Noise Floor Hiss From Rivera Knucklehead Tre Head

[blf1]

Hi All,

First post here! I've had the above amp for about a year now & absolutey love the tone the ability to use the effect loop dials as a wat to push the power tubes at low volume

I was told this hiss I get is attribute of "high gain" amps, but notice a noise floor hiss that my noise reduction (ISP) wont get rid of --- its there until you put it on standby.

Its a tad annoying when you play clean & I can live with it , but want to know from the experts whether this deserves a look from an authorize tech?

[blf1]

No one?

I use a Single Rectoverb as an A/B with it & no such hiss on the Mesa. Just the usual Buzz/Hum I can eliminate with noise reduction. The hiss is there regardless of gain or volume

Any ideas would be great - thanks again.

[J M Fahey]

Start by getting the schematic and posting it here, so useful solutions can be suggested.

[g1]

Have you tried other preamp tubes?

[blf1]

Have you tried other preamp tubes?

It's been doing this since I got it new

[blf1]

Start by getting the schematic and posting it here, so useful solutions can be suggested.

http://www.webphix.com/schematic%20h...nucklehead.pdf

I have a 2011 model which I believe is "updated" though

[g1]

It's been doing this since I got it new

Do you mean, a) yes, the preamp tubes have all been changed since it was new,
or b) no the preamp tubes have not been changed since it was new, but a new preamp tube could not have been noisy?

[Enzo]

Your noise reduction is placed in the FX loop?

Remove the loop stuff, plug the guitar into the FX loop return, and turn volume control on the guitar to zero. Is the hiss still present? If so it is somewhere between the return jack and the power amp.

You have apparently got level controls for both send and return on the loop. With zero guitar still into FX return, turn return level control up and down. Does the hiss go up and down too, or is it unaffected?

My suspect is the IC on the FX loop circuit has gone noisy. I am trying to isolate that section as much as possible to verify that or point elsewhere.

[blf1]

Your noise reduction is placed in the FX loop?

Remove the loop stuff, plug the guitar into the FX loop return, and turn volume control on the guitar to zero. Is the hiss still present? If so it is somewhere between the return jack and the power amp.

You have apparently got level controls for both send and return on the loop. With zero guitar still into FX return, turn return level control up and down. Does the hiss go up and down too, or is it unaffected?

My suspect is the IC on the FX loop circuit has gone noisy. I am trying to isolate that section as much as possible to verify that or point elsewhere.

Enzo - thanks so much for your help/time! I did what you said and yes the hiss even gets louder as you turn it up on the return knob with just plugged into the return. The hiss is there even with no guitar or anything plugged in as well.

I plugged direct into the front of amp and even without using the FX Loop, the hiss is still there. Def sounds like the return makes it worse when you turn it up!
See this vid i just shot to illustrate side by side with my Mesa -- I A/B them - same Furman Power Conditioner too --- Im using ISP Decimators to rid the normal buzz/hum & they do that on both amps BUT this hiss is always underneath everything on the Rivera as soon as you take it off standby - http://www.youtube.com/watch?v=4OZJb...ature=youtu.be

[Enzo]

Then that IC on the FX loop board is still my prime suspect.