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Roland Cube 30 Bass or: Putting a sock in it.

N

N Cook

Jan 1, 1970
0
Reported as fuzzy sound on the bass guitar E string even at relatively low
levels
but otherwise fine sound rendition or backing off the bass control .
Feeding a signal generator in then indeed a distinctly fluttery distortion
in the range 50 to 70 Hz on top of the wanted output, ok above or below that
range.
No external speaker output on this cube and before getting inside to scope
it or run an external speaker I took the front grille of in case of
parasitic rattling but no change. But putting a sock in the front/back vent
tube in the speaker surround cured it.
Where to go from here ? sci.acoustics.repair ? charge for an old sock ?
 
A

Arfa Daily

Jan 1, 1970
0
N Cook said:
Reported as fuzzy sound on the bass guitar E string even at relatively low
levels
but otherwise fine sound rendition or backing off the bass control .
Feeding a signal generator in then indeed a distinctly fluttery distortion
in the range 50 to 70 Hz on top of the wanted output, ok above or below
that
range.
No external speaker output on this cube and before getting inside to scope
it or run an external speaker I took the front grille of in case of
parasitic rattling but no change. But putting a sock in the front/back
vent
tube in the speaker surround cured it.
Where to go from here ? sci.acoustics.repair ? charge for an old sock ?
Interestingly, I have had a similar problem on several Ashdown bass heads.
Just as you describe, fuzzy distortion at around 44Hz only, otherwise
sounded fine. On each occasion, it has been really bad joints on one of the
main smoothing caps - to the point where the cap is effectively not there.
With a 'scope on the supply rail, just about full level ripple, but
curiously, not a hint of hum on the undriven audio. Only when that string on
the bass guitar plucked, or a sig genny put in at that frequency. I
completely missed the first one that I had doing it, as it sounded perfectly
well on all other material, so sent it back to the shop. He came back a day
later armed with a bass guitar, and demonstrated the problem ...

Arfa
 
R

Ron(UK)

Jan 1, 1970
0
Arfa said:
Interestingly, I have had a similar problem on several Ashdown bass heads.
Just as you describe, fuzzy distortion at around 44Hz only, otherwise
sounded fine. On each occasion, it has been really bad joints on one of the
main smoothing caps - to the point where the cap is effectively not there.
With a 'scope on the supply rail, just about full level ripple, but
curiously, not a hint of hum on the undriven audio. Only when that string on
the bass guitar plucked, or a sig genny put in at that frequency. I
completely missed the first one that I had doing it, as it sounded perfectly
well on all other material, so sent it back to the shop. He came back a day
later armed with a bass guitar, and demonstrated the problem ...

Arfa

I have also had that fault, we call them Trashdowns around here. I agree
with Arfa that it`s probably a dry joint. Roland combos are generally
better constructed, or at least, they were!

I had a similar fault on a Peavey bass combo, and it turned out to be
air fluttering in the bass port, I presume the speaker had somehow
deteriorated, a wodge of dacron in the port stopped it temporarily.


Ron(UK)
 
M

Meat Plow

Jan 1, 1970
0
Reported as fuzzy sound on the bass guitar E string even at relatively low
levels
but otherwise fine sound rendition or backing off the bass control .
Feeding a signal generator in then indeed a distinctly fluttery distortion
in the range 50 to 70 Hz on top of the wanted output, ok above or below that
range.
No external speaker output on this cube and before getting inside to scope
it or run an external speaker I took the front grille of in case of
parasitic rattling but no change. But putting a sock in the front/back vent
tube in the speaker surround cured it.
Where to go from here ? sci.acoustics.repair ? charge for an old sock ?

Try a different speaker.
 
G

G

Jan 1, 1970
0
Try a different speaker.

Well it seems like it could be electronic or mechanical. Putting a sock around
a vent will usually make the cone move more and create more distortion, if
that is the problem. I can't believe there is a vent, and a 10 inch guitar
speaker can't reproduce 50 Hz unless its a HIFI driver. The description about
speaker surround, baffles me.

greg
 
N

N Cook

Jan 1, 1970
0
G said:
Well it seems like it could be electronic or mechanical. Putting a sock around
a vent will usually make the cone move more and create more distortion, if
that is the problem. I can't believe there is a vent, and a 10 inch guitar
speaker can't reproduce 50 Hz unless its a HIFI driver. The description about
speaker surround, baffles me.

greg

The vent is clearly seen at lower left on
http://media.zzounds.com/media/feed/large/ROLCUBE30BASS.jpg
looking like a tweeter but
the tweeter is mounted co-axially to the main cone.

Blocking up this vent means you can turn the bass control up and the volume
up without the fluttering noise in the 50 to 70 Hz range. Will take apart
tomorrow and scope, external speaker etc.
No problems with the reservoir cap solderings
 
N

N Cook

Jan 1, 1970
0
Decoupling the negative black lead (not ground) via a 10u polyester cap to
the scope ground the electronic trace was fine at all frequencies and
powers. Semi-permanently blocked off the reflex/bass port or whatever that
hole is called and the intrusive 50 to 70 Hz induced flutter has gone. Just
the normal low level flutter , for low frequency, high power output due to
vortexing/cavitation or whatever the normal distortion due to bulk shifting
of air mass by a cone is called.
 
R

Ron(UK)

Jan 1, 1970
0
N Cook wrote:
Just
the normal low level flutter , for low frequency, high power output due to
vortexing/cavitation or whatever the normal distortion due to bulk shifting
of air mass by a cone is called.

We call it crapping out ;)
 
P

PhattyMo

Jan 1, 1970
0
Meat said:
Try a different speaker.


Just normal "port noise" aka "chuffing" ? Mebbe they need to change the
diameter of the port.
 
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