Not-For-Profit MM/MC Phono Stage
The DIY bug has bitten Steve Graham, again. And he gets in a bit deeper than he bargained for, again.
Warning: This will get a bit wordy. Vinylphiles and/or tubephiles probably won’t mind. Digiphiles won’t likely be reading this, but they are most welcome to.
Have you ever noticed the almost carnal look on the face of a tube-loving audiophile when he, it’s always a he, first claps eyes on an attractive tube amp? It can be a miniature Earmax headphone amp with three small nine-pin tubes or an Audio Research Corp behemoth sporting row upon row of power tubes. The desire is almost palpable. Do solid state amps inflame in quite the same way? Perhaps, but not with the ardour that a tube amp can engender. If you are susceptible to tube lust, read on. You just might just crush on my latest project.
For someone who swore off vinyl three decades ago, I’ve really taken to it again. It doesn’t hurt that I have friends with lots of vinyl that theyère willing lend. Not that LP’s form a large part of my music collection – but it is a musical part. Vinylphiles will think it heresy, but I really enjoy LP’s ripped to 24/192 and then played back with my NAD digital music player and PS Audio DAC. In fact, ripping friends’ LP’s is the only way to enjoy out-of-print recordings without scouring used record sites for vinyl that may be in questionable condition.
The five-part series I wrote on the DIY Tetra phono preamp and subsequent listening, including comparisons to other phono amps, has not dimmed my enthusiasm for this good-sounding, unfussy and over-achieving piece of gear. The Tetra uses four common 9-pin dual triode tubes. The prototype Tetra I built for the series is my go-to phono stage when digitizing LPs.
Then along came the EAR/C.L.E.A.R. 834, using three 12AX7 tubes (part 1, part 2). Though the C.L.E.A.R. out-performed the Tetra in a few areas, I found it to not be quite up to the Tetra’s overall music-making abilities. The challenge I then set myself was to see if a simpler and less expensive phono stage could mount a “sound” (groan) challenge to the Tetra.
To this end I started with a much-copied commercial design, changed the tube types, and substituted a power supply similar to the one in the Tetra. Also like the Tetra, the filament supply is regulated. This enables easier tube rolling, as tubes of various filament current draws can be accommodated simultaneously. The Tetra has a quasi dual-mono high voltage (B+) supply, and I employed something similar for the N-F-P Phono. As an added feature, a switch selects between Moving Magnet (MM) and low output Moving Coil (MC) cartridges. MC carts receive a boost via built-in Set-Up Transformers (SUT’s). True tube lovers have a natural fondness for transformers too.
I went old-school and wired everything on prototype and turret boards. I did what I advise others against doing, and made this a two-chassis build, power supply in one case and amplifying section in another. As well, I used some tube types that I’m not normally keen on, but ones that make many tubephiles weak in the knees. Noise and interference reduction techniques learned from other phono amp builds were applied too.
Rather than a toroidal or EI core power transformer, I found a small R-core transformer on eBay that was tailor-made for this project. R-cores have a Fritz Lang-meets-Nikola Tesla vibe that I find cool looking. Or maybe I just have an over-active imagination.
Quality Belton tube sockets were purchased instead of the ubiquitous white ceramic variety seen in many amps. Beltons get a much firmer grip on the tube’s pins, which is confidence inspiring, especially when a component may be subject to possible distress due to shipping. The main amplifier board has extra supports close to the tube sockets. This will reduce the likelihood of circuit damage during the inevitable rolling of tubes that “valve” fanciers are wont to do.
The first tube in the amplification chain is enclosed in the cabinet because of its sensitivity to interference. The other two protrude perkily through the top plate, with no ill effects.
I’m not writing up any sort of build instructions, nor providing a schematic. Any hardcore DIY’er who wants to tackle this project can probably read between the lines, look at the pictures and suss out what I’ve done. It would cost about $400 Canadian (approximately $300 US) to duplicate the unit shown here. But you would have to track down some vintage Bogen T-155 or T-157 microphone transformers, used here as SUT’s, and get them for about $50 a pair to stay on budget, should low-output MC compatibility be desired. Ditch the SUT’s, and costs could be brought down to around the $350 CDN (~$260 US) level.
If more upscale SUTs are desired, without completely breaking the bank, cast your eyes over what’s available from Jensen Transformers, Softone Audio, or entry-level Lundahls or Cinemags. For higher performance have a look at the more upscale Lundahls, Cinemags or maybe Sowter trannies. It’s possible to spend as much or more on SUT’s than the whole rest of the N-F-P Phono amp, if one gets carried away.
N-F-P you ask?
Like my N-F-P Line Stage project from a few years ago the N-F-P (Not-For-Profit) Phono is being offered for sale. The full purchase price paid for the N-F-P Phono will be donated to Hospice Huronia, a charity near and dear to me. The hospice will soon have to vacate the aged facility it currently shares with a few other community services. Fundraising is currently underway to build a new dedicated structure.
So how does the N-F-P sound? Is it as good as the Tetra?
For simplicity, consistency and if I’m honest, just plain laziness, I spun many of the same LP’s used in the C.L.E.A.R. rehabilitation project, see links above. Knowing what I expect to hear from these records, I can cut to the chase, sound-wise, very quickly. I also played a bunch of other vinyl just for pleasure, listening without my reviewer’s hat on. As soon as I’d put a hundred or so hours on the N-F-P, I fired up my Tetra prototype and switched back and forth between the two phono amps. Equipment used was the same as on the C.L.E.A.R project. For a more information on the Tetra’s sonic character click, on the C.L.E.A.R. project links above, as well as our patron’s description of his Tetra from the build series.
To get the most from both phono amps, I also employed a previously-reviewed K&K Audio Premium SUT, thanks to a kind loan from a friend.
I decided to spin Kind Of Blue to start. The Tetra has a lovely warm sound that seems to hang on to the notes. Not that it slows the music down, but seems to follow the decay of notes nicely. This, I think, is why the Tetra is good at capturing the acoustic of the old Columbia 30th Street studio in New York, originally the Adams-Parkhurst Memorial Presbyterian Church, where KOB was recorded. The N-F-P was not quite as good at capturing the studio acoustic as the Tetra. But on the initial start of notes, the attack if you will, noticed especially with piano, the N-F-P is faster and more lively-sounding.
I pulled out my MFSL reissue of James Gang Rides Again, a stoner party favourite from 1970. On Tend My Garden, the dirty sounding organ, surely a Hammond B-3, had more bite when played through the N-F-P. The immediacy of attack on piano notes was also noticed on this recording too. I was wishing the Tetra was as good in this regard. After scratching my head a bit, I remembered that my Tetra uses Mundorf Supreme silver oil capacitors for coupling and output duties. These are renowned for their smooth musicality, but maybe in this instance it was just too much of a good thing.
Several high-end manufacturers bypass large value coupling capacitors with smaller value ones. The theory being, that the smaller cap will respond faster to the leading edges of transients and pass higher audio frequencies better. The larger value cap has trouble getting out of its own way, in a manner of speaking, so the smaller cap helps the larger one out, to the overall benefit of the audio signal. Tube gurus including Morgan Jones, author of Valve Amplifiers, and John Broskie of Tubecad.com, have both been known to employ this strategy.
Some of Broskie’s favourites are the Cornell Dubilier 940 and 942 series polypropylene film and foil capacitors. The 940’s are also recommended on the Capacitor Test page at Humble Homemade HiFi.com. Word on the DIY audio forums suggest it’s better to stick with the same type of cap for bypassing, in order to preserve sonic consistency across the audio spectrum. It wouldn’t be best, so the theory goes, to bypass say, a polypropylene cap with a paper-in-oil cap. Same with bypassing a PIO with a Teflon cap, not recommended. As luck would have it, I was able to hijack four C-D 942 series 0.01uF caps awaiting use on another project. These were pressed into service to bypass the oilers in my Tetra. Though these bypass caps are polypropylene without oil, I called it close enough for the purpose of this experiment.
Like the C.L.E.A.R. preamp that I refurbished and rehabilitated, the N-F-P Phono uses C-D 940 series for coupling caps. The N-F-P’s output caps are Mundorf EVO aluminum oil that were orphaned from another project.
I broke in the Tetra’s new bypass caps using my standard procedure of connecting a DAC to the phono amp through an inverse RIAA circuit. I then set my streamer to an internet station, usually trance/house (yuck, but they have lots of whump, tizz and what could pass for vocals) to present the component under burn-in with a more or less ‘wide sonic spectrum’.
I had a quick listen after 24 hours, and the results were encouraging. So, I let it run about another 80 to 100 before serious listening recommenced. It’s been reported that some capacitors, most notably ultra-expensive Teflon types, require hundreds of hours to reach peak performance. I’m going to hazard a guess that the five dollar caps used here didn’t need this much run-in time.
Back to stoner land. On Tend My Garden, the organ, as heard through the N-F-P, was still slightly “dirtier” and a bit more immediate sounding. The Tetra had made progress and mostly closed the gap in this regard. The extra twenty bucks worth of capacitors used for bypassing the main caps was money well spent. In the bass, there wasn’t much to choose between the two. The Tetra might have been a bit deeper and smoother, but it was a tough call.
Vaughan Williams Lark Ascending sounded very similar through both preamps. Again, the N-F-P was slightly brighter, the Tetra a bit smoother and more spacious, capturing a bit more of the hall acoustics.
Listening again to Kind Of Blue, the N-F-P remained slightly better portraying the initial bite to notes, especially piano, but as with the other albums, the Tetra had made gains here too. The Tetra retained its advantage at portraying the decay of notes and the recording venue acoustics.
I have the 24/192 download of KOB and it made an interesting comparison to the MFSL 45 RPM two-disk set I’d been spinning up to this point. My digital front end is more accomplished than my analogue one, and very possibly the digital KOB might have been mastered differently too. All the same, the N-F-P sounded closer to the 24/192. The Tetra, sounding warmer and smoother, was potentially less accurate (whatever that may be) but was the one I preferred. The Tetra seemed to have better musical flow than either the N-F-P or the digital source. I’ll make a 24/192 rip of the KOB vinyl when time permits.
The N-F-P isn’t overly “tubey” sounding with vintage GE and RCA tubes installed. If desired, its character could likely be nudged in that direction with ancient Telefunken, Amperex or Valvo tubes. A sleeper choice, at semi-reasonable prices, might be East German RFT tubes. There is still NOS stock of these under-appreciated tubes around and a quick listen with a pair of mine was encouraging. The RFT’s have a sort of vintage Telefunken vibe to them, but as always, YMMV.
In the end I mostly prefer the suave sounding, though still very detailed Tetra, to the upstart N-F-P. But the N-F-P sounds very good considering it can be built for just a little over half of what it costs to build a Tetra. In absolute terms there are better phono stages available, but I’m skeptical that this pair could be outdone by anything close to what they cost.
Listening with the Built-in SUT’s
I also connected my Ortofon Quintet Bronze directly to the N-F-P Phono’s MC inputs, employing the internal Bogen SUT’s. Yes, the built-in SUT’s sounded like a low rent version of the upmarket Lundahls in the K&K Premium. The Bogens lacked the smooth presentation of the K&K, and the latter has better bass extension too. But let us not forget, at $600 US for the kit version, the K&K costs a lot more than the N-F-P Phono and even more than a Tetra phono stage.
The way that this unit is built, i.e. not using circuit boards, means any decent electronics tech can easily repair it in the future. (A schematic will be supplied to the buyer of this unit.) All parts are from quality manufacturers, over-specified for their positions in the circuit, and will likely last for many years. The tubes are run conservatively for long life, and the types used are common ones still in production. I’ve run this unit for more than two hundred hours without a hiccup. It sounds decent too, especially in view of what it cost to build. The performance of the N-F-P Phono had moved me to improve my more expensive Tetra.
Even the MC input through the microphone transformers, repurposed as SUT’s, isn’t too shabby. Could I have changed the sound by tube rolling? Most likely. I’ve run short of the tube types used in this amp, after selling off much of my hoard to help finance this project. Besides, a new owner will likely want to roll their own anyway. And hey, after a cool wet spring, it’s summer where I live. There are better things to do on a nice day than play tube jockey.
So, to answer my own question – yes, the N-F-P can mount a credible challenge to the Tetra. Budget permitting, the Tetra is the way to go, but the N-F-P has nothing to be ashamed of. Now if I can just get that damn tune wedgie (aka: ear worm), Tend My Garden, out of my head……
Own This Amplifier!
What you see in the pictures above (not the picture where the N-F-P is shown with the Tetra obviously), is what the winning bidder will receive. A set of vintage tubes made by GE and RCA, selected for low noise and low microphonics, will be supplied. As stated earlier, it would cost about $400 Canadian (approximately $300 US) to duplicate the unit shown here. I’m putting this unit up for auction with an opening bid of $260 US. If a Canadian is the winning bidder, then I’d prefer to be paid by Interac/EMT. I’ll accept PayPal if the winning bidder resides in the USA and ponies up an additional 4% (hey, it’s for a good cause), but a Western Union money transfer at the bid price would be appreciated. The winning bidder will also have to cover shipping costs. U.S. bidders should also note that there will not be any import duties as the selling price will fall far below the threshold that attracts attention from U.S. customs.
If you are seriously interested, please email me your bid, at: firstname.lastname@example.org. The opening/minimum bid is $260 US. For simplicity, all bids should be in US Dollars.
And please, no low-ball bids, this is for charity after all.
EDIT: Bidding has ended and this phono has a new owner, who wishes to remain anonymous. Thanks for your interest.
|Nbr Of Bids:||3|
|Deadline to bid:||Aug.15, 2019
AUCTION HAS ENDED
|Winning Bid:||$525.00 USD|
Special Offer to the Winning Bidder
Caption: The boxes are a bit beat, but the tubes are NOS and available for another 60 Bucks
As an added bonus, again keep in mind that this is for a worthy cause, I’ll include a second set of NOS NIB General Electric tubes for an additional $45 US on top of the bid price, if the bidder wishes. Three vintage tubes are included with the N-F-P at the winning bid price; these extra NOS, NIB tubes, shown in the picture immediately above, are optional. That’s only $15 US per tube(!). They have been specially selected for low noise and low microphonics from my personal stash. I’ve run them for 24 hours in the N-F-P to make sure they’re OK. The 45 bucks will go to the hospice too. Before anyone asks, no, I won’t sell just the NOS tubes separately, well not for 45 bucks anyway.
Thank you for your support.
And Thanks to the following people for their help with this project:
Dan and Grant Travers of Midland Tool and Machine for metal-working on the tricky bits I couldn’t do myself.
Mark Miller of LaserMarkEngraving.com for laser engraving the chassis.
Editor’s Note: Thank you Steve, for another great build, and for your generosity, supporting a charity with what amounts to your own sweat and effort. Having been the winning (and only) bidder on the RJM phono Steve buit last year, I’ll again attest that his work is superb. The phono amp will be quiet and you won’t be disappointed in the SQ. I have the same Bogen SUT’s and they sound very good as well…
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