Re: Amp noise Pt. 2 (w/pic)
- From: "RickH" <passport@xxxxxxxxxxxxxxxxxxxxx>
- Date: 17 Feb 2006 09:28:04 -0800
docgorpon@xxxxxxx wrote:
To recap: Marshall type combo. 60 watts. All tube.
Static noise that sounds like the ocean with some popping and hissing
starts about 5 minutes after amp is on. Noise responds to volume knob
and disappears when it's turned all the way down. All other knobs
affect the tone of the noise to one degree or another, particularly the
treble knob. Noise stops when standby is put on. Noise continues even
with no guitar plugged into the amp.
I opened up the chassis and poked around with a stick. I can hear
myself tapping through the amp on some of the prongs and wires on the
preamp tube farthest from the powertubes. Also, I get the same reaction
when I tap the smallest yellow cylinder thingy (second yellow thingy
from the right).
Pic of the inside of my chassis at www.trackthecurse.com/amp.htm
What do y'all think?
My 1965 VOX AC10 with all original parts does the same noise thing,
I've had a couple of techs tell me that first I need to eliminate all
the mechanical possibilities like pot wipers, jack switches,
microphonic tubes, tube sockets dirty, cold joints, etc.
If this still does not fix it, then that ocean and popping noise is a
noise commonly associated with resistors. Here is a good article on
resistor noise:
http://www.aikenamps.com/ResistorNoise.htm
There may be aspects to the basic amp design of that Marshall however,
where that noise is going to be more suseptable than other designs,
like having high meg ohm grid resistors in the input stage, or
resistors at the edge of their operating wattage. This article has
some good tips, but would suggest you have a tech do the resistor work
if you are unfamiliar with how to keep yourself from getting killed by
B+.
You however should be able to eliminate mechanical causes by getting
some good pot and contact cleaner (absolutely not WD40) and clean it up
and try out different tubes, etc.
.
- References:
- Amp noise Pt. 2 (w/pic)
- From: docgorpon
- Amp noise Pt. 2 (w/pic)
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