JCM 800 Emulator pedal build

[paulyy]

@Magnus= I remember you mentioning this was on your to do list a few years back. I hope you have better luck with this than I did. Love the board. Very nice.

[Magnus]

Hello,
yes, you're right, I have build some other stuff first, but I will build the JCM800 this year 

Thank you 


Greetings
Magnus

[Joseeduardosn]

Hello,
yes, you're right, I have build some other stuff first, but I will build the JCM800 this year 

Thank you 


Greetings
Magnus

Cool.. but do it this year 
It has more gain than the D. Boogie?
I hope your answers, thanks...

[deadastronaut]

Hello,
yes, you're right, I have build some other stuff first, but I will build the JCM800 this year 

Thank you 


Greetings
Magnus

It has more gain than the D. Boogie?

no..quite a lot less imo.....

[Joseeduardosn]

Hello,
yes, you're right, I have build some other stuff first, but I will build the JCM800 this year  

Thank you  


Greetings
Magnus

It has more gain than the D. Boogie?

no..quite a lot less imo.....

Why?
If this project has 6 FETs, one more?
It discouraged me, logically thought it would make more gain.

[Joseeduardosn]

Somebody?

[deadastronaut]

this was posted on page 1... it definately won't get into dr boogie gain territory...just the way it is i'm afraid!..

when i builtmine it was more of an overdrive than full on metal...

http://www.youtube.com/watch?v=ZOyuhPC-A5Y

if you want full on metal, checkout jok3rx's ''black forest' thread...

[J0K3RX]

Somebody?

Thanks Rob!!  

Joseeduardosn,

Have you ever played a stock JCM800? They don't have that much gain unless cranked or if attenuation is used... The JCM's get a lot of punch from the power section which this ain't got!   The amount of transistors used in these jfet pedals can be deceptive and this pedal is a real good example! First you have Q1, Q2 and Q3 and then Q4 is a buffer before the tone stack. After the tone stack is a simulated phase splitter circuit which you could probably leave off...

If I was going to build this I would turn Q4 into another gain stage or just add another gain stage and leave the buffer which would be Q5 then... Also I would  add a resistor form the gate of Q2 to gound for added gain/boost, maybe start at 10k and see how it sounds... If it's too much or too little gain then adjust accordingly until you find the right value... I would also add 1N4148 diodes between source and gate on Q2, Q3 and Q4 if you turn Q4 into a gain stage... I would make the buffer stage (Q4) a close variant of the 3rd stage (Q3) maybe add a cap 4.7uF from source to ground... This should give you some real high gain I am pretty sure and still retain the Marshall tone... hot rodded!

Or you could just build deadastronaut's SpitFire  That has some hella gain and a Marshall brown type sound!

BTW - The new JCM800 2203kk have a "Beast Boost" with Assault Intensity and built in noise gate... 

[Joseeduardosn]

Thanks for the explanation on both.

In truth, I thought I would have more gain than Dr. Boogie that I have applied the simple logic that if you have more FETs would have more gain. But I see it not so much so.

I end up in a future anyway, but I know what I'm getting.

Thank you again.

[full shred]

I thought i contribute to this with my demo!
here it is hope you enjoy.
http://www.youtube.com/watch?v=xSo694uBJS8

This thing needs a lot of biasing to get a good sound. To me it sounds like a good foundation overdrive. But to get some high gain tones it needs extra biasing cos it gets sqare soundwaves and it becomes fuzzy.

[Magnus]

Hello,
sorry, I did not built my pedal in 2012 - just too less time...

...but I have wired it up today  

Only with jacks and potentiometers and an dc-clip - everything out of the enclosure.
I have installed the potentiometers on a piece of thick paper, to have a good overview and to try the pedal - sounds great!

I have to try the mods from Stratman7000 next time


Greetings from Germany
Magnus

[rroza]

I just wanted to circle back around to this pedal and design.  This design I built up and had a LOT of positive things about it.  It was a little too bright and fizzy.  Looking over an actual 2203/2204 and in the Phase Inverter circuit.  I didn't care for the gain, volume, then master volume.  The original circuit only has gain and volume and I don't want to fight volumes thru the circuit.

I would like to build this up again and see how it is.  Then, change the values to more represent the 2203/2204 circuit and see if better or not.  If it is better...keep it.  I'd like to also include a 9V/18V LO/HI switch on it.

I'd like to then add some switches to change a few things such as Jose Arredondo MODs, maybe a 3-position on the NFB as well as 3-way on the presence cap value and possibly add a Depth/Resonance MOD, but first to get the baseline.  There has been some suggested MODs over the years.

I also recently purchased a Friedman BE-OD.  Again, there are characters very similar to the original amp, but again a little too bright and fizzy and missing a MIDdle control.  I will be reverse-engineering it this weekend and work on it's shortcomings.  If anyone is interested in the PCB, Layout, and BOM, let me know and we can Vero it also...and work on improvements to the design.

[Tomker]

is there information about the pots value?

[Marcos - Munky]

Your best bet is to try to track the original schematic. The page of the user who created it is no longer active, so it'll be a hard work.

I'm pretty sure the original values from the JCM800 amp schematic will work.

[J0K3RX]

is there information about the pots value?

look here  > http://www.uk-electronic.de/Download/BeschreibungJCM800.pdf