What is the burn-in time? Should the unit be left continuously powered?

High quality, high-resolution audio gear is perceived by many to slightly improve its sound through a period of something called “burn-in”.  We recommend that a newly-purchased unit be left powered-up continuously for the first (one) month. We believe based on our perception and the feedback of clients that the greatest reported changes occur from three days to one week of being powered up.

What does ‘settling in” sound like? Users report that bass tends to get deeper and tighter, the midrange and treble open up, and the unit assumes a subtly more open and easy presentation.

We attribute this primarily due to the electrolytic and non-polarized capacitors continuing to form their dielectrics to the actual applied DC bias and operating voltages.

 “Should I keep it powered up, or turn it on only when I used it?”  This is a common question. 

After the initial first month, we recommend that users apply their own discernment. A one-hour warmup is normally sufficient to confer most of the benefits of “Always-On”.

The units are filled with all-class-A circuitry which dissipates more power than competitive units. Our thermally-managed design which prevents ‘hot spots’ in crucial areas of the power supply and gain circuitry.

Our designs utilize the entire thick aluminum chassis serves as an effective radiant heatsink. Units run approximately 10 to 20 degrees Fahrenheit above ambient, or slightly more if operated on their side or tucked inside an equipment rack without ventilation. We suggest adequate ventilation be employed especially for the MP8B and MP7B in order to fully maximize anticipated lifetime.

What is the jumper configuration on the SU-7 (and SU-6)?

The following is from the view of the unit with the input/output jack panel to your left, and the AC inlet in the bottom corner.

Loading: The upper left bank of headers controls the Resistive loading to the Left channel and the lower left bank of headers control the Right channel.

The left-most position is 47 ohms, and the right most position is 47K.  Nominally, the settings are 47 ohms, 100 ohms, 220 ohms, 470 ohms, 1K, 5K, and 47K as you progress to the right.

Gain: The upper right bank of headers controls the Gain for the Left channel and the lower right bank of headers controls the Gain for the Right channel.

Nominally, the upper-most position is +26dB, the next down is +23dB, the next +18dB and the lowest position is +12dB.

Note: The SU-6 has four loading positons, similar to those described above. On the SU-6, the left-most position is 47 ohms, the next is 100 ohm, the next is 220 ohms, and the right-hand-most position is 470 ohms.

Currently we ship units set to 220 ohms and 23dB gain (for the SU-7) and 220 ohms (with fixed 20dB gain) on the SU-6. The SU-5 offers +20dB gain and a 100 ohm load, and is not adjustable.

Should I upgrade the external power cube?

No…there is NO NEED to do so. Darlington Labs technology differs substantially from other units with which you might be familiar.

Our power supply cube is NOT a switching power supply.

It is also NOT an external DC power supply.

It’s simply an external, AC to AC, 5:1 ratio step-down transformer, 120VAC (or 230VAC, 10:1, for non-US) to 24VAC. This transformer mounts on the wall and keeps the radiated hum field away from the electronics. It may look like other power cubes but this type of true, simple AC-to-AC transformer is now quite rare in consumer electronics.

One of the advantages of buying a Darlington Labs product is that it comes from the factory '“already completely optimized”…there is NO NEED to purchase any type of “upgraded” power supply.

We could probably make more money by dangling the prospect of an intentional “big impressive outboard power supply upgrade path”. However, this would be contrary to our intent of providing “superb sound from the very start that continues for a very long time.”

We have considered all of the parameters of our power cube, including subtle and non-obvious ones like winding inductance and capacitance, regulation vs. load response across varying line voltages, and others. The cubes are custom-wound to our own specifications by a subcontractor in the Far East.

In fact, we humbly suggest that if your manufacturer is encouraging you to buy an external power supply upgrade, they have - intentionally or unintentionally - failed to truly address the fundamental limitations of their power supply topology in an effective way and are instead using a ‘brute-force’ approach.

Internally our MP-7, MM-6 and MM-5 units convert the AC line voltage delivered through the power cube at 24VAC via rectification to around 75 to 80VDC. Following passive Radio Frequency Interference filtering, the raw DC supply is then regulated down to 64VDC and then again to 61VDC.

The 61V of clean DC is then re-regulated down to 56VDC with an extremely sophisticated all-discrete low-noise, low-impedance, and sonically benign circuit of our own design. Depending on the model, we have 160 to 180dB of isolation from the AC power line. This is extremely rare, even on the highest-end equipment. The MM-5 currently has two levels of regulation, to 64V (monolithic) and then 56VDC (discrete).

The SU-7, SU-6 and SU-5 use internal bipolar power supply rails, with three levels of regulation per polarity, for a total of six stages of regulation. We believe this is unique in the industry, in a product of this nature and certainly compact size.

The external raw 24VAC provided by the power cube is rectified and filtered to approximately +/-35V to 40VDC, then passively filtered to reject RFI and EMI. Then it heads into regulators outputting +/-29V, and subsequently +/-26V, all four stages using high-performance and low-noise monolithic technology.

This is capped off by a completely discrete, very-high-performance all-discrete FET-reference-amp regulators. Each polarity receives a separate one, for +23V and -23V DC rails. The direct-coupled input J-FET array runs on the positive rail, and the output stage utilized the entire bipolar supply (for a total of 46VDC).

These high voltages relative to the 5mV output of an MC stage provide more than 60dB of low-distortion audio headroom, one of the keys to our great sound. It is also one reason that it took us a total of 5 years to develop our active Step-Up MC line. We have incorporated ideas from literally 10 separate major prototypes, including 3 completely clean-sheet re-starts.

The successful regulators in the SU-7, 6 and 5 will underpin a future line of Headphone Amplifiers as well as further offerings down the road.

To recap, our integrated package – the chassis and the standard wall cube – outperforms very large ‘conventional’ approaches to high quality sound.  

These methods of design enable us to place a great deal of money into passive components and gain circuitry while still providing unparalleled value to our clients. It also results in a compact, very high performance unit that doesn’t need the hassle of a large second enclosure for a “remote power supply.”

The only ‘disadvantage’ accrues to us, and that is the need to stock both 120V and 230V version power cubes.

We understand the spirit of well-meaning attempts and recommendations by people unfamiliar with our tech.

However, the use of external large AC transformers (whether conventional or toroidal), or similar standard audiophile approaches — such as substituting a particular brand of capacitor — will have limited benefit.

In some cases they may actually decrease the performance or long-term reliability of a Darlington Labs product.

What’s the maximum output cable length?

The output stage of our MP8B, MP7B, and MM6B feature a class-A output stage with an effective output impedance of approximately 200 ohms.

For best results and maximum phase linearity at the high end of the audio spectrum, the output cable capacitance should be less than 4,000pF (0.004uF). For low-capacitance cable (20pF/ft) this means a run of 200 feet or shorter. With standard capacitance cable (40pF/ft) the cable run should be less than 100 ft.

For good results without much measured loss at the highest frequencies, the output cable should be less than 15,000pF (0.0015uF), or in other words, less than 750 ft of low capacitance cable (20pF/ft) or less than 375 ft of standard cable (40pF/ft).

In other words, in all practical or easily-foreseen real-world installations, cable output length should not be an issue with Darlington Labs products, if using quality cable from a reputable manufacturer, with quality connectors, and dressing it carefully away from close proximity to AC cables.

How do I open the unit for making user adjustments?

New models have internally-user-adjustable features. Care is required to open the unit and be safe in making the adjustments (as indicated in a section below, on “Jumpers”.

The jumpers are accessed by removing the top cover of the unit. Care is required to open the unit and be safe in making the adjustments.  While this procedure may be safe to do with the unit powered up, ONLY WHILE IN THE HANDS OF A TRAINED AND COMPETENT TECHNICIAN, it is not recommended for the average user while the power is ON.

INCORRECT USE OF THIS PROCEDURE OR DAMAGE TO THE UNIT WHILE ATTEMPTING TO DO ADJUSTMENTS WITH THE UNIT POWERED UP, MAY VOID YOUR WARRANTY. DARLINGTON LABS DISCLAIMS ANY AND ALL LIABILITY TO A USER OR A USER’S SAFETY IF THEY ARE ATTEMPTING TO OPEN THE UNIT WITH POWER APPLIED, OR NOT SAFELY DISCHARGED AFTER REMOVAL OF POWER.  TAKE OFF ANY WEDDING RINGS OR JEWELRY!

The tops of electrolytic capacitors, particularly the shiny metal circles near the left side, are at more than 100V above chassis ground under certain conditions.  DO NOT TOUCH THEM! KEEP ONE HAND IN YOUR POCKET AT ALL TIMES.  DO NOT USE TWO HANDS INSIDE THE UNIT UNDER ANY CIRCUMSTANCE.

ESSENTIALLY WE RECOMMEND THAT YOU DO NOT OPEN THE UNIT WITH THE POWER SUPPLY CONNECTED TO THE REAR.  ALLOW at least 10 MINUTES after disconnection of power before removal of any chassis hardware. Do NOT remove the lower Phillips screws, nor the lower allen-head screws. Too much disassembly and the rear panel will come out of alignment and the front LED may become misaligned.

The top cover comes off with removal of the top two Phillips screws in the rear, and the top two Allen-head (Hex-Head) bolts in the front - which use 2.5mm hex key wrenches. Label the front and rear first.

The black portion is a clamshell design and the top will be able to be removed while the PCB remains affixed and trapped by slots in the lower half of the claimshell.

It will go back together only one way; if you are having trouble, rotate it by 180 degrees and try again.

Do NOT remove the lower Phillips screws, nor the lower allen-head screws. Too much disassembly and the rear panel will come out of alignment and the front LED may become misaligned.

THE FOLLOWING IS A SERVICE PROCEDURE FOR FULL DISASSEMBLY: NOT APPLICABLE TO JUMPER SETTINGS!!!

A qualified service technician would fully disassemble the unit by removal of the PCB which slides out towards the rear, followed by unsoldering the I/O rear jack panel from the PCB.

Units run on a UL and CSA-listed AC power cube, but internally the voltage is rectified and stepped up to approximately 80V or higher (depending on AC line voltage conditions). Do not touch the metal top of the electrolytic capacitors which can have more than 40VDC above ground potential.

One slip of a screwdriver or a wedding ring could be catastrophic, generating sparks, pops and smoke. This is an actual high-end design, not a small op-amp unit operating at low voltages which uses a few milliamps of current. It is comprehensively designed for long-term reliability, but does not quietly tolerate abuse or careless internal handling.

Such damage may not be covered by our 1 year limited warranty.

Are there physical mounting recommendations or restrictions?

If side-down (short-vertical) operation is desired, the word “Darlington” in the corporate logo should be below the word “Labs”; in other words, rotate the unit counterclockwise by 90 degrees and have it sitting on the long edge of the left side.

Doing so allows the AC power inlet cord to provide minimum interference with audio cables and is also ideal from an internal EMI and thermal management perspective.

Sitting it on its front panel will be unstable without additional external support but is possible; using zip-ties, for example. Cover the front panel in some non-obtrusive manner to prevent scratching as well as to prevent damage to the front panel.

Do not disassemble or modify the unit by drilling holes in the enclosure for screw-type mounting feet or external L-Brackets without full consideration for the PCB internal mounting.

The PCB is approximately 2mm from the bottom panel and our use of a substantial power supply could produce spectacularly unpleasant results if a screw protrudes into the circuit board, either while powered, or at the next power-up cycle.

Help! I have no sound and/or the Darlington unit is not receiving power.

Rest assured that we test each unit multiple times before shipping, including an audition. We have also never yet experienced a shipping-related issue which has caused a DOA. Therefore, we suggest that you start with the assumption that the unit itself (chassis and all internal electronics) is able to operate normally.

However, that does leave the power adaptor. We test our units with verified benchtop fixtures, not the actual power adaptor that is in your box. This is because our cubes have proven so reliable that independent verification is not cost-effective. The failure rate is very low, about 0.02% to 0.05%. Proceed now to “trust but verify”, as Ronald Reagan used to say, and consider using the following logical troubleshooting steps.

First, do you appear to have power to the Darlington Labs unit? Is the front LED lit up? If you have no power to our unit, please remove the power inlet by 120 degrees and reinsert into the rear of our unit, twisting gently while inserting. Make sure the plug is deeply seated, but, do not force it. Is the problem resolved?

If not, we suggest that you take off the top cover (following the directions in the manual) and confirm that there are numerous yellow LEDs inside which are lit up.  If you have yellow LEDs lit up inside, but no front panel light, the jumper which controls the front panel LED may have come loose or not be fitted propery. If it still appears you have no power, it’s time to reconfirm that the outlet which is feeding our remote cube is good, such as by substituting a desk lamp or nightlight or other simple device.

If it still appears you have no power, and you have access to an AC voltmeter, test the output of our AC cube to see if you have approximately 24 to 28V AC between the outer sleeve and the inner sleeve.

If you do have power to our unit, it’s time to reconfirm that you are feeding a line level input which is able to pass a signal. Try feeding a CD player, tuner or other device into the line input you are using. Try different audio cables between the Darlington Labs output and your line input. Try a different patch cable between your turntable and the input to the Darlington Labs unit.

Next, check the jumpers. The Low-Frequency EQ Trim on an MP7B or MP8B needs a jumper on each channel. While we ship them at “flat”, if you have removed, rather than moved, the jumper on one or both channels in that section, no signal will pass and the unit may appear to be dead. Likewise, if you have removed one of the four jumpers associated with the MM/MC mode switching on an MP7B or MP8B, you may have temporarily broken the signal path.

At this point, it’s worthwhile to check obvious things again. Have you sure you’ve plugged your turntable into the INPUT of the Darlington Labs unit? Are you taking the OUTPUT of the Darlington Labs unit TO your following line-level input? If someone else is available, it could be worthwhile to have them follow the signal path, and verify that power is being received by our unit. Another pair of eyes, or a peer-review, is a well-worn path to success. If it is late, try approaching it again when you are fresh the next day.

If you have another phono preamp available (including a “built-in” one), try to connect it instead as a test. Re-read the relevant portion(s) of the manual, and don’t hesitate to contact us if you have questions.

Did your unit work properly for many months or perhaps years, and now appears to be dead? Troubleshooting in this section is also highly relevant. It is exceedingly rare to have a unit itself fail (to DOA/no power) suddenly, even after a large power spike or surge that may have affected some of your other electronics.

Very occasionally a power cube will fail after months or years of use. If yours has, we will normally supply a replacement cube quickly and at no cost to you. We are generous with repairs to units previously purchased, and out of formal warranty (partially because our designs have proven so reliable). Reach out and let us assist.

I powered off my Darlington Labs phono preamp with the audio level still up. My amp went into Standby or Protection. Is that normal?

It can be, yes. Our units have a great deal of power supply capacitance and a very sophisticated discrete supply regulator. They display well-behaved power-up and power-down behavior, especially compared to some competitors units which contain feedback loops that are unstabilized during a power-supply sequence.

However, like any high-gain phono preamp, a best practice is to always power up the phono preamplifier first, then the line preamplifier, then the power amplifier. Powering off the system should be in the reverse order.

Adding high-quality active muting would unnecessarily increase cost, in our view, with limited benefit.

Why is the power switch on the rear?

The power switch is in the rear for technical reasons.

To place it in front, it would be necessary to run long traces up the side of the PCB with 24VAC which will tend to inject hum in the rest of the circuitry. As it is now, the AC inlet is near the power switch and all circuitry is carefully laid out on the PCB to maximize signal to noise ratio.

I have heard a very slight hum under certain conditions. Any advice?

Our external AC power cube cord carries 24VAC which is higher than some competitors units which use 16VAC or 12VAC. It is perhaps one reason why many manufacturers use external DC power supplies. (Our use of 24VAC is, however, arguably less intrusive than a regular 120VAC power cord, and allows us to provide very high performance at an unusually-high value).

Proper physical routing should reduce the effect to a minimum.

Users have reported that routing the power inlet cable immediately to the left and down (as viewed from the front) and as far away from the unit and other cables as possible is optimum.

AC hum induction is usually into the Phono Input lead (to the MP-7 or equivalent) rather than the Line Output. So the distance between the AC adaptor lead and the audio cable from the turntable/cartridge is the one to focus on, and maximize. If your turntable offers a detachable audio cable, choosing a well-shielded one is important.

The output side of our units is much more tolerant of moderately shielded audio cables. We have used braided regular line-level Kimber Kable (PBJ and better) for more than 30 years, and use it on the outputs of our Darlington Labs units. Its unshielded braided design offers extremely modest RFI and EMI rejection, yet the low impedance output of our phono preamps (<100 ohms) effectively prevents much interference.

Our heavy aluminum enclosure is extremely well-shielded on its own, but still should not be placed in close proximity to other equipment with large (or unshielded) power transformers.

There are three other main sources of more serious hum.

The first is related to 60Hz power, but is induced into the cartridge directly.  The unshielded Grado cartridges would sometimes pick this up from proximity to a turntable motor, particularly many original AR (Acoustic Research) manual turntables.  It is a low-pitched hum with some buzz.

The second is a ground loop.  It is caused by a difference in the voltage between the chassis of the phono preamp, turntable plinth and/or tonearm, and the associated amplifier.  It is typically low-pitched like the first.

The third is radio-frequency interference (‘RFI’) from radio stations, computer accessories/routers, cell phone towers and the like.  This tends to be a buzz that changes sound over a few seconds to a few minutes.

You may try moving the power cube to a different outlet, shortening it's length (by tieing back excess), changing interconnect cables, etc.

Please give us an email if you are experiencing trouble. Our units are robust in their design, and interface well into almost all systems. However, we have decades of experience in solving issues of this nature in professional and broadcast environments as well as in consumer audio.

I am brand new to vinyl LP playback and notice that when I open the gain ‘wide open’ with no record playing, I can hear a slight hiss if I place my ear against the tweeter. Is this normal?

A certain amount of background noise is inevitably associated with LP’s. Electronically this is due to the large level of amplification required of the signal generated by the cartridge. Unlike a CD or DAC where you effectively hear silence between program selections (most DACs fully mute their output) it is normal to hear a slightly-audible level of hiss with your ear at the tweeter and/or hum with your ear against a midrange or bass driver.

However, the background noise should be only barely noticeable at the listening position, even at the loudest normal listening levels, and it should not be distracting nor should it be reasonably audible (again, at the listening position) with a record playing and between selections or during quiet portions of program material. Normal groove noise, even on a clean LP, should predominate.

If these attributes are achieved, then —in general — you have a normal and well-performing analog system. User feedback supports that our units are among the quietest in the marketplace. Our specifications are intentionally very conservative; and many competitors specs are published not reflecting the attachment and use of a real-world MM-style cartridge which is highly inductive and causes a notable increase in noise from the midrange into the top-most octave.

I bought an MP7, MM6, MM5 or MM3 second-hand and it seems to have a slightly elevated low-frequency noise floor.

Certain MP7s produced between September 2022 and June 2023 have been reported to exhibit a slightly elevated level of background hum depending on your AC line condition. When present, it is not power supply ripple, but rather rectification current induction into the non-zero impedance of the internal board ground plane, in certain rare DC offset conditions on the AC power line. While this design revision had positive attributes and was received well, we made modifications in June 2023 which reduced this noise by about 10dB (120Hz, 240Hz and 360Hz in 60-cycle countries). Our newest models, the B series — MM6B, MP7B and MP8B, have almost completely inaudible background hum as a result of their Balanced Supply Generation (BSG) technology.

If you have an MP7 unit that seems to be exhibiting an excessive amount of low frequency buzz or hum, even when your turntable is disconnected, please contact us by email and have your serial number and production date (if shown) available. If those are unavailable, we may ask you for a photo of the unit with its top cover removed. Most properly operating MP7s have a certain minimal amount of low frequency noise which is about equal to the hiss level, when the volume is cranked wide open and the tonearm is off the record. In general, people called them “dead quiet in real-world use compared to the competiton.” However, if the buzz is greater than the hiss level, then it is a candidate for modification, even if you purchased it second-hand.

One other LF noise issue of a different type may have affected a small number of early units.

Early MM6s with serial numbers around 200130 to 200160 (the second run, from approximately Feb. 2021 to June 2021) and all of the Early MM5s from serial number 200101 to approximately 200150, Oct. 2020 to June 2021), and all of the small number of MM3s that were sold (200101 to ~200112) (Oct. 2020 to late 2021), use internal square blue trimmer potentiometers to set fine bias calibration. In certain conditions, those can become noisy and create a low-frequency “rushing” or “rolling-thunder” type of sound. If your unit has 4 blue Bornes 3296-type square blue rectangles inside, then we can remove them and replace them with the closest-value fixed resistors, and due to the age of the unit, make other modifications or replace your PCB with one that is of a newer vintage at no cost to you, other than your cost of shipping it to us. Note: Pre-approval via email is necessary for this offer to be valid. Additional note: NO MP7s ever shipped with these blue variable pots even though early PCBs have holes for them; they were wired with fixed resistors.

When I play vinyl LPs, I occasionally need to turn up my volume control higher than when playing CDs or digital media. Should I be concerned?

If your system is able to achieve the loudest desired listening level (using a record which is itself reasonably quiet i.e. not "cut hot") with your volume control on the line preamplifier "at or near maximum", then we believe that you have the perfect gain structure for an analog preamp using records, and no gain is being ‘wasted’, so to speak.

DACs and CD players typically have a standard output level of 2.0V RMS with a digital peak level of 0dBFS (referenced to “full scale”). When CDs were first introduced, CD mastering practices resulted in peak levels that were significantly lower than occured later, from circa 1990 onwards, when peak limiting and multiband compression of a modern nature began to be employed. The lower average levels of the first CDs effectively produced output that was closer to 0.5V output (500mV) which is typical of average modulation from a vinyl LP through an average cartridge.

Most ‘popular music’ modern CDs and digital files, mastered after the early 1990s, and used with an ordinary and typical DAC, will therefore often be louder in practice for the same volume control position, than will a properly and typically-operating analog LP chain.

In some cases with volume controls which are implemented electronically in AV-type receivers, in fact, regular use of volume control travel which requires significant attenuation (from 8AM to 11AM or so on a single-turn volume pot) could exhibit certain unsuspected technical limitations - ‘clipping’ of an internal buffer stage before your volume control which may exacerbate the inevitable surface noise of LPs.

Passive attenuation could be employed in-line with the analog interconnect cables from (only) your digital sources, if needed, via an easily-constructed external resistive loss “pad”, details of which are widely available online.

Passive line preamplifiers, with 0dB gain, however, are usually not recommended for use with a phono preamplifier (ours or competitor units) due to a confluence of the above factors. A regular “line level preamp” with around +12dB gain is highly recommended to follow the phono preamp, before your power amplifier. (Note that this line-level preamp is already integrally present in a typical stereo or AV-receiver).

Certain technical reasons exist that result in the relative rarity of phono preamps offering significantly beyond +40dB gain at 1kHz. We have detailed these at length in the main SH forum thread.

What is Darlington Labs approach to long-term reliability?

With our engineering team’s professional background, whereby equipment failure can lead to loss of professional reputation or have direct economic consequences, rather than being just a simple inconvenience, reliability is paramount in our design process.

Our products use high quality components, conservatively rated, and specifically tested where necessary for the application at hand. We use no vacuum tubes or other active parts which by their nature have a finite lifespan. Our calibration and selection processes are expected to remain stable indefinitely.

Beta and alpha units have been operating in the field trouble-free for more than seven years, and the general design dates back even longer. While we provide a limited 1-year warranty for legal reasons, we design with a multi-decade lifespan in mind. We believe that our products will perform so well that they can be considered a long-term investment. Additionally, the ‘through-hole’ placement of electrolytic capacitors promotes long-term serviceability.

After many years of continuous use, as with most electronic products, the electrolytic capacitors may need replacement due to their internal electro-chemical and heat-related processes. Our quality construction, and high performance, would make this both possible—and a solid investment in that long-term refresh, particularly on the MP-7 and the MM-6.

Some products are built to last.

One of our test bench amplifiers has main capacitors and semiconductors over 55 years old which are still in great shape (we secretly brought it to AXPONA 2024 and used it to drive demo speakers and headphones; Ralph K of Atmasphere (MN) recognized it hiding under black velvet and remarked that he serviced many of these in the early 1970s as a student).

While we cannot guarantee such longevity, quality like that does inspire us. Darlington Labs products are the antithesis of a conventional, disposable, consumer commodity item.

I’m having trouble getting my patch cables to fit!

Some minor difference in insertion force is normal, due to the casting process used. Unlike competitor jacks which are often made of pressed tin and plastic, ours are very strong. You can use a substantial (hand) force to initially 'mate' our plugs. If you are having difficulty, we suggest using a bit of WD40 or machine oil on the inside collar of your plug, then using a clockwise rotating motion to insert your cable.

There is no universally-accepted dimensional definition of the "RCA" type of plugs. So, if necessary, as with many RCA jacks, the careful use of a needle-nose pliers (potentially with a thin cloth barrier to protect the surface) can be utilized to either loosen the collar on the mating plug, or to tighten it.

JUMPER COLORS AND MEANING:  

The MP8B, MP7B and MM6B products contain many user-adjustable options (so do the SU7 and SU6; this section, however, is focused exclusively on the MP/MM).

PDF Reference guide now included in the owners manuals and reproduced here: Jumper Reference Guide for MP8B and MP7B (parts also applicable to the MM6B): Jumper Reference Guide

The jumpers are accessed by removing the top cover of the unit. This is accomplished in the following manner:

The top cover comes off with removal of the top two Phillips screws in the rear, and the top two Allen-head (Hex-Head) bolts in the front - which use 2.5mm hex key wrenches. It will go back together only one way; if you are having trouble, rotate it by 180 degrees and try again.

This jumper section is applicable if you have a unit with a model number on the bottom of the chassis ending in a “B” suffix, which stands for Balanced Output Option, as well as the updated series of products introduced in January 2024.

In the following section, the visual reference is the unit with the top removed, and the rear panel to your left, and the front panel to your right.

In the following section, bold indicates the factory setting:

WHITE: Mode Select (LOMC or MM) (N/A on MM6B). Left is MM and Right is LOMC. The two upper jumpers control the Left channel; the two bottom jumpers control the right channel.

BLUE: Subsonic Filter: Bypass, 6dB@16Hz, 12dB@16Hz. The two left side jumpers filter the input stage at 6dB/octave. The right two jumpers are interposed between the input and output stage and filter at 6dB/octave.

If 6dB of total rolloff slope per octave is desired, use the RIGHT side jumpers (interstage) as this will preserve DC coupling from the cartridge to the input stage. If a 12dB/octave slope is desired, remove the left side and right side (all four) jumpers.

Use no more subsonic filtering than is truly necessary for your installation; some visible woofer flutter is normal and acceptable in vinyl LP playback. Use filtering only if you are experiencing severe woofer bottoming or other issues.

First attempt to solve your issues mechanically and by rearranging the physical location of your turntable, especially as regards the relative position of your loudspeakers.

Lastly, we suggest making sure that your arm/cartridge resonance is between 8 to 12Hz. If necessary, obtain a more suitable cartridge-compliance-to-arm-mass combination through a change in tonearm or cartridge.

RED SECTION 1: MM Capacitance

The MM Capacitance section is the rightmost block of Red jumpers, in a section of two blocks of three set side by side. It is comprised of 3 loads that may be chosen in combination: 50pF (leftmost), 100pF (middle), and 200pF (right). The upper block of MM Capacitance controls the Left channel. The lower block of MM Capacitance controls the Right channel.

AVAILABLE OPTIONS: 0pF, 50pF, 100pF, 150pF, 200pF, 250pF, 300pF, 350pF

0pF: 50pF OFF, 100pF OFF, 200pF OFF

50pF: 50pF ON, 100pF OFF, 200pF OFF

100pF: 50pF OFF, 100pF ON, 200pF OFF <—As shipped

150pF: 50pF ON, 100pF ON, 200pF OFF

200pF: 50pF OFF, 100pF OFF, 200pF ON

250pF: 50pF ON, 100pF OFF, 200pF ON

300pF: 50pF OFF, 100pF ON, 200pF ON

350pF: 50pF ON, 100pF ON, 200pF ON

RED SECTION 2: MM Resistance

The MM Resistance section is the leftmost block of Red jumpers, in a section of two blocks of three set side by side. It is comprised of 3 loads that may be chosen in combination: 62K (leftmost), 150K (middle), and 240K (right). The upper block of MM Resistance controls the Left channel. The lower block controls the Right channel. When none of those three loads is selected, there is 1 Megohm load present which is the bias return for the input stage.

Appropriate parallel combinations of the three resistances will yield the following options: 38K, 44K, 47K, 62K, 92K, 150K, 240K or 1Meg

38K: 62K ON, 150K ON, 240K ON

44K: 62K ON, 150K ON, 240K OFF

47K: 62K ON, 150K OFF, 240K ON <—As shipped

62K: 62K ON, 150K OFF, 240K OFF

92K: 62K OFF, 150K ON, 240K ON

150K: 62K OFF, 150K ON, 240K OFF

240K: 62K OFF, 150K OFF, 240K ON

1 Megohm: 62K OFF, 150K OFF, 240K OFF

RED SECTION 3: LOMC Resistance (N/A on MM6B)

The MC Resistance section is the uppermost left block of Red jumpers, above a section of two blocks of three set side by side. It is comprised of 3 loads that may be chosen in combination: 100 ohm (leftmost), 220 ohm (middle), and 470 ohm (right). The upper block of MC Resistance controls the Left channel. The lower block of MC Resistance controls the Right channel. When none of those three loads is selected, there is 62K load present which is the bias return for the LOMC input stage.

Appropriate parallel combinations of the three resistances will yield the following options: 60 ohm, 69 ohm, 82 ohm, 100 ohm, 150 ohm, 220 ohm, 470 ohm, or 62K.

60 ohm: 100 ON, 220 ON, 470 ON

69 ohm: 100 ON, 220 ON, 470 OFF

82 ohm: 100 ON, 220 OFF, 470 ON

100 ohm: 100 ON, 220 OFF, 470 OFF

150 ohm: 100 OFF, 220 ON, 470 ON

220 ohm: 100 OFF, 220 ON, 470 OFF <—As shipped

470 ohm: 100 OFF, 220 OFF, 470 ON

62K ohm: 100 OFF, 220 OFF, 470 OFF

YELLOW: LF and HF EQ Trim (N/A on MM6B)

LF Trim: 0dB, +0.75dB, +1.5dB. LF response is increased by moving the jumper to the right.

LF Neutral: Yellow jumper to left-most positon.

LF Boost 1: Yellow jumper to middle position (+0.75dB at 20Hz).

LF Boost 2: Yellow jumper to right-most position (+1.5dB at 20Hz)..

Note: The overall gain at 1kHz decreased by an amount equal to the boost at 20Hz; note this if you are A/Bing the various options. Additionally, if the jumper is removed, no audio will pass in that channel: 1 of the 3 options must be selected.

HF Trim: -4dB to 0dB to +4dB in multiple steps

Note: Gain at 500Hz is not affected by the various HF trim settings.

NOTE: Additional DIP header jumpers are “added” to the PCB board by the user in order to decrease the upper HF response. Moving the single existing jumper (present from the factory) to the left will increase the treble response.

Treble Cut 4: A: ON, B: ON, C: ON, D: ON, E: ON (265). Approx. -4dB at 20K.

Treble Cut 3: A: OFF, B: ON, C: ON, D: ON, E: ON (250)

Treble Cut 2: A: OFF, B: OFF, C: ON, D: ON, E: ON. (220)

Treble Cut 1: A: OFF, B: OFF, C: OFF, D: ON, E: ON. (175)

Treble Neutral: A: OFF, B: OFF, C: OFF, D: OFF, E: ON. (100)=Flat. <—As shipped

Treble Boost 1: A: OFF, B: OFF, C: OFF, D: ON, E: OFF (75)

Treble Boost 2: A: OFF, B: OFF, C: ON, D: OFF, E: OFF (45)

Treble Boost 3: A: OFF, B: ON, C: OFF, D: OFF, E: OFF (30)

Treble Boost 4: A: ON, B: OFF, C: OFF, D: OFF, E: OFF (15)

Treble Boost 5: A: OFF, B: OFF, C: OFF, D: OFF, E: OFF (0) Approx. +4dB at 20K.

Note: Intermediate positons are possible in the Boost and Cut methods. The basic value ratios are as follows: A: 15, B: 30, C: 45, D: 75, E: 100.

GREEN: GAIN. The combination of +35dB, +37dB, +40dB, +49dB, +51dB, +54dB, +61dB, +63dB, +66dB, +67dB, +69dB, +72dB gain is made in two sections: (1) The gain of the main +40dB section which can be reset to +37dB and +35dB; and (2) the gain of the internal LOMC Head Amp, which is natively +32dB. It can be padded down to +26dB or +12dB via internal selection.

LOMC Gain: +12dB, +26dB, +32dB (N/A on MM6B)

Gain is Increased by moving the jumper to the Right.

MM Gain: +40dB, +37dB, +35dB

Gain is Decreased by moving the jumper to the Right; i.e., it functions like a “Pad” control although electrically it is controlling the gain of the output stage. Lowest measurable distortion will be found in the +35dB gain setting if input levels are also in a normal range.

+35dB: Mode: MM. MM Gain: +35dB. MC Gain: N/A.

+37dB: Mode: MM. MM Gain: +37dB. MC Gain: N/A.

+40dB: Mode: MM. MM Gain: +40dB. MC Gain: N/A. <—-As shipped

+47dB: Mode: MC. MM Gain: +35dB. MC Gain: +12dB.

+49dB: Mode: MC. MM Gain: +37dB. MC Gain: +12dB.

+52dB: Mode: MC. MM Gain: +40dB. MC Gain: +12dB.

+61dB: Mode: MC. MM Gain: +35dB. MC Gain: +26dB.

+63dB: Mode: MC. MM Gain: +37dB. MC Gain: +26dB.

+66dB: Mode: MC. MM Gain: +40dB. MC Gain: +26dB.

+67dB: Mode: MC. MM Gain: +35dB. MC Gain: +32dB.

+69dB: Mode: MC. MM Gain: +37dB. MC Gain: +32dB.

+72dB: Mode: MC. MM Gain: +40dB. MC Gain: +32dB.

BLACK SECTION 1: Located to the far left, lower section, near the Output jacks

Output Configuration: BALANCED or UNBALANCED operation.

Balanced Operation requires removing both black jumpers which are near the output jacks. Unbalanced requires replacing those jumpers. The jumpers are fitted so as to be in parallel with the back panel rather than 90 degrees to it.

To utilize Balanced output operation effectively, a user will need to supply (construct, or order to these specifications) an audio cable with the following characteristics (any custom cable vendor should be able to handle):

PHYSICAL CHARACTERISTICS of Cable Connectors:

MP8B End: Qty 2 of standard 2-pin RCA Cable plus insulated Spade Lug to fit US #6 post.

Receiving Component End: Male XLR or Male 1/4” Tip-Ring-Sleeve Plug.

ELECTRICAL WIRING OF Cable Connectors FOR XLR BALANCED OUT:

‘Hot’ of RCA plug to Hot of XLR (pin 2)

‘Cold’ of RCA plug to Cold of XLR (Pin 3)

Male Insulated Spade Lug (with 6 inch free clearance) to GND (Pin 1) of XLR

ELECTRICAL WIRING OF Cable Connectors FOR 1/4” TRS BALANCED OUT:

‘Hot’ of RCA plug to Tip of 1/4” TRS plug

‘Cold"‘ of RCA plug to Ring of 1/4” TRS plug.

Male Insulated Spade Lug (with 6 inch free clearance) to GND Sleeve of TRS 1/4”.

USE OF BALANCED OUTPUT CONNECTION:

Insert the two Spade Lugs under the GND post of the MP8B. Remove the two Balanced DIP headers inside. Insert the RCA plugs in your custom cable into the Output of the MP8B. Insert the XLR plugs into the appropriate XLR jacks on , or the Male 1/4” TRS plugs into the appropriate 1/4 TRS receptacle, on your line level preamp, A/D or other following device.

If Unbalanced operation is again desired, reinsert the 2 DIP headers in the correct location on the MP8B and use standard stereo RCA cables between the MP8B and your downstream line-level component.

USE OF BALANCED INPUT CONNECTION (FROM DIN-5 CABLE):
DIN GND - To #6 Spade Lug, connected to GND post on MP8B or MP7B

DIN L Ch HOT: To HOT of L ch RCA input

DIN L Ch COLD: To COLD of L ch RCA input

DIN R Ch HOT: To HOT of R ch RCA input

DIN R Ch COLD: To COLD of R ch RCA input.

USE OF BALANCED INPUT CONNECTION (FROM TWO XLR-3 CABLES):
XLR L. Ch. Pin 1: To #6 Spade Lug, connected to GND post on MP8B or MP7B

XLR L. Ch. Pin 2: To HOT of L ch RCA input

XLR L. Ch. Pin 3: To COLD of L ch RCA input

XLR R. Ch. Pin 1: To #6 Spade Lug, connected to GND post on MP8B or MP7B

XLR R. Ch. Pin 2: To HOT of R ch RCA input

XLR R. Ch. Pin 3: To COLD of R ch RCA input

Note: The RCA connectors on MP, MM and SU series Darlington Labs are not grounded directly to the chassis. The COLD (shield) portion of the RCA jacks travels via twisted pair to the internal PCB for appropriate electronic processing.

BLACK SECTION 2: Located to the far upper right hand corner near the LED.

FRONT LED ILLUMINATION: Bright, Medium Bright, Medium, Medium Dim, Dim

NOTE: Moving the DIP header to the bottom will decrease the LED brightness. To fully extinguish the LED, you may remove the jumper. Not all positions will produce linear change, based on the color LED illumination as different color LEDs require different currents and the 5 section resistive illumination divider is fixed.

BLACK SECTION 3: Located to the far left, upper middle, near the Input jacks

Mono strapping On/Off: for running a dedicated mono cartridge or TT without having purchased the external Mono switch. Install a DIP header onto these two pins, oriented vertically (in parallel with the rear panel). The unit is shipped with NO jumper in place…the result is normal stereo operation (overridden by the external Mono switch, if so equipped).

Production Update: As of 12/10/2024:

Oldest outstanding order: 11/17/24 (MP7B), 10/29/24 (MP8B), 11/5/24 (MP8B Upgrade), 11/22/24 (MM6B).

Total orders outstanding: about 2 dozen (+2 eBay) including a small number of pending updates.

New order timing: 2.5 to 4 weeks. Orders are PCBs for all outstanding orders received through 12/5 and many more are at 95% completion and await final calibration and final physical assembly.

Note: We will try to fulfill orders which were received by 12/5 to ship out by Christmas, but we are not guaranteeing to do so. Orders received from here on out are unlikely to be received by Christmas as we work through about 20+ units. The good news is that our production rate is the highest it has ever been, with multiple teams in multiple locations creating and finishing our products.