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3-stage amp configurations: tube vs. solid-state in the preamp, saturating power amp, and linear final amp

Purpose of additional final amp

Using an additional, linear final amp permits post-saturation placement of time fx, as follows:

  1. Preamp
  2. Saturating power amp
  3. Load (A: guitar speaker. B: dummy load.)
  4. Post-breakup fx
  5. Linear final amp
  6. Monitor speaker (A. full-range speaker. B: guitar speaker.)
When using a very low-wattage tube power amp, or a dummy load, a 3-stage amp enables power-tube saturation at quiet levels, with final monitoring level independent of Tone-generation concerns.

See also 3-stage rig architectures using various combinations of guitar speaker, full-range speaker, dummy load, cab-sim filter, and mic.

Importance of each stage for the overall amp-breakup tone

Preamp - somewhat important
Saturating power amp - most important
Linear final amp - least important

The use of the terms "good" and "bad" in this classification system follows from the dominant importance of the type of saturating power amp, compared to the lesser importance of the type of preamp.

Classification of hybrid amps

For example, "ST" designates solid-state preamp, tube power amp.

Classification of 3-stage amps

For example, "TTS" designates tube preamp, tube power amp, and solid-state final amp.

The TTS configuration is the classic 3-stage amp configuration

It is not very likely that a *solid-state* power amp driving a dummy load would be of great interest; we can ignore those 4 permutations. Thus we can say that a 3-stage amp-rig is this general rig architecture:

preamp (tube or solid-state)
tube power amp driving a load
final amp (tube or solid-state)

I consider the TTS configuration to be the classic 3-stage amp configuration as far as type of processing stages (tube vs. solid-state):

Tube preamp
Tube power amp
Solid-state final amp

This configuration provides the best combination of Tone, cost, weight, and reliability. Where distortion occurs, tubes are used. Where linear amplification is needed, solid-state is used. Because the power tubes are not being used for final, loud amplication, a single small power tube can be used, and this tube can even be a so-called "preamp tube" type such as 12AX7. So the tube complement for a TTS rig could be as little as two small, inexpensive preamp tubes. For further cost reduction, the preamp stage could be a well-voiced solid-state preamp: a great-sounding STS rig could use as little as one so-called "preamp" tube, such as a 6SN7 or 12AX7. It only has one small tube, but that tube is placed in the most key position: in the saturating tube power amp, rather than in the preamp or in the final amp.

Actual examples of each configuration

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