Sonic Frontiers SFL-2 Two Chassis Dual Mono Balanced Preamp
General:
The Sonic Frontiers SFL-2 is a balanced dual-mono, two-chassis tube preamplifier known for its excellent build quality and impressive sound. Like many Sonic Frontiers components, it combines thoughtful engineering with a clean, understated design that still feels substantial and high-end.
Plus you know it's something special when it's Stereophile Class A Rated and is featured on the fantastic vintage HiFi website The Vintage Knob!!
Features include balanced XLR and single-ended RCA inputs, along with a tape loop for added flexibility. The separate power supply chassis helps reduce noise and improve serviceability, with the two units connected via an umbilical cable ( all internal wiring is KimberKable). It’s also tube rectified — something rarely seen in preamplifiers — and uses eight 6922 / 6DJ8 tubes in the audio circuit.
All inputs were fully tested and the entire unit was thoroughly inspected electronically prior to listing. The tubes are strong and healthy, and all controls have been cleaned for smooth, noise-free operation.
The SFL-2 would pair especially well with the Sonic Frontiers SFS-80 amplifier we recently listed, both sonically and aesthetically.
Included with the preamplifier are its original shipping box for safe transport and a printed copy of the owner’s manual.
SkyFi Cosmetic Notes:
The power toggle switch on the power supply is slightly bent, but fully functional. Very light wear on some of the brushed surfaces. Overall condition is very good.
Ownership:
Single Owner
Connections:
RCA and XLR inputs, IEC power input,
General Sound:
Smooth, uncolored, undistorted natural and clean
Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.
Working Condition:
Working perfectly and tested in our lab and listening room.
Included:
Unit, Box, Manual
Packing:
Original Manufacturers Packing
Specs:
Frequency Response:
- 2 Hz to 100 kHz ±0.5 dB (100K load)
- 350 kHz -3.0 dB
- THD & N (@ 1 V output):
- <0.1% from 20 Hz to 20 kHz
- Typically <0.03% @ 1 kHz
Gain:
- 22 dB @ 1 kHz (single-ended)
- 28 dB @ 1 kHz (balanced)
Noise:
- 120 µV unweighted (balanced outputs, volume control @ 12 o’clock)
- -85 dB below @ 2 Volt R.M.S. output
- SMPTE (IMD) @ 2 V output:
- <0.05%, typically 0.03% (balanced)
Input Impedance:
- 50 K ohms (single-ended)
- 100 K ohms (balanced)
Output Impedance:
- 160 ohms @ 1 kHz (single-ended)
- 320 ohms @ 1 kHz (balanced)
- Minimum Recommended Load Impedance: 10 K ohms
Output Voltage (100K/100pf & 10K/1000pf loads):
- Maximum 30 V R.M.S. (single-ended)
- Maximum 60 V R.M.S. (balanced)
Maximum Input:
- 2.5 V R.M.S. (Volume control fully clockwise)
Stereo Separation (Crosstalk):
- 70 dB @ 1 kHz (single-ended)
- 75 dB @ 1 kHz (balanced)
Power Requirements:
- 135 VA (75 VA in standby mode) 50/60 Hz
- 1.1 Amps @ 120 V A.C.
Fuse Requirements (2):
- 1.5 Amp 250 V fast-blo (100 V to 120 V Countries)
- 0.75 Amp 250 V fast-blo (200 V to 240 V Countries)
Tube Complement:
- 8 × 6922 (6DJ8 types)
Dimensions:
Each chassis:
19" Wide × 13" Deep × 4.5" High
(48 cm × 33 cm × 11.5 cm)
Weight:
55 lbs.
Approximate Age:
1995
Link to Manual:
Click Here
Recommended Cables:
Kimber Kable - RCA Interconnects - Better
Kimber Kable - RCA Interconnects - Best
Kimber Kable - Phono Interconnects
Kimber Kable - BALANCED XLR Connectors - Better
Kimber Kable - BALANCED XLR Connectors - Best
Kimber Kable - Power Cords - Better
Kimber Kable - Power Cords - Best
Testing Process:
We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.
When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface.
The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1 KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope.
We then switch to a 1 KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment.
Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. If the preamp under test has balanced inputs and/or outputs these are tested as well.
We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected.
If the preamplifier has remote control functions these are also tested. Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions.
Description
General:
The Sonic Frontiers SFL-2 is a balanced dual-mono, two-chassis tube preamplifier known for its excellent build quality and impressive sound. Like many Sonic Frontiers components, it combines thoughtful engineering with a clean, understated design that still feels substantial and high-end.
Plus you know it's something special when it's Stereophile Class A Rated and is featured on the fantastic vintage HiFi website The Vintage Knob!!
Features include balanced XLR and single-ended RCA inputs, along with a tape loop for added flexibility. The separate power supply chassis helps reduce noise and improve serviceability, with the two units connected via an umbilical cable ( all internal wiring is KimberKable). It’s also tube rectified — something rarely seen in preamplifiers — and uses eight 6922 / 6DJ8 tubes in the audio circuit.
All inputs were fully tested and the entire unit was thoroughly inspected electronically prior to listing. The tubes are strong and healthy, and all controls have been cleaned for smooth, noise-free operation.
The SFL-2 would pair especially well with the Sonic Frontiers SFS-80 amplifier we recently listed, both sonically and aesthetically.
Included with the preamplifier are its original shipping box for safe transport and a printed copy of the owner’s manual.
SkyFi Cosmetic Notes:
The power toggle switch on the power supply is slightly bent, but fully functional. Very light wear on some of the brushed surfaces. Overall condition is very good.
Ownership:
Single Owner
Connections:
RCA and XLR inputs, IEC power input,
General Sound:
Smooth, uncolored, undistorted natural and clean
Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.
Working Condition:
Working perfectly and tested in our lab and listening room.
Included:
Unit, Box, Manual
Packing:
Original Manufacturers Packing
Specs:
Frequency Response:
- 2 Hz to 100 kHz ±0.5 dB (100K load)
- 350 kHz -3.0 dB
- THD & N (@ 1 V output):
- <0.1% from 20 Hz to 20 kHz
- Typically <0.03% @ 1 kHz
Gain:
- 22 dB @ 1 kHz (single-ended)
- 28 dB @ 1 kHz (balanced)
Noise:
- 120 µV unweighted (balanced outputs, volume control @ 12 o’clock)
- -85 dB below @ 2 Volt R.M.S. output
- SMPTE (IMD) @ 2 V output:
- <0.05%, typically 0.03% (balanced)
Input Impedance:
- 50 K ohms (single-ended)
- 100 K ohms (balanced)
Output Impedance:
- 160 ohms @ 1 kHz (single-ended)
- 320 ohms @ 1 kHz (balanced)
- Minimum Recommended Load Impedance: 10 K ohms
Output Voltage (100K/100pf & 10K/1000pf loads):
- Maximum 30 V R.M.S. (single-ended)
- Maximum 60 V R.M.S. (balanced)
Maximum Input:
- 2.5 V R.M.S. (Volume control fully clockwise)
Stereo Separation (Crosstalk):
- 70 dB @ 1 kHz (single-ended)
- 75 dB @ 1 kHz (balanced)
Power Requirements:
- 135 VA (75 VA in standby mode) 50/60 Hz
- 1.1 Amps @ 120 V A.C.
Fuse Requirements (2):
- 1.5 Amp 250 V fast-blo (100 V to 120 V Countries)
- 0.75 Amp 250 V fast-blo (200 V to 240 V Countries)
Tube Complement:
- 8 × 6922 (6DJ8 types)
Dimensions:
Each chassis:
19" Wide × 13" Deep × 4.5" High
(48 cm × 33 cm × 11.5 cm)
Weight:
55 lbs.
Approximate Age:
1995
Link to Manual:
Click Here
Recommended Cables:
Kimber Kable - RCA Interconnects - Better
Kimber Kable - RCA Interconnects - Best
Kimber Kable - Phono Interconnects
Kimber Kable - BALANCED XLR Connectors - Better
Kimber Kable - BALANCED XLR Connectors - Best
Kimber Kable - Power Cords - Better
Kimber Kable - Power Cords - Best
Testing Process:
We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.
When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface.
The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1 KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope.
We then switch to a 1 KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment.
Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. If the preamp under test has balanced inputs and/or outputs these are tested as well.
We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected.
If the preamplifier has remote control functions these are also tested. Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions.
