Roland Bolt-60 static hum ...

hey there,

I found a nice roland bolt-60

the sound is amazing. tried it at the guy selling me, it was fine.
back home, the old 6L6 tubes were dying, really blue-purple lit up ... no sound any more. okay. changed the tubes. the sound is back and sounds really good, BUT there unfortunately is a big hum ... static hum ... more like a buzz. it gets louder when I get close to the amp / speaker magnet with the guitar. but the buzz stays when I turn off the guitar volume, or unplug it. the buzz is there immediately after turning on the standby switch. it doesnt fade or change ...

the buzz is less on channel 2, the overdrive, but that's not really an option. somehow I have the feeling that the buzz is becoming less when I turn up the master, to 7-8 ... but maybe then it's just drowned out from the normal tube hum ... don't know.

I have a very big suspect. a really strange and badly soldered effect loop switch, and all the stuff connected with this effect loop. maybe the buzz is coming from there. there is settings "pre-eq, post eq, post-volume"
the channel is loud and clear in the pre-eq and kind of the post eq-setting, but when switching to the post-volume mode (without anything connected to the effect loop) the channel volume drops, significantly, simply less volume.

also tried another 12at7 phase inverter tube ... same thing. the bolt only has the two 6L6 and the 12at7.

would it be safe if I just took out anything related to this effect loop from the amp? the switch and the cables ... (of course after the usual safety measuresin tube amps, unloading caps, etc.). if i wouldnt need it.
in this thread there is a whole section about this damn shi*** effect loop switch.

https://music-electronics-forum.com...ng-repair/39829-roland-bolt-60-reconditioning


bye
thanks
all the best


... sounds like pretty standard ground-buzz, but from the amp, not the guitar. and annoying in a flat-playing setting.

 

first pic ... is the pcb spot of the crappy effect loop switch ...

and the other two images ... well, the backside of the pcb for the phase inverter tube - connection of preamp and power amp?

there is this cap ... kind of melted into the pcb. that doesnt look good ... is it leaky? might something like that cause the buzz?

 

thanks for the reply !

do you think its possible to ditch the fx loop altogether? disconnect all fx loop cables from the pcb terminals, dismount the switch and ready to go?

or would that block the whole sognal path, or disturb it?

i thought the cap was simply melted into the pcb ...

 

well i guess the only problem is the ****ty „consumer“ switch used by roland

i will try to understand the switch and will hardwire/jumper the pcb in a fixed position ...

pre eq
post eq
post volume

are my choices.

what would make the most sense??
i guesse post eq is the standard routing of an fx loop

AND
i simply removed the leaky/melted cap
it seems to have been some kind of mod, because on other images on the net of the preamp pcb there is no cap there ... my amp still works fine... what sense could it have been, to implement a 0.01uF cap sonewhere in the preamp circuit? do you have any idea

thank you !! very much

 

well
i removed the crappy switch ... and found some markings on the pcb. might be too easy, but are these the lines i need to jump? ...

seems to me like a really wild jungle of alternatives ... to eq, from eq ... to power amp, etc.

 

well, if there is anybody out there reading, who know what ports I need to jumper with a wire, to get the three differenct settings. pre-eq, post-eq and post vol

thank you so much for that! would be great.

 

okay .... I got the logic

A, L, H and P are the general connectors ... to the adequate connection:

the top is the pre-eq, middle ist post-eq and bottom of the the three is post-volume

so for example, post-eq should be:

A > C
F > H
J > L
N > P

Q ... seems to be the ground of the switch. ground? well it connects the chassis of the switch with the circuit.

 

hard-routed it is ... in the "post-volume" setting. this setting has a little less volume and I have absolutely no idea why ... BUT the (volume independent) buzz is even more decreased with this setting ... so maybe another badly electromagnetically interfered cable out of the picture.

it seems there is simply to much electromagnetic field in this little amp ... and some crappy cables.

but I've gotten the buzz down to almost zero... and that might be "normal"

 

hey there

thanks again
i will look into it

i am pretty new to pcb modifying. up til now it was only the wiring inside my telecaster ... ; )

 

right now the amp sounds fine, but i will try to find a whole bypass of this pcb segment, so nothing has to go to and from the fx sends...

do you have any idea why the pre and post eq paths are a little louder than the post vol path?

might post vol be feeding the fx signal completely after the preamp into the power amp module? and therefore not adding signal to the actual preamp circuit ...

 

schematic:

https://schems.com/bmampscom/roland/Bolt_60 - Schematic.jpg

 

wow
i think my mind bursting ... no real idea. new to schematics ...

you think that this connection would bypass the whole fx loop limbo?

 

haha or simply this ...

and is the magic just to find these exact spots of the schematic on the pcb?