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View Full Version : Amp hiss...any thoughts?

phishmarisol
08-18-2008, 02:24 AM
The other day my amp developed a noticeable hiss. It is increased drastically by turning up the volume, presence, or engaging the bright switch. I am thinking maybe the preamp tubes so I ordered some new ones but in the meantime any other suggestions? It was recently checked out by a tech and given a clean bill of health.
Blue Strat
08-18-2008, 06:33 AM
What amp? Tubes are the first place to look.

If it's an older amp, plate load resistors, treble cap, or anything in the audio path before the volume control (since the volume control affects the noise level) could be noisy.

If something was missed by the tech it's because the problem started after you got the amp back from him.
donnyjaguar
08-18-2008, 08:54 AM
Probably not a problem with the amplifier you have, but I have seen this once on a modified amp. One of the low-level signal leads was nearby the rectifier tube and picking up some of the rectification hash.
HipKitty
08-18-2008, 01:52 PM
What amp? Tubes are the first place to look.

If it's an older amp, plate load resistors, treble cap, or anything in the audio path before the volume control (since the volume control affects the noise level) could be noisy.

If something was missed by the tech it's because the problem started after you got the amp back from him.


+1 Start with those preamp tubes first.

I assume that you're running your guitar straight into the amp....also, have you tried another (known good) guitar cable?
phishmarisol
08-18-2008, 02:29 PM
It's a Fender HRDx. The hiss did start after I got it back from the tech, but it was over a month after so everything was fine then. It happens when I run pedals or straight into the amp the same. I have not tried a different cable but I will try that and report back.
Blue Strat
08-18-2008, 03:51 PM
Check the amp with nothing plugged in at all. That's the true test of whether it's the amp or something in front of the amp.
phishmarisol
08-18-2008, 06:25 PM
Ok, not the cable and it happens just as loud with nothing plugged in at all. I'll post once those tubes come in.
rockon1
08-18-2008, 07:13 PM
No offense intended but a perfect example of why everyone(with a tube amp) should have spares. Bob
phishmarisol
08-20-2008, 09:16 PM
Ok, got some JJ 12ax7s in today and put them in and the hiss is the same. From the back of the amp I can also hear a low level buzz/hum. I guess I'll just take it back to a tech.