My first "British" distorsion project : need advices !

[Darkness, Darkness]

Hi everybody !

I am building a distorsion stompbox that would help me to get closer to the sound of a well known british amp used by former GN'R guitarist Slash (->Lead tone on Estranged, Sweet child o' mine...) I know I can not get the exact sound of Slash, even with all its own equipment....but I am sure I can get a descent sound very reminisent of my favorites GN'R tunes. It is for using  with an Emery Sound Superbaby amp running with 12AX7/EL34, a Gibson Les Paul and a few effect including a compressor. My amp is wonderfull on itself but it is more in a vintage vibe than in modern sound if you see what I mean. So the distorsion pedal is intended to shape a bit the distorsion and let the amp with its  EL34 to add the final touch

So I started by building the ROG Thor because it was the closest thing to the targeted amp sound that I found on the web. I thought it was a good starting point. And it works at the first time Thanks for the guys at ROG because it sound really great, much more than what I expected indeed ! (By the way, if it works at the first time, it is surely thanks to a tip I found in the forum FAQ : using an audio probe to check each stages as I built them)

Now I would like to go a bit closer to the 2555 sound by tweaking the thor design. I look more in depth at the schematics of ROG thor, thunderchief and the amp they are inspired of. Also look at the 2555 schematics. I've got basic knowledge in electronics so I am not an expert...so i would very appreciate a few advices

So I started by adding some clipping diodes/LED in the cicuit    (see links to schematics below) and it brings a bit more "grind" in the sound.  Good ! I tried them first between first and second stage but the signal was to low here to produce an audible effect. So I put them after the second stage. Is it good like this ? Could it be done even better ?

Then I wanted to add the tonestack of the 2555 but it does not work as good as expected (but it works) : a relative loss of signal, which is normal when adding passive filter but the resulting sound is not better : I prefer it without the tonestack indeed but I need the tonestack to shape the sound as my amp has only a basic tonestack which I don't use as I can bypass it)  I was wandering if the bad results were not due to the different  coupling caps between the different stages... so I try to replace them (the caps in orange im my draft schematic) with values as used in the 2555 but it sounds much too trebbly after that change in my opinion  I try also to add an extra stage to boost the signal before of after the tonestack but it does not sounds good (more distorsion which I do not need and the EQ is not working better) Maybe I was wrong or made an error  when adding such an extra stage) .It seems to me that the opamp in the last stage is used as an active filter and maybe as a third distorsion stage at the same time Could it interfer badly with the tonestack ? I don't know the theory around this circuit to tweak the values here on my own.... Any website link where it is explaned ? What would you suggest to make the tonestack work and sound properly ?

Any other ideas/advices/mods to suggest to get closer to the expected sound with this distorsion stompbox? (it's easy for me test changes as the prototype pedal is currently built on a breadboard)

Links to schematics :

• the prototype schematics with current mods : http://aronnelson.com/gallery/v/darkness_fx/Thor2555.gif.html
• the Thor schematics as the base of the project : http://www.runoffgroove.com/thor.html
• inspiration for the mods : http://www.blueguitar.org/new/schem/marshall/2550redraw.gif

Thanks ! 

[Darkness, Darkness]

Hello,

Times for a small update on my tone quest project :
- Thor is just sounding better without any changes so I build one that I gave to a friend.  He likes it a lot (thanks ROG guys !)
- Following, all the great threads on submini tubes, especially from Frequency Central and Renegadrian (and all the others that I can't name here !), I started to explore the Marshall amp design with submini tubes ... here are a few details on my experiments

For the moment my breadboard is setup with a Marshall 1959 preamp, with an extra gain stage mod (following readings on the mythology of the infamous #39 amps that Slash might have used during the AFD sessions...). Also change a couple of caps, especially cathode resistors bypass caps for higher values (more boost, boost all the frequencies). The results are really pretty cool. I first started with 12AX7...(quite good results with the Emery sound amps,  but awful results with other amps such as Vox). Then I moved on the submini tubes... Big improvement on the Emery Sound. I have not yet been able to check on other amps but it might be better (don't forget that a small increase of volume at the input of the emery sound really push it  into distorsion at its power tube stage... that's why I think it was working quite good with 12AX7... the circuit was probably just shaping the sound, increasing a bit the signal without really creating distorsion as any distorsion stompbox would do)  The current setup with subminis provides great sounds for solos, but a bit too much gain for rythm parts in my opinion... no big suprise with that 4th gain stage added.... well still some tweaking to perform  I'd like also to try some basic 2203 and 2250 designs too someday...

In order to play with the gain of each stage, I replaced all the cathode resistors with some pots. My circuit is running at 24V. Actually it is using a mix of 6111 and 12U7 tubes.... I have not tried to switch between both model to compare the sound... I just use what was available and more easy to fit in the breadboard. I don't put a schematic...just look a the Marshal l1959 schematic, and use the second stage as a model for the extra gain stage

Also a crazy try...  I put the phase inverter stage with a 6111 tube in the circuit.... I keep the exact components values from the 1959 amp... but as there is no output transformer... I just get directly the Output signal through a 47K resitor for the feedback.... I get the ouptput signal from the joint of the two .22 coupling caps (I did not put the 220K resistors because it killed the volume) Also change the presence control cap with a .68 value. Great  sound in the end (with a bit volume boost) A the distorsion is already high with the 4 gain stage, I can't tell if the phase inverter brings a bit more of distorsion to the signal... but I think it does. Very nice the presence control with a nice cut in the mids.

I'd like to get your opinions on the phase inverter thing : is it Ok to have the feedback loop as I done it ? Any improvement suggested ?

Next steps :
- fine tune gain stage / tone shaping
- change the HP on my amps : Weber 12F150B (BF tone with greenback punch) -> Weber Greenback replica....That will help me to get closer to the tone I am looking for....
- improve the PI ? Other improvements ?
- study how to put all that stuff in a stompbox  especially the LM317 part of the circuit which is running hot getting 12,6V/0,6A from the 24 V (actually, I use a PC fan to help it cool...). What kind/rating of power dissipation device are you using ? 


Here it is....you know all the story now If some of you are as crazy as me to have some tries, I am very interested in your results !    Otherwhise, if you just have some ideas of improvements, remarks, questions, ...

Picture of the (messy) breadboard http://www.box.net/static/flash/box_explorer.swf?widgetHash=702ktu5g1y&cl=0

Thanks to all of you that contribute to make this forum a great source of ideas, informations and fun !