- Written by Jim Clements
- Published on 03 April 2013
Design of the the Funk LAP-2.V3 Preamplifier
The Funk LAP-2.V3's circuit design is based on a sophisticated active matrix switch. The primary advantages of this topology are that you have no mechanical contacts in the signal path, and there are no signal losses, even with numerous outputs. Important secondary benefits include low crosstalk and immunity to phase shifts. The matrix switch is buffered with a set of high quality op amps which leads to the super high input impedance.
This preamp features six selectable line level inputs, two preamp outs, four record outs and a front panel headphone jack (1/4"). All jacks are high quality with gold-plated contacts.
The power supply is a super quiet choke-regulated design with filter caps and low power draw – only 4.7 watts under normal operating conditions. It provides exemplary isolation from power line irregularities.
Funk selected an ALPS analog volume potentiometer in designing the LAP-2.V3. Funk's promotional materials indicate that digitally controlled volume controls compress dynamics and introduce distortion at low gain levels. They are willing to allow small traces of interchannel crosstalk and tracking nonlinearities to get the lower distortion results. Funk says they hand select the stereo pots and align the resistor network around each pot to obtain less than 0.5 dB of channel imbalance. This should be inaudible in any conceivable real world environment. Bear in mind that these numbers are measured on a new unit, and the imbalance would be expected to increase as the unit ages.
The Funk's headphone amp was a conundrum to me. Most high end headphone amplifier output stages are designed using discrete circuits or a mix of discrete and integrated circuits. Not here. Instead, Funk uses a low distortion op amp that is rated for higher impedance headphones (300 – 600 ohm). Funk includes a current limiter circuit to prevent overload so the unit will work with low impedance phones and earbuds. Funk says that my review unit is from an early production run. The new units have more current output, but Funk acknowledged that the headphone driver's current capability is ultimately limited by the unit's small power supply and the thermal limit imposed by the box's size. Be that as it may, Funk recommends headphones in the 200 – 600 ohm range for best results.
Normal operation of the Funk LAP-2.V3 is solid and confidence-inspiring. The user depresses the input button to select the input for playback and the matrix engages with a satisfying mechanical click. Holding the button mutes the line outputs but retains headphone out and the green light for that input dims. To select a source for recording, the user holds the "Record" button and then depresses the desired input and the red light for that input illuminates. The detented volume control has a precise and competent action.
The LAP-2.V3 has a great deal of underlying flexibility including features such as jumpers to covert the line outs to a fixed level, provisions for a processor loop by way of additional jumpers, and the option to trim gain levels for each input to accommodate the varying levels of your different source devices.
The Funk has many RCA jacks on the back panel. These jacks are grouped in rows and columns but they are really differentiated in large part by their labels. So the end user is cautioned to be careful when connecting components to this preamp. There are cases where the user may introduce a feedback loop and this could cause problems like spoiling a recording or damaged equipment. We are working on a separate technical article that will cover this topic.
Funk designed this unit to have a line output of 25 dBu, which is 13.8 volts RMS. In order to achieve this high an output voltage, Funk had to run the chips at their Absolute Maximum Rating. This design choice is perplexing to me because the target output voltage is far higher than what is required for consumer equipment and running a chip at its Absolute Maximum Rating is not good practice. This could lead to future reliability problems.
The Funk LAP-2.V3 is available in a number of finishes - white paint or anodized in black, blue, dark red, silver, or gold. My review unit was configured for use in North America (110 V, 60 Hz) but the power cord still had a German plug, so I had to dig out my Euro-style adapters for the review.