If your amp has a lot of hiss and background noise, you may want to check and see if the wire connecting the input jack to the grid of the first preamp
tube are made with unshielded wire. If so, replacing it with shielded wire should decrease noise. Here, we’re stripping the shielding from one lead prior
to soldering the connection, then tinning the gathered shielding lead that we’ll solder to the input-jack side.
MOD 8:
Adding Shielded Wire to
Reduce Noise
Our final project here is a mod that will
subdue hiss or unwanted background
noise in your amp. A lot of the time when
an amp is plagued with this malady, it’s
because it uses unshielded wiring in key sections of the circuit. Strategically replacing
these lengths with shielded wire is a fast,
easy way to improve the amp’s noise floor.
Perhaps the best place to start adding
shielded wire is the section going from the
amp’s 1/4" input jack to the grid of the
first preamp tube. The grid in question for
a 12AX7/ECC83 or 12AT7/ECC81 tube
socket will be pin number 2. Any noise
picked up in this part of the signal path is
passed through each of the amp’s gain stages, getting amplified each time, so adding a
shielded wire here should yield significant
noise reduction.
To perform this mod on an amp like our
Twin Reverb:
•;Snip;the;lead;or;desolder;the;wire
where it attaches to the input jack.
(A standard soldering iron will work
for desoldering, but a solder sucker/
desoldering pump will create a cleaner
joint for the new connection by
removing excess solder.)
•;Snip;or;desolder;the;other;lead;where
it attaches to the grid pin of the pre-amp tube. The grid on a 12AX7 will
be pin 2 or 7
•;Solder;the;two;leads;from;a;length
of new shielded wire to the newly
vacated spots.
Ground the new wire by soldering the
shielding on the input-jack side to the
ground on the input jack. On a vintage
Fender-style amp, this is the lug that is
making contact with the chassis. Only
ground this shield on one end.
Go Forth and Mod
I hope you’ve found some modifications
here that seem like projects worth pursuing on one of your amps. Although these
projects yield pretty significant and impressive results considering how little work is
involved, I know it can be pretty daunting to poke around inside a device with
NOTE: It’s a good idea to tin the leads of the wire you are
installing before attempting to solder it
into place. To do this, simply wick a small
amount of solder onto each bare end of
the new wire. Tinning the new wire before
installing it improves the quality of connection it makes in the circuit.
NOTE: Often the shielding on shielded wire is braided
and needs to be unwound. I like to use a
pointed object to get between the braided
fibers to unravel them. Once you’ve unraveled enough shielding on the end that will be
attached to the input jack, gently twist the fibers together to create one uniform shielded-wire lead—which you’ll then want to tin.
significant safety risks for the first time. The
safety measures we’ve outlined should alleviate any danger, however if you have any
doubts about your ability to pull these off,
it’s always better to be safe than sorry. But
even if you decide to have a qualified tech
execute these mods for you, at least this
information will give you a better understanding of some of the nuances and possibilities of guitar amp modifying.
