Velodyne F1800R Subwoofer - Hum, and occasional LOUD popping

[Bob F]

This sub hums a lot when first turned on, and once in a while starts popping
very loudly shortly thereafter, at which point I have to turn it off. It seems
"unstable" at turn on, making funny noises before the popping. The rest of the
time, the hum fades down to barely noticable, and everything is OK other than
the low hum.

I talked to the manufacturer, who said this old design had this problem, and the
only solution was to send the amp to them for repair/replacement for $285. They
describe this amp as a "beer-can" amp or something like that, IIRC. The power
amp part is in an aluminum can of some sort.

If anyone has dealt with this unit and this problem, I would love to receive
hints for repair.

My first thought is just to replace the large filter caps and see if this helps.

 

[Bob F]

Certainly a good place to start.

I'd also suggest the "tap on the PC board and components with a
piece of dowel or other insulated stick, and see if you can make it
pop" trick.

I suspect that there may be a broken and thus intermittent solder
connection somewhere in the amp. Transistor leads soldered to the PC
board traces are probably the first place to check. These leads can
carry a lot of mechanical stress... as the amp heats up and cools
down, the expansion of the leads can fatigue and eventually break the
solder junction.

Re-do the junction with fresh solder (a drop of RMA flux doesn't hurt)
and you may well fix the problem.

I had an amp go flaky in this way last year, with symptoms that sound
like yours... popping, snaps, and a sort of sizzling hiss in one
channel. One of the driver transistors on the main PCB had cracked
loose in this way.

Remembering something else the Velodyne guy said on the phone. The power amp in
the "can" is supposed to be a "3-dimensional" circuit inside the can. I don't
know exactly what this means, but he implied that it was not repairable. Thus,
the hope it is just the caps, perhaps.

 

[Leonard Caillouet]

This sub hums a lot when first turned on, and once in a while starts
popping very loudly shortly thereafter, at which point I have to turn it
off. It seems "unstable" at turn on, making funny noises before the
popping. The rest of the time, the hum fades down to barely noticable, and
everything is OK other than the low hum.

I talked to the manufacturer, who said this old design had this problem,
and the only solution was to send the amp to them for repair/replacement
for $285. They describe this amp as a "beer-can" amp or something like
that, IIRC. The power amp part is in an aluminum can of some sort.

If anyone has dealt with this unit and this problem, I would love to
receive hints for repair.

My first thought is just to replace the large filter caps and see if this
helps.

Look for the obvious, like a separated surround. IIRC this may have been
one of the units with the accelerometer in the woofer and a servo circuit.
Separated surrounds would cause this kind of symptom on them.

Leonard

 

[Bob F]

Look for the obvious, like a separated surround. IIRC this may have
been one of the units with the accelerometer in the woofer and a
servo circuit. Separated surrounds would cause this kind of symptom
on them.

The surround look perfect. Pushing in on the cone, I notice it seems to have a
very stiff suspension.

 

[Leonard Caillouet]

The surround look perfect. Pushing in on the cone, I notice it seems to
have a very stiff suspension.

Lots of their amps are made with a heat sink wrapped around most of the amp
circuit. They are a PITA to service. With that kind of symptom, I'd be
looking for a cap or a leaky FET, possibly an op amp going bad.

Leonard