F1-X Hiss

[melvin7822]

I'm not sure if my F1-X has always been so hissy, but it has been getting on my nerves lately.  I'm running out of the fullrange out into my Crest CA-9.  Without anything plugged in the CA-9, the CA-9 is whisper quiet at the -10 range of the attenuator (where it usually lives).  
 
Now with the F1-X plugged in and the volume at 0, there is no hiss until I flip the deep switch to the up position.  I find this to be a bit strange.
 
I follow proper gain staging and max the volume on my bass and set the F1-X at around 5 which is the highest I can set it without driving the tube with my active bass.  I then use the CA-9 to set the overall volume.  
 
With the EQ on my bass flat, and the EQ on the F1-X at 2-10-2 with the deep switch and bright switch off, I get plenty of hiss, especially if I flip the bright switch.
 
At this point I have tried swapping several tubes, cleaning the jacks, and checking to make sure the chassis ground is connected.
 
I don't want to get rid of the F1-X, but the amount of hiss is making me reconsider.

[melvin7822]

I've recently tried lifting the ground on the F1-X, cleaning the tube socket, and isolating the F1-X from the CA-9, but to no avail.

[David Houck]

Hi Melvin, welcome to the board!
 
Just to make sure you've tried all the basic stuff:
 
- You've tried more than one bass.
 
- You've tried more than one good quality instrument cable between the bass and the F-1X.
 
- You've tried a different preamp.
 
- You've tried more then one good quality patch cable between the F-1X and the CA-9.
 
- You've tried a different power amp.
 
- You've tried a different good quality speaker cable between the CA-9 and the speaker cab.
 
- You've tried a different speaker cab.
 
If you've eliminated every thing else in the chain that might introduce noise, especially cables, then:
 
up, being careful not to electrocute yourself, and do a visual inspection, making sure all the solder joints look good.

[melvin7822]

Hey Dave,
I've pretty much tried everything you've mentioned.  Inspection of the preamp shows everything to be in pretty good shape.  I don't really see any bad solder joints nor components that look burnt.  
 
Perhaps the op-amps might be the culprit but I have no way of knowing.

[mica]

Just to further isolate the problem to the F-1X, plug in the total system, observe the hiss. Unplug the guitar cord from the F-1X. This will tell you how much hiss is left in the F-1X (any reduction of hiss is hiss from your input source (bass)).
 
Still hiss? Then plug in the total system, turn all three tone controls to 0, leaving the volume to where you had it set at 5. If you still have hiss, then it's not the tube.
 
Still hiss? Turn volume down and it goes away, then it's input noise on the opamp.

[melvin7822]

Thanks Mica. It appears to be input noise at the opamp.

[melvin7822]

Well, I received the opamp and swapped it out.  Still hiss.  Looks like there may be a bad cap or resistor.

[mica]

Hi Mike,
 
While you're welcome to send the unit in for testing, and there is no charge for testing except the return freight charges, by replacing the opamp, it pretty much determines that you are experiencing the normal hiss of that unit.
 
The tube comes before the volume control and the op amp comes after the volume control. You should be able to set the volume of the F-1X higher and the power amp lower, get less hiss and have the same overall volume. Let me know.
 
Also, if you decide to send your preamp in for testing, please email the helpdesk when you do so that we can be expecting it.