Home Visit: Intact Audio Autoformer Preamp
Letter from NYC (71) 2017(10)
Regular readers of this blog will have read about my friend Robin the Scot, who now lives in Taipei. Those who don't can read about his setup in my visit last year. Robin and I share remarkably similar musical and audio preferences and he uses a R2R deck! I just got an email from him. As usual, his writing is thorough and worthy of publishing, so here it is below. Around the same time in NYC I paid a brief visit to reader Richard, who also employs an Autoformer Preamp in his system, hence I here group these two disparate articles together.
pic of Townsend Allegri from HiFi+. Click to enlarge.
"...I’ve made some major improvements to my hi-fi system since you came to visit us last year — you’d probably hardly recognize the sound now. Just after your visit, I discovered that one of my Yamaha FX-3 tweeters was seriously damaged, and had been so for at least a couple of years. No wonder I always felt the sound had a harsh edge to it! The tweeters for te FX-3 are basically Unobtanium (they’re slightly larger than the ones for the NS-1000), but I’d had an eBay search set up for one for quite a while before that, and to my amazement an auction listing for a pair of FX-3 tweeters suddenly appeared in my inbox. I snapped them up, swapped out the damaged one, and hallelujah! — all was clarity and finesse, finally, in the speaker department. And did I mention stereo imaging? The dfference from before is like night and day.
I also fixed the Thomas Schick tonearm, which as you’ll remember had somehow been knocked squint. I wrote to Thomas, and he sent me instructions for straightening it out by myself, which basically amounted to grabbing it firmly in one hand and then pushing the bent end down sharply against a table top with the other hand. Against all my predictions, this somehow sems to have done the trick! (As I told Thomas, his advice reminded me of my grandmother, whose solution when any piece of electrical equipment failed was: “Just hit it with a hammer!”)
However, I’m now using as my main turntable for the MC cartridge a Kenwood KP-1100 direct drive, which I bought from hifido in Japan (Link.) It has a wonderful, rigid metal X-plinth tucked away inside the unassuming wooden box exterior, which some people think makes it more effective than the Technics SP-10. (I don’t know enough to say ... but the Kenwood cetainly sounds VERY nice, and it’s also great to have an auto-stop at the end of the record — something I haven’t had since the late 1970s.)
I stripped down the Garrard 301 and gave it a complete overhaul and refurbishment, and then set it up as a mono-only rig, using the Schick tonearm and an Ortofon 2M Mono SE cartridge — played via an ultra-cute 1954 George Gott tube phono preamp, which I bought because like the McIntosh C-20 it has all the pre-RIAA alternative phono equaliation settings available. It’s fascinating to hear how LPs from the 1950s can sound so different, once you play them with their correct EQ adjustment. For example, Decca FFRR records sound thin and tizzy, by comparison, if you play them through the later RIAA setting. However, in the interests of better overall sonics, I’ll probably retire the Georg Gott soon, and instead use …
My spanking new Icon Audio PS-3 Mk II phono preamp! (Link)(It’s currently in the customs bay in Taipei, awaiting final clearance, so I should have it by the end of this week.) It has a volume knob (and both MM and MC inputs - the latter using the company’s own stepup transformers), so I’m planning to run it directly into the MC-275 amp. Well, not quite directly…
First, the signal will run through my newly acquired Townshend Allegri passive preamp (Link.) I bought this a couple of months ago, and it’s met all the high expectations I had of it. CDs and R2R tapes sound astonishingly natural and “all there” when played through it, and it makes one realize how much grunge and grayness gets added by even a pretty good preamp like my ARC SP-11. I haven’t yet played any LPs through the Allegri, as I’m still waiting for the Icon Audio phono preamp to arrive. But I have high hopes for that!
In the HI-fi Plus review, Alan Sircom explains it very well: because, uniquely, the Allegri uses single-coil “autotransformers" (as opposed to regular, adjacent-coil transformers) to adjust the volume level, the preamp acts like a “gearbox" rather than a traditional attenuator. That is, it matches the source impedance to the power amp impedance very closely at each of the different preamp volume settings (just like a car gearbox matches road speed to engine speed, to minimize the loss of torque in different road conditions). This results in clarity and depth across the frequency range, no matter what volume level you select — so for example, you no longer have that disappointingly thin sound at low listening levels.
All so different from the way that active preamps — and most passive preamps too — deal with the volume level question. Suffice it to say that I’m thoroughly sold on the idea, now that I’ve actually experienced it. The only sad part is that my trusty old SP-11 (although somehow I’d already started feeling a bit bored with its sound) will need to be taken off the rack and gracefully retired, at least for the meantime..."
"...There’s actually a couple of things I forgot to put into it — I've bought a Yamaha B-2 power amp (the early 1980s one that uses V-FETs), which has a great, almost tube-like sound; and I’m now using an ultrasonic cleaner to clean LPs..."
Home Visit: Slagle Autoformer Preamp
Reader Richard first encountered my Blog after he acquired a Nagatron cartridge. I rarely venture into town these days but last Sunday I managed to pay him a belated, though brief visit. Richard likes to build things, so naturally has a DIY bent and is obviously a tweaker who has spent a lot of time adjusting his system. He system is rather complex:
Analog Front End: Technics SP10 MK2; Tone arm 12" Ortofon AS212 (modified by Alfred Borkland); Cartridge Glanz MFG 610 LX.
SUT: Technics SH-305MC
Phonoamp: iFi iphono 2 (used as MM).
Digital (CAS): Mac Mini, Focusrite red net 3, Antelope live clock, Mutec mc3+usb reclock,
Metrum Octave dac, Player software Chanel D Pure Music.
Preamp: DIY passive pre with Bent audio Tap X autoformer volume controls by Dave Slagle
Amp: Ben Jacoby modified VTL compact 100 mono blocks running 2 KT120 tubes ea.
Loudspeakers: Custom Ohm Walsh 2.2000
Subwoofer System: DSPeaker antimode 2.0 for DSP room correction of 4 REL Q201e subwoofers
Richard's Living Room is typical of a medium sized NY apartment, with a layout not particularly advantageous for audio. Obviously a family man, the room is stuffed with heirloom furniture. Obviously a considerate person, the audio is laid out along the long wall with the loudspeakers minimally in-room. In HK's small apartments I also see a lot of setups placed this way.
Yet the sound (from both CAS and Analog) was quite enjoyable, smooth yet detailed. Note R's Ohm's are custom, that is truncated at the bottom, in height as well as frequency response, nothing below 50 Hz, where the DSP'ed distributed subwoofer systems take control.
I am not a fan of CAS, but this (complex) one is definitely one of the better ones I have heard. The TT is the mighty Technics SP-10, one of my favs, and the rare Glanz cartridge seems like an unusually detailed MM, in the vein of my Shelter 201.
Most interesting to me, of course, is the Autoformer Preamp. David Slagle's designs are rather famous, heard here in a Bent Audio variation, but Intact Audio sells direct for DIY'ers, and there are other companies, like the very expensive Vinnie Rossi, that employ his autoformers. Although I am a horn user and personally prioritize the "jump factor" and hence don't prefer passive preamps of any kind, I do have a keen interest in their use as buffer amps. Given my recent experience with Schiit Saga, I was particularly interested. I was not disappointed. I think in the future if I have time I'd DIY an autoformer preamp to use as a buffer amp.
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