Hey, guitarists who know about the mysterious magic inside guitar amps..
I've got an old Cube 60 (the orange one) that's been collecting dust in an attic for a few years because it had a low-level distortion in the sound which I thought was the speaker needing replacement but I never got around to doing it - anyway, pulled it out this week for an upcoming jazz gig and it was fine!
...but wait, there's more.. after having it on for several hours the distortion came back - and it's worse.
It's definitely not a blown speaker because it was sounding fine a minute ago then it went all distorted - and then after a while of that, the sound came back like before and it was fine again..
So, the sound is like a squelchy, farty fizz that sucks the attack off all notes and buzzes as they sustain - it's also about two-thirds the volume from when it's normal..
(oh, I also know it's not the speaker cos I'm using the line out directly into my soundcard doing some recording)
Sounds electrical to me.. is it the caps?? Have I got to replace them?
Sorry for the elementary troubleshooting here, but, given that the amp has been "collecting dust" in an attic for a few years, here are a few things to try first:
1. Is the guitar cable known to be good? Is it working correctly with another amp? (check the cable you're using for line out too)
2. Is the input jack on the amp loose or oxidized? (trying plugging in and unplugging a few times then, while plugged in, move the plug (the one plugged into the input jack) a little to see if the jack has come loose or has a bad/weak solder joint.
3. Have you tried rotating all the pots fully clockwise, fully counter-clockwise a few times? Dirty pots can do crazy stuff.
4. Press all buttons a few times to dislodge any dust/dirt
If none of these resolve the fizzy, weakness, you'll likely need to take it to a tech.
My old orange Cube-60 isn't dependable either. I haven't used it on a gig in years. Right now, the reverb doesn't work. I would have had it serviced, but my tech moved to Florida, like everyone else.
If I were you, I'd use another amp, and get yours serviced.
Rolijen great list. I think (as pointed by rolijen) it is always best to start simple. I can not count the number of times something was not working right and it was because a cable was not plugged in. I was bought a used Blues Deluxe and took it home. It sounded great in the store (a local store in Cotati CA), but when I turned it on at home it sounded bad. (If I remember right, the high end had decreased). I called the store and they said bring it back in. I took it back to the store, plugged it back in and it sounded great again. The sales person (I think he name was Vinnie), he asked how old is your cable. All I knew was that the cable was old. He gave me the cable I used in the store and sent me home. Of course the amp was fine.
Sounds like the power resistors, those ceramic encased thingies, are fried. Generally, the amp powers on all right and when the damaged power resistors start heating up you get crackles and distortion.
Check to see if the pcb is charred around the power resistors.
Last edited by Jabberwocky; 07-22-2022 at 11:19 PM.
I suggest wiggling all the wires, including the ones to the reverb tank if there is one. Reverb tank wires are sometimes RCA jacks with little wings that can get folded too far in to make contact. Pressing them in all the way may not be enough. You might have to bend the little wings out with a needlenose plier, a 10 second job. I mention it because I had an Ampeg amp with vaguely similar symptoms and that's what it turned out to be. And, it's free and easy to check.
Don't get electrocuted.
Then, I'd think about heat. Maybe open it up, blow air on it with a fan and see if the problem goes away. Long shot, but not impossible.
The electronics aren't all that likely to burn out in my non-professional opinion. But, stuff that can vibrate loose eventually does. Wiggling things, pressing on things will sometimes reveal a problem.
My JC55 had similar issues. It was because the pots are soldered into the circuit board. That permits mechanical stress on the solder joints and they can crack and work intermittently. Flexing the faceplate reproduced the problem. Twice, I've had to open up the amp and reheat the solder joints. I never figured out which one was bad, but doing all of them, which took just a couple of minutes, worked. You have to figure out how to expose that side of the board and there's a risk for messing something up, so it might be a job for a tech.
The simplest thing to try first with old amps is to clean all the pots and contacts. Try a can of DeOxit D5. After turning off the amp you can spray DeOxit liberally into the jacks, then plug and unplug it several times. You can also spray the plug itself. Then spray it into the pots. It’s better if you can get inside the amp, but it’ll probably help either way. Spray the pot contacts and work the pot back and forth several times.
I’ve revived some pretty noisy old amps this way. If it doesn’t help it certainly won’t hurt, but I think there’s a good chance it’ll solve your problem. And a can of this stuff is handy to have around. It’s not cheap, but it’ll last a long time. Its also great for old funky guitar pots, jacks and switches. Good luck.
p.s., I make it a habit to keep some sort of cover over amps when not in use. And never store them where there’s excessive dust or extreme temperatures. That’s just asking for headaches.
Last edited by Jonathan0996; 07-23-2022 at 01:08 PM.
Besides all the stuff rolijen suggested, also plug a jack in and out everywhere a few times (including effects loop if the amp has one). I even had a solid state amp that did similar things and it turned out to be the power cable not making good connection.
But still, if it's an old amp and you're gigging with it, I would have it checked by a good pro. Or replace it even if it's unreliable.
The strange distortion doesn't occur until the amp's been on for a while (i.e. heat)
aside from that, the only thing that's not 'working' on the amp is the "pull-out volume knob for extra treble" so maybe that's what the burned-out cap was for..?
does anyone know if/where I could get a schematic for this amp - it looks like a dead easy fix if I can find out what 'value' that cap was.
sorry it's not very easy to see it - had trouble getting my phone to focus up that close - anyway, the side of this component (I think it's a cap - not sure!) has 'popped' off, looks charred..
thought I'd let you know that I went inside mine yesterday and the reverb is sooo simple that if it's not working it's almost certainly just a connection that's broken.
It's just a physical spring with 2 wires going from it into 2 kind of RCA jacks on the main board.
It might be a dead easy fix..
The amp is not hard to access either - it was like 4 screws..
You not only will get the schematics but the service manual.
You’re off to a good start in troubleshooting 101.
Google is your friend.
(At least they say so, and we can trust them, right? I mean, they have our best interests at heart. They must, they’ve learned every darn thing about me. )
thought I'd let you know that I went inside mine yesterday and the reverb is sooo simple that if it's not working it's almost certainly just a connection that's broken.
It's just a physical spring with 2 wires going from it into 2 kind of RCA jacks on the main board.
It might be a dead easy fix..
The amp is not hard to access either - it was like 4 screws..
Thanks for the suggestion, but was yours made in the US or Japan?
Mine was made in Japan, and I've counted over 20 screws on the top and back that have to be taken off to get into the top and/or back of that thing.
What might seem easy for an electronics genius like you, would be like attempting a brain transplant for an electronics pinhead like me.
I used to have a guy who now works for Bell Labs repair that amp for me. The head of it would detach itself from the base of the amp, and he'd have to glue it back together for a whopping $30!
When he got the Bell Labs gig, I had to use my friend's son, who had a repair shop of his own. Finally, the digital technology got too much for him to take, and he joined his daddy in Florida.
He claimed that there was no way human beings invented all this digital technology, and he knew for a fact that it was all recovered from a crashed flying saucer in Roswell! That's when I knew I had had a top class tech working on my gear.
However he did have a Cube-60 schematic, and was proficient on the Cube, and my SF Twin, which he did an an expert makeover on, if anyone is interested in buying it. Of course you'd have to come over here and get it. I'm not going to ship a monster like this!
Most of those websites that promise free downloads of manuals and schematics should be avoided. I would only download from sites that are obviously run by hobbyists and enthusiasts.
Actually, the entire 4 bars could be played in the first position if you use open strings but it may sound country especially if you're playing a Tele. :pig:
Unfortunately I can't notate open strings with the Chord Writer app I have, but the top strings are open, so all the chords I posted, except for two, contain the 5th of the chord: the open G string....
The OP's question is voicings of #11's with the 5th. I gave one example.
There are others but the chord charts you posted seem to omit the 5th. Also I don't see any open strings in the charts.
And there are many C Lydian voicings with open strings - more than any other chord if you count Am7 & Em7 voicings.
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