What is a J-FET and how does it compare to a conventional transistor?
The 1956 book “Handbook of Semiconductor Electronics” edited by Lloyd P. Hunter provides a succinct overview. ‘The field-effect transistor operates on a different principle than that of the conventional transistor. Stated simply, the field effect transistor consists of a bar of semiconductor material whose resistance is modulated by varying the effective cross-sectional area of the bar by electrical means.” […] p. 1-7.
“The input impedance of this device is quite high, and the output resistance is moderately high.” p. 1-8. (We account for the output resistance through use of additional, carefully-tailored circuitry to interface each stage with necessary downstream components).
The book’s preface states, “In this book, an attempt is made to collect in one place all the major principles of the field of semiconductor electronics. Since the field is so new, it is possible to do this in a reasonable amount of space.”
How widely are J-FETs used by other manufacturers?
While J-FETs are not necessarily widely known by most audio consumers, they have a long history in certain applications, including audio, since their commercialization in the mid-1960s.
Virtually every high performance FM tuner since 1968 with an analog front end has used a J-FET, or MOSFET, for the RF Amplifier stage. This produces a large reduction in cross-modulation and extraneous signal detection.
In the 1970s, it was common to see a 2SK30 FET used in the Baxandall tone control network in Japanese receivers. This provided a high input impedance which prevented loading of the tone control elements.
In 1972, John Curl used J-FETs in the JC-2 and JC-3 phono preamplifier circuits designed for Mark Levinson.
In 1973, McIntosh used a 2SK34B FET in the second stage of the phono preamp in their Stereotech 1200 receiver, which was sold until 1976. It used a 2N5087 PNP in the front end, operating at an unusually low current. This was the only model McIntosh outsourced. It performed so well that it stole sales from the name-brand Mac 1900 receiver and was discontinued in 1976, when the Stereotech name was phased out.
In 1974, professional open-reel tape recorder manufacturer Otari came out with their MX-5050 reel deck. The Mark I circuitry used discrete J-FETs as second stage voltage amplifiers in the playback amp and the record amp.
In 1976, Spectral used J-FETs in the input stage of its preamp design which would later become the DMC-10 and remains in the still-current DMC-30 series.
In 1977, Tom Holman would use one J-FET at the input to the phono preamp in his Apt-Holman phono equalizer (the similar but prior design for the Advent 300 receiver used a BJT transistor instead).
In 1979, David Berning would use a P-channel FET (2N5461) in the bottom of a cascode with ½ of a 12AX7 in the top for the gain stages in his TF-10 preamplifier. They may have been quite linear, but the limited gm (transconductance) and high noise of the P-channel FET produced a higher than usual noise floor. Berning went back to an all-tube RIAA section in 1988 with the TF-12.
In 1981, Nelson Pass (then of Threshold) would use FETs in the input stage of his FET-One and FET-Two preamps. This would continue into the classic 1985 design of the FET-nine and FET-ten units (using the NPD5566 dual-FET). He uses them widely in the current Pass audio products.
In 1983, Jim Strickland designed the Acoustat Trans-Nova FET preamplifier which impressed J. Gordon Holt in a review up against the JGH reference of a 1979 Berning TF-10 tube/FET hybrid preamp.
In 1985, Audio Research would combine FETs (2SK117) with tubes (6DJ8s) in the SP-11 preamp, and in the scaled-down SP-9 unit for 1986.
In 1986, Roland Research released the Consonance preamp which featured a differential FET input.
In 1987, Conrad Johnson would release the Motif MC-7 and MC-8 designs to complete in the Mark Levinson/Krell/Roland high end solid-state market. For the second stage of their RIAA, CJ developed a single-ended +44V rail circuit using complementary J210 and J270 J-FETs for the input, cross-coupled to another J210/J270 pair for the output.
This provided a measure of distortion cancellation (with lowered 2nd HD relative to 3rd HD). Similar circuitry was fitted to the Conrad Johnson PF-1 (see Martin Collom’s rave review in Stereophile December 1990), PF-2, and PF-R.
In 1988, John Curl released the SCP-2 phono preamp. His company, started in 1981 with the TCP-1 Phase Coherent Crossover, also had previously offered the SCP-1, a 28dB active head amp/step-up stage to be used with an existing MM-style (roughly 40dB) preamp. The Vendetta Research name reflected falling out with major manufacturers who simplified his purist designs “just enough to be practical for mass production” then didn’t pay him. The NPD5566 dual FET, and large geometry Toshiba J-FETs such as hand-selected-for-noise 2SK146/147 were key active devices. All are long-since discontinued.
Extensive commentary on the SCP-2 and the associated Parasound JC3 and JC3-Jr are found in our “History” section under 1988, which is when JGH reviewed the SCP-2 in Stereophile.
In 1988, Hafler joined the discrete FET market with the Iris, a remote controlled preamp with excellent user interface. JA of Stereophile reviewed it and placed it in Class D of R/C. (See the 1983 entry on the Acoustat Trans-Nova FET preamp, a similar architecture). In 1990, the Halfer SE-100 preamp continued the all-FET approach.
Mark Levinson uses a dual discrete J-FET with folded cascode in their current No. 526, which was reviewed against a 1980 ML-7 by Larry Greenhill in Stereophile (wherein the No. 526 was considered slightly better).
Today, in 2026, a single-discrete J-FET input with one or more 6H30 high voltage medium-current tubes and passive EQ is common in high end gear. up. All-tube 12AX7 designs similar to the Marantz 7 using feedback are still common. Mic-preamp-chip + IC-op amp units are used by Lehmann, Parasound (JC-3), Sutherland, and others offer all-IC-op-amp based units ranging in price from $20 to $5000 or more.
Why did Darlington Labs choose the J-FET (Junction Field-Effect Transistor) for voltage gain?
The 1969 textbook “Electronics: BJTs, FETs. and Microcircuits” by E. James Angelo, Jr, provides a useful, and succinct, explanation.
“The physical processes occuring in the BJT [Bipolar Junction Transistor aka ‘conventional’ transistor] involve both minority and majority carriers, whereas only majority carriers play a significant role in FETs. This fact is responsible for the word ‘bipolar’ in the name of the device, and for the same reason the FET was known at one time as a ‘unipolar’ transistor.” (p. 213).
“In comparison with the FET, the BJT can provide substantially greater gain, and its performance at very high frequencies is somewhat better than that of the FET. On the other hand, the BJT generates more waveform distortion than the FET in many applications, and it has a low input impedance which, for practical reasons, is very troublesome in many cases.”
“Thus each type of transistor has applications in which it excels, and optimum design often results in both types being used in one piece of equipment.”
Darlington Labs uses high-quality BJT (conventional) transistors for supporting roles within our circuitry. Those BJTs — in special configurations — allow our core technology High-Voltage J-FETs to provide voltage gain in the most clean and transparent manner.
For our Active MC Step-Up stages, we use low-noise high-transconductance J-FETs, as well as low-noise BJT transistors, on the input stage, to achieve low noise with the very low associated impedance from an LOMC cartridge. However, unlike some companies, our active SU stage uses high voltage power supply rails (a total of 46V) even though the input signal level (0.5mV) is relatively low. It is our belief that doing so enables the circuitry to perform optimally with an easy, clean, low-distortion sonic signature.
Why use Discrete Design instead of Op-Amps?
Discrete design refers to individual gain elements – transistors (J-FETs and BJTs), resistors, capacitors – arranged in the necessary configuration to provide the desired function. By comparison, the term Op-Amp (short for Operational Amplifiers) usually refer to small monolithic devices which are also called an Integrated Circuit.
The concept of the Operational Amplifier dates from the 1930s in a discrete vacuum-tube format for use in analog computer applications. Discrete solid-state op-amps came into being in the late 1950s. The first widely-used Monolithic Op-Amp was developed by Semiconductor Process Engineer Dave Talbert and Robert Widlar in 1964 (their uA702). 1965 brought the team’s follow-up, the uA709, acknowledged as the first truly mass-market op-amp. Talbert and Widlar moved to Molectro in late 1965 (which would later be acquired by National Semiconductor). At National Semi, they continued to build a linear dynasty, with the LM101 series.
In 1968, Dave Fullagar, working for Fairchild, designed the LM741. This op-amp was some would say, “exceedingly very much like” the LM101, except that by virtue of the Fairchild process in use at the time, the typical external 30pF compensation cap was placed “inside the chip” on the substrate, making a close relative of the LM301 but one that was internally compensated instead of “externally”. Op-amp frequency compensation is considered to be a black-art by many engineers, and therefore, the unity-gain-stable and therefore easier-to-deploy 741 is the most widely known classic op-amp. It remains in active production today, 56 years later.
These ‘building block modules’ require only a few external components to define their operational parameters. This greatly simplifies the design process, giving the engineer a far easier job than with traditional discrete circuitry, where numerous individual decisions have to be made. At the same time, ICs have important limitations on their performance when applied to audio applications – even the newest types.
Bob Widlar, the original inventor of monolithic op-amps, was quoted at a 1974 technical conference that they were never intended for audio use. (This quote was confirmed by John Curl online in 2017 and by Walt Jung in Audio eXpress, successor to TAA, in 2012; both men were in attendance).
With Discrete Design, we gain tremendous flexibility in setting the gain, frequency response and distortion characteristics of our circuits. Importantly, we also can operate our circuitry at much higher voltages than competitors who rely on IC op-amps. This provides a substantial increase in “inherent linearity”, producing an output that is more true to the input signal.
DEEP LINKS LIST to Forums Etc (a sampling):
Steve Hoffman Forum (other than the main thread which is available at our Review tab):
https://forums.stevehoffman.tv/threads/new-nagaoka-mp-700.1222214/
https://forums.stevehoffman.tv/threads/nagaoka-cartridge-fans.1133307/
https://forums.stevehoffman.tv/threads/nagaoka-mp-500-owners-club-and-pictorial.1197905/
https://forums.stevehoffman.tv/threads/whats-the-benefit-of-a-separate-phono-preamp.1164507/
https://forums.stevehoffman.tv/threads/audio-technica-at33ptg-ii-step-up-transformer.1163601/page-2
https://forums.stevehoffman.tv/threads/turntable-recommendations-2500-budget.1159308/page-5
https://forums.stevehoffman.tv/threads/phono-preamp-recommendations.1157895/
https://forums.stevehoffman.tv/threads/should-i-go-phono-preamp-shopping.1147311/page-4
https://forums.stevehoffman.tv/threads/does-phono-stage-matter-for-low-fi-systems.1110522/page-2
https://forums.stevehoffman.tv/threads/help-upgrading-phono-preamp-from-lounge-audio.1113522/page-2
https://forums.stevehoffman.tv/threads/poll-do-you-leave-your-audio-system-powered-on.1105034/
https://forums.stevehoffman.tv/threads/worth-upgrading-a-darlington-labs-mp-7-to-mp-8b.1215875/
https://forums.stevehoffman.tv/threads/schiit-stjarna-tube-phono-preamp.1220027/
Audiokarma:
https://audiokarma.org/forums/index.php?threads/stanton-681eee-s-vs-881.446122/
https://audiokarma.org/forums/index.php?threads/a-tale-of-two-phono-stages-and-more.1008393/
https://audiokarma.org/forums/index.php?threads/anyone-tried-darlington-labs-preamp.952712/
https://audiokarma.org/forums/index.php?threads/whats-my-boggle-with-phono-preamps.1037079/page-4
https://audiokarma.org/forums/index.php?threads/anyone-tried-darlington-labs-preamp.952712/page-4
https://audiokarma.org/forums/index.php?threads/a-new-phono-stage-discussion-and-more.1011366/
Pink Fish Media
https://pinkfishmedia.net/forum/threads/phono-stage-ideas.275841/page-2
Super Best Audio Friends:
https://superbestaudiofriends.org/index.php?threads/darlington-labs-phono-preamps.10320/page-4
HiFi Sentralen (Norwegian website)
https://www.hifisentralen.no/forumet/threads/ymirs-audiofile-liv.72643/page-41#post-3678302
HiFi Haven:
Audio Science Review:
Needles and Grooves:
https://www.needlesandgrooves.com/threads/darlington-labs-mm-6-usa-tour.1653/page-16
https://www.needlesandgrooves.com/threads/darlington-labs-mm-6-phono-preamplifier-review.1534/
Vinyl Engine:
https://www.vinylengine.com/turntable_forum/viewtopic.php?f=19&t=129528
Canuck Audio Mart Forums:
https://www.canuckaudiomart.com/forum/viewtopic.php?f=32&t=62918&p=1043803&hilit=darlington#p1043803
>>“Dead quiet, relaxed, with explosive dynamics and huge soundstage. If this was a power amp it'd be a Krell.”
Audiogon:
https://forum.audiogon.com/discussions/suggestions-for-a-phono-preamp
https://forum.audiogon.com/discussions/budget-phono-preamp-2
Audio Asylum:
https://www.audioasylum.com/cgi/vt.mpl?f=vinyl&m=1211215
Decware Forum
https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1655409666/7#7
Audiocircle:
https://www.audiocircle.com/index.php?topic=176284
https://www.audiocircle.com/index.php?topic=177738.0
Reddit:
https://www.reddit.com/r/audiophile/comments/15lj8sh/darlington_labs_su7_first_impressions/
General Industry Reading:
https://www.youtube.com/watch?v=cIBxJjmsAAk - Michael Fremer interviews John Curl (August 2025)
https://www.youtube.com/watch?v=jzLe8YsVHOg&t=3378s - Rick Beato interviews Bill Schnee: Engineering Steely Dan's Aja; discussing Doug Sax and Lincoln Mayorga and much more (2024). Producer’s Workshop was the studio immediately behind the Mastering Lab (a 700 audio cable run direct from the console to the TML cutting room). In 1973 Schnee engineered Lincoln Mayorga & Distinguished Colleagues - The Missing Linc, Volume III, and in 1975 he produced and engineered the Thelma Houston and Pressure Cooker album, I've Got the Music in Me.
https://www.youtube.com/watch?v=oKC23lUUv14 - Bascom H. King (BHK) Interview from 2015 w/PS Audio discussing the Infinity HCA from 1978
https://www.youtube.com/watch?v=BBPVuA8ClaU - BHK Interview Part 2
https://www.youtube.com/watch?v=toJMJ2VDMBo - BHK Interview Part 3
https://www.youtube.com/watch?v=tdG03dNtkII - BHK Interview Part 4
http://5bbd05afd3e2e6fdc44b-c5d6c9adce36979e1961ce685c8cc59c.r96.cf2.rackcdn.com/Arnie%20Nudell%20Podcast.mp3 - Arnie Nudell interviewed by Paul McGowan
https://www.stereophile.com/content/arnie-nudell-infinity-genesis - Arnie Nudell interview by Robert Harley from 1995
https://www.reddit.com/r/HobbyDrama/comments/moapci/audio_the_rise_and_fall_of_rheadphones_favorite/
https://www.superbestaudiofriends.org/index.php?threads/audio-science-review-review.9827/
ASR’s recommendation methodology is more than 88 years out of date - literally and factually - not incorporating important scientific recommendations from 1937, 1949 and 1961, in terms of the human ear’s response to distortion. Modestly, if you don't have a Darlington Labs phono preamp, or a much more expensive very-high-end preamp, and don’t trust your ears, and don’t talk to FM radio programmers - who often source from vinyl because they can see real-time listener ratings - then you genuinely may have very little actual understanding of why people bother with vinyl.
https://forum.audiogon.com/discussions/the-audio-science-review-asr-approach-to-reviewing-wines
https://vasiltech.narod.ru/CD-Player-DAC-Transport.htm
https://www.dutchaudioclassics.nl/the_complete_d_a_dac_converter_list/
https://en.wikipedia.org/wiki/List_of_three-letter_broadcast_call_signs_in_the_United_States
Specific review notes of interest:
MP8B:
Vs. ELAC Elac PPA-2: https://www.needlesandgrooves.com/threads/the-darlington-labs-thread-new-2024-models.2512/page-4#post-840011 (5/20/24)
Archived MM-6 Reviews from 2020 to 2023:
MM-6:
An extended review with a Nagoaka MM, SL1200 Mk7 TT, and Focal speakers:
“As I listened to an old Capitol Records album of Dolores Gray (which I know the orchestral nuances quite well), bringing the volume up only lay emphasis on the subtle textures created by the strings, guitar, glockenspiel, drums and bass, without straining, and without being obnoxiously loud, in your face. I hear more separation between instruments, specially vocals. The sound overall is round, light yet bold, easier to listen to than the Schiit Mani (which I still like BTW!!!). The Mani is going to my second set up, in the bedroom.”
A day later the review continued:
“A few more observations regarding the sound of the MM6. It's simply astonishing how George Shearing's piano sparkles in ways I haven't heard prior to the MM6. Dynamics are also remarkably realistic (since I play the piano myself, can really tell). And lastly, for now, I'm finally enjoying increasing the volume and not feeling disturbed by how loud it sounds. It just sounds BIGGER, not louder. And I guess, overall, it also has to do with my Nagaoka cartridge, now having a chance to show a little more of it's capabilities. Consequently, my entry level Focals are better than I thought. The MM6 is serving my entire system really well!!!” -
Four more days pass:
“I'm amazed...Today I listened to an amazing album, arranged by the great Claus Ogerman, with Jan Akkerman on guitar. Was blown away by how much "air" and space there is around the orchestral textures, as well as the ease of Akkerman's guitar sound. I know this album really well and that's the first time I get to experience it this way.”
“After 4 days playing records, the MM6 is blooming. I'm ReDiscovering my record collection. I've been telling a few friends who love audio how great the MM6, working with my Technics [SL-1200] mk7 TT. I'm done upgrading my analog set up for possibly a very long time, if ever.”
- Gus C, from a Boston, MA suburb (May 2021)
“I can’t recommend the Darlington Labs MM-6 more highly.”
“Outstanding phono preamp. ”
eBay listing #193815954999 from eBay user guava23 (2870) - March 2021
“MM6 is richly musical, made listening to favorite LPs a new joy! Real audio value!”
eBay listing #193767347260 from eBay user ‘diamondbackdave’ - January 2021
“This thing is amazing. So open and natural, and that bass! Wonderful sound!”
Jack G’s assessment of the MM-6 from an eBay purchase - February 2021; 193815954999
Archived MM-5 Reviews from 2020 to 2023:
MM-5:
“I'm really enjoying the MM-5. Absurdly quiet and three dimensional. I was concerned that returning to a solid-state phono pre would be lacking, but this is extremely well implemented. The mono switch works very well and I'm glad I added it.” - Anthony in WA (Jan. 2022).
The above client had purchased a competitor’s T-11 Vaccum tube unit via the biggest online seller, and had two of them fail in rapid succession.
“Just a short note to say thank you for creating an affordable (high quality) preamp (mm-5). It has enabled me to enjoy my vinyl.” - Paul in WV (Jan. 2022).
“Awesome phono preamp; wipes the floor with my vintage Yamaha Naturalsound integrated phono preamp - now I have extended freq. response, optimized gain staging for my power amp, lower noise floor, and above all: a very pleasant sounding preamp that I enjoy listening through!” classicvintageproaudio (560) in October 2021
“Just wanted to send a note to say thank you for your communication with my purchase. The sound quality of this preamp is ridiculous compared to the price. Nice wide soundstage, great dynamics, and the midrange are just unbelievable. There is almost no sound [noise] floor whatsoever.”
Feedback from Michael S, a client in northern MN (May 2021).
“The MM-5 is an excellent product beyond brand names and conditional reviews. It delivers great musicality and amazing detail retrieval and tight bass.”
ma_51me_foaihnale (26), a purchase from our eBay store (#193759333606) (April 2021)
“A very coherent and rich texture accentuated by an elevated level of detail not expected at this price point.”
Greg M. (March 2021) a satisfied client (and high end industry veteran) regarding his MM-5. (March 2021)
“Wow! What an upgrade. Really brings my old vinyl to life. This is really a fabulous sounding preamp.”
eBay listing (#193759333606) from eBay user ‘markedat2222’ (January 2021)
“High quality build. Great value. Heavy constuction. Very satisfied with my MM-5!”
eBay listing (#193759333606) from eBay user ‘deertracebill’ (January 2021)
“One of the best sounding phono stages you can find. Very clear and dynamic.”
eBay listing (#193759333606) from eBay user ‘tonehaus’ (December 2020)
“Non-congested and effortless…Very clean sound, like I was listening right from a console feed…”
“It just begged you to turn up the volume it sounded so good.” - Ryan A, a client from WI (December 2020)