Groove Tubes Soul-o 45 Operator's Manual

Congratulations

You’ve just purchase what we believe is
the best amp on the planet! Welcome
to the growing list of artists who share
our mutual lust for tone. Now, we’d
like to better acquaint you with your
new Soul-o 45 amp.

Construction details:

1 - All components are hand soldered.

There are no quick disconnects, 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 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 selected
power tube!
4 - We use only double sided, double
thick PC boards with double thick
traces. We use chassis mount type
power tube sockets hand bolted, hand
soldered, 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 hand
labor 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 and
construction 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 their
design. These of coarse have magnetic
guitar pickups which are by definition
high impedance, low level output
devices. However, most players use a
foot pedal before the preamp, and
pedals are low impedance, high output
devices. The result is the pedal adds
two effects, the one you intended
(maybe distortion or chorus), and the
second 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 first
ever

“Pedal Friendly” guitar amp,

with a preamp that will not overload
when pushed by today’s high output
pedals. This means it has “tons” of
headroom so the pedal breaths better
and remains open and transparent
sounding...and improves the punch
and tone of any pedal!
The S45 preamp stage has five dual
triodes, each performing multiple
functions in the circuitr y. The preamp
design has Gain, Bass, Middle, Treble,
and Volume. We did not design this
preamp for massive amounts of
distortion as you can get distortion and
other effects using your favorite foot
pedals. The S45 was deigned to be
pedal friendly, so the preamp will not
“mush out” no matter how hard you
play. Our design provides loads of
headroom in the preamp stage to get
the best possible results with your
pedals. However, an increase of the
Gain 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 in
overtones.

The Passive Tone Controls

The tone controls of the S45 amp are
the Passive type, similar to those used

in older, classic tube amps. Many
amps made today instead use Active
type tone controls, which have a
separate gain section for each tone
band which literally “suck tone” from
the preamp. That’s why we don’t use
them. Passive controls use a
common tube gain stage to boost
the entire frequency range, then
divide the Bass, Middle, and Treble
with passive filters to shape your
tone. 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 the
Treble control (compensate
the volume loss by
increasing Gain or Volume).
Because passive controls
share a common gain
stage, turning any one of
them fully up (or down!)

diminishes the effect of the others.

Also, our Passive tone controls are
“post Gain”, giving you a truly touch
sensitive amp that reflects your
personality. 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. By
contrast, if you play with a lighter
touch, 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 and
have 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 dead
room, and less for live rooms. Season
to taste!

The Reverb Control

We’ve included perhaps the one effect

Groove Tubes Soul-o Series Guitar Amplifier Operators Guide

Soul-o 45

The

TM

All tube “Pedal Friendly” guitar amp with tube reverb.

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 and
harmonically rich, designed to
run in parallel so it doesn’t sap
highs as you crank it up. If your
heart is set on Surf Music, our

reverb will oblige....so go for it!

The Power Amp Stage

Your Soul-o 45 can use any of 14
different Pentode tube types
currently available from our GT
catalog allowing you to customize
your amp for you’re playing and to
dramatically change the power, tone
or response. Order you S45 with
any 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 with
many types of power tubes, but
also have secondary windings for
selection between 4, 8, and 16
ohms speaker loads. You have
two speaker jacks. Use the #1
speaker jack if using one speaker,
the #2 jack is for adding a second
speaker. The #1 jack has
shorting circuitry which turns the
amp off if there is no speaker
connected.

The Parallel FX Loop

This is the most tonally
transparent FX loop you have ever
heard. When properly set, this
loop allows you to use any digital
or analog FX unit mixed in parallel
with 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, fat
tube 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 and
the 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 the
desired 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 an
ordinary foot volume pedal
between the output of the FX and
the Return of our loop. You
increase or decrease the FX level
with the volume pedal without
changing 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 volume
level. Worse yet, if the Mix is
fully to the FX side without an FX
unit in use, there will be NO
output from the amp at all!

“Power Tube Tone Tips”

• Warm & bouncy round old USA
Tweed type tone, tr y any of the

6L6/KT66 tubes. Power output of
a 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 type
used.

Biasing Your S45 Amp

This is the most critical setting of
your amp and should always be

readjusted when changing tube
types or performance rating.

NOTE: Be sure to have your amp
biased by a qualified amp service
tech each time you change to a
different tube type. Do NOT
attempt this procedure yourself
as you can seriously damage
your amp as well as yourself!

The bias control pot is located
inside the amp on the PCB but can
be accessed without removing the
chassis from the wood. Use a
small slotted head screwdriver and
look 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 fundamentally
different than any other
commercially available guitar
cabinets on the market. We use a
lightweight 5/8” baffle board and
slant it upward on an angle for
better projection. They can be
either open back, or closed back
at your option. Lastly, we have a
baffle board designed to raise the
cabinet resonance for guitar
which produces a tight, powerful
bass without the common mushy
“Big E” string syndrome.
They come loaded with one of our
Classic Clone speakers including:
the CC112/A made in America by
Eminence; the CC112/B, or the or
the 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

www.groovetubes.com

GROOVE TUBES LLC

Groove Tubes LLC
Custom Shop Products

1543 Truman Street
San Fernando, California 91340 USA
Tel [phone]
Fax [phone]
www.groovetubes.co

©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 and

D75 are trademarks and service marks created

and owned by Groove Tubes LLC. All other marks

are the property of their respective owners. All

specifications subject to change without notice.

Tech
specs

Input

1/4 “ phone jack

Input Level

-10 dB nominally

FX level

-10 dB nominally

Preamp
Section

3 x GT12AX7
1 x 12AT7
1 x 12AU7
used as follows:
V1a - 1/2 12AX7

1st Gain
stage
V1b - 1/2 12AX7
2nd Gain stage
V2a - 1/2 12AU7
Reverb recovery stage
V2b- 1/2 12AU7

Tone - Cathode
Follower
V3a+b - 12AT7
Reverb Driver Stage
V4a - 1/2 12AX7
Loop send
V4b - 1/2 12AX7
Loop Recovery &
Mixer
V5a+b - 12AX7
Phase Inverter or
Driver

Power Section

Tube Options - 6L6
types
GT5881
GT6L6A
GT6L6B
GT6L6C
GT6L6CB
GT6L6GE
GT6L6S
GTKT66HP
GTKT66C
be Options - EL34
types
GTEL34C
GTEL34R
GTEL34R2
GTE34Ls
GTKT88C
GTKT88SV
GT6550C
GT6550R

AC requirement

internally selectable
100
117 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

Weight
S45 Combo

42 lbs.

S45 Top

32 lbs.

Soul-o 45 Combo

on a SFX 112 decoder cab
w/ Backrack attaching
SFX E1 encoder
and Stereo FX unit

Soul-o 45 Amplifier Operators Guide

“Hear the Difference”