Noisy and oddly working "old" amp combo

Bandeira · #1 06-06-2010, 11:07 AM

I've had this Hughes and Kettner Bassforce XL combo amp for more than 10 years... thing is that It hasn't seen a bass and power outlet for about 4 years... and It has been stored in a far from ideal space... (my father's place which happens to be near the coastline)

I grabbed it back and tried plugging in but the lights go on, but no sound or noise...
WHen I used to play it (5y ago) I used to use my pedalboard on the effects loop so now, when testing I tried plugging a normal cable between send and return... and bang... it works...

but... it has some annoying rattle, hum, buzz (dunno what to call it, as I am no native english speaker, so it is kind of difficult to me...)... like some bad connection... it plays with no interruption but it has this noise... When I turn the tweeter on, it get worse...

I have some knowledge in electronics (I do all my bass wiring, have assembled some DIY effect pedals) but never with amps so I don't know where to start...

Any help is appreciated!

Thanks!

Rick Auricchio · #2 06-06-2010, 11:10 AM

Spray some contact-cleaner onto a 1/4" plug and run it in and out of all the jacks. This should fix the send-return problem, and it may improve the overall sound.

A rattle is a mechanical noise. Some causes of hum and buzz are bad mains grounding, bad capacitors, cables, electromagnetic interference (e.g. from fluorescent lamps or wiring inside walls), or the instrument.

Bandeira · #3 06-06-2010, 11:16 AM

the noise seems to be like there is some bad connection, not like bad grounding...
it's more like there is some white noise in each note I play and making to sound kind of muddy....

Rick Auricchio · #4 06-06-2010, 11:58 AM

Try connecting a different speaker cabinet; it could be a bad speaker.

JimmyM · #5 06-06-2010, 12:32 PM

Quote:

Originally Posted by Bandeira

the noise seems to be like there is some bad connection, not like bad grounding...
it's more like there is some white noise in each note I play and making to sound kind of muddy....

corroded connections can make it sound that way, too. i still think you should get some deoxit and clean it before you proceed further.

Bandeira · #6 06-06-2010, 12:48 PM

I opened it up, cleaning all conacts with denatured alcohol in spray...

every 1/4 jack and the connectors between the boards....

I took pictures during disassembly so I would not screw up when putting it back together...
but when I did put it back together... nothing comes from the speaker... If I plug my headphones to the headphone-out it does play... but nothing from the speakers... I triple checked all the boards and jack connections to make sure I did not connect anything wrong....

and also, yes.., I did let it dry for about half an hour...

WingKL · #7 06-06-2010, 01:16 PM

Well it troubleshooting time. Get a schematic (try the manufacturer) and trace the signal down. You'll need a signal generator of some sort (ipod, PC, whatever works) and an oscilloscope. You might be able to get away with using a multimeter set on AC input instead of a scope.

Bandeira · #8 06-06-2010, 02:20 PM

so... good and bad news....

its is back working... but the noise is still
what was the problem? I simply don't know!

when re-connecting every wire and jack for the zillionth time, it came back to life...

but the loop problem still the same way... the combo will only play if i have a short cable plugging send and return...

EDIT: when playing for longer, the noise comes and goes when playing through both PASSIVE and ACTIVE inputs... the loop problem does intrigue me...

Bandeira · #9 06-06-2010, 03:03 PM

more updates...

I connected my bass --> Hartke VXL preamp predal --> H&K combo loop IN

and the noise is still there... so we can put the whole internal preamp with the inputs jacks, the pots out of the equation...

PS: i haven't stick with one bass... I double checked that...

Bandeira · #10 06-06-2010, 06:59 PM

any clue of how can I decide if the problem is in the power section of the amp of in the speaker?

I don't happen to have a spare speaker or cabinet.

Cheers

Rick Auricchio · #11 06-06-2010, 07:01 PM

The easiest thing is to borrow another cabinet.

Bandeira · #12 06-06-2010, 08:20 PM

more updates...
I have a practice combo here with is a 20w 8" small one...

I happily found out that the speaker is not soldered, is just connected to the amp...
there i go, I just made a small cable connecting the "External Cabinet OUT" from my Hughes and Kettner to the poor 8" speaker...

to shorten the story.. the noise is still there...
distorting everything and coming and going...

seems that the problem is with the power section in the H&K, rihgt?

Cheers!