freestompboxes.org

Hi friends
This design is an attempt to simulate the harmonic distortion characteristics of a triode valve (vacuum tube) using an n channel jfet in an unusual configuration. The design is based on an idea by Dimitri Danyuk, who presented it at an Audio Engineering society meeting in Berlin 2004. His emulator ran off a bipolar 15 volt supply and included a blend control to allow folks present to hear the difference between the emulator and a bypassed musical signal. he also included a peak detector to show the onset of distortion etc.
My version is adapted to fit in a Hammond 1590B case and runs from a 9 volt battery, 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. The design uses an MAX1044 charge pump to allow the fet to properly bias.
There are two trim pots - one adjusts the fet bias to achieve the triode type harmonic distortion law, the other adjusts the gain of the op amp for unity gain through the jfet stage.
If anyone is interested in Dimitri Danyuk's AES paper, please PM me with your email address and I will be only to happy to send you a copy for your info.
In closing, this is not your average overdrive or distortion pedal - it is not a tubescreamer or fuzz face etc, so do not expect endless smooth sustain from it, but if you build it, I am sure you will find it a very useful and unique sounding pedal, and there are many different distortion characteristics lurking in thesetting of the jfet bias trim pot, not necessarily triode sounding but definately interesting tweaking here.
I have been using this, my second revision of this design ( the original ran off 9v and is still in use by a local guitarist who looooves the way it drives his Fender Hot Rod Deville - he does not use the amps drive channel, he prefers the TE boost) for the last month and I like it so much, it hardly gets bypassed - the other guys in the band seem to like it too, because they have not told me to "turn that thing off"

anyway - here are the schems, layouts etc.
hint: I print and cut out the overlay and glue it to the component side of the PCB board (after drilling the holes) then I use a sharp point (pencil compass etc.) and poke through the paper overlay - makes component placement a no brainer
enjoy
bajaman

triode emulator boost plus schematic
overlay
PCB tracks
composite

That looks great baja! I'll have to try this one.... I was playing with a similar idea the other day but yours looks much more advanced and complete!
Great work

Really looks cool I will have to try it on the breadboard at some time. You'll have to explain what the op amp in the feedback loop does, when you get a chance.

Good work Steve! Looks really cool. Might be my next build.

"anyway - here are the schems, layouts etc."

Where is the link please?

Stephengiles wrote:"anyway - here are the schems, layouts etc."

Where is the link please?

a little bit more below, at the bottom of the posting.

analogguru

"anyway - here are the schems, layouts etc."

Where is the link please?

At the very bottom of the post Stephen
cheers
bajaman

DougH wrote:You'll have to explain what the op amp in the feedback loop does, when you get a chance.

Yeah, some explanation to trigger out a discussion would be pretty nice...

Servo?

From the original AES paper (thanks Steve):

(IC3 is opamp in feedback loop of IC2)

"Operational amplifiers IC2 and IC3 form a highly linear current-to-voltage converter (Fig.6), which acts as a load to the FET stage and sets the gain. As the drain voltage of the FET is held at a constant level, the non1inearities associated with FET output network and gate-to-drain capacitance vanish. JFET has enough voltage across it to operate in the saturation region, while not that much to generate excessive noise due to reverse gate current. IC3 is used as a noninverting integrator in a servo feedback loop to ensure that the dc voltage at the output of the current-to-voltage converter remains close to the desired zero level. The IC3 stage works also as current source referring to the inverting input of IC2."

I see now, many thanks.

Very clever do you not think
(Dimitri's ideas)
bajaman

Very interesting.

Thanks baja for this project!

I just modify little pcb:
http://www.picvalley.net/u/67/16634_195.PNG
I remove a little gnd to prevent antenna effect.

there is nothing changed.

I remove a little gnd to prevent antenna effect.

I have not had any problems, but that is cool by me.
i was playing mine again last night at the practice room - I REALLY like this pedal - it complements the sound of my Fender/Mesa/Vox hybrid 4xEL84 amp and single 12 inch speaker combo perfectly - fuzz at high drive settings, BUT with definition
bajaman

As with all my projects here at freestompboxes.org, you are most welcome to build, share, mod or generally do whatever you like with them. I do not require any royalties or licensing agreements etc. They are my gift to the WHOLE community - enjoy them as my way of giving back to the many that continually inspire me in my madness
bajaman

bajaman, may you send us some samples please ?

PS: thanks for aes issue

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

Hi,

I'm interested in AES issue: it's possible to get one?

Thanks for your help.

Mauro.

Is that scale on the side of the PCB inches? Any tips on how to print it properly (I'm having problems printing 'em)?