ROLAND BOLT 30- 60 cycle hum...

[oc disorder]

52 Bill Are you sure? I agree with the ungrounded pot cases adding buzz, but he sez the buzzing is worse. That's why I think it would be helpful to get a very clear description of the noise. Is it hum or buzz

And 52 Bill I'm beginning to wonder if the cabinet had internal shielding , foil or conductive paint?
It seems there are a few posts regarding noise in this series around the web.

czech-one-2 post #8

Originally Posted by oc disorder
"Actually it's probably more likely it has a few cracked solder joints particularly an amp of it's age .
Check around the switch and pots and any large loose objects !!
Could even have a hairline crack on the pre-amp board or a loose ground somewhere."

Ok, I inspected and re-flowed the pots, all terminals and a few suspicious areas. Still buzzing.
The 'main in' is utterly silent from buzz. The buzz has nothing to do with volume/gain/eq tweeks.
The buzz is the same with the volume at zero or 10.
I tried the 'chopstick' method on all the wires to see if any movment changed the buzz, nope...

czech-one-2 Could you tell us where the main grounds are ? Couple of gut shots here may help.
I notice a ground is on one of the front jacks perhaps if you undo them and scratch around a bit on the inside of the chassis then put it back tightly.
Hopefully it's got a star washer.

I'm certainly scratching around here

And where does the ground from terminal 11 on the power board go. That's the ground for the 48v supply B1.

[52 Bill]

Nice recap. My suggestions are only to help determine the cause. Czech-one-2 described the noise as 60 cycle hum. Perhaps he can post a recording of the sound/symptom to give you a better clue.

[czech-one-2]

Hope you guys havn't given up on me [and my buzz] ...

[oc disorder]

Hope you guys havn't given up on me [and my buzz] ...

I thought you had enough!! ? Well the end is nigh well nearly...


Can we pick it up again from my post #2
where the Fet input is grounded and a few power supply dropping resistors are to be temp removed?

Attaching schematic of what the amp resembles at the moment and some highlighted ground points
which need investigating

[czech-one-2]

Good to see you OC, I thought I had over-stayed my welcome!
I'll crack it open tomorrow and continue my quest for silence [ with your assitance of course I'm hoping! ]

[oc disorder]

Good to see you OC, I thought I had over-stayed my welcome!
I crack it open tomorrow and continue my quest for silence [ with your assitance of course I'm hoping! ]

Hopefully there's enough info there after "Ok seems to be heading back to the power supply ... we have 1 fet preamp !" (which comes up as post #69 in one of my browsers !) to keep you going for another 3/4 of an hour !
Once we work out that there's nothing weird happening around that fet its back to grounding issues.

[czech-one-2]

Oc, It looks like I've missed your last 5 posts as they didnt show up. I had to click on 'more posts below current depth' ? So I guess posts dont go to a page 3 here?
Anyway let me catch up on your post today!

[czech-one-2]

52 Bill, I listened to a youtube demo demonstrating 60/120 cycle hum and mine definately sounds like 60 cycle. When the preamp board is assembled with the pots and nuts attached to the chassis the buzz is still there and quite noticable. Touching the pot shafts when the pcb is secure to the chassis doesnt effect the hum.

[czech-one-2]

And 52 Bill I'm beginning to wonder if the cabinet had internal shielding , foil or conductive paint?
It seems there are a few posts regarding noise in this series around the web.

Actually, there was about a 3 inch square of shielding tape applied to the top of the cabinet. I went ahead and fully covered it with foil tape shortly after getting the amp to see if it would help. It did not...

[czech-one-2]

czech-one-2 Could you tell us where the main grounds are ? Couple of gut shots here may help.
I notice a ground is on one of the front jacks perhaps if you undo them and scratch around a bit on the inside of the chassis then put it back tightly.
Hopefully it's got a star washer.

I'm certainly scratching around here

And where does the ground from terminal 11 on the power board go. That's the ground for the 48v supply B1.

Terminal 11 on the power supply board has 3 wires
1] to terminal DC0.2A on the PT
2] to terminal # 11 on the preamp board
3] to TP #5 on the preamp board

Here's some gut shots of the grounds:

[DrGonz78]

Oc, It looks like I've missed your last 5 posts as they didnt show up. I had to click on 'more posts below current depth' ? So I guess posts dont go to a page 3 here?
Anyway let me catch up on your post today!

Up top on this thread you will see the word Display with a drop down arrow. Click it and set to read the thread in Linear Mode, makes it much easier to follow all the posts.

[czech-one-2]

Thank you DR. Now page three is visible!

[czech-one-2]

I notice a ground is on one of the front jacks perhaps if you undo them and scratch around a bit on the inside of the chassis then put it back tightly.
Hopefully it's got a star washer.

Ok, got the jacks with grounds contacting bare metal on the chassis with star washers. Still buzzing.

[czech-one-2]

Just before I hit the sack I presume the amp is properly grounded at the power inlet?
Check resistance from the chassis to the ground pin on the power plug.

.000 ohms

[czech-one-2]

Can we pick it up again from my post #2
where the Fet input is grounded and a few power supply dropping resistors are to be temp removed ?

Happily, but could you refresh my memory as to how to proceed as I dont see it in post #2.
And we already lifted the two resistors and grounded the fet right? Or do you want me to proceed further?