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Stephenson Amplification

Custom Amplifier

Custom Amp

The Custom is designed for distortion tones.

Features:

  • single-channel preamp
  • single-channel power amp
  • Power Scale™ master volume
  • FAT control (feedback attenuation circuit)
  • ultra-linear / pentode operation
  • foot-switchable boost (preamp gain boost)
  • bright switch (front panel)
  • gain switch (front panel)
  • cut switch (front panel)
  • power tube select switches (back panel)

Front Panel

Custom Amp Front Panel (1)

Gain Mode Switch

- switch in the up position produces more gain and more mids from the preamp.

- switch in the down position is cleaner tone - great when using booster pedals for the OD tone

 

Bright Switch

- switch in up position produces the brightest tones.

 

Gain Potentiometer

Controls preamp gain. This control, used with the bright and gain mode switches, can dial in clean and punchy to saturated distorted tones.

 

Treble, Bass, and Mid Potentiometers

These are the amp's EQ controls.


Custom Amp Front Panel (2)

Drive

The Drive works together with the Power Scale control to keep the amp's tone at any wattage. In other words: cranked tone at any volume. When the Scale is set to maximum, the power amp produces full wattage; any other Scale setting will produce less than full wattage. Scale set to minimum gives you the amp's stand-by mode.

The Drive control determines the amount of saturation and compression that the power amp produces. As the amp is Scaled down, the Drive should also be turned down to keep the amp's natural full-volume tone. A good rule of thumb is: adjust the Drive and Scale controls together. In other words: if you adjust one, then adjust the other to dial in the best tone. Of course there are no right or wrong settings - dial these controls in to achieve the tone you're looking for.

Keep these simple points in mind:

- High drive settings and low scale settings will produce a saturated/compressed tone.

- Low drive settings and high scale settings will produce the cleanest tone.

 

Cut Switch

The Cut switch works in conjunction with the Drive control. With the Cut ON (switch in the Up position) there are less highs and upper mids.

To keep the tone more focused and the bottom tighter, keep the Cut Off (switch in the Down position) and the Drive dialed back.

 

FAT

FAT = feedback attenuation, and controls the amount of negative feedback that is employed in the power amp. The production of negative feedback is a common guitar amplifier method to control the tightness and gain of the power amp. Too much negative feedback can cause a thin, constricted-sounding amp, and too little can cause a bloated-sounding amp. With the FAT set to minimum, a great deal of negative feedback is employed, which keeps the power amp tight with less body and gain. With the FAT set to maximum, the power amp is running open-loop (no negative feedback), for maximum gain, body and wattage from the power amp.

 

Power Scale

This is the amp’s wattage control. This technology was developed by Kevin O’Connor at London Power and is used under Licensed Agreement.

Lower settings produce less wattage.

Higher settings produce more wattage.


Rear Panel Features

Rear Panel

Rear-Panel Items:

AC input – Ultra switch – Foot Switch jack - Valve select – Speaker output – Effects loop

 

Ultralinear Switch

Ultralinear Switch & Foot Switch Socket:

Ultralinear operation has a smooth, warm sound. The Off position is the standard mode of power amp operation. Generally, lower Power Scale settings sound fuller when the Ultralinear is enabled. The Foot Switch jack is a standard stereo ¼ inch connector for controlling effects loop and internal gain boost.





Valve Switch

Power Amp Valve Select:

These switches turn the 3 power tubes on or off. A variety of power tube combinations is possible with the 20-watt amplifier. Any of the tubes can be turned on or off; of course all turned to the off position produces no sound!





TubesThe tube on the left is a EL84 and is enabled with the EL84 switch.

The two octal tube sockets can accommodate several tube types and are enabled by switches V-2 and V-3. The tube types that can be used are: 6V6, 6L6, 5881, 6CA7, EL34, and KT77.

Any combination of these tubes can be used with no re-biasing required, simply plug and play.

The EL84 and V-2 work together, producing one half of the audio waveform, and V-3 works alone producing the other half of the waveform.

The example in the picture is an EL84 combined with a 6V6, and V-3 is using an EL34. This is one of my favourite tube combinations to use in this amplifier. The output signal is very balanced and produces 30 watts!


Output

Output:

This is the speaker output section. The impedance selector is labelled 1- 2 -3 because any setting can be used with a 4ohm, 8ohm or 16ohm speaker cabinet. Use the setting that you like the best. When using different output tube combinations, listen to the different impedance settings to see what one you like best.




Effects Loop

Effects Loop:

This effects loop is a 6SN7 tube-driven parallel type with variable send and receive levels that will accommodate both pedals and rack gear. This loop is based on a design by Kevin O'Connor of London Power. I've been using it for many years now and it just works great.



Foot Switch

Foot Switch
Controls boost function
Controls effects loop









Chassis Features

Chassis

  • Custom made-in-Canada toroidal power transformer for low-noise operation
  • Custom made-in-Canada toroidal output transformer for full-bodied tone
  • Aluminum chassis
  • Two 12AX7 tubes in preamp
  • One 6SN7 tube in effects loop
  • One 6SN7 tube for phase inverter
  • Three-tube power amp. Single EL84 blended with two octal tubes (6V6 etc.).

Interested in a Custom Amplifier? See our Price Page for ordering information!