Manual

The Technical Stuff
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About “Class A”
“Class A” electronic devices such as the LA-610 are designed so that their active components are
drawing current and working throughout the full signal cycle, thus eliminating a particularly
unpleasant form of distortion called crossover distortion.
About Negative Feedback
Negative feedback is a design technique whereby a portion of the preamplifier’s output signal is
reversed in phase and then mixed with the input signal. This serves to partially cancel the input
signal, thus reducing gain. A benefit of negative feedback is that it both flattens and extends
frequency response, as well as reducing overall distortion. Turning the LA-610 front panel Gain switch
clockwise (i.e., increasing it) reduces negative feedback, which has the effect of also increasing the
amount of the input tube’s harmonic distortion, a major contribution to the “warm” sound
characteristic of tube equipment. ( see #1 on page 4)
Impedance Matching
Depending upon their design, different microphones provide different output impedances. Typical mic
impedances range from as low as 50 ohms (the symbol for ohms is Ω) to thousands of ohms (K
ohms). The LA-610 Mic input can be set to either 500 ohms or 2.0K ohms, allowing it to accommodate
virtually every kind of microphone. Switching between these two positions while listening to a
connected mic may reveal different tonal qualities and/or gain differences (be sure to carefully level-
match when doing comparisons because louder tends to sound better). Generally speaking, a
microphone preamplifier should have an input impedance roughly equal to about ten times the
microphone output impedance. For example, if your microphone has an output impedance of
approximately 200 ohms, the switch should be set to the 2.0K position. However, making music is not
necessarily about adhering to technical specifications, so feel free to experiment with the settings to
attain the desired sound: doing so will not result in harm to either your microphone or the LA-610.
( see #2 on page 4)
The LA-610’s Hi-Z input is intended for electric guitar, electric bass, or any instrument with a
magnetic or acoustic transducer pickup, and can be set to either 47K ohms or 2.2M (million) ohms.
The 47K ohms setting is best suited for the -10 dBv level signals typically provided by active basses
and guitars, while the 2.2M ohms setting is more suitable for instruments with passive pickup
systems. Since a particular instrument’s output impedance may actually be somewhere between the
active and passive levels, feel free to experiment to achieve the best sound at the desired level.
Again, changing the input impedance will not harm your instrument or the LA-610.
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