Groove Tubes Soul-o Series 75 Operating Manual

Congratulations, you've just purchase what we believe is the best
amp on the planet! We'd like to welcome you to the growing list
of artists who share our mutual lust for tone. Now, we'd like to
better acquaint you with your Soul-o amp new amp and show you
how to get the most out of this incredible hand built tube amplifier.

Some of our unique construction details:

1 - All components are hand soldered. There are no quick dis-
connects, wire nuts, or dipped connections and over 120 hand
soldered connections on the tubes sockets alone
2 - All transformers are custom designed and made exclusively for
Groove Tubes.
3 - GT amps are designed to use your choice of 6L6, 5881,
European E34Ls or KT88s power tubes. Choose from a total of
13 different tubes which are currently available from our GT cata-
log. Customized your S75 for tone and power from 35 RMS watts
to 95 RMS watts, and the S150 from 80 RMS watts to over 190
RMS watts!
4 - The entire amp chassis for the combo package is shock mount-
ed on rubber isolators to reduce adverse interactive vibrations and
microphonics at higher playing levels.
5 - The critical V1 preamp tube is also shock mounted on a spe-
cial rubber isolator to reduce adverse interactive vibrations and
microphonics at higher playing levels.
7 - We use only double sided, double thick PC boards with double
thick traces and no PC mounted sockets. Instead we use chassis
mount type sockets bolted and hand wired to the PCB. This is the
best of both worlds; PCB and point to point construction.
8 - There are more than 28 hours of hand labor in each Soul-o
Series amp. Each amp is custom to built to order!
S - S
OUL O ERIES
75/150 O
9 - There is no particle board in any part of our cabinetry, only
solid core American plywood.
Of course these features and construction details cost more, but
you can really hear the difference!

The Front Panel Features...

The Preamp Stage

The Soul-o Series preamp stage has 5 GT12AX7 dual triodes, each
performing multiple functions in the circuitry. The two channels
are designed with entirely different purposes and therefore have
vastly different gain structures and voicing. You may switch
between Clean and Scream, or combine them as Both for more
really interesting possibilities. These can be switched from the
front panel or by the optional footswitch, in which case the front
panel switch must be in the center, or Both, position. It is also
possible to adapt the footswitch jack to work with most remote
rackswitching devices.
The Clean Channel has the basic 5 controls you've likely seen
before: Gain; Bass; Middle; Treble; and Volume plus a Brite switch
for that real "cutting edge" sound. You may want to turn the Brite
switch off if you've got a Telecaster. The Clean channel is not
designed to produce heavy distortion, hence it's name. However,
an increase of Gain and decrease of Volume will produce a gradu-
ally fatter, warmer tone while the opposite will produce the bright-
est sound and most dynamics or headroom.
The design of the tone controls on this channel are passive, as
used on older style amps. Active designed tone controls, most
common in newer amps, have a separate gain section for each
tone band, in effect they act like a series of effects loops which
"suck tone"...so we don't use them. Our tone controls are more
interactive with your style of playing and are simply more musical.
To get the most out of passive tone controls, start by listening to
the channel with all tone controls at the 12 o'clock position. Then,
if you want more bass, either: 1) crank up the Bass control; or 2)
lower the Treble control, raising the gain to compensate the vol-
ume loss. Passive controls are interactive, so turning any one of
them fully on, or off, diminishes the effect of the others and alters
the gain structure. Experiment with this advice in mind.

The Scream Channel

The Scream Channel also has the same basic 5 controls plus a Fat
switch, which does just what is says. However, since this channel
is designed to produce a wide range of distortion tones from Blues
to Metal...the Gain and Volume ratio are everything! If you want
more distortion, raise the Gain and lower the Volume. This chan-
nels tone controls are also passive, but of a different design than
the other channel. This tone circuit is called a cathode follower
type and changes it's tone depending on how hard you pick the
string of your guitar. Notice as you push the note harder with your
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PERATING ANUAL