JCM 800 Emulator pedal build

[paulyy]

I thought I give this a try but cant seem to dig up allot of info on it. I'm using this layout.

Iv found some videos on youtube but cant seem to find much on this pedal at all. It seems It would be a fun project to do and hopfully I can get it to work. If any body has any info or tips about this layout. That would be great. Thanks.

[petemoore]

  Looks like it could be a JCM schematic re-drawn for Jfets.
  Trimmers to bias the Fet's, otherwise the same values as the preamp ?
  That simple [if it compares to amp schem].
  Or...see Fetzer Valve and other reads for a deeper look into Jfet/Tube conversions.
  Whether Simple or Deep, 'it' should be able to be made to work, if 'Deep' is chosen, some study and design modifications might be good before starting to populate.
  Not being particularly familiar with JCM, but suspecting that much of "JCM sound" is constituted to a large degree by a volume control being turned CW to a point where speaker/output tubes contribute to the distortion.
  I read ''they use diodes in JCM'' [to contribute to getting the distortion]...about JCM's, but didn't investigate it.
  It looks to be a 'boost the source to the next Jfet input' distortion, a number of Jfets boosting signal [similar to the way tubes prepare signal for an output amplifier stage]. The source signal peaks boosted can reach a 9volt supply very quickly [compared to 100+V, whatever the triode tube stages use]...essentially making this a very different circuit than a tube-preamp.
 

[Bucksears]

That's my layout.
Like a lot of my earlier PCB designs, I put the ground rail all the way around the circuit. I have modified some of mine now to a 'U' shape, leaving the 9V rail across the top.
This SHOULD cut down on some noise.

If I have time while I'm off this week, I'll update them to this config. (mainly just involves moving that 100uF cap closer to one end of the 9V rail - like closer to the volume pot - and connect to the ground rail there).

Thanks,
Buck

[Bucksears]

This is actually Electrictabs' (a member here) JCM800 preamp emu design as a stompbox. He also designed the (now legendary) Dr. Boogey and the Boogeyman (Mark II emu).
Just givin' credit where it's due......

[Brymus]

If you like this one be sure to look at "The Meteor" circuit too.

[paulyy]

Well I have my pcb done. Just need to add the rest of the junk with it. Still need to get a encloser and few other thins and should be done. I'll post picks of the pcb later. I think it might be to big. Thanks for the info so far everyone.

[paulyy]

Heres the board all ready to go. I traced it out with a sharpi. Not pretty but it works.

[Brymus]

For just using a sharpie that looks fantastic,heck it looks good for any type of a transfer IMO
Nice job.
Post a sound clip when your done.

[Ibanezfoo]

I made one of those a few months ago... it was ok... didn't really sound like a JCM800 to my ears... mine sounded kind of woofy/farty.

[rousejeremy]

I've seen that layout before, always wanted to hear it before trying to build it.
Any sound samples?

[paulyy]

No sound clips yet. Still waiting on an encloser and some other things in the mail. I heard a few on youtube that sounded ok. Not great videos but sounded like it has potential. Hoping it sounds just as good as my Dr. Boogie

For just using a sharpie that looks fantastic,heck it looks good for any type of a transfer IMO
Nice job.
Post a sound clip when your done.

Thanks. It seems this is the only way I can make my own boards. Iv tryed the pess n peel but it doesnt work for me. I think It might be my printer. Its a inkjet. I think I need a laser printer.

[ghostsauce]

Well, this really interested me so I scouted YouTube for them and I could only find 2.. The first one sounds better IMO but still sounds thin and a somewhat harsh, but maybe that's just his settings. I'd love to hear a real demo of the pedal to see what it can do.

http://www.youtube.com/watch?v=2Z_g5DMVK-E
http://www.youtube.com/watch?v=ZOyuhPC-A5Y

[audioguy]

I've built this guy... its got a good solid tone, but does have a LOT of treble on hand.
I've noticed that the 2.2n going to the volume pot is crucial to good tone. To my ears a poly cap sounds much warmer and not as shrill as a multi-layer ceramic.  I've used the 2 different types with totally different results- with all else being the same. I don't understand the 'why' I just understand the end result. 

[rousejeremy]

Well, this really interested me so I scouted YouTube for them and I could only find 2.. The first one sounds better IMO but still sounds thin and a somewhat harsh, but maybe that's just his settings. I'd love to hear a real demo of the pedal to see what it can do.

http://www.youtube.com/watch?v=2Z_g5DMVK-E
http://www.youtube.com/watch?v=ZOyuhPC-A5Y

I think the first video was a Lovepedal Purple Plexi.

[paulyy]

http://www.youtube.com/watch?v=c3XHlPyo3lg&feature=related
http://www.youtube.com/watch?v=s4TWXd8Jhug&feature=related
These were the ones I could find. I did see one of those videos but not the crazy train one. Still waiting on parts. Maybe Ill get them tomarrow. Looking forward to putting this together. Hoping it sounds better than the ones on youtube. I notice that some pedals sound differrent on youtube. Hoping this sounds really good.

[paulyy]

Got my parts in today. Might have something next week. We'll see.

[Ibanezfoo]

Well, this really interested me so I scouted YouTube for them and I could only find 2.. The first one sounds better IMO but still sounds thin and a somewhat harsh, but maybe that's just his settings. I'd love to hear a real demo of the pedal to see what it can do.

http://www.youtube.com/watch?v=2Z_g5DMVK-E
http://www.youtube.com/watch?v=ZOyuhPC-A5Y

Mine didn't have nearly that much gain...

[paulyy]

OK! I got it up and some what running. From what I can tell It has really nice tone to it and good amount of gain. Not as much as the Dr. Boogie but good enough. The tone seems bright but can be tamed with out being ice picky. The problem I'm having is setting the trim pots for the Master Volume and Main Volume. Its kind of a pain in the a##. The other three trim pots were easy. No different than the Dr. Boogie. It seems depending on how you set the trim pots for the volumes. The Volume pots will cut out. Almost as if the volume pot are setting the biase as well. Odd. I'll post pics soon. For now I'm going to see if I can fix this little problem. Got get some sleep.

[paulyy]

Here it is. all wired up.

I think Im going to let this one go. Im not having much luck with it so no sound clips. But maybe I'll come back and see if I can do anything with it some other time. I tryed

[Brymus]

Ah hey dont give up !
Have you measured the trimmers in question to make sure they didnt get messed during soldering ?
No solder bridges ? bad caps ?
Trace the circuit and see if the volume pots are indeed hooked up in a way that would effect the transistors bias.
Wht are your voltages ? and are you getting any DC on the pots ?

FWIW that looks like a nice job build wise,I hate to see that effort go to waste
But I know what you mean sometimes a few days or couple of weeks break from a project makes it better coming back fresh.