Tips on Modding this circuit (Roland Amp)

[Matteran]

For 25 dollars I bought this Roland Cube-40 (40 watts) 10 inch combo. That I think sounds incredible for the price. It's from the late '70s, so i haven't been able to find a schematic at all. I have been able to take a few pictures of a board, so i'll link to those.

I was wondering, how hard is it to add a 12ax7 tube to a circuit like this? The overdrive channel sounds really close to a tube amp, but i want to add some warmth, and the natural smooth compression of a tube (or multiple, i have a space where the spring reverb is, and since the reverb sucks, i'd basically get rid of it.). I'm thinking it wouldn't be too hard, just attach pins on the tube socket to specific parts on the circuit (finding out which parts, i have no idea, but that's why i'm posting this).

Secondly, If this circuit at all looks familier, or if someone's able to find a schematic, I'd like to make a stompbox version of the preamp. I really like how it sounds on bass (a nice gnarly fuzz), but i obviously don't want to use this amp as opposed to my 4x10 bass rig. Maybe there's a DIY distortion pedal that has a simliar circuit?

Anyway, here are the pictures. Sorry I couldn't get a better shot of the bottom of the circuitboard, but that thing was in there real tight.

http://img.photobucket.com/albums/v154/matteran/Roland/board5.jpg

http://img.photobucket.com/albums/v154/matteran/Roland/board4.jpg

http://img.photobucket.com/albums/v154/matteran/Roland/board3.jpg

http://img.photobucket.com/albums/v154/matteran/Roland/board.jpg

And here's a picture of the combo (may help with finding info on it online)

http://img.photobucket.com/albums/v154/matteran/Roland/cube10.jpg

http://img.photobucket.com/albums/v154/matteran/Roland/cube6.jpg

[Rob Strand]

I remember this schematic being on-line:
http://www.mif.pg.gda.pl/homepages/tom/schematics.htm


Modding to tube would require adding a high voltage supply, and a heater supply.  One alternative is to run the tubes at lower voltages.  Another alternative is to use a multiplier CKT to get the higher voltage of the existing supply.    While you might be able to get around the plate voltage issue it doesn't get away with the heater supply  problem.

[Matteran]

awesome website, thanks

http://www.mif.pg.gda.pl/homepages/tom/files/cube40.gif

[Matteran]

no one like puretube has anything to say about this one?

[puretube]

no one like puretube has anything to say about this one?

I`m not: "purecube", but when I look at that closer, you`re right:
maybe some moderator should decide wether linking to such sites
with legally questionable contents (IP) could hurt the existence of this forum...
:?:

[Matteran]

oh, is that site with all the schematics illegal? I guess it would be.

But seeing that i'm modding something i bought, what i'm trying to do isn't illegal.

Has anyone ever tried adding a tube to a solidstate amp?

[puretube]

Has anyone ever tried adding a tube to a solidstate amp?

Yes, R.G. knows a good way concerning s.th. similar with stompboxes:
http://www.geofex.com/FX_images/realtube.jpg

tip for beginners: start with a smaller 12AX7, before you try SE EL34...

[Regan]

That takes me back, my second amp was a cube 40- they are rock solid and very loud for the size. I had an instructor who had one of these and it fell off of a truck going down the road- he used it that night at band practice!
I would just use it like its intended. Mine sounded really good with pedals.
Regan

[Matteran]

yeah, i'm gonna have to buy a new speaker for it, because mine was thrashed by the previous owners. I was just thinking it would be cool to try something like this.

Any experience with Celestion G10 Vintage?

[Mark Hammer]

Instaling something INSIDE the existing circuit will be unnecessarily complex and problematic.  A far better strategy to pursue is to use the existing effects loop to patch in some sort of tube stage which you can then drive appropriately with the effects send.  That may even provide BETTER tone from the tube stage since you can use the Cube 40's controls to determine HOW you drive it.  I might remind you that the old Butler Tube Driver also used a solid state front end to make a tube behave nicer

The other advantage is that if you ever decide to sell you Cube 40, it will be intact and retain its value, rather than be buggered up with initial failed attempts to cram tubes in there.  Not to mention the fact that you get to keep your tube device for the *next* amp.

[JimRayden]

Yea, I think too that it's not the best idea to take a perfectly fit guitar amp and start rebuilding something in it (especially high voltage tube stuff) when you don't have much experience in electronics.

My recommendation is to build a tube pedal and use it either between guitar and amp or in the effects loop. That way, if you blow something up, it won't be the amp.  :roll:

A speaker change would be a cool idea though. I've heard many positive comments on Celestion Vintage series.

------------
Jimbo

[Matteran]

i can't believe in didn't think about putting something like that in the effects loop. Hmm... are there tube boosters or anything that will only add some tube characterisitics to the sound, without seriously distorting the sound?

[Mark Hammer]

Absolutely.  It's all in the way you set the gain.  In the case of the Cube 40, you are blessed with having the output level control *before* the effects send, which means you can feed a gentle signal to the tube-based unit for moderate coloration and restore the level to where it should be with the tube-device's output level control.

[toneman]

2 tube "units" come 2 mind..
the PAIA StackInABox(SIAB)....1 on ebay right now.
& the RealTube by TubeWorks.
Both use a single 12AX7.
Either could B used in the effects loop 4 that "puretube" sound.
staytubed(what else?)
tone

[Matteran]

what a DIY tube unit?

[Regan]

I'm going to commit blasphemy here, and thus be tarred and feathered and ran out of the community through a gauntlet of forumites wielding charged high voltage capacitors.
Try running a pod or vamp, something like that through it. Probably do a better job than either companies own amps and may be just the ticket for what you need. Also probably won't cost you more than a tube preamp.
Remember we are talking about a small amp with a 10" speaker.
Regan