Mixer problem.

[Anders N. Vinje]

Hey.
I have this old Samic SM-810 Mixer that generates alot of hum. And somtimes
there is a short burst of current that passes trough making a loud pop!.
This is really annoying when making music.

I have replaced the Opams that where inside with Burr Brown OPA1342. It
helped alot against the humming and noise it was generating. The old Opams
where ST TL072CN type. One Channel even had a Philips NE5532. Well i bought
i used. So i guess the guy who had it before made som changes. well anyway
this part goes into my old parts container. But here is still alot of hum.
But i am wondering what generates that pop somtimes. Bad capacitator
somewhere, maybe? I was thinking of replacing the the electrolytic mains
filtring capacitators. With som lager ones. Something like 10000uf. There
are there are two SMC 25V 2200uf on the + to gnd And two at the - to gnd. I
only have a multimeter or else i would have seen how much ripple its
generating in none use mode. The OPA 1342 uses a couple of mA more then the
TL072. But i have heard the NE5532 is a sucker on quicent current. Maybe it
sucking to much current allready?. I dont know. I have been looking for the
schematic for this mixer, but i seems that Samick dosent exits anymore.
Anyone know where to get it?

Any suggestions on this mixer especially the poping would have been much
helpfull.

Anders.

PS. After i have been posting on this newsgroup. I get those irretaing MS
advise or something mail with a virus. I should never have used my own mail
address.

 

[John Popelish]

"Anders N. Vinje" wrote:

Hey.
I have this old Samic SM-810 Mixer that generates alot of hum. And somtimes
there is a short burst of current that passes trough making a loud pop!.
This is really annoying when making music.

I have replaced the Opams that where inside with Burr Brown OPA1342. It
helped alot against the humming and noise it was generating. The old Opams
where ST TL072CN type. One Channel even had a Philips NE5532. Well i bought
i used. So i guess the guy who had it before made som changes. well anyway
this part goes into my old parts container. But here is still alot of hum.
But i am wondering what generates that pop somtimes. Bad capacitator
somewhere, maybe? I was thinking of replacing the the electrolytic mains
filtring capacitators. With som lager ones. Something like 10000uf. There
are there are two SMC 25V 2200uf on the + to gnd And two at the - to gnd. I
only have a multimeter or else i would have seen how much ripple its
generating in none use mode. The OPA 1342 uses a couple of mA more then the
TL072. But i have heard the NE5532 is a sucker on quicent current. Maybe it
sucking to much current allready?. I dont know. I have been looking for the
schematic for this mixer, but i seems that Samick dosent exits anymore.
Anyone know where to get it?

The filter caps may be the trouble, but only if the original ones were
quite bad. Any of the opamps you list should have enough power supply
ripple rejection to not respond audibly to any reasonable supply
ripple. I suspect something else. Perhaps a bad ground on some
shielding, or a piece of shielding missing. The pops might also be
electrostatic pick up from things on the AC line turning on and off.
You might pass a desk lamp near the unit, while turning the light on
and off to see if you are getting this kind of interference that
indicates poor shielding.

--
John Popelish