Universal 6or12SL7 Kit Phono Preamp (Now Available!)

(4 customer reviews)

$600.00$799.00 US

SKU: N/A Category:


Caution! This is our most complicate Kit (yet) and we don’t recommend it for First time Kit Builders.

Note:  Rega owners please see grounding discussion at very bottom.

The Universal 6or12SL7 Phono Preamp is a Dual Mono Design that can play any 6SL7 or 12SL7 ever made, including the re-based Loctal 7F7 & 14F7, many of which were made in the 1930’s, 40’s and 50’s (see schematic for a complete list of compatible tubes).  No magic or complicated circuitry is required to switch the filament voltage from 6v to 12v, all you do is plug a 6v or 12v SMPS in!  Switch Mode Power Supplies are those bricks we power our laptops with.  And best of all SMPS’s put out DC.  And using DC for the filaments (aka heaters) is a great way to reduce the noise floor in a preamp.

We’ve carefully selected every part and component. From the Vishay coupling capacitors to the solid Cherry Wood Plinth and Hand Brushed Aluminum Top Plate, to the Universal Voltage Dual Secondary power transformer.

The Preamp comes as a Full Kit that includes all parts and an unfinished Solid Cherry Wood Plinth, Finished 3/16″/ 5mm Aluminum Top Plate and 2mm Aluminum Bottom Plate.

Build Information includes a Color Schematic of the Power Supply and Preamp, also a Build Series of Videos is on YouTube under Mellow Tone Kits.  The videos are the Build Manual.

Sound Signature:  Dynamic Warm Rich Detailed Sound,  Excellent Stereo Image & Soundstage.

Sample Audio @ 24/96 WAV

System Compatibility:  Perfect for most moving magnet cartridges with a measured output of approximately 5mVac.  Note moving iron cartridges like the Grado line have a lower output, testing so far has shown them to work just fine (and sound amazing), but you can expect a slightly higher noise floor.  NOT suitable for moving coil cartridges.

Build Complexity:   Medium High – if you’ve already built one of our Kits – You Can Build It!

Shipping Extra (to check on rate, make an account, place item in cart and go to check out page)

Discount Codes – don’t work on Kit Amps – the margin is too tight to offer discounts.

Not included:  Tubes, SMPS, IEC power cord, Solder, Coffee


Universal Design Can Use Any 6SL7 or 12SL7
Universal R-Core Power Transformer
Household Voltage (100 – 240vac)
Dual Mono
Input Sensitivity: 5mvrms = output 0.989Vrms @ 1Khz
Gain:  46dB
Signal To Noise Ratio: -53.8dBr @ 1Khz
Input Impedance:  A) 47Kohm B) open (2 jumpers to set impedance A or B)
Input Capacitance: 0.00pf / 100pf / 200pf (2 jumpers to set capacitance)
Output Impedance: 910 ohm
Power Consumption (preamp): 5.1w + 7.6w (smps)
Tubes:  2 x 6SL7GT 1 x 6SN7GTA/B or 12SL7GT 1 x 12SN7GTA/B (see schematic for full list)

Size:  10″w x 13″d x 4.75″h (25.5cm x 33cm x 12cm), 9lbs/4kg


6or12SL7 Tubes

6or12SN7 Tubes

SMPS (switch mode power supplies)

IEC Power Cords


Full Specification Sheet

RIAA Curve

Power Supply Schematic

Amplifier Schematic

Build Videos – follow along with Jim on YouTube as he guides you through the build process step by step.

Recommended Tools:  Link to Tools in the Store*

Temperature controlled solder station (I use: Lonove 926LED III available at Amazon)

Electrical Solder  63/37 tin/lead rosin core 0.8mm/.031” (Kester “44” 24-6337-0027)

Rosin Soldering Flux (I use: Caig “no clean” paste RSF-R39-2)

Volt/Ohm Meter (CAT III 600v – minimum) c/w probes & clip-on leads

Variac  0-130vac/20A or 0-260vac/10A  (helpful but not required)

Hot Glue Gun – a mini craft type will work just fine

1/4″ Socket Wrench & Deep Sockets 3/16 &  7/32″ c/w  3″ (75mm) extension

*Wire Stripper

*Solder Sucker

*Needle Nose Pliers

*Side Cutters

*Ratcheting Crimper (Note: this is NOT your standard red/blue/yellow crimper)

*Mini Hot Air Gun (very very useful)

*Mini Utility Knife

*Mini 1/8″ Slot Screwdriver

*Torx Driver T10

Fun Fact:   For years i’ve suffered with various “commercial” phono preamps and to me they all sounded lifeless.  So I started work on a dynamic warm rich sounding design that I hoped would make any vinyl fan grin from ear to ear – that was our lofty goal at least!  Little did I realize it would take 6 months of development work that at times felt like hard labour to finally reach that goal.  And like most difficult endeavours, in the end we forgot all about the hard brain work (and lots of butt scratching) after the first few seconds of listening to the Universal Phono Preamp – hopefully you enjoy it as much as we do.

Rega Special Grounding Method – if you own a modern Rega, the entire line deviates from the normal turntable grounding method of providing a chassis ground from the turntable to your phono preamp ground post.  What they’ve done is attach the chassis ground to the LEFT RCA SHIELD.  Not surprisingly this has caused Rega owners all kinds of grounding issues, most notably ground loops, noise and hummm.  The solution is simple, cut the ground connection at the left RCA shield OUT jack and connect a separate ground wire from a machine screw on the tonearm base to your phono preamp ground post.  A totally inexperienced customer figured this out and made the revision without a problem – and of course all of the noise issues disappeared.




4 reviews for Universal 6or12SL7 Kit Phono Preamp (Now Available!)

  1. John Fort (verified owner)

    Just finished completing the build of my Mellow Tone Kits Universal Phono Preamp. First off, I have to give a big congratulations to Jim and Charles on this Phono Kit. It is an excellent kit with everything you need to build including extra parts just in case. The attention to detail and documentation is above the norm. The Videos for instructional build cover everything you need to get this up and running. Jim explains the circuit and helps you understand the design and schematics. I love the modular design of this with the separate boards and the ability to service and upgrade very easily. The dual Mono design is a big Plus. Finding a good, affordable Phono Preamp that uses Octals is hard to come by and especially one that supports both 6 and 12 volt variants is impossible. This is a very unique Preamp. The build was very straightforward and was accomplished without any problems.

    The sound quality from first plug in is very good and it certainly gets better after running it in for a while. It is very quiet, especially for a tube preamp. The bass and dynamics are excellent. Soundstage and imaging are really nice with very stable placement of instruments and singers. Not too forward and not too recessed. It has a dimensional quality that makes the speakers disappear and the music to sound more real. There is a liveliness to it, and it doesn’t exaggerate anything or get bright or harsh. It will show the difference quite easily between your good recordings and the average. It draws you in and makes you want to listen to the music. I’ve had some pretty expensive Phono Preamps that do the Audiophile thing and most don’t get the musicality correct. The presentation is to my taste, doing an excellent job of balancing all the variables. I’m using the early Sylvania Loctals from Jim that he re-bases to Octals, I highly recommend these! You do want to use the best gear with this you can, because it will reward you. I plan to try many more combinations of cartridges and cables to see what the magic combo will be.

    This Phono preamp is a keeper and certainly an outstanding bargain. Highly recommended.

    John F.

  2. Rasmus (verified owner)

    I was one of the test builders of this kit. Paid full price, but I got some good tubes with it (Sylvania Loctals re-bases to Octals).

    I really like the philosophy behind the design, with the modular setup for easy repair/upgrades, and the approach with minimal parts in the signal path.

    This was not my first build (but first from Mellow Tone Kits), I have some experience with the soldering iron. But this kit was by far the best, and easiest, to assemble.

    It can be done even with minimal DIY and soldering experience.

    Instruction videos are great with all the needed info. Parts are of premium quality, and there are spares in the bags.

    Plinth and top aluminum cover/plate is also top quality. Enjoyed the build a lot!

    Now for the sound. I’m using the tubes I got with the kit as part of the test builder program.

    First thing that hit me was the holography, just the 3D feeling of everything. It is better than my digital sources (a couple of pretty good DAC’s).

    Instrument placement is so good with this amp. And it’s very, very musical. I find myself wanting to test listen to a certain track and ending up listening to the entire album.

    It also made me realize my turntable had some slight issues that I had not picked up on before. All the details are coming through here, and after fixing the issues my table now sounds awesome.

    I highly recommend this kit, both for the joy of building it and of course for the stellar sound quality.

  3. Rachael Warlond (verified owner)

    Here is a link to the Full Review

    This review was carried out using the following equipment:
    • Rega Planar P6 with standard RB330 tonearm
    • Nagaoka MP-500 & Goldring 2500 moving iron cartridges
    • Two other (borrowed) phono pre-amps, one of which has a retail price of several thousand dollars for comparison purposes.
    • NAIM NX5 XS 2 streamer/DAC for comparison purposes
    • Cayin Soul 170i integrated tube amplifier
    • Q Acoustic Concept 500 floor standing speakers
    • High quality interconnects and speaker cabling
    • Suitably treated room

    First of all, my Rega had a problem with hum and buzzing. After a lot of experimentation, it was found that Rega earths (grounds) its turntables in quite a unique way. The turntable does not have a separate earth lead and instead, uses the left channel ground as the grounding point (RCA coax cables use the outer braid as both a shield and ground return path ed.). This problem was solved by running an earth wire from one of the tonearm’s mounting screws to the phono pre-amp’s earth lug and disconnecting the earth wire to the left channel ground. This is a simple modification that even I was able to do, so if you own a Rega, do not be discouraged.

    Now for some serious listening!

    As mentioned above, I used the excellent streaming capabilities of the NAIM NX5 XS 2 to compare the streamed version of the tracks with that produced by the phono pre-amp.

    It was immediately apparent that the Mellow Tone Universal Phono Pre-amp is no slouch. While keeping to streamed tracks which had not been re-mastered, without exception, the phono pre-amp bettered the streamed version in just about every area. To my ears, the following really stood out. The phono pre-amp had a little more sparkle in the top end, while brass instruments were presented with a very pleasing amount of bite. The human voice, both male and female, is also beautifully natural, while the bass is surprisingly articulate with a satisfying amount of texture and tone.

    The soundstaging ability is also excellent and as is usual with vinyl records, the variation in mastering quality is very much hit and miss, but given the right recording, of which I have many, the phono pre-amp is easily capable of expanding the sound stage beyond the bounds of the speakers. Not only this, instrument placement across the soundstage is also quite precise. Presumably, this has a lot to do with the decision to utilise a “dual mono topology” for each channel. In fact, I have an original (1972) album called Stormy Weekend by The Mystic Moods Orchestra which has rain, lightning and thunder as well as dogs barking and the sound of steam locomotive whistles, and these effects give the illusion of the listener actually being in the storm, meaning that the sound wraps around you 360 degrees! Impressive and spooky all at the same time.

    This phono pre-amp is also very dynamically alive, and using either cartridge, presented the music with a nice amount of atmosphere. I also love the sound of piano, and again, I was not disappointed, as it was reproduced in a very realistic fashion. Piano is extremely difficult to record, but there are recordings that do get it right – and so too did the phono pre-amp. Talking about atmosphere, which is NOT “air” that many speak about, is something that most digital recordings cannot quite achieve. True, a digital recording can be crystal clear, but then, so can the phono pre-amp, but with this added atmosphere, which I believe most people might describe as musicality (I know, it’s very cliché), the phono pre-amp is an absolute pleasure to listen to music through.

    • The Missing Linc – Lincoln Mayorga and Distinguished Colleagues Volume II – Sheffield Lab
    • Lincoln Mayorga and Distinguished Colleagues Volume III – Sheffield Lab
    • The King James Version – Barry James & His Big Band – Sheffield Lab
    • Discovered Again! – Dave Grusin – Sheffield Lab
    • I’ve Got the Music in Me – Thelma Houston & Pressure Cooker – Sheffield Lab
    • A Talking Picture – The Pasadena Roof Orchestra
    • Peter and the Wolf Young Person’s Guide – London Symphony Orchestra – Mia Farrow & Andre Previn as narrators
    • Oxygene – Jean Michel Jarre
    • Make Your Move – Captain & Tennille

    All the above recordings are very early pressings from around the mid 1970s to about 1980. I did play quite a few other pressings, some that are much more recent, including some of which have been remastered at 45RPM.

    Still, without exception, the Mellow Tone Kits phono pre-amp’s “special sauce” produced an experience that was totally captivating.

    The Cartridges:
    Nagaoka MP-500 – an excellent cartridge with a smooth yet extended top end, a midrange with a nice amount of warmth, and upper bass/lower midrange which is very slightly fuller than the Goldring 2500.
    Goldring 2500 – another excellent cartridge, and if you want a cartridge which is a little more neutral than the Nagaoka MP-500, then this comes highly recommended.

    Still, even though there are minor differences between these two cartridges, when properly aligned and set up, either would be an excellent companion to the phono pre-amp. I prefer the Goldring 2500, but it’s such a close match that if I hadn’t listened to the Goldring, then I would be more than happy with the Nagaoka. BTW, while the Nagaoka MP-500 is obviously made by Nagaoka, it came as a bit of a shock to learn that the Goldring 2×00 series are also made by Nagaoka!

    Is the Mellow Tone Kits phono pre-amp excellent for the money? A big fat NO! The MTK phono pre-amp is excellent regardless of the money, and I do not believe that I can be any more complimentary than this.
    In a word, buy it, assemble it, and sit back and enjoy the music…it’s really that simple!

  4. bradleybcraig (verified owner)

    I was lucky enough to be a test builder again! I also built the GU-50 mono blocks last year. As with those kits, the Phono Preamp is really well designed and thought out. Kudos to Jim and Charles for another great kit.

    I have been listening for several days now. I had a hum issue that with Jim’s awesome help we figured out pretty quickly – I had a couple safety ground mistakes that were easy to remedy (additional build video to be added ed.). Speaking of the videos, Jim does a great job and really makes the build very easy to follow.

    Listening setup:

    Fluance RT85 w/ Ortofon Blue
    Freya+ preamp w/ Bad Boys and GEs
    SublimeAcoustic active crossover set at 60hz and 24db slope
    Jeff Rowland bridged monos connected to Magnepan .7s
    2 REL Audio T9x subs

    Miles Davis – Kind of Blue
    John Coltrane Quartet – Ballads
    John Coltrane – Giant Steps
    Mingus – Mingus Plays Piano
    Dexter Gordon – Go
    Adderley, Davis, Jones, Jones, Blakey – Somethin’ Else
    Duke Ellington & John Coltrane
    Dire Straits – Dire Straits
    Dire Staits – Communique
    Norah Jones – …’Til We Meet Again (Live)
    Alan Parsons Project – I Robot

    Sonically the phono preamp is as advertised. Clarity across the board, sound stage presents really well, with instrument placement and vocals. Bass is crisp and warmth as is expected from a tube amp, is right on the money. Background is dark and instrumentals and vocals hang nicely.

    I would highly recommend this kit to add a nice listening experience to your rig.

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