL064 quad op amp instead of the specified TL084 used in my design.

please remove 3pcs of 2.2K resistors from op-amp outputs to ground. They are making op-amp output stages working in class-A, but this is extra 12mA from V+.

dimitri · Post by **dimitri** » 09 Jun 2008, 01:11

bajaman, try to put 0.0047-0.047uF in series with 2.2k and 47k DRIVE pot

Baja Triode Emulator Boost Plus [documentation]