Diezel VH4 Pedal [schematic]

[440hz]

Very cool, bajaman!

If you end up with a spare working board, I'd be interesting in buying one off of you.

If not, I'd be down to split an OSH Park order with someone, if anyone else is interested.

[roseblood11]

Bajaman,
if you don't plan to sell these boards yourself, they should be available via madbean, 1776 or Aion! Or maybe uk-electronic.de in germany?

[bajaman]

Bajaman,
if you don't plan to sell these boards yourself, they should be available via madbean, 1776 or Aion! Or maybe uk-electronic.de in germany?

But first - I will build one - the boards are with the fabricator at the moment - enclosure and pots all ready - just need to get the board, populate and test it then we can discuss distribution etc.
The boards will definitely be available but let us not "jump the gun" until we have a fully built and tested working prototype - patience please
cheers
bajaman

[440hz]

Any more news, bajaman? Still waiting on those boards to come in?

[edy_wheazel]

My contribution to this project.
I attached the schematic, layout and pcb. It fits in a 1590BB enclosure.
The pot's are not placed on the pcb (see schematic).
It's still UNTESTED, I will made this in a few days, after I get my parts.

Have fun!

[bajaman]

Any more news, bajaman? Still waiting on those boards to come in?

I am still populating the pcb and waiting for some OPA2134 chips - i thought i had some but only had the single and quad versions
So far all the parts are fitting ok so won't be too long before i can run it up and verify it - I will have two spare boards so one is earmarked for you.
cheers
bajaman

[orcl2]

Waiting the result of your work! XD

[modman]

Ok - built tested and verified working 100%
I didn't know the value of the inductance bead at the input so just bridged it with a wire link.
I am still waiting for my OPA2134 chips to arrive so in the meantime used a socketed TL072.
I ran it off a 12v 1A switching supply plug pack - opamps are running +10v and -10v rails.
my 12v plugpack whines log a baby (cheap chinese shit ) so i plugged in a Boss 9v adaptor and measured +7v and -7v on the opamp power supply pins - still sounds good even on lower supply voltage
I used 1u multi layer ceramic capacitors in place of the 1u electros - just because i have a ton of them
Here are some build pics.
I will share this board layout now on OSH PARK - search for bajaman and you should find it ok

IMG_3221.JPG

IMG_3222.JPG

IMG_3223.JPG

IMG_3224.JPG

cheers
bajaman

[bajaman]

I have one spare board - $US10 includes airmail postage.
pm me quick if interested
bajaman

[bmxguitarsbmx]

How brutal is it? 8D

[bajaman]

How brutal is it? 8D

very nice - low noise floor and very wide range of gain possible - nice for cleanish blues at low gain settings.
very different to the Friedman BE-OD in many ways but still a good high gain pedal to have.
I ran a few sims as well and it is easy to see why Diezel uses reverse log pots for the presence and deep (resonance) controls because with linear pots nothing much happens until the last 5% of clockwise rotation on the sims.
The presence on full, has almost 20db of boost at around 1.6kHz which is a very low frequency compared to the friedman presence circuit, and considerably larger
The deep control on full, puts a very sharp 20dB Q peak in the response at around 120Hz which is slightly higher than the friedmans bass control.
The 3 section passive tone circuit behaves very much like a typical marshall tone stack - nothing exciting here.
Overall a lot more flexibility tone wise compared to the Friedman, but the Friedman does a more convincing 100 lb violin tone and is a tighter crunch in my opinion.
Both pedals are completely different in many aspects of their design but both are worth having. the Friedman is a bit of a one trick pedal and it does that trick really well, but the Diezel is a lot more versatile and less prone to oscillation and noise artifacts.
Like comparing Fords and Chevs I guess
have fun and keep rockin'
bajaman

[bajaman]

I just ran some more sims - this time to investigate the clipping behaviour in an interactive simulation.
Surprisingly the first clip occurs in IC2b the third gain stage and AFTER the stage with the zeners in the feedback loop AND AFTER the back to back 1N4148 diodes - in fact removing the zeners and the 1N4148s from the simulation made no change at all to the output waveform.
Not sure exactly when or if these diodes have any effect on the clipping behaviour of this pedal but the primary clip appears to be within that third TL072 gain stage

Okay I was inputting an 8mV sine wave signal at 1kHz when I measured the onset of clipping in IC2b.
I increased this signal level up to 130mV before i was able to detect any appreciable clipping behaviour BEFORE IC2b indicating that the diodes were now conducting - that is over 16 times the signal level which makes me wonder if the pedal would sound any different without the diodes in place at all

[Groovenut]

I just ran some more sims - this time to investigate the clipping behaviour in an interactive simulation.
Surprisingly the first clip occurs in IC2b the third gain stage and AFTER the stage with the zeners in the feedback loop AND AFTER the back to back 1N4148 diodes - in fact removing the zeners and the 1N4148s from the simulation made no change at all to the output waveform.
Not sure exactly when or if these diodes have any effect on the clipping behaviour of this pedal but the primary clip appears to be within that third TL072 gain stage

Okay I was inputting an 8mV sine wave signal at 1kHz when I measured the onset of clipping in IC2b.
I increased this signal level up to 130mV before i was able to detect any appreciable clipping behaviour BEFORE IC2b indicating that the diodes were now conducting - that is over 16 times the signal level which makes me wonder if the pedal would sound any different without the diodes in place at all

Baja, thanks for all the contributions! Very valuable info.
Most modern tube amp designs tend to clip the stage closest to the power amp first and it is usually biased as a symmetrical clipper, then the next stage closer to the input clips and so on until you get to the input stage. The main exception to this is the cold clipping stage many (Soldano, Mesa Rectifier, Peavey 5150, Engl) have in the 3rd stage. It is usually biased near cutoff and will clip asymmetrically and very early.

I find both the BEOD and VH4 pedal versions of the actual amps to be interesting from a design emulation standpoint. I don't think either get the actual sound of the amp but they get close enough for anyone who has never played the actual amp, to feel satisfied about their purchase. They are also good sounding units on their own regardless of comparison to the amps they are supposed to emulate.

[bmxguitarsbmx]

Thank you Bajaman and Groovenut!

Interesting stuff. Interesting how two of the best high gain tube amp simulations are using tl072's! Who knew?!

The 1n4148's are a simple noise gate (my apologies if that is obvious). Signal at that stage is significantly steep to usually not impart too much crossover distortion, not that croddover distortion is bad.

[bajaman]

Thanks for the clarification on the noise gate bmxguitarsbmx
and thanks for the tube amp explanation Groovenut - you are 100% here - most folks do not realize that it is the driver or phase inverter stage that overloads and clips first in 90% of all tube guitar amplifiers. The vain idea that someone can purchase a boost pedal to drive the front end of their amplifier into overload is of course total nonsense because the driver stage will saturate WELL before this could EVER happen
What I find interesting with this Diezel VH4 pedal design is the tone stack is AFTER the clipping 3rd stage whereas in a tube amplifier it is always BEFORE - and it is the TL072 clipping which is then modified by the following treble, mid, bass, presence and deep controls that defines the sound (plus the high cut filter tagged on the guitar amp output socket to roll off the fizz! )

bajaman

[bajaman]

just a heads up

I made a few minor changes to the OSH PARK shared pcb - enlarged the footswitch holes slightly (I had to crimp the pins on my originals to fit the switch),
added extra pads for where two controls join to the board.
It is not necessary to connect any of the potentiometer pins not listed on the pcb - the pedal functions perfectly ok without them - the screen printing has been amended to reflect this.
have fun building it
cheers
Steve

[bajaman]

Ok
Just ran a 1kHz sinewave through my build and confirmed that it is the IC2b stage clipping FIRST in this pedal - it took more than 10 times the input signal level before i noticed ANY clipping in the stage with the two zener diodes and by this stage the IC2b stage looks like a square wave - very heavy clipping which I would doubt anyone would achieve in practice
I would think that the 2 x 5.6v zener diodes are totally unnecessary and could quite easily be left out.

Incidentally i noticed that the bottom of the sine wave clipped slightly before the top at the output pin of IC2b

cheers
bajaman

[bmxguitarsbmx]

Thanks for the clarification on the noise gate bmxguitarsbmx
and thanks for the tube amp explanation Groovenut - you are 100% here - most folks do not realize that it is the driver or phase inverter stage that overloads and clips first in 90% of all tube guitar amplifiers. The vain idea that someone can purchase a boost pedal to drive the front end of their amplifier into overload is of course total nonsense because the driver stage will saturate WELL before this could EVER happen
What I find interesting with this Diezel VH4 pedal design is the tone stack is AFTER the clipping 3rd stage whereas in a tube amplifier it is always BEFORE - and it is the TL072 clipping which is then modified by the following treble, mid, bass, presence and deep controls that defines the sound (plus the high cut filter tagged on the guitar amp output socket to roll off the fizz! )

bajaman

Maybe non-master volume designs... In most of the amps I own, the phase inverter is driven by the effects loop return amp. I can tell you I can get some deafeningly loud cleans by plugging directly into effects return. Maybe I'm a pussy, but my phase inverter is never overdriven.

The high output impedance of vh4 pedal is mind boggling. Easily, this pedal could be driving the 75pF of 1 foot of instrument cable into a delay pedal (for instance), or the 1nF of cable capacitance of a 20 feet of instrument cable to the input of a guitar amp. Drastically different LPF corner frequencies. It's either idiotic or genius It does sound damn good, so who am I to say?

[bajaman]

Maybe non-master volume designs

granted

Just for giggles, I tried a pair of 5.6v zeners connected like the preceding stage to IC2b and noticed they clipped just before the opamp on the scope.
However when i listened to this combination it seemed to muffle the top end and compress the dynamics too much - i took them out and i actually like the sharper edge that the TL072 clipping gives
I may try a string of 4 pairs of red leds back to back next and see how that sounds
cheers
bajaman

[bmxguitarsbmx]

Can I ask what your rig is Bajaman?

I mostly build 100 watt heads and run them through 4x12's. I don't use stompboxes much but the be-od and this vh4 have me checking freestompboxes multiple times/day. Hahaha.

I did rig up a 20 watter with a fender Blackface clean running into an open back 1x12 with a celestion g12-65 to test these stompbox distortions. Other than that my builds are influenced by famous modded marshall's, soldano, Jose, Diezel, and Splawn. I have a BE100 and access to a couple different years of the vh4. I haven't built the vh4 pedal yet, but I did build a couple versions of the be-od.

Anyway...

Running a pedal that simulates an amp into a clean channel has me puzzled. Especially this one with a FMV tonestack that is then run through another FMV tone stack. I usually just do a plexi clean, I find the midscoop on the fender tone stack to be ridiculous! So I used multisim 11 to differentiate a marshal tone stack with a fender tonestack to create the marshall response through my new fender clean channel. I still haven't designed the circuit yet, but here is the sim. 8dB boost at ~400Hz. Simple enough

Hope it loads into multisim 14!