Loud hiss from pre out

  • Thread starter Thread starter veenife
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veenife

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hi,
I got a very loud noise going on when i try to plug the pre out from an amp into my interface...
i got an tascam 600 audio interface...

so i was trying to record the bass, plugin the pre out from the bass amp into one of the interfaces input.... but it happened to be very noise ... even before i turn the bass amp on...

as a test to find out what the problem is i did the following things...
1 - i plugged an guitar amp with the same method (preout-interface) and the loud hiss is still the same as with the bass amp
2 - i tried the same thing but now using my peavey PV6 usb and works totaly fine with NO HISS...
3 - i plugged the peavey mixer (main out) into one of the tascam interfaces input, and the hiss came back .. VERY LOUD....

the things is that THE PEAVEY MIXER records a much lower quality audio than the TACAM 600... thats why i still wanna find a solution for it!

I DONT KNOW EXACTLY WHAT THE PROBLEM IS.... BUT SEEMS THAT ANYTHING THAT HAS A DIFFERENT SOURCE OF POWER AND IS PLUGGED INTO THE TASCAM CAUSES AN INTERFERENCE THAT CREATES A REALLY LOUD HISS...

but im not an expert ... so i need help....
maybe im doing something wrong that im not aware of ...
please if you have any idea... dont hesitate to tell....
thanks!
 
I think the power source thing might be a coincidence.
Usually ground loop problems or the likes present themselves as a low hum rather than hiss.


At a glance the Tascam US600 appears only to have microphone inputs and Direct/Instrument inputs.

Neither of these are suitable for line level sources which I guess your sources are?
Out of mic, line, and instrument level, line level will be the hottest, so the signal your feeding to your interface is too hot.


You'd need some kind of matching transformer or pad I think to go between your line level source and microphone (Or DI) input.
 
Steenamaroo said:
I think the power source thing might be a coincidence.
Usually ground loop problems or the likes present themselves as a low hum rather than hiss.
Click to expand...

Except for digital ground loops that sound like static / hiss.

Alan.
 
Apparently you can set input on for line rather than inst (my bad), and it looks like that would give you two line inputs.

Have you done that?
 
yeah that is a hiss/hum... you are right.... and if i turn the channel louder ... the hum turns louder too...

but alright that helps to understand ... tx....

but i still have doubts...

.... there are 4 inputs on the tascam and they are:

1 - mic/inst (unbalanced)
2,3,4 - mic/ line in (balanced)

and the bass amp pre out is UNBALANCED...

so after researching in the net I came to the conclusion that there is no way to plug the (preout-interface) unless I plug the pre out into a DI box then to the interface...

RIGHT???
 
ok,that switch i saw was on a us200 :facepalm: sorry.

so, 2,3 and 4 appear to mic/line as you say, so try plugging you stuff into 3+4 with jack cables.
 
ok ... i tried yesterday (pre out - line input)

the hiss happened to be much lower... but still annoying to a point that is impossible to record....

and whats even weirder and i didn't mentioned before is that, when you plug the pre out into the interface ... the hiss is not just happening when you record but it also comes out from the actual speaker from the bass amp...

the manual says that i totally can record from the pre out... so thats for sure not the problem.... so i think that it just can be a ground loop thing going on....

so how can one fix a ground loop problem???
DI???
 
veenife said:
so how can one fix a ground loop problem???
DI???
Click to expand...

What is the exact set up? Computer Desk Top or Lap Top? Exactly what is the signal chain? What monitors are plugged in? Active or passive?

Cheers

Alan.
 
bass speaker with/to bass amp --- bass amp (pre out) into mic/line in from the interface (tascam us600) ---- interface via usb to lap top (pc)

I`m not using any monitors at all.... but just headphones

I don't really understand the active or passive thing... but there's nothing else connect apart of what I just described above
 
veenife said:
bass speaker with/to bass amp --- bass amp (pre out) into mic/line in from the interface (tascam us600) ---- interface via usb to lap top (pc)

I`m not using any monitors at all.... but just headphones

I don't really understand the active or passive thing... but there's nothing else connect apart of what I just described above
Click to expand...


Do you get less noise if you unplug the laptop power supple and run the laptop on battery?

Also the hiss could be the bass amp pre-out being noisy? Does the noise level increase and decrease with the bass amp input level control?

Cheers

Alan
 
ok... the loop stops when i unplug the laptop power supply or the usb from the interface....

.... but my laptops battery is kinda old and not working properly... it doenst last more than 10 minutes...

what would be the best solution to stop the loops without unplugging the laptop from the power?????
 
I had this before.
The problem came from the Usb interface being bus powered and the laptop having no true connection to mains ground.
The laptop ground was a few volts off mains ground and gave me a terrible constant hum.

My four solutions were either

1: Use an interface that is mains powered.

2: Plug the laptop into something mains powered via firewire/usb. (Creating a path to earth)

3: Plug a mains powered preamp into your interface.

4: Manually mains ground the chassis of the interface.

Number 2 is the safe and easy test. If you can even borrow an mains powered interface from someone and plug it in just to see, that'll tell you if you have the same thing. Luckily I had a 003 which immediately proved the theory.

Over here we have three pin mains, one of which is earth. In the end I manually tied the chassis of the interface to earth with a home made cable.


I can't stress enough though, I don't know how 'cool' that is, and do nothing unless you know what you're doing.
 
There are devices which isolate a usb device and break ground loops. Google for: usb galvanic isolation

The range in price so check around.

Paul
 
veenife said:
ok... the loop stops when i unplug the laptop power supply or the usb from the interface....

.... but my laptops battery is kinda old and not working properly... it doenst last more than 10 minutes...

what would be the best solution to stop the loops without unplugging the laptop from the power?????
Click to expand...

You could try lifting the shield at the Tascam 600 end of the cable between the bass amp and the Tascam, if that does not work, Plug one of these between the line out of the bass amp and the input of the Tascam 600, it completely isolates the bass amp from the Tascam and therefore no ground loop. I have several around my studio between computers and signal ins/outs and the studio noise floor reduced to 100 times, I know it is called a hum destroyer but it removes any form of ground loop.

Cheers
Alan
 
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