7 Approaches to Power Tube Saturation at Low Room Noise Levels

New Summary (2006)

Key to My Standard Amp Tone Abbreviations

Communication to the uninitiated is important, but technical notation is required at an advanced level.

di � Direct Inject, meaning especially the idea of tapping a line-level signal to listen to it or send it to line-level processing.

R � resistive load

fr-spk � full-range speakers

g-spk � guitar speaker

d-load � dummy load

isobooth � speaker cabinet isolation booth, usually including a microphone

soundtap � point in a circuit where you tap a line-level signal and listen to it

ctrlrm � control room

atten - attenuation

p-tube - power tube

pwr - power

hotplate - THD Hot Plate power attenuator

spk - speaker

dist - distortion

Rig approaches to controlled power tube distortion

isobooth (miked g spk acting as load)
attenuation (load split between R and miked g spk) [this page doesn't address the power-supply-based attenuation approach]
d-load + miked g-spk
d-load + spk-sim
unmiked spk w/ spk-sim (unmiked g spk acting as load)
load is mostly g-spk in isobooth, partly a miked spk
mix miked spk w/ DI-spk-sim
load: partly a g-spk, partly R, DI-spk-sim

Factors to permutate

load = g-spk, R, or combination
soundtap = miked g-spk, DI-spk-sim, combination
listento = ctrlrm g-spk, isobooth g-spk, ctrlrm fr-spks. or, how hard pushing g-spk

Permutations

miking g-spk, load = g-spk (#1 above)
miking g-spk, load = R (3)
di spk sim, load = g-spk (5)
di spk sim, load = R (4)
miking g-spk, load = R + g-spk (2)
di spk sim, load = R + g-spk (8)
What would produce (6) and (7) above?
6. load is mostly g-spk in isobooth, partly a miked spk (load = g spk miked + g spk unmiked, sound tap via mike only) reduces to (1), with 2 isobooths driven to diff't wattage/spl -- mic the isobooth g-spk, listen directly to controlrm/livrm g-spk.

The most complex/advanced system possible

load = g-spk in isobooth + g-spk in ctrlrm + R (hotplate: spk out 1 to isobooth, 2 to ctrlrm, atten 20%)

soundtap = miked g-spk in ctrl rm + miked spk in isobooth + DI-spk-sim (hotplate Line Out > spksim)

also add: hotplate Line Out > eq > ss amp > other g-spk in isobooth || other g-spk in ctrl rm

Degrees of Tone Compromise for the Various Rig Approaches

1. miked g-spk w/ spk dist, w/ direct p-tube/spk interaction (0 degree reduc: has g spk, g spk dist, direct interact)

2. miked g-spk w/o spk dist, w/ direct p-tube/spk interaction (1 degree reduc: no g spk dist)

3. di of amp that sees mixed r/spk load (2 degree reduc: no g spk, no g spk dist. is some interaction in system b/c load is spk/R combin)

4. miked g-spk w/ spk dist after bringing line-level p-tube sound up to hi-pwr (1 degree reduc: no direct interact)

5. miked g-spk w/o spk dist after bringing line-level p-tube sound up to hi-pwr (2 degree reduc: no direct interact, no spk dist)

Thus 1 in the present list will sound best, 2 (wimped spk) and 4 will sound good (reconstituted), 3 (no spk, from linelev) and 5 worst (wimped spk, reconstituted from linelev)

Older Material

Building Blocks for Guitar Rigs Using Various Speaker Approaches

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

SPEAKER SYSTEM including any of the following:
inductive load
partial power step-down load
guitar speaker cabinet
speaker isolation cabinet
mini speaker isolation cabinet
guitar speaker
mini guitar speaker
microphone
speaker simulator (low-pass filter)

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

=================================================
Overview of 7 Approaches to Guitar Speakers

Arranged in order of artificiality of load, compared to driving a traditional large guitar speaker directly.

Includes guitar speaker approaches rated in terms of room noise level,
physical bulk, and tone purity.

The ideal is (noise: 0. bulk: 0. tone: 10).

LOW-POWERED TRADITIONAL AMP:

1. Very Low-Power Amp into Guitar Speaker ("low-powered mini-amp")
(noise: 7. bulk: 7. tone: 10)

DIRECT INTO SPEAKER IN ISOLATION CABINET:

2. Direct Amp Output into Guitar Speaker in Isolation Cabinet ("speaker
isolation cabinet") (noise: 6. bulk: 9. tone: 9.5.)

3. Direct Amp Output into Mini Guitar Speaker in Mini Isolation Cabinet
("mini speaker-isolation cabinet") (noise: 4. bulk: 3. tone: 9.)

PARTIAL POWER-STEP-DOWN LOADS DRIVING A GUITAR SPEAKER:
4. Partial Power Step-Down Load into Guitar Speaker in Traditional
Cabinet ("step-down load with speaker") (noise: 2. bulk: 8. tone: 8.5.)

5. Partial Power Step-Down Load into Guitar Speaker in Isolation Cabinet
("step-down load with speaker isolation cabinet") (noise: 2. bulk: 10.
tone: 8.)

6. Partial Power Step-Down Load into Mini Guitar Speaker in Mini Speaker
Isolation Cabinet ("step-down load with mini speaker isolation cabinet")
(noise: 1. bulk: 4. tone: 7.5.)

COMPLETE INDUCTIVE LOAD, NO SPEAKER AT ALL:

7. Full Inductive Load with Low-Pass Guitar Speaker Simulator and No
Mic ("inductive load with speaker simulator") (noise: 0. bulk: 1. tone:
7.)

Speaker approach #7 is unique and fake in 3 ways:
o It is the only system that uses a full inductive load rather than a partial
power step-down load
o It is the only system that uses a speaker simulator (low-pass filter)
rather than a real speaker
o It is the only system without a microphone.

While a line-level speaker emulator is a single package, its load and its
speaker simulator are two separate subsystems.

Lacking a real speaker and microphone, and slamming the entire power
output against a non-speaker load, it's a challenge for this approach to
emulate the traditional mic'd speaker hooked directly across the output
transformer.

===========================================================
Complete Guitar Rig Systems for the Various Guitar Speaker Approaches

Only the middle, speaker-oriented items differ in each approach.

LOW-POWERED TRADITIONAL AMP:

1. Very Low-Power Amp into Guitar Speaker (noise: 7. bulk: 7. tone:
10)
("low-powered mini-amp")

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

guitar speaker cabinet
guitar speaker
microphone

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

Product examples: www.torresengineering.com 5-watt amp kit, Hi-Mu
7-watt studio amp

DIRECT INTO SPEAKER IN ISOLATION CABINET:

2. Direct Amp Output into Guitar Speaker in Isolation Cabinet (noise: 6.
bulk: 9. tone: 9.5.)
("speaker isolation cabinet")

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

speaker isolation cabinet
guitar speaker
microphone

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

Product examples: Traditional amp driving a Demeter speaker isolation
cabinet

3. Direct Amp Output into Mini Guitar Speaker in Mini Isolation Cabinet
(noise: 4. bulk: 3. tone: 9.)
("mini speaker-isolation cabinet")

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

mini speaker isolation cabinet
mini guitar speaker
microphone

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

Product examples: Hi-Mu 7-watt amp driving a Micro Room mini speaker isolation cabinet, bypassing the inductive load.

PARTIAL POWER-STEP-DOWN LOADS DRIVING A GUITAR SPEAKER:

4. Partial Power Step-Down Load into Guitar Speaker in Traditional
Cabinet (noise: 2. bulk: 8. tone: 8.5.)
("step-down load with speaker")

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

partial power step-down load
guitar speaker cabinet
guitar speaker
microphone

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

Product examples: Traditional amp through Marshall Power Brake or THD
Hot Plate, then driving traditional cabinet. The Tom Scholtz Power Soak
was similar, but resistive rather than inductive.

5. Partial Power Step-Down Load into Guitar Speaker in Isolation Cabinet
(noise: 2. bulk: 10. tone: 8.)
("step-down load with speaker isolation cabinet")

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

partial power step-down load
speaker isolation cabinet
guitar speaker
microphone

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

Product examples: Traditional amp through Marshall Power Brake or THD
Hot Plate, then driving Demeter speaker isolation cabinet

6. Partial Power Step-Down Load into Mini Guitar Speaker in Mini Speaker
Isolation Cabinet (noise: 1. bulk: 4. tone: 7.5.)
("step-down load with mini speaker isolation cabinet")

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

partial power step-down load
mini speaker isolation cabinet
mini guitar speaker
microphone

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

Product examples: Traditional amp driving a Micro Room mini speaker
isolation cabinet.

COMPLETE INDUCTIVE LOAD, NO SPEAKER AT ALL:

7. Full Inductive Load with Low-Pass Guitar Speaker Simulator and No
Mic (noise: 0. bulk: 1. tone: 7.)
("inductive load with speaker simulator")

pre-distortion eq and eq-oriented effects
distortion
post-distortion eq and effects
saturated power tube and output transformer

inductive load
speaker simulator (low-pass filter)

post-power-tube eq and time-based effects
non-saturated power amp
full-range monitor

Product examples: ADA's Ampulator; Groove Tubes' original 30-watt amp
emulator; Traditional amp driving Harry Kolbe's Silent Speaker and
speaker emulator; Traditional amp driving the THD Hot Plate in its full
inductive load mode (rather than just as a partial power step-down load).

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