Our Testing Process

Each piece of equipment that comes through the doors of SkyFi Audio undergoes an intensive multipoint inspection, cleaning, and verification process to ensure proper functionality and sonic fidelity.

We are audio enthusiasts and collectors ourselves, and we understand how frustrating it can be to receive a piece of equipment that is either not functioning as advertised, or performing out of spec.

Throughout this process it is not uncommon to find components that require replacement due to age, overheating, or other factors consistent with normal use. If exact replacement parts are no longer available, we cross-reference the best possible substitutions which are generally accepted by the audio restoration community. In order to avoid counterfeits, we only source replacement parts from reputable distributors.

Our laboratory is equipped with a variety of test devices that allow us to verify manufacturer published specifications, such as rated RMS output power (a true consistent rating of output power), and THD (Total Harmonic Distortion).

Our bench test procedure is the first and most important step in our verification process, but we've found that it is not possible to capture every nuance of performance by looking only at scopes and meters.

For this reason the majority of our pieces undergo a listening test on our reference system before being listed for purchase. We also value this step for the insight that it gives us into the sound, performance, and features of each individual piece, allowing us to make better educated recommendations to our customers.

Bellow you will find detailed testing procedures for each type of component. Note that we are always learning something new so the process is evolving all the time.

The SkyFi Testing Process for Preamplifiers:

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 PCB’s 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 1KHz 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 1KHz 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.

The SkyFi Testing Process for Solid State Amplifiers:

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.

If the amplifier passes visual inspection, we move on to a controlled power on sequence using a Sencore safety analyzer to monitor current draw in real time. Once the amplifier is determined to be safe to operate, we connect it to full AC mains for function and power testing. We connect the speaker outputs of the amplifier to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1KHz test signal at the amplifier’s input and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. If the device under test has both balanced and single ended inputs they are both tested at this time. We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.

The SkyFi Testing Process for Tube Amplifiers:

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 resistors and other passive components for signs of overheating. If tube arcing has occurred in the past we can usually spot discoloration on the output tube sockets. On vintage units we often spot check select capacitors for value and ESR.

If the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use an Amplitrex AT-1000 Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy. We document the results of each tube and replace any weak or suspect tubes before proceeding. When we power on tube amplifiers for the first time we usually use a variac and current limited AC supply and slowly raise the voltage up to nominal mains level while monitoring plate, screen, filament, and negative bias supply voltages where applicable. If everything is in order we feed a low level test signal into the amplifier’s input and monitor its output on an oscilloscope across an 8 ohm dummy load. At this point we are just looking to verify basic function and confirm that the output transformers are not damaged. Once we have verified that the amplifier is safe to operate, we connected it to full mains power. For fixed bias amps we set the bias to manufacturer spec. For cathode biased amps we monitor the plate to cathode voltage to determine if the output tubes are operating in a safe range. Once the output section is verified we move onto bench evaluation.

We start by feeding the input of the amplifier with a low level 1KHz test signal, slowly increase its amplitude while monitoring the amplifier’s output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. We finish off the bench evaluation with a 1KHz square wave check and a 20Hz to 20KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours. For tube amps we like to run this test at least twice. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when it has fully come up to temperature. We find this step to be essential, especially for vintage units.

The SkyFi Testing Process for Tuners:

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. Vintage analog tuners also have moving parts related to the tuning gang and dial string. These parts are inspected for smooth operation.

If the unit passes visual inspection it is bench tested for a handful of key performance parameters using a Sencore SG80 AM/FM Stereo Analyzer. The SG80 allows us to “simulate” an ideal radio station using precision test signals instead of music. This device, in conjunction with an oscilloscope allows us to properly evaluate the following parameters:

1. AM Reception (Where Applicable)

2. FM Mono Reception & Tuning Meter Function

3. FM MPX Reception (Stereo)

4. Dial Tracking - How accurately the tuner dial or display indicates the actual frequency of the broadcast being received.

5. Stereo Separation - A properly working stereo tuner will have minimal crosstalk between the left and right channel.

6. Sensitivity & Signal Strength Meter Function - By lowering the output of the SG80 we can simulate weak stations and determine how well the tuner will be able to pull in weak distant stations. This adjustment also helps us verify signal strength meter function.

If the tuner has acceptable performance related to the parameters above we connect the unit for listening tests with a simple dipole antenna. We listen for audio reproduction quality of local stations and evaluate how many stations the tuner can receive while we sweep through the dial. We are looking to verify that the tuner can decode stereo on strong local broadcasts and pick up a wide variety of local stations at the bottom, middle, and top of the frequency band. At this point we also test convenience features such as muting, filters, built in oscilloscope function, etc.

We finish up with an extended listening test on our long term test rig. We tune in a strong local station and monitor for drift over a 2-3 hour period.

The SkyFi Testing Process for Speakers:

Our speaker evaluation process starts with a visual inspection of all drivers. We are looking for damaged or deteriorating woofer surrounds, dented tweeter domes, and cone damage. We also inspect the speaker connection points for loose or broken connectors.

After the initial visual inspection we connect the speakers to a reference amplifier with our preferred test tracks. With the speakers placed with proper distance we listen to each driver to make sure that they are producing the intended frequencies with no signs of distortion or rattle. During listening tests with test tracks we check for proper stereo imaging and bass response at various listening levels. If there are any audible signs of issues, the speakers are taken to the bench where we perform a frequency sweep to isolate the issue so that it can be resolved by component repair or replacement.

The SkyFi Testing Process for Subwoofers:

Our subwoofer evaluation process starts with a visual inspection of all drivers. We are looking for damaged or deteriorating woofer surrounds, cone damage, or rubbing voice coils. We also inspect the input connections for damage.

After the initial visual inspection, we connect the sub at our bench and perform a sine wave sweep from about 200Hz down to around 10Hz. During this sweep we are listening for excessive rattle or other signs of improper function. If the sweep passes, we then increase the input level to evaluate how the woofer performs at high output levels. If the woofer has built in crossover features or multiple connection options these features are tested at this time.

We complete the subwoofer evaluation by feeding the unit with an audio signal in conjunction with our house music system to see how it responds to low frequency content in real world conditions while paired with a full range system.

The SkyFi Testing Process for DACs:

After the visual inspection we connect the DAC’s RCA outputs to our Sencore PA81 Power Analyzer which simulates a real world input impedance and allows us to monitor the output on an oscilloscope. We are equipped to test optical, coaxial, and USB inputs at Redbook CD Quality. We start with a test signal to verify signal lock and proper output on both channels. If the DAC has balanced outputs these are also tested at this time. If the DAC has multiple Optical and Coaxial inputs they are all checked for proper lock. USB inputs are tested with a Macbook Pro.

After proper function is verified, we set the DAC up for a listening test to evaluate general audio reproduction quality and monitor for clicks, pops, or any other audible signs of issues related to dropped signal lock or failing audio output stages. We often connect DACs under evaluation to our long term test rig for a long test stint to verify stability under real world operating conditions.

The SkyFi Testing Process for CD Players:

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 resistors and other passive components for signs of overheating. When the unit is first powered on we check the drawer mechanism function.

After the visual inspection we connect the CD Player’s RCA outputs to our Sencore PA81 Power Analyzer which simulates a real world input impedance and allows us to monitor the output on an oscilloscope. We start with a test CD with precision test signals to verify proper output on both channels. If the CD player has balanced outputs these are also tested at this time. If this check passes, we move onto evaluation with actual music CDs. We listen for clicks, skips, and drops during playback. At this time we also check the transport functions including skip, ff, rw, play, pause, repeat, and programming if applicable. If the unit has a remote control, all remote control functions are verified.

If the CD player is capable of SACD playback we test its ability to read SACD layers on multiple discs including standard and hybrid SACDs. At this time we also check the unit’s digital outputs where applicable. If SACD layers are being properly read we should see the digital outputs mute during playback. On redbook CD playback we verify that each digital output maintains proper lock on our bench DAC.

After bench testing is completed, CD players are set up for testing on our long term test rig. During extended testing we make sure that unit can play through several different discs from beginning to end with no skips or lock ups.

The SkyFi Testing Process for Cables:

Cables are generally pretty simple and do not require a great deal of testing. We do, however, perform a visual inspection of all of the connectors for damage or significant wear. Most power and interconnect cables can be verified with a simple continuity test with a digital multimeter. Some cables feature dielectric bias systems which are powered by external power supplies or batteries. These devices are checked for proper function if applicable.

We do not perform A/B comparisons of cables in real world conditions and cannot offer objective observations in this regard.

The SkyFi Testing Process for Turntables:

First we try to identify any mechanical issues, particularly in the tonearm bearings. We check for freedom of movement or any resistance on both the horizontal and vertical range. There is a quick test for this which involves placing the table on its front edge and allowing the arm to swing freely like a pendulum. We then make any adjustments necessary to achieve minimal resistance and sometimes adjust the bearing pressure. On gimbal tonearms we inspect the cone tip with a magnifier.

We then asses the platter speed by using one of several methods, the most accuse is a playing a test tone on a test record and measuring the frequency out put with a frequency counter or oscilloscope. We also utilize test equipment to measure the wow and flutter to ensure its within spec. We do this for all speeds available for that particular model. Adjustments are then made to achieve proper speed which will vary depending on table drive design. Some require an adjustment of an internal or external potentiometer, some will require a pulley or motor adjustment. We also inspect the platter bearing to ensure its properly lubricated keeping in mind that some don't require lubrication at all.

We then inspect the power supply and address any issues with overworked capacitors particularly on Linn and later Thorens machines which tend to need attention.

On fully mechanical vintage tables like the Thorens TD124 and Garrard 301/401 we will go thought the entire mechanism, replace any worn parts and lubricate all components necessary to ensure smooth operation, speed change and low mechanical noise.

When fitting a new cartridge we will go through our detailed calibration process which can involve as many as 12 steps depending on the arm design. We perform this work on our custom turntable calibration rig which was developed in-house.

Some of these steps include:

• Pivot to spindle adjustment

• Tracing force

• Anti-skate

• Tonearm height

• Lifter height

• VTA

• Azimuth

• Stylus Distance and Overhang

We then do a critical listening test using our test records and our test system to ensure proper sonics.

The SkyFi Testing Process for Phono Cartridges

We start by doing a detailed physical inspection under light magnification to asses the cantilever condition, its position in the cartridge body and the condition of the suspension. We also inspect any coil wires and the output connections to make sure it hasn’t been strained. We then perform a light cleaning with specialized agents and blow it dry with compressed air.

We then perform a more detailed inspection with our Wild Heerbrugg professional microscope. From there we can asses the wear and quality of the stylus and determine how much use it has had and if there are any mechanical issues. We can also identify if it needs further cleaning or care.

We then move the cartridge to a digital microscope where we take photo os the cantilever for future reference.

We then move to the test bench where we can check for continuity of each channel and resistance.

On certain cartridges and it the technician feels necessary we install the unit on a turntable and run a few test records to ascertain tacking ability, distortion and compliance.

The SkyFi Testing Process for Tape Decks and Reel to Reel Machines:

First steps are performed to determine if the unit is a candidate for our full restoration process or if its just in need of a light service.

We first do a basic functionality test to ensure proper playback fast forward and rewind. We look for smooth operation of the motors, transport engagement and associated rolling parts.

We then do an internal physical inspection to ensure the belts and rubber consumable parts are up to spec.

Internal components are checked to make sure that there are no signs of heat stress or damage particularly in the power supply section. 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.

A light service will involve replacement of belts and rollers, external cleaning of heads, mechanism and boards and basic record and playback tests.

A full restoration will often include disassembly of the drive system and replacement of all consumable and wearable parts including pinch rollers, belts, brakes, bearings. We then clean lubricate and re-assembly the drive and perform basic mechanical alignment to ensure proper tape path and head alignment.

Final calibration will involved adjustment of playback erase and record heads and optimization of the bias for a specific tape type. We do this with the aid of a Soundtech 1510A tape deck analyzer and a Nakamichi T100 unit and reference calibration tapes.

Final listening tests are done while monitoring with our reference Grado HP1 headphones and a variety of factory and custom reference recordings. We find that there is no better system for critical listening on tapes than the headphones specially when comparing a live feed to a recorded feed.

The SkyFi Testing Process for Power Conditioners:

We test every outlet with a voltmeter to ensure proper functionality and voltage throughout the unit. If applicable we test the switching of the outlets, specially if they are timer activated and ensure all fuses are intact and of proper value.