Darlington Labs SU-7 Moving Coil Head Amp Reviewed

The Darlington Labs SU-7 Moving Coil Head Amp is a product that Vinyl Enthusiasts will adore; in more ways than one!

This evaluation is a follow-up to my January 2023 review article on the Darlington Labs MP-7.  I often see members of the high-end audio world ramble on in forums or at shows about how a certain playback format or amplifier topology is the only one that will give your music ultimate realism. Being a person that goes past the specifications and looks into the design itself and its merits knows that there is a kingdom full of good designs out there that can bring you ultimate musical realism and enjoyment.

As my quest back into the vinyl playback fold continues, I have seen and learned a lot that has gone on in this arena over the years since I was last involved back in the 90s. In my 2 years back into record playback I have learned that vinyl enthusiasts probably have the highest percentage of folks believing their way is the only way.! 

When I was inquiring about putting a moving coil cartridge on my vintage turntable while most advised that it would work fine with the table I am using, a very small percentage told me I was wrong or even crazy suggesting such a thing. In their mind, only the best turntables are built for and deserve a moving coil cartridge. While I have seen plenty of examples to prove them wrong (I am not putting such a cartridge on a Crosley or one of the other cheap tables) I knew better than to argue with these people as they seem to love to go on and on about their opinions on these things!.

THE COMPANY

Darlington Lab’s way of designing and building its products is as much about tried and true as it is about leading-edge tech. They study all the old designs taking the best from them but also seeing the new technologies and form factors using these new ideas to make the products better.

Like its brother, the MP-7 phono preamp,  the SU-7 head amp uses a wall wart transformer that steps down the voltage from 120 to 24VAC. Then the SU-7 takes this 24-volt power and puts it through the rest of the power supply circuitry inside the unit to regulate and isolate the voltage. DO NOT mistake this for being like other devices that use a small 5-volt dc cheap wall wart! The MP and SU-7 take advantage of having an out-of-case transformer and will not cause noise, while the smaller chassis has all the important isolation and conditioning circuits in the case. Doing this allows the units to save you space in your rack by not having a separate power supply case for their products.

Unlike SUT(step-up transformers) that have classically been used for moving coil cartridges, the SU-7 is fully adjustable.

There are eight current-matched low-noise J-Fets used in the input stage as well as a linear output stage that promises an improved dynamic range compared to a SUT. The user-adjustable gain and loading are great for use with almost any low-output cartridge and have gain settings at +12,18,23, or 26dB. The loading adjustment has settings at 47 ohms, 100 ohms, 220 ohms, 470 ohms, 1K, 5K, or 47K.

These settings are adjusted using jumpers in the case of the SU-7(unlike some competitors that use switches or dials on the front panel). While this is less convenient and it can be hard to see the jumpers I had no issue setting things up for my cartridge with the SU-7.

While the SU-7 is built to go with the MP-7 as a Darlington Labs full package the SU-7 can also be used as a step-up head-amp with any moving coil phono preamp available. This will give people another high-quality fully adjustable option other than a SUT that can only change its settings when you change cartridges!

Sound Quality:

The set-up was so easy with the SU-7 that anyone familiar with hooking up equipment will have no issues whatsoever. Just take the SU-7 out of the box, use the instructions to open the case, set your desired gain and loading, hook your turntable to the SU-7, and then the SU-7 to your phono preamp or in my case the MP-7. Also, I connected the ground wire to both ground lugs on the MP-7 and SU-7 to insure grounding to both units(your mileage may vary).

After connecting things up, I turned everything on and was shocked at how low the noise floor was while the gain was not affected by adding the SU-7. to the system. Playing a test record allowed me to make sure both the cartridge was set up correctly and that the SU-7 was working fine with the MP-7. It went without issue and worked perfectly.

Since my Audio Technica, AT 33PTG/II cartridge was brand new and needed to break in. After a while, the AT cartridge loosened up and came into its own. As stated above initially I was worried about the noise being higher since the SU-7 and MP-7 have about 63dB of total gain when combined! I have also heard horror stories about the amount of noise a SUT can sometimes bring to the table in a vinyl system. I did not do any measurements to see the difference but in my room, the noise did not seem to change at all adding the SU-7!

Eventually, I finally sat down with my critical ears on for some listening.

John Coltrane’s 1957 album Blue Train Blue Note Tone Poet Series is a great place to start evaluating this new cartridge and Darlington SU-7 combo. I was not disappointed as the Audio Technica cartridge showed its stuff and allowed me to hear more into the music on this great album than my previous moving magnet cartridge. The main thing I kept thinking about is that the addition of the SU-7 was not taking anything away from the performance and only letting my new cartridge shine! The Bass was strong and detailed; the midrange was smooth and soulful. And treble was also detailed but took on the smooth character that the AT33 PTG/II cartridge is known for.

Iron Maiden’s 1984 album Powerslave to me is a heavy metal classic that shows this band at its best.  Given that it is not the last word in studio work or mastering it does sound good for a metal album, especially in the early 80s.

The Audio Technica AT33 and Darlington Labs SU-7/MP-7 combo drove home the point that this is an incredibly great-sounding combo for the money. Again bass was tight, and detailed, with Steve Harris’s bass guitar Gallups being in full audio display in my system. Both guitars sounded realistic without too much-distorted sheen and the drums had great body letting you hear the drum heads being struck. I love this album and cherish having it on vinyl so I am very picky about the way it sounds in a system– with the Darlington Labs/ Audio Technica combo I was very impressed, to say the least.

Conclusion:

 As an audiophile that is stepping back into the vinyl playback world after some 30 years away, I am impressed with what is available today. There are options out there at any price and performance level. If you are also on your vinyl journey and are interested in getting an outboard phono preamp combo that can rival many more expensive units the Darlington Labs MP-7/SU-7 combo is hard to beat for the price.

I can fully recommend the SU-7 as an accompanying component to the already great MP-7 for sure. But I would also advise someone looking for a step-up transformer to take a look at the SU-7 as a super clean adjustable step-up head-amp at a fantastic and realistic price! This unit just might do a better job than some rival head amps at double the cost. Highly recommended and a BEST BUY!

Review System: Speakers: Spatial Audio M3 Turbo S open baffle./ REL T9x subwoofer/ Digital: Denafrips Venus II, / Modified PC-based Music server/streamer. Analog: Vintage Hitachi PS-17 Turntable, Darlington labs MP-7, and SU-7 phono preamp, Audio Technica AT33 PTG/ii cartridge Amplification: Hegel P20 preamp. Pass Labs X150.5 power amp. Conditioner: PS Audio Quintet. Cables: Iconoclast Series 2 SPTPC speaker cables, Iconoclast Generation 2 ETPC XLR cables and Gotham 4/1 RCA interconnects, Iconoclast BAV REL subwoofer cable  

Price: $499.00

Darlington Labs

sales@darlingtonlabs.com

Darlington Labs LLC

Boston, MA 02131

SPECS:

GAIN: +12dB, 18dB, 23dB, or 26dB, user-selected via internal DIP headers.

LOADING: 47 ohms, 100 ohms, 220 ohms, 470 ohms, 1K, 5K, or 47K, user-selected via internal gold-plated DIP headers, in parallel with 0.001uF. Soundsmith loading options including 750 ohms are available; email for info).

FREQ. RESPONSE: 20Hz – 20kHz +/-0.1dB.

THD: <0.01% at normal operating level of 5mV out. <0.02% up to +20dB above normal operating level; second harmonic predominates (quoted at +23dB gain).

S/N: >73dB A-Wtd re: 0.4mV input.

Optimum Cartridge Match: 0.18mV to 1.2mV output LOMC (Low-Output Moving Coil).

Headroom: 64dB above a nominal 5mV output (assuming the following RIAA stage has infinite headroom)…not a misprint.

Example: SU-7 set for +23dB gain: 0.35mV cartridge input results in 5mV at SU-7 output subsequently driving a +40dB RIAA gain stage with a line-level output of 500mV (0.5V) at 1kHz.

Maximum Out: >8V (+20dBu) into 10K load.

Power: 120V or 230V wall-mounted AC cube with 24VAC output (included).

Chassis: 5-inch wide, Silver front/black exterior aluminum chassis matching other current products..

Warranty: 1 year.

Matching Products: Designed especially to work alongside our MP-7 and MM-6 +40dB RIAA units.