console hum

my console a Tascam m600 have a 50hz terrible hum problem
im looking at the grounding and trying to come up with something to solve the problem.
In a starground solution should the powerground from the supply also be connected there ?

Start off by disconnecting everything from the console. Plug in headphones. Does the console hum? If so,
power supply problem. Then start plugging in various I/O, listening always to headphones. Stop when you get hum. At this stage you have an interface problem with the last thing you plugged in.
Is it balanced? If not, balance it or throw it away!

Here are some pictures of what i have done

All the modules out


The main buss card that provides the input modules with power,ground and all the signal from the modules goes here


I add seprate terminals to the ground rail and broke the grounding link between the cards


did the same to Pgm,Aux,Meter cards, you can see the blue terminal on the cards


The worst is that it dosent solve the hum problem....
I disconnected everything, only keept the mastermodule in and listened and the hum was still there...can it maybe be a psu problem.. yes i listen throu headphones

radardoug said:

Start off by disconnecting everything from the console. Plug in headphones. Does the console hum? If so,
power supply problem. Then start plugging in various I/O, listening always to headphones. Stop when you get hum. At this stage you have an interface problem with the last thing you plugged in.
Is it balanced? If not, balance it or throw it away!

Click to expand...

Thanls for the reply  ;D
yes i did exactly so but shame i didnt listen before i grounded all the cards...

Kir_For_Pleasure said:

... have a 50hz terrible hum problem ...

Click to expand...

sounds like a supply problem at or pre rectifier. I'd check the rectifying diodes first.

Console grounding is not a trial and error, or brute force exercise (with the exception of shielding which is brute force).

Ground strategy depends on the circuit approach as local grounds will need to be forward and back referenced as signal is passed across the physical distances spanned.

The advice to use headphones and isolate specifically where you have mains frequency hum corrupting the audio path is spot on.

JR 

Did it start happening recently or has it always been a problem?

Are you sure it's 50hz and not 100hz?  Usually you'll get the rectified line hum with a grounding problem, not the line hum itself..

Also, do you have the console plugged into a line circuit that has any other equipment/machines/appliances plugged into it as well?  Sometimes you can get noise from other devices plugged into that circuit, or get ground loops/offsets from other equipment plugged into the line circuit and the console too.

Thanks for all replys....the hum has always been there.Here is the power supply schematic

just to add my 2 cents:
I remember having 50hz levels on my console that were unbearable...
I inspected all possible causes (ground loops, faulty psu,etc..) and really spent too much time on it... much later I found out that MOTU gear I was using was radiating mains emi when positioned within less than a meter from the mixer!
the idea is: test the console with all rack gear switched off!

when i was troubleshooting, the only gear i had on was the mixer. i even turn off the luminous lamp, they can be a serious problem sometimes..

new schematic with values for diods,opamps and rectifiers

hi,
I repaired a Tascam M600 mixer as your one years ago, it had a problem similar to yours.. I no longer have the schematic, remember that the problems lie in the schedules of the input channels. Please post the Tascam input schematic and then I will be able to explain where to make the change. I also cut the ground track on the PCB isolating the ground from the flat cable and I soldered a copper wire, creating an new  star ground near the power connector . I made this change to all input and out channels  and now the mixer does not have any more noise, improved crosstalk between channels and the the mixer dynamics . I apologize for my bad English and I hope to have been chiaro.
Saluti from Italy
Francesco

ghibson said:

hi,
I repaired a Tascam M600 mixer as your one years ago, it had a problem similar to yours.. I no longer have the schematic, remember that the problems lie in the schedules of the input channels. Please post the Tascam input schematic and then I will be able to explain where to make the change. I also cut the ground track on the PCB isolating the ground from the flat cable and I soldered a copper wire, creating an new  star ground near the power connector . I made this change to all input and out channels  and now the mixer does not have any more noise, improved crosstalk between channels and the the mixer dynamics . I apologize for my bad English and I hope to have been chiaro.
Saluti from Italy
Francesco

Click to expand...

Hello !!
sounds fantastic, the crosstalk between the cahnnels isnt fun at all, with your solution i maybe wants to use it to mix on some day  ;D
dont worry about bad english you wont come near my 
i had this shematic laying, is it the one you had in mind ?

Hi Kir_For_Pleasure ,
sorry for delay, I worked out of Italy in recent days. The input  channel  is connect to 1 small circuit board  where you find the input xlr and the insert jack. If you look the schematic you find one smal capacitor connect to xlr pin 1 ,if my memory is correct, this capacitor isolates  the input ground  from input board . You must cut the capacitor and put one 0 ohm resitor or one jumper . And the same job onto all  output  xlr board. In the input channel you must cut the ground near the flat cable and connect one wire (1mm) on the ground board ( C143-C144). I try to find some picture for explain better .
best regards
Francesco

Hey Kir_ ,

Check to make sure that  C004, C005, C012 and C016 filter caps in the supply are "well soldered".
I have often seen power supply filter caps "solder joint" go bad from long term thermal cycling(expansion/contraction).  The cap may be holding in the PC board, but may have bad or intermittent contact.

Hope this helps.

Sylvain

Thanks for your help  ;D for the moment i laying clinkers at my basement floors, but as soon as possible i try your solutions.

Francesco do you remeber something more about your mod of the console ?

taking a old thread up to surface again 

Havent the mixer up and running yet... but it getting closer : measured the power from the supply today and that was a intresting thing to do... at the +16v i got 28v out...all the other voltages was ok

so this means pehaps that something is wrong with the njm 7815 ?

someone had make some upgrades to the supply already i have two 10000uf capacitors hanging out at the side of the supply rack..which i bolted to the rack,they are connected to c004 and c005 first thought was ahaa buffer capacitors for more even voltage stream to the channels..but they are filtercaps...right ?..why bigger filter caps ? the supply pcb also had some groundwires linked at the trace side at some points...i thinking of recappping the supply and change the 7815..do you think i should keep the already made mod with the 2 capacitors ?

Kir-

first, yes change the 7815.  you probably will get closer to 15 volts instead of 16 volts
it sounds like it is shorted, giving you the raw unregulated power on the positive rail.
That ought to make noise.

Maybe someone added the extra caps to try and get rid of the hum.
I would replace C-4 & 5 with 2200uf caps and loose the ones hanging off wires.
are there date codes on the caps in the power supply?
if they are less than 10 or 12 years old they are probably not the problem, but it's
hard to go wrong putting better caps in power supply... but possible if you are not careful.

the caps tascam used generally last a pretty long time.

Agree with Queef Bag.
If the original capacitors were causing hum, leaving them in the circuit while adding more capacitance in parallel won't solve the problem.