Appreciat Diagnostic Help for Old Roland Orange Cube-60 Guitar Amp

[mikelazich]

Appreciate Any Advice on my amp's problem.

I just picked this amp up used. It's a vintage early 80's Roland Orange Vinyl covered Cube-60 amp with an Overdrive & Normal Channel (normal has pull-bright knob for that channel). This is not a later Cube-60 amp COSM effects, etc. It's the first offering apparently from Roland.

Ok, the problems:

1. Either plugged into the Normal channel or Overdrive channel, the amp's volume fades in and out.

2. Plugged into the Normal channel the volume fades in and out, plus the amp distorts, sounding horrible, but then once in a awhile the amp's Real True Sound fades back in at a louder volume with a Nice Clean Sound as it should be, then it fades out after awhile. Most of the time, it's mushy lower volume distortion on the Normal channel, but again (without touching any controls), the amp fades back to a higher volume and I get the proper sound that the amp should yield all the time.

I appreciate any ideas.

I rotated the knobs a whole bunch to clean the "pots" (if dirty pots were the problem), but that made no difference.

I found the schematic, but was not able to find a service manual or owner's manual. If anybody has either of these manuals to post, that would be appreciated as well. The Roland site does not have Cube amp files this old on their site.

thank you

[Amp Kat]

Plug a cord from the send to return jacks and see if it stops fluctuating.

[mikelazich]

Tried Advice It Did Not Work

1st Thank you for the advice, it's appreciated, but unfortunately it made no difference.

I plugged a 1/4 inch plug jumper cord from the "pre-amp out" to the "main in", which are the closest, I believe, to the effects out/in plugs you refer to (I assume Roland used different names for these).

Okay, the amp on Normal channel sounds muddy and dirty. Sort of like there's an poor sounding "overdrive" shifted on, but there is not. This is the clean/Normal channel. As I said, once in awhile the amp gets louder (without touching any controls) and has the "clean" mellow guitar sound one would normally expect, but then it goes back to horrible sound which makes any guitar sound like crap. I tried humbucking and single-coil, but the result is still the same. I used a Les Paul Standard and a Fender Stratocaster (both with various pickups selected).

[Amp Kat]

What does the preamp out to another amp sound like ? And try another amps preamp out or send (not speaker ) to the return .

[mikelazich]

Early Roland Orang Cube 60 Amp

Once again, thank you very much for the "common sense" approach to diagnose what section of the Roland Cube 60 has the problem. That's the first step. I never thought of that :-) Hey, some of us are more equal than others ;-)

The short answer is the power amplifier section is causing the mild distortion, muddy sound and fading in and out.

To review, I followed your directions.

1. Plugged the Roland's "pre-amp out" into "the effects in" of another amp. I tried plugging a guitar into both the "normal" and "overdrive" guitar input jacks of the Roland. The sound was clean and what one would expect for the "Normal" input channel and "overdriven" for the drive channel as one would normally expect of this little Cube 60 amp. Both channels worked as they should through the pre-amp section of the Roland.

I did notice on the "normal" channel, when I pulled the volume knob up to get the "bright" setting, that the bright did not make a real difference as if you clicked on the "bright" switch of an old Fender Pro Reverb for example. Still, there was some difference, although small. I don't know if that is a problem or just Roland's design 30 years ago.

2. Plugged the other amp's "effects out" into the "main amp input" plug of the Cube 60. The sound was muddy, mildly distorted and faded in and out.

3. Plugged a known good extension speaker bottom into the Cube 60's "Extension Speaker Output". Proper Ohms rating was observed by me. The Roland is now running by itself with a guitar plugged into it. I got the same muddy, etc. sound through the extension speaker as I was getting through the Roland's internal speaker. This would lead me to believe that the Roland's internal speaker is Okay, since a known good external speaker bottom has the same muddy, etc. sound.

**Now that we've gotten that far, can you (or anyone) suggest what components in the power amp section may be causing the problem and need to be replaced/repaired?

**Is the "bright" on the "Normal" channel supposed to anemic with these early Cube 60's? If they are not, any suggestions as to components to address in the pre-amp section?

I do have a wiring schematic that I got off the internet which seems to match this early Orange Color 60 Cube with no COSM effects. It's has just "Overdrive" and "Normal" inputs and nothing more like later Cubes in the Roland series with COSM, etc.

Thank you.

[Amp Kat]

I really can't say without the amp right there in front of me and without a scope and signal generator. With everything working right it's hard to say but an amp that old I would have to suspect maybe the 2200uf 50 filter caps may be discharging and the output can't replenish them fast enough. The transistors wouldn't make sense because they either work are they don't . Pots could still be subject even if they seem to act right. I would check you're rail DC voltage from ground to the output transistors Q12 & Q13 and make sure you get +/- 44 volts steady at the collectors and emmitter and check the -48 vdc at the power supply. Could be a faulty cap or even a severely out of tolerance resistor so use the schematic to check them.

The Free Information Society - Roland Cube 60 Electronic Circuit Schematic

[52 Bill]

Have you tried cleaning the headphone jack?

[mikelazich]

Roland Cube 60 Early Orange Vinyl Version

Thank you for the suggestion. Cleaning the headphone jack did not make any differnce.

[mikelazich]

Roland Cube 60

Hello Amp Kat.

Thanks once again for sharing your expertise. It's appreciated.

Also, thanks for the additional info and the link to the proper schematic for the old Cube 60.

I have enlisted a friend who is far more adept at electronics repair than me, but not knowledgeable about guitar amps and the like. I must wait until he has a chance to stop by due to his crazy work schedule.

When, he does, the expert information you provided will help I'm sure in his possible diagnosis of what is wrong with the power amp stage of this amp causing "muddy" mildly distorted sound.

If you (or anyone else in the forum) has any other ideas or specs to share to check for my friend who'll help me, please let know.

If I don't hear more from you or anyone, I'll post as to what we've found, so others may benefit.

Thank you.

[Fragger]

You have a friend coming over, do the old ginger amp a favor and get a can of DeoxIT D5 to clean every pot., switch and jack while you have the amp seperated.

No need to make a mess, have a q-tip handy to wipe up or spread cleaner on a patch cord end and insert.

I`m betting DeoxITing will do it `cause that`s what it took on my Peavey KB300 with similar symtoms.

[J M Fahey]

*Both* the internal speaker and the external speaker jack receive audio through the leaf switches built into the headphone jack, so it is a prime suspect in this case.
Deoxit as suggested, but I would get a new one, just in case.
Anyway deoxit everything else as suggested.

[mikelazich]

Thank you for your suggestion. We'll do that too.

[mikelazich]

Cube 60 Headphone Jack

Thank you for your input. I didn't understand the significance of the headphone jack. My friend and I will check that out, clean it and/or replace it if need be.

Just an aside, when I run the "pre-amp" out of the Roland Cube to another amp; it works as it should. When I run the "pre-amp" out of another amp into the "main amp in" of the Roland Cube, I get the muddy distortion, etc., although the other amp used is perfectly "clean" when I let the signal go thru its amp stage.

[Amp Kat]

If the jacks turn out to be ok and since we know the problem is from the power amp in (main in) to the speakers then have you're friend test everything from that point to the speaker. There are 3 diodes I belive D1,2 & 3- so make sure they are good. It is possible the transistors are weak so doing diode checks on them is a good idea. Also look around the 2200uf filter cap power supply caps for white powder looking stuff or any bulging on the top of any electrolytic caps period for that matter as an indication of failure. IMHO if it were mine with an amp that old I'd do a total E-cap job on it just to make it sound 10 fold better. I mean sooner or later they are going to fail and the life expectancy on an E-cap is 15 years and you've exceeded that a long time ago.

[mikelazich]

Roland Cube Amp Specs & Components to Check in Amp Stage

Thank you most kindly for the additional information. It's appreciated.

Talking to my friend on the phone, he suspects this amp may require a good effort as the problem is not "dead" versus "alive" as the amp runs. It's easier to fix something sometimes when it's totally dead, I guess.