M-Audio 81602 About Soft Clipping and the 20dB Pad Switch, The Input Impedance Selector

About Soft Clipping and the 20dB Pad Switch:

Soft clipping (often referred to as tube saturation in tube gear) is often desirable to add the perception of warmth to a recording.TAMPA exhibits a gradual soft clipping characteristic, where distortion increases with signal level.This distortion exhibits a non-linear curve as shown.

Soft clipping is tied to the internal signal level —a function of input level and gain. The OUTPUT LEVEL METER shows the internal signal level and is therefore a good indicator of soft clipping. In general, the more the OUTPUT LEVEL METER moves, the more soft clipping is present. The 20dB PAD reduces the output level without changing the internal level. Engaging the 20dB PAD switch (thereby attenuating the analog output signal) allows you to drive the internal signal level higher, without overloading outboard gear and producing a warmer sound (for a more neutral sound, leave the 20dB PAD turned off.)

By engaging the 20dB PAD switch, you are allowed to increase the preamp GAIN knob setting, thereby bringing out the TAMPA’s “soft-clipping” characteristic. The higher the gain from the preamp, the more that soft- clipping will occur (up until the point of actual clipping). Increasing the amount of soft-clipping will give you a sound similar to what is known as “tube saturation,” which is what occurs when increased signal levels are used in a tube-type preamp. This feature is unique to the TAMPA preamp and gives you emulation of tube warmth across the full frequency spectrum, at your discretion and complete control.

Feel free to experiment with this feature. It may be something that you choose to use with one instrument or mic and not another. It’s up to you and your particular taste and needs.

NOTE: The 20dB PAD only affects the analog output circuitry. Engaging the pad will have no affect on the signal at the digital outputs—in the digital domain, the only way to avoid soft clipping is by running at lower signal levels.

The Input Impedance Selector

On some microphones, such as vintage or tube mics, you will want to match the TAMPA’s input impedance to the output impedance of the microphone. On others, such as modern solid-state FET mics, the input impedance can be set to 10x the microphone’s output impedance or more. TAMPA’s Input Impedance selector is designed to optimize performance with different microphones.

For vintage (older tube or ribbon mics) or modern tube mics, check the output impedance listed in the microphone’s documentation, then set the INPUT IMPEDANCE selector to the closest setting. If in doubt, try the 300 Ohm or 600 Ohm setting.

For a FET mic (solid-state), start with the 2400 Ohm setting. For any mic, some experimentation might be in order. You may achieve varied results from alternate impedance settings, and the effect that you hear in tonal quality may be a desirable one.

Using the Phase Invert Switch

When a single microphone is in use, phase will rarely be a consideration and the PHASE switch should remain in the NORMAL position.When multiple microphones are in use, the positioning and acoustic relationship of the mics and the room can cause phase problems resulting in loss of level and tonality.This often manifests as an atypical “thin” or “hollow” sound. In this event, try switching the phase of one of the microphone preamps.

To change the phase of TAMPA’s output by 180 degrees, set the PHASE switch to the INVERT position. If the sound does not improve significantly, return the PHASE switch to the NORMAL position and look elsewhere for the cause.

Using the Low-Cut Filter

Unwanted low frequencies can sometimes be a problem when recording with a microphone. Moderate soundproofing, for example, tends to absorb

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