Groove Tubes Soul-o Series Guitar Amplifier Operators GuideTheSoul-o 45TMAll tube “Pedal Friendly” guitar amp with tube reverb.
Congratulations
You’ve just purchase what we believe isthe best amp on the planet! Welcome
to the growing list of artists who share
our mutual lust for tone. Now, we’dlike to better acquaint you with yournew Soul-o 45 amp.
Construction details:
1 - All components are hand soldered.
There are no quick disconnects, wirenuts, or dipped connections and over
120 hand soldered connections on thetubes sockets alone.
2 - All transformers are custom
designed and made exclusively for
Groove Tubes.
3 - GT S45 amps are designed to use
your choice of power tubes. Choose
from a total of 11 different tubes which
are currently available from our GT
catalog. Customized your S45 for tone
and power from 40 RMS watts to 65
RMS watts, depending on the selectedpower tube!
4 - We use only double sided, double
thick PC boards with double thicktraces. We use chassis mount typepower tube sockets hand bolted, handsoldered, and hand wired to the PCB.
This is the best of both worlds; PCB
and point to point construction.
5 - Each amps is handbuilt to order.
There are more than 18 hours of handlabor in each Soul-o Series S45 amp!
6 - There is no particle board in any
part of our cabinetry, only solid core
American plywood.
Of course these features andconstruction details cost more, but you
can really hear the difference!

The Preamp Stage
Most amp designers use a nice Gibson
or Fender guitar while developing theirdesign. These of coarse have magnetic
guitar pickups which are by definitionhigh impedance, low level output
devices. However, most players use afoot pedal before the preamp, andpedals are low impedance, high output
devices. The result is the pedal adds
two effects, the one you intended(maybe distortion or chorus), and thesecond effect “mush” as the pedal
overloads the amp’s preamp which
was intended to see a guitar pickup.
With this common problem in mind, we
designed the Soul-o 45 to be the firstever “Pedal Friendly” guitar amp,

with a preamp that will not overload
when pushed by today’s high outputpedals. This means it has “tons” ofheadroom so the pedal breaths betterand remains open and transparent
sounding...and improves the punch
and tone of any pedal!
The S45 preamp stage has five dual
triodes, each per forming multiple
functions in the circuitry. The preamp
design has Gain, Bass, Middle, Treble,and Volume. We did not design thispreamp for massive amounts ofdistortion as you can get distortion andother effects using your favorite footpedals. The S45 was deigned to bepedal friendly, so the preamp will not“mush out” no matter how hard you
play. Our design provides loads ofheadroom in the preamp stage to get
the best possible results with yourpedals. However, an increase of theGain knob and decrease of the Volume
knob will produce a fatter, warmer tone
while the reverse produces a cleaner,brighter sound. And when the pedals
are off, you get an amp that’s clean
and loud, yet warm and rich inovertones.

diminishes the effect of the others.

The Passive Tone Controls

We’ve included perhaps the one effect

The tone controls of the S45 amp are
the Passive type, similar to those usedin older, classic tube amps. Many
amps made today instead use Active
type tone controls, which have aseparate gain section for each tone
band which literally “suck tone” fromthe preamp. That’s why we don’t use
them.
Passive controls use acommon tube gain stage to boost
the entire frequency range, thendivide the Bass, Middle, and Treble
with passive filters to shape yourtone. Passive tone controls are
more musical and interactive.
To get the most out of
passive tone controls,
start with all controls at
the 12 o’clock position. If
you want more bass,
either: a) crank up the Bass
control; or b) lower theTreble control (compensatethevolumelossbyincreasing Gain or Volume).
Because passive controls
share a common gainstage, turning any one ofthem fully up (or down!)

Also, our Passive tone controls are“post Gain”, giving you a truly touchsensitive amp that reflects yourpersonality. Strike the string harder,
and the gain increases into the tone
section, increasing it’s influence. As
you play harder and “push” the tone
section, the tone will brighten up. Bycontrast, if you play with a lightertouch, it gets rounder and fatter.
Lastly, remember as you play at louder
volumes, you will need progressively
less Bass level to reduce a mushy
bottom end. Experiment with this andhave some fun!

The Presence Control
This control is a part of, and interactive
with, the power amp stage. Increasing
it adds highs into the feedback loop of
the power stage and increases the“touch” and “drive” of the amp while
also making it brighter. Use more
Presence for an acoustically deadroom, and less for live rooms. Season
to taste!

The Reverb Control

www.groovetubes.com
Techspecs
Input
1/4 “ phone jackInput Level-10 dB nominally
FX level-10 dB nominally

PreampSection
3 x GT12AX7
1 x 12AT7
1 x 12AU7
used as follows:
V1a - 1/2 12AX7
1st Gainstage
V1b - 1/2 12AX7
2nd Gain stage
V2a - 1/2 12AU7
Reverb recovery stage
V2b- 1/2 12AU7
Tone - CathodeFollower
V3a+b - 12AT7
Reverb Driver Stage
V4a - 1/2 12AX7
Loop send
V4b - 1/2 12AX7
Loop Recovery &Mixer
V5a+b - 12AX7
Phase Inverter orDriverPower Section
Tube Options - 6L6
types
GT5881
GT6L6A
GT6L6B
GT6L6C
GT6L6CB
GT6L6GE
GT6L6S
GTKT66HP
GTKT66C
be Options - EL34
types
GTEL34C
GTEL34R
GTEL34R2
GTE34Ls
GTKT88CGTKT88SV
GT6550C
GT6550R

that pedals or rack effects units
just can’t seem to duplicate at
any price...a 3 spring all tube
Reverb. Our Reverb is deep andharmonically rich, designed torun in parallel so it doesn’t sap
highs as you crank it up. If yourheart is set on Surf Music, ourreverb will oblige....so go for it!

The Power Amp Stage
Your Soul-o 45 can use any of 14different Pentode tube types
currently available from our GT
catalog allowing you to customize
your amp for you’re playing and todramatically change the power, toneor response. Order you S45 withany tube you like, and rest
assured you can always change
them later if the mood hits you
with just a simple bias
adjustment.
Speaker Impedance Selector
and Speaker Output Jacks
The GT custom designed output
transformers not only work withmany types of power tubes, butalso have secondary windings forselection between 4, 8, and 16
ohms speaker loads. You havetwo speaker jacks. Use the #1
speaker jack if using one speaker,
the #2 jack is for adding a secondspeaker.
The #1 jack has
shorting circuitry which turns theamp off if there is no speakerconnected.

AC requirement
internally selectable
100117 VAC
230 VAC only
H.T Fuse
1 Amp Slo-Blo
AC Fuse@ 100 -120VAC
use 3A Slo-Blo@ 230 VAC
use 1.5A Slo-Blo
WeightS45 Combo
42 lbs.
S45 Top
32 lbs.

©2002 Groove Tubes LLC.
All rights reserved. Groove
Tubes, the “GT-in-a-circle”
logomark, Groove Tubes
Custom Shop, Groove Tubes
Custom Shop Products, Dual 75 andD75 are trademarks and service marks created
and owned by Groove Tubes LLC. All other marks
are the property of their respective owners. Allspecifications subject to change without notice.

Soul-o 45 Amplifier Operators Guide
The Parallel FX Loop
This is the most tonallytransparent FX loop you have everheard. When properly set, thisloop allows you to use any digitalor analog FX unit mixed in parallelwith your original preamp signal
with no sacrifice of tone. Most
guitar amp loops are Series types,
so the FX is between the preamp
and power stage and the nice, fattube preamp signal is converted
to a thin, wimpy transistor tone.
We call this “the tone sucking
transistor FX loop syndrome”.
Our exclusive design cures it!
Our parallel loop has two signal
paths; the original dry path andthe FX path. These are mixed on
the rear panel via the Mix control.
Set your FX unit for 100% Wet
and 0% Dry then use the FX loop
Mix control (b/w your in/out on
the rear panel )to blend in thedesired level of FX. Best results
happen with the Mix level set @98% Dry signal and 2% of FX
signal.
Another neat trick is to insert anordinar y foot volume pedal
between the output of the FX andthe Return of our loop. You
increase or decrease the FX levelwith the volume pedal withoutchanging the actual volume!
NOTE: When not using your loop,
be sure the Mix control is set fully
to the “preamp” side. Otherwise
it can reduce your amp’s volumelevel. Worse yet, if the Mix isfully to the FX side without an FX
unit in use, there will be NOoutput from the amp at all!

“Power Tube Tone Tips”• Warm & bouncy round old USA
Tweed type tone, try any of the6L6/KT66 tubes. Power output ofa S45 ranges from 40 to 55 watts
depending on 6L6/KT66 used.
• British Metal punch/crunch
tone, tr y any EL34 type. Our
favorite is the new high power
GT E34Ls.
Estimated
power output of a S45
ranges from 45 to 60 watts
depending on EL34 typeused.

Biasing Your S45 Amp
This is the most critical setting ofyour amp and should always bereadjusted when changing tubetypes or performance rating.
NOTE: Be sure to have your amp
biased by a qualified amp service
tech each time you change to adifferent tube type.
Do NOT
attempt this procedure yourself
as you can seriously damage
your amp as well as yourself!
The bias control pot is locatedinside the amp on the PCB but canbe accessed without removing thechassis from the wood. Use asmall slotted head screwdriver andlook for the rubber isolated hole on
the underneath side of the chassis
just behind the power tubes.

Soul-o Speaker Cabinets
Our cabinets are “tuned” for guitar
playing and made fundamentallydifferent
than
any
other
commercially available guitar
cabinets on the market. We use alightweight 5/8” baffle board andslant it upward on an angle forbetter projection. They can beeither open back, or closed backat your option. Lastly, we have abaffle board designed to raise thecabinet resonance for guitar
which produces a tight, powerfulbass without the common mushy“Big E” string syndrome.
They come loaded with one of ourClassic Clone speakers including:
the CC112/A made in America byEminence; the CC112/B, or the orthe CC10/B made by Celestion.
EX112 - 1 x 12” CCB speaker
EX212 - 2 x 12” CC speakers
EX410 - 4 x 10” CCB speakers.
COMBO - 1 x 12” CCA speaker

Soul-o 45 Combo
on a SFX 112 decoder cab
w/ Backrack attaching
SFX E1 encoder
and Stereo FX unit

GROOVE TUBES LLC“Hear the Difference”

Groove Tubes LLC
Custom Shop Products
1543 Truman Street
San Fernando, California 91340 USA
Tel 818 361 4500
Fax 818 365 9884
www.groovetubes.co