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Cloning Bogner Modified JCM800 used on Alice and Chains' "Facelift" Effects Pedals, Units & Accessories
Old 11th February 2012
  #1
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Cloning Bogner Modified JCM800 used on Alice and Chains' "Facelift"

I have been given the opportunity to attempt to replicate the modification done by Bogner to a marshall JCM-800, this is THE amp that was used on Alice in Chains' facelift. I have access to the modded amp, as well as an unmodified JCM800 of exactly the same specs. I've never reverse engineered a circuit before, so I'm not sure where to start.

The mod basically involved cutting the preamp section of the JCM800 off of the main board, and replacing it with a new board. The new preamp board was soldered up mad-scientist style with only some of the screen-printed components installed and with some jumpers as well, components are installed on both sides

So my question is, what is the best technique for reverse engineering a circuit board? Especially one like this...

Here's some pics.
Attached Thumbnails
Cloning Bogner Modified JCM800 used on Alice and Chains' "Facelift"-p1030110.jpg   Cloning Bogner Modified JCM800 used on Alice and Chains' "Facelift"-p1030126b.jpg   Cloning Bogner Modified JCM800 used on Alice and Chains' "Facelift"-p1030124b.jpg  
Old 11th February 2012
  #2
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Draw a schematic! It will take time and patience but you will have a better understanding of the circuit.
Old 11th February 2012
  #3
Are you forming an Alice in Chains tribute band?
Old 11th February 2012
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Quote:
Originally Posted by Jim Williams View Post
Are you forming an Alice in Chains tribute band?
yes, and everything has to be PERFECT, I'm even getting a FACELIFT heh

Actually the thing just sounds bad f*cking ass, my buddy who owns the stock JCM800 "needs that TONE". Any recommendations for places/books to learn about tube amp circuits?
Old 12th February 2012
  #5
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the sound you seek is not nessarily the circuit, but the parts used as the differences of the parts plays a whole of the design in tone. and no, there isn't any schematics for this board cause it was a one off. do you have the other mod installed? (master volume actually is a bias voltage control). If you have possesion of that amp, look at the values and type of componates used down the line and you'll notice parts that are not on the marshall schematics and some values were changed.


ok, back to doing my "mad scientist" work of my own.
Old 12th February 2012
  #6
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Quote:
Originally Posted by a zombie View Post
Any recommendations for places/books to learn about tube amp circuits?
Look here: tubebooks.org - Vintage info from the age of vacuum tubes under Technical Books and also Tube Data. Download "Basic Audio" by Norman Crowhurst to begin with. Eventually you will want the Radiotron Designer's Handbook, 4th Ed. and RCA RC-30 Receiving Tube Manual.
Old 12th February 2012
  #7
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No advice to give. Just posting to follow the thread because it sounds like fun.
Old 12th February 2012
  #8
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Quote:
look at the values and type of componates used down the line and you'll notice parts that are not on the marshall schematics and some values were changed.
Yep there are definitely some little changes here and there, I will get to those eventually.

The only actual technique I have found is to photograph the board on both sides, as little lens distortion as possible and with even lighting. Then you draw all the traces in with photoshop. From there I guess you construct a schematic. One question I have about this technique, relating to this project, is; since he only used a small portion of the PCB, do I need to include the unused pads on my repro to get the same sound? (seems ridiculous to me, just throwing that out there)

Maybe I could save money by building it on terminal board, since it could probably be about the same size.

Once I do make the schematic, I will post it here for validation, just to be sure that it makes sense. In the mean time I will check out some books that give me an Idea of basic tube amp layouts.

Ok last question, does anyone know the style of circuit that this amp likely uses, could someone post a schematic that would likely be similar?
Old 12th February 2012
  #9
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Am I gonna need a scope for this project?
Old 16th February 2012
  #10
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what do you guys think about doing the build on turret board instead of pcb?
Old 16th February 2012
  #11
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Should be fine as long as you have somewhere to mount the tube sockets. Keep all your leads as short as possible.
Old 29th February 2012
  #12
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Quote:
Originally Posted by sam adams View Post
Just posting to follow the thread because it sounds like fun.
+1.
Old 29th February 2012
  #13
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Quote:
Originally Posted by a zombie View Post
yes, and everything has to be PERFECT, I'm even getting a FACELIFT heh

Actually the thing just sounds bad f*cking ass, my buddy who owns the stock JCM800 "needs that TONE". Any recommendations for places/books to learn about tube amp circuits?
can you make a YouTube video or soundcloud, to hear the differences?
https://www.gearslutz.com/board/gear-...s-audio-tests/
Old 29th February 2012
  #14
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Sure, still haven't done the mod. But I will post sound clips when I'm done.
Old 29th February 2012
  #15
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"...what do you guys think about doing the build on turret board instead of pcb? ..."

according to the top end mic pre designers, any two of them could be given the same circuit and same parts and the end result would sound different because of how they laid out the board and the physical proximity of the parts to each other, lengths of the traces etc. Take it for what it is worth, but according to them, any change that you make from what you see in front of you could change the end result.
Old 29th February 2012
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I would study the crap out of that thing, draw up a schematic, study it some more, and if you're brave go for it. But likely you'll end up very frustrated w/a broken jcm-800.
Old 29th February 2012
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Quote:
Originally Posted by dysenterygary View Post
I would study the crap out of that thing, draw up a schematic, study it some more, and if you're brave go for it. But likely you'll end up very frustrated w/a broken jcm-800.
I'm with you on the first sentence...

Once the schematic is checked and re-checked (x10) I don't see why I won't be able to lay it out on turret board successfully.
Old 1st March 2012
  #18
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Quote:
Originally Posted by a zombie View Post
Sure, still haven't done the mod. But I will post sound clips when I'm done.
No, i mean the original vs. the "original"mod vs. your mod.
Old 1st March 2012
  #19
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Ok, got it. It might be hard to get good samples of before and after. but I can find another JCM800 and do: My mod, Original Bogner Mod, and Stock JCM800.
Old 9th March 2012
  #20
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I would check out some more guitar amp-oriented forums for assistance on this. The Gear Page, Rig Talk, and Harmony Central Amps Forum (if you can cope with the massive amounts of OT crap on the third) would be likely resources- and probably really into the project as I remember Jerry Cantrell's tones getting lots of love on those places.

The former two especially have boutique builders all over them, and Rig Talk seems to specialize in high gain amps.
Old 10th March 2012
  #21
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Quote:
Originally Posted by Maschinenraum View Post
I would check out some more guitar amp-oriented forums for assistance on this. The Gear Page, Rig Talk, and Harmony Central Amps Forum (if you can cope with the massive amounts of OT crap on the third) would be likely resources- and probably really into the project as I remember Jerry Cantrell's tones getting lots of love on those places.

The former two especially have boutique builders all over them, and Rig Talk seems to specialize in high gain amps.
Cool thanks for the advice, I'll check that out.
Old 10th March 2012
  #22
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hi, you might try slocloneforums as well. Probably, there are a number of people interested in reverse engineering such an amp. (Note that you need to sign up to see the forums.)
Old 10th March 2012
  #23
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You don't actually need to learn anything much to copy something so simple, because there's nothing to it apart from drawing it out...easy... just pick somewhere to start(tube base?) identify the component, then draw where the connections go..and so on.. If I could draw out and build a big muff pedal, pre-internet, at age 13..I'm sure anyone can do it.
Old 27th March 2012
  #24
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I just found this thread. I'm new here. I'd love to see what that mod is. I've built some amps of turrets and eyelets and I'm about to start teaching myself about PCB design. I'd like to offer my help if you still need it. In any case I'd really like to see as many photos of the amp as possible. Hope I don't come across as rude. I'm just interested.
Old 30th March 2012
  #25
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Quote:
Originally Posted by JeruThe View Post
I just found this thread. I'm new here. I'd love to see what that mod is. I've built some amps of turrets and eyelets and I'm about to start teaching myself about PCB design. I'd like to offer my help if you still need it. In any case I'd really like to see as many photos of the amp as possible. Hope I don't come across as rude. I'm just interested.
Not at all, thanks for the response. I could message you some schematics once I do the tracing so you can help verify that it would work
Old 1st April 2012
  #26
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yeah man, that sounds cool to me.
I see your in Seattle, from Liverpool, over the water, i had my frist experience of seattle last september. such a nice city.

I can take a look when you're done for sure.

that board its on looks pretty big! i wonder if bogner made a bunch of generic boards with which to do all kinds of mods.
Old 1st April 2012
  #27
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Cool!

Yeah it seems like he must've, the board doesn't have any kind of information on it, just a bogner logo. From what I've heard the guy is pretty out there!
Old 23rd September 2014
  #28
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the mighty Snorkler© AIC tone....

Hello,my name is Ronnie S. Champagne...i was,along with Dave Jerden,the engineer on AIC Facelift...i am the the owner and creator of the Snorkler © amp used as Jerry's primary amp on that record.It is indeed a Bogner modified jcm800 that i bought as a stock combo amp in Canada in the early '80's.When i was recording Janes Addictions 'Ritual' record i got a call from Andy Brauer studio rentals giving me the heads up about Mr.Bogner's mods...i rented one for that record and subsequently had Rhienhold mod mine (after much begging and arm twisting,and cash)...i found the Snorkler© badge on an old fire extinguisher at Eldorado studios in Hollywood and as a joke put it on the head cab i made...it relates to the coke use in Seattle....ive modded it more myself and is now my trademark and copyright...i would love anyone who says they have access to it to get a hold of me...because its not true.it hasnt left my side for all the time ive had it...its my platinum secret weapon which i have used on a hundred records...it is my tone,my amp and yes there are guys out there so full of b.s. that it makes my head spin...theres even a guy making a snorkeler (notice the misspelling) amp that he said he made a mod from listening to facelift....imagine!!!!after all the e.q. and compression we used mixing and mastering that fine record,someone thinks they can do a mod that is the sound...thats just ******** if you know anything at all about audio...if anyone wants to dispute... my email is [email protected],me and my lawyer are always available....heres a link to photos... https://www.facebook.com/photo.php?f...type=3&theater
...if anyone tells you they have the goods...refer them to me please...and do not buy a fake!!!Have a nice day!
Old 23rd September 2014
  #29
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hi, thanks for sharing the story about the amp. I'd like to check out the pics but unfortunately the link doesn't work.
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