My old equalizers produce 50Hz...

[yggdrasil]

I have a pair of Technics SH-9090 equalizers which produce 50Hz when they are turned on. :(

I can make it go away for a while by giving them a friendly tap on the side.

I have tried to use a local electronics repair shop, but with no effect.

Do any of you have ideas on how to repair?

Do any of you have experiences to share with digital equalizers?

[boputnam]

I have a pair of Technics SH-9090 equalizers which produce 50Hz when they are turned on. :( Hmm...

Hey, Johnny -

I'm thinking the 50Hz hum is a sign of a ground-loop. I do not know the Technics EQ, but are you combining consumer (unbalanced) with pro (balanced) gear? Smacking it ain't a full-time fix - you need to isolate the source of the hum.

1) Unplug the inputs into the amps, so only the amps are connected to the speakers - any hum? If not...
2) Then connect the EQ to the amps (no pre-amp yet) - any hum? If so, the EQ is the problem. If it is the EQ, you need an isolation transormer between it and the amps. If not...
3) Connect the pre-amp to the EQ, BUT DISCONNECT ALL THE INPUTS INTO THE PRE-AMP. We need to check the pre-amp+EQ+amps alone. Any hum? If not...
4) One-by-one connect your inputs to the pre-amp and listen for the one producing the ground-loop. That one(s) needs be isolated from your pre-amp using a isolation transformer - which are easy to find.

Search the Forum for "Ground Loops" for other ideas.

[scott fitlin]

I have a pair of Technics SH-9090 equalizers which produce 50Hz when they are turned on. :(

I can make it go away for a while by giving them a friendly tap on the side.

I have tried to use a local electronics repair shop, but with no effect.

Do any of you have ideas on how to repair?

Do any of you have experiences to share with digital equalizers?That you can make it go away for a while by tapping it? Have a technician check the power supply decoupling capacitors! Could be a cap goin bad, or just a loose solder connection!

[yggdrasil]

All equipment is unbalanced.

It is for sure the equlizers, mainly the one used for left channel.

Both equalizers have had all their capacitors changed a couple of years ago.

[scott fitlin]

But you see, to me that you can make the hum go away for a while by tapping the unit indicates an intermittent problem such as a capacitor going bad, or maybe a connection that isnt 100% secure! ( cold solder joint )

A loose, or bad decoupling capacitor for the power supply will create the buzz your hearing! I had this problem with a component some years ago!

If your good with a soldering iron you can take the EQ,s board out, and resolder all the connections, you might very well hit the problem and fix it!

:)

[johnaec]

I agree with a cold solder problem, especially if these capacitors were replaced in the last couple years. I've found this problem a couple times, especially on the larger filter capacitors used for the power supplies.

John

[Oldmics]

Check the center tap connection in the transformer.


Oldmics

[paragon]

That`s it when you use many electronics part. That´s why i turned to passive crossovers. I had the same problem with this high efficiency speakers. You hear everything and it`s difficult(?) to ......them from hum (sorry).

Eckhard

[boputnam]

Check the center tap connection in the transformer. :thmbsup:

[yggdrasil]

Thanks a lot for all your input.

I'll try to resolder the left channel equalizer later on this week.

[scott fitlin]

Oldmics, whose knowledge I respect, says check the center tap connection, I said check the decoupling cap connections, and Bo, who I also respect seconds the center tap!

What I see here, is everyone is in the same place! The Power Supply! Im betting youll find your problem there, too!