Modifying/Changing a Roland JC 120 Distortion

[Monkeyboy]

Newbe here,

I would like to change the distortion on my JC 120.

What I what I would like to do is to replace the circuitry of the integral distortion with that from a BOSS Blues Driver that I have and for the distortion controls on the amp to operate the effect as though the Driver were the distortion as installed by Roland - all else the same.

Has anyone done this? What is involved? Would I be able to get the same sound as the Blues Driver by just modifying the current distortion???

[phatt]

For blues JC120 is the one amp you would never want to use.

If the blues driver improves the sound somewhat then just keep the blues driver and loose the JC120 and get a better Amp.

I'm sorry if that insults some user of JC 120 but IMHO of 40 years experience with many amplifiers of varying quality,,,, JC distortion is one of the worst I've ever used.

Yes what you ask is ,,possible but cheaper to get a decent amp.

Cheers, Phil.

[teemuk]

Why not just use a pedal?

That's the easiest solution to ratty distortion of JC's.

Don't like external boxes? Cut the traces leading in and out of the distortion and replace the circuit section with a board of a good-sounding distortion. You can rob the power for the board from the amp's supply. Fitting potentiometers to control the new circuit will require some thought, though.

--

Improving the distortion of these amps is a very commonly asked question. If there was a simple and doable solution we would have heard it already several years ago. There's no magic component you can change to make it sound good. It pretty much requires a total rebuild and a different architecture. I'm pretty sure people have been pondering with the issue ever since these amps came up.

Oh, one difficulty is also that there are several different versions of the JC-120 circuit. Not all of them are even similar. That also applies to the distortion circuit.

Personally, I wouldn't pick JC-120 for any other purpose but clean tones. Even in those cases it has very good challengers from the stereo chorus amps of Ampeg and Crate - which also have a magnificient distortion channel, if you playe extreme metal that is.

[Enzo]

ANything is possible, but really.  WHy not just set the amp on clean and use the pedal?

[Monkeyboy]

Thanks for the insight. I appreciate any help. Reconnecting the leads seems a bit simplified. But as far as some "food for thought" for me. Would you guys make some recommendations as to where to start?

[J M Fahey]

Both essentially the same topics have been merged into one, to avoid clutter.
All questions and answers are here, ordered by time.

[phatt]

Hi monkeyboy,
                   I know *Teemu* means well and with his incredable insight I have no doubt that if HE lived next door to me I would be brave enough to take on such a project.

*IF* that is not the case and you are starting out with little knowledge of electronic circuits then ,,,some things you might wish to consider???

The amp in *Un-altered Original Condition* will fetch considerably more money than many other SS Amplifiers that are technically better SS Amps for blues. (as Teemu mentioned)

I believe JC's are in the hall of fame of the most famous Amplifiers,,even though they are all SS.

Mess with it and make it useless means you have blown the value of a resonable investment.
IMHO,,, get another amplifier and go crazy with that one instead. :tu:

If that money value does not bother you then go crazy and to hell with original.
Phil.

[teemuk]

I agree with Phatt: Don't mess with it.

The pedal is the easiest solution. I think many of those amps could even faciliate the use of external preamp (with the cost of losing the stereo revered chorus effect though). Can't get that to work? Sell the thing with good profit and buy something different. There are plenty of stereo chorus amps out there that are almost comparable - except that they have better distortion tones too.

That chorus effect and the very clean tone are the sole reasons why that amp is so legendary - not to mention that it's a legendary amp (sounds funny but it's truly also an aspect in creating that status). Truthfully though, in my opinion, time has run past that design.

If that amp would have made it's debut today people would likely wonder why Roland releases such a thing when they already have those great Cube amps with DFX and the Blues Cube amps. It was grounbreaking in it's day but evaluated by today's standrds not as much so.

If those two features (clean + stereo chorus) are not fitting you then honestly you'd be way better off with another amp. I wouldn't even consider having the JC-120 as my stand alone amp because there are way more things that I look for in an amp than a clean tone and a chorus feature. I don't think I'd even need the latter as much to justify the purchase of JC-120 because it's rather expensive and sort of a one-trick pony.

[Destroid]

What does the "Distortion" sound like on the JC120s? I'm curious now.

[phatt]

Just find one of those horrible fuzzboxes from a bygone era where you can only play one note at a time,, only just passable as a musical note.
THEN try and play a full bar chord and the result has no correlation to any harmonic at all.
Off course these days that maywell be appealing to some music lovers  :lmao:
Phil.

[Monkeyboy]

Thank you for the advice gentlemen, MUCH apprectiated! I really like this site because I am just learning this electronics thing and really enjoy it.

But, I guess I'll stick to modding pedals ... for now. I play Jazz guitar but do Blues to be able to play with other musicians in the area since where I live it appears there is only Blues and Rock. LOL!

The clean channel is why I purchased the amp (it was a steal at $300 US! Sitting unused, like new, in a funeral parlor for the past 15 or so years) but wanted to modify it so that I would be able to play the two genres without messing with pedals.

Maybe I'll try to build an amp how I like it. I know how about an overdrive/distortion pedal with tubes ... hmm. Any ideas.

P.S. Destroid, like Phatt said. It's fuzzy and REALLY muddies up the sound. Not usefull at all for other than one note leads (aka whimpy/weak guitar playing) and mucks up chords.

[J M Fahey]

Marshall's Blues somewhat pedal *is* good, many find it emulates quite well an old JTM45 combo (think Clapton/Bluesbreakers).
I think GGG or DIY Stompboxes has a layout/PCB for it, piece of cake.