“steampunk” 12in Transcription Tonearm

Transcript

“SteamPunk” 12in transcription tonearm How you too can make a “low-end” but high-performing 12in (305mm) phonograph arm Robert E. (Robin) Miller III BSEE AES SMPTE BAS ©12/3/2016 Filmaker Technology www.filmaker.com rev.1/4/17 A quick solution, intended only for evaluating a rehabilitated 1940s 16in turntable, was made with ordinary hardware. However the resulting low mass 12in (305mm) tonearm worked and sounded much better than expected, tracking as low as 1g. It led to appreciating the evolution over more than a century and a half of the analog phonograph, which is enjoying a comeback. For audiophiles, instructions for making the arm as a DIY project for near $0 can be rewarding. 1. Background & purpose Even if you don’t have, or plan to acquire, any 16in diameter “electrical transcription” (ET) discs, and 16in broadcast turntable to play them, your vinyl/shellac record collection can benefit from a long tonearm. 1 In the US sometimes termed “16in,” they are ~12in effective length, arm pivot to stylus tip. More common are shorter ~9in effective length arms for playing 33⅓rpm LPs. With a smaller offset angle, longer arms do not suffer much “skating” (inward force due to friction). Add a shorter overhang, they have lower distortion due to tracking error, where cantilever is not tangent to groove. 12+in tonearms were/are professional equipment for disc mastering, broadcasting, and archiving, implying high reliability and reproduction quality. Professional turntables often have two arms, in order to accommodate more conveniently two disc formats. One can add an outboard armboard to an existing turntable for a second tonearm of 12in. audio, none equal live listening – we are far from virtual reality (that requires 3D recording & reproduction). Yet with well made records from the hi-fi era on, the phonograph sounds much better than one might expect. Fourth, the century and a half of recorded history is preserved mostly on analog electro-mechanical records. My first job, not working for my dad, was at a 250 Watt #70 market radio station, where its 16in turntables had 12in tonearms. They were reliable (never skipped) and sounded great. Along with their industrial Art Deco aesthetic, handling them felt good; back-cueing and slip-cueing, they just seemed ‘right.’ Then they added a sense of professionalism, agree peer reviewers of this paper. Today, they can add to the experience of playing vinyl. In the Golden Age of Radio from the mid 1920s to the mid 1960s, program syndicators mailed to local stations recorded music and complete programs by the thousands on 16-inch ETs (LPs are 12in, some 10in). Although at 33⅓rpm, ETs have the coarse grooves of Standard Play (SP) 78 rpm shellac discs. ETs were supposed to be returned or destroyed after two airings, but many survive today, bearing drama and musical variety of stars Sinatra & Fitzgerald, and Basie & Ellington big bands of the era. Even after introduction in 1948 of the 12in LP that shrunk the monophonic microgroove stylus to 1mil across, broadcasters continued to use their indestructible 16in turntables with later, even better handling and performing 12in arms. Today as an audio engineer and conservator, I’ve restored and use daily five turntables (two 16in), three typical 8~9in, and five 12+in arms. “Steampunk” 12in tonearm compared to a more typical 9in arm. Although long arms were intended for 16in discs on 16in turntables, they also have advantages for 12in records on 12in turntables. Never mind it’s not pretty. Underlying this project are several realities of acoustical-, then electro-mechanical phonograph reproduction. It deserves appreciation for development over more than a century and a half, at first as an art-form, then as a science. Second, we must acknowledge that technically superior methods have succeeded it, such as high performing magnetic tape and digital sampling. Yet the phonograph in its evolving incarnations offered superior quality in distribution. Third, notwithstanding the great strides in 1 Also used as turntables for early Vitaphone motion picture talkies. Compared to light 9in arms, typical 12in arms have higher mass – more moment of inertia – matched by lower compliance (springiness) stylus cantilevers. Cartridges made by Pickering and successor Stanton were favored by disc mastering engineers and Golden Age broadcasters. Pickup cartridges far outlast their interchangeable styli that range from 10 to 30 compliance units (CU). Originals still appear at auction, although new-old-stock (NOS) are disappearing. With a still useable cantilever, Expert Stylus, UK, can evaluate and re-tip a stylus for reasonable fees. Expert says wearing of grooves and diamond tips is minimal up to 3 grams vertical tracking force (VTF). At this pressure, the DIY arm described can mate with 10~14CU styli, e.g. a Stanton 500 with 10CU D5100A(L) spherical stylus or 12CU D5100E(L) elliptical. But with its variable mass, it can also accommodate 18~30CU styli (Stanton 680\681 or 880\881 pickup, along with Ortofon, Shure, and Audio Technica, etc.) tracking at 1~1¼g, as with a light-weight 9in tonearm (SME-3009). 9in arms take less room, but require anti-skating compensation, are more prone to hop grooves, and generate 50% more tracking distortion than 12in arms that have less cantilever-to-groove tangent error. What follows are steps for making an experimental low mass 12in transcription tonearm.2 Its industrial design & construction are simplified as much as possible. You need a modest shop’s typical hand tools (pliers, screwdrivers, hacksaw), a vise, a drill press, file, emery cloth, and a 30W soldering pencil. Perhaps atypically, you will need a pop-rivet set, and a ⅜x16 thread tap. Cost: a day or so of your time, but <$30 US in parts – less if you have them already, as I did ($0!). It’s engineered so the precision of parts and machining is forgiving. Modest craftsmanship is acceptable, except items marked * that require extra care. The help-line is discussion by your peers at the friendly audio forum http://www.lencoheaven.net/forum/index.php?topic=25067.0 . But I cannot warrant your results, nor be responsible for errors & omissions or any collateral damage. For continued improvement, design and instructions are subject to change without notice; the latest revision is indicated by the date below-right in the byline at www.filmaker.com/papers/RM-Exper%2012in%20ToneArm.pdf The contents of this paper are organized in nine (9) sections: 1. 2. 3. 4. 5. 6. 7. 8. 9. Introduction & purpose; Bill of materials and initial machining; Fabricate wand sub-assembly; Wiring (up to preamp connectors, left to user’s choice); Fabricate finger lift, armrest & clamp sub-assembly; Tonearm installation on plinth, alignment, & testing; Fine tuning – adjust arm resonance, preamp interfacing; Conclusion – further considerations, and what to expect? Addenda – pictorial tips, reports in use, 2nd prototype. Sections §2~5 cover construction of the arm; §6 installing it on a turntable. §7 & 8 address performance of the arm, link to a paper on cartridge-preamp issues, with $30 DIY preamp that, adding a low rumble turntable, complete a largely DIY phonograph. §9 adds has pictorial tips, including a DIY stylus pressure gauge. I recommend that you read this paper entirely prior to beginning. □ □ □ Two (2) #6-32 long screws, 2in length. Six+ (6+) ea. #6-32 nuts, flat washers, nuts, & lock nuts. Several #5 x ½in Phillips steel screw (select for potential polishing a conical point; also for replacing pivot point in future). □ Two (2) ea. #4-40 screws ⅜in long & #4-40 lock-nuts; several sizes #4 flat washers (for adding mass to cartridge). □ ⅛ x ⅛in grip steel (not aluminum) pop rivet, and tool. □ Two (2) 5/16in and one (1) ¾in self-stick felt pads. □ One (1) droplet of grease (prefer white with Teflon). □ 5/16 x 2in strap snipped from ⅛in aluminum flat stock. □ Salvage 1¼in long piece ½in ID rubber garden, air hose, or ¾in OD neoprene power cable jacket). Slit down one side. □ Optional wood 1x4+ arm-board, cut to long dimension of turntable plinth, plus attachment hardware as needed. □ Pickup\stylus to work with variable-mass arm. Tested 1¼~5g VTF with Stanton 500 & 680 with 10~25CU styli.endnote NB □ *Salvage an analog mouse cable 4-conductor+foil shield (very flexible stuff), with outer jacket carefully slit & removed. □ □ □ □ □ Four (4) push-on phono cartridge connector tabs. Two (2) #6 tinned spade lugs. One (1) heaping tablespoon of BlueTac putty. 1in square of MagicEraser. (Whaa?) One (1) steel jumbo paper clip. (Whaaa?!!) 2. Bill of materials and initial machining (check off as you go) □ *½x½ x 1/16in-gauge aluminum angle, cut 16in long. □ ⅜-16 zinc-plated steel all-thread, cut to 2¾in length. □ ⅜-16 “coupler” ⅝x1¾in zinc plated steel (53g weight). □ Two (2) ⅜-16 x ¾in zinc-plated full-thread steel screws. □ Two (2) ¼-20 zinc-plated steel all-thread, cut 5+in long. □ A half dozen+ (6+) ¼-20 nuts & combination lock-nuts. □ Four (4) each 1in OD x ¼ ID chrome-plated flat washers. □ Four (4) 1in OD x ¼ ID soft rubber washers ⅛in thick. □ One (1) ¼-20 stainless steel wing nut. 2 Now on a cleared, well-lighted workspace, organize parts, tools, reading glasses\magnifiers, bottled water, Ibuprofen, etc. Mistakes won’t cost much, so just settle in for hands-on fun! Parts for 12in tonearm are ordinary hardware. Clockwise from left: pop rivet, #5 pivot screw, cartridge & connector tabs, ⅛in aluminum for finger grip, ½x½ in aluminum angle, ⅜ & ¼in all-thread, ⅜-16 coupler ⅝x1¾in, MagicEraser, ⅜-16 round-head screws & felt stick-ons, 1¼in neoprene cable jacket (or garden\air hose), BluTack, ¼in all-thread for arm-rest, what’s left of the mouse and its harvested cable, 6in scale, 1in rubber & stainless washers, #6-32 x 2in screws & lock-nuts, and jumbo paper clip. Note that the result – an experiment, or prototype – is not pretty. So when demonstrating in front of your audiophile friends, you are welladvised to have them HEAR the arm BEFORE you allow them to SEE it. p2 Experimental 12in transcription phonograph tonearm– Robin Miller ©2016 3. Fabricate wand sub-assembly 3 This is the first of four groups in §3~6 of construction steps: □ Measure 1⅛in from one end of the aluminum angle and flatten in a vise. Twist flatted end to be 45º to remaining flanges. Caution: especially using power tools, wear safety glasses; consider gloves. To avoid especially magnetic particles from fouling cartridge, after cutting or drilling, remove burrs with emery cloth. Clean with forced air (30psi), wash part & your hands, towel dry part, and thoroughly air-dry with forced air. □ □ *Under the other end of the wand, mark from end ¾in, Only snuggly install two (2) #4-40 screws & nuts from the underside (for later mounting the cartridge and finger lift). 3in, & 4in. Double check innermost mark is 12in to flatted end. □ *Clamp wand horizontally in the drill press vise, with the open “V” shape facing up, blocked with 45-45-90º wood chocks. □ *Drill the innermost marked hole at 4in using a ⅛in bit. □ *Drill two end holes at ¾ & 3in with a 9/64 bit. L - Steel pop rivet, carefully drilled out to 7/16in. Note 45\45\90º wood blocks in drill press vise. R – Drilled dimple atop ¼in pivot post for pivot screw, installed in wand rivet. Precision machining is not necessary, as tonearm is self-righting even with a non-level plinth or outrigger armboard. □ Install a ⅛ x⅛ in grip steel pop rivet from the underside in the hole 4in from the back end of the wand. L – Underneath arm, intersecting lines mark mounting holes, after drilling 7/16in, with offset angle 18º. “Walking” of drill is negligible only if it affects holes identically, preserving precise geometry. R – Stanton 500 pickup installed. Blue-tac supports wiring and damps arm resonance. □ *Use a protractor, and refer to the photos. On underside of wand’s flatted end, mark a line from the end corner on spindle side at precisely an 18º angle to wand’s length. Sets the critical offset angle. Double-check angle from other side of the wand. 4 □ *Mark a second line precisely perpendicular to first line. □ *Mark a point on the perpendicular line precisely ½in from the intersection of the two lines. □ *Mark a third line perpendicular to the second. Confirm that it is at precisely 18º to wand’s length, or REDO last 5 steps. □ *Double check that the first and third lines above are precisely ½in apart (parallel) everywhere along the lines. □ *Center-punch the intersections, and drill 7/64in holes. 3 This paper avoids prior DIYers’ generally more complicated work, harvesting hard-drive bearings, etc. Subject arm continues to evolve, so these instructions might be at variance. You might think of better ways to accomplish the same result – please share these in forum discussions. 4 □ *Spinning in the drill press, polish smooth a cone and point of the #5 x ½in Phillips screw using a file & emery cloth. □ *Screw from top half way into rivet #5 x ½in screw as perpendicular as possible to wand. Point should protrude ~3/16in below rivet flange. □ □ *Mark a point from the end corner precisely ⅛in more than the tip-to-ears dimension of the cartridge you intend to use. □ *Clamp the wand in the drill press vise, with 45\45\90º wood blocks; drill out the pop rivet using 3/32in tool steel bit. Install from top two (2) #6-32 x 2in screws in wand holes at ¾ and 3in. □ Underside on each 2in screw, spin up a #6-32 flat and lock-nut. Only finger-tighten for now to allow for aligning later. □ *Mark & center punch center point on ⅜-16 coupler side. □ *Drill coupler through other side using a 5/16in bit. □ *Tap ⅜-16 coupler, hereafter called “counterweight.” □ Thoroughly wash debris, and blow-dry counterweight. □ Clamp in vise between blocks ⅜-16 x 2¾in all-thread. □ *Mark dead center ¼in from each end straddling threads. □ *Drill through holes using 9/64in bit. Wash debris & dry. □ Spin counterweight about half-way onto ⅜-16 all-thread. For a Stanton 500 (Pickering V15) or 680\681 (XV15), this is 9/16in. p3 Experimental 12in transcription phonograph tonearm– Robin Miller ©2016 □ □ □ □ □ *At preamp end, solder to chosen connectors, & shield #6 Spin up ¾in on 2in screws #6-32 nuts + lock washers. spade. Left pair opposite, ditto right pair, not pairs side by side. 5 Add a jumbo paper clip at one end, double-loop side out. □ *If heat-shrinking, insulate shield wire & at end of shield. □ *With wand down-side-up, arrange cable, with a bit of Slide all-thread with counterweight up arm’s 2in screws. Add two (2) lock-nuts. Slide all-thread down 2in screws and adjust lock-nuts flush with ends of 2in screws. □ *Align counterweight sub assembly parallel with wand. Tighten all nuts (6), aligning paper clip on-axis with all-thread, clamping the end of the clip’s single-loop. (See photos below.) excess length at the cartridge end. Secure with a dollop of Bluetac in random places along underside of wand, being careful not to disturb twist of conductors. The last dollop should be ~1in in front of pivot. Smush over top of cable to secure it (see photo). □ Underneath head of wand, install pickup cartridge, with stylus removed for its safety, under the #4-40 screw heads. If moving iron type (MI), tape over mounting tube to prevent magnetic particles entering. Press on the four conductor tabs to correspond with the L+, L-, R+, and R- wires at the preamp end. L – If counterweight all-thread is not aligned with wand, use a screwdriver to pry parallel. Counterweight ranges 1~5+g vertical tracking force (VTF). R – Wand from pivot back, featuring “anti-roll & dive control” paper clip. □ Stick two (2) 5/16in felt pads on the ends of ⅜-16 x ¾in all-threaded screws, and trim felt edge inside the screw diameter. □ □ Thread ⅜-16 x ¾in felted screws in counterweight ends. Underside of finished wand. Shown for high RFI environments is optional 100% braid-shielded 4-conductor phono cable, with ground eyelet under one cartridge mount screw head. Secure at random points with BluTack, ending ~1in before the pivot screw. Smear putty over the phono cable to hold it when suspended. (Shield should not make contact with the wand.) Later, putty may be added, subtracted, or moved to dampen resonance. Test that felted screws arrest counterweight spinning. This completes fabricating wand sub-assembly; set it aside. Congratulations! You qualify to finish project, as no further steps are more difficult. Let’s take a break and solder! 5. Fabricate finger lift, armrest, & clamp sub-assembly □ *Drill two (2) ⅛in holes ½in apart at one end of the 3/16 x 2in aluminum strap (finger-lift). □ *Opposite, form a finger diameter inverted “U” (⅞ Ω?). □ Install atop wand flat end under #4-40 nuts holding cart. □ *In center of rubber hose opposite slit, drill a ¼in hole. □ Screw in 5in ¼-20 all-thread to protrude ¼in inside tube. □ Fasten inside tube with ½in stainless flat washer and ¼- 4. Wiring (up to preamp connectors, which are user’s choice) □ □ Power 30W soldering pencil; allow to reach temperature. Meanwhile, unravel ends of the 4-conductor mouse cable back 1½in. Strip shield. Strip inner conductor insulation 3/16in. □ Clean soldering tip on damp sponge. “Tin” by applying thinly #22 flux-core electrical solder (prefer 63\37 eutectic). □ *Tightly twist ten (10) wire ends. Tin thinly with solder. □ *If heat-shrink tubing & gun are available, insulate shield wires & shield terminations. Slip ⅜in shrink tubes over eight (8) inner wires and back from ends for after the next step. □ *Form a hook in each tinned wire end, pass through the eyelet of a pickup connector tab, gently crimp, and solder (4). 20 nut. Adjust until end of all-thread is flush with nut. □ Fasten outside tube (its bottom) with larger stainless washer and ¼in lock-nut. Tighten until tube slit opens ~⅜in. □ □ Apply ¾in felt stick-on to all-thread & nut inside tube. Loosely add ¼in nut, 1in stainless washer, two (2) 1in rubber washers, 2nd 1in stainless washer, & lock-nut (see photo). □ *If heat-shrinking, stress-relieve wires and end of tabs. 5 p4 This is “star-quad” configuration to minimize crosstalk & hum pickup. (Standard colors: L+ white, L– blue or black, R+ red, R– green\yellow.) Experimental 12in transcription phonograph tonearm– Robin Miller ©2016 6. Tonearm installation on plinth, alignment, & testing Next, prepare the turntable plinth, or if cramped an external arm-board alongside, minimum size ¾ x 3½+in. If the only arm, locate it along right side of turntable; if a 2 nd arm, locate at back facing left. On plinth or arm-board, mount pivot post & armrest: □ *Near desired position for tonearm pivot post, mark an arc of 11¼in from the spindle, and a second arc of 12¾ in. □ *With a straight edge bisecting the angle between spindle and the imagined armrest, draw a line connecting the two arcs. Exercise caution anytime you move the arm wand, as the pivot point can jump off its pivot post and cause damage. □ *Slide wand assembly onto pivot post. Re-test & readjust paper clip inner loop for no rolling of the arm about its axis when at record height. Test arm swing for no resistance, horizontally or vertically (until it reaches the dive limit of the paper clip). □ *Examine whether cartridge is precisely perpendicular to record surface, straight up & down. To adjust, forcibly twist arm near pivot to bend “roll & dive control paper clip” left or right. □ *Install the stylus, exercising care in the steps that follow. □ *At the two (2) marked intersections, drill two ⅜in holes. □ *Using a sabre, scrolling, or coping saw, finish a ⅜in slot To avoid breaking delicate styli, anytime tonearm is not playing a record, return it to armrest and secure in clamp. for easily sliding (about 1¼in) the ¼-20 pivot post assembly. □ *Check pivot wing nut so arm is parallel to top of record. Remove arm from record (clamp it in armrest) before adjusting wing nut, then re-check. Finally tighten wing nut. Check again! □ Lay a square of MagicEraser on a stylus pressure gauge, kitchen scale (or 2.5g penny balanced on a cardboard “see-saw”). Shim under pressure gauge so surface is flush with record on turntable platter. Above or below will read in error! □ L: Arm is easily returned to the grip one-handed by prying open outside of clamp with the outside of a free finger. R: “Roll & dive control paper clip” is snug to pivot post. If plinth room limited, install in ⅜in wide slot shown, plus ⅜in hole for armrest, in outrigger board firmly affixed alongside plinth. □ *Precisely punch dead center at one end of the ¼-20 allthread. Clamp in drill press vice using wood blocks near top end. □ *Using ⅛in bit, slowly drill a dimple top of all-thread. Slowly continue to depth ~⅛in, pausing at bottom to polish. □ Thread a ¼-20 wing nut (wings first) about 1½in onto the pivot post. Add a 1¼in chrome washer and rubber washer. *Set the stylus on the MagicEraser atop the pressure gauge, and read the current vertical tracking force (VTF). 6 □ Remove stylus to armrest. Loosen the counterweight locking screws, and spin counterweight an estimated distance (total range 1~5+g) outward to lighten, inward for heavier VTF. □ *Repeat measure until VTF = stylus manufacturer’s spec. (Typical range for this tonearm is 1¼ ~3g.) Snug end screws. □ *Print this page with “Scaling: none.” Measure overhang gauge below, so on paper it is precisely 1.50in square. Cut it out. □ *Adjust wing nut up\down to raise or lower top of pivot post, so wand will be horizontal with cartridge resting on a disc. □ Insert the pivot post through the plinth slot, underneath adding a second rubber washer, chrome washer & lock-nut. □ On plinth underside, hand-tighten a second ¼-20 nut against first. Using two box wrenches, lock the nuts together. Hereafter, move pivot post in plinth slot using topside wing-nut. □ To locate armrest, mark plinth or armboard 9 to 9½in ahead of pivot post, comfortably away from turntable platter. □ Drill ⅜in hole, install pre-assembled armrest, with rubber washers either side of plinth\armboard, aligning slit toward pivot. □ Place a tiny droplet of Teflon grease in the pivot post dimple. Completely mop up any spillage outside the dimple. □ *Preparing to install wand, test & adjust (slightly widen using a pliers) the inner loop of paper clip “roll & dive control device.” Bend to re-form clip to be snug around the pivot post. p5 Tonearm alignment minimizes tracking distortion to 0.47%. Aim scale at arm pivot, parallel to the DIY arm wand, not the cartridge. Slide the pivot post until the stylus tip rests on the 13mm mark directly opposite the post. □ *Using sharp (Exacto) knife, slice blue lines to remove center diamond. Scale sets distance of stylus-past-spindle. □ *Straddle gauge on pencils on either side of spindle. (Or center gauge on a flat 45rpm adapter.) Rest stylus gently on the paper gauge, with graticule inline with and opposite pivot. Read and note ____mm current “overhang.” Return arm to rest. 6 MagicEraser cleans styli by poking it several times. Counterweight should be horizontal to optimize tonearm’s H v. V moments-of-inertia. Experimental 12in transcription phonograph tonearm– Robin Miller ©2016 □ *Loosen wing nut, move arm & post in its slot. 1. Check the cartridge (not a twisted stylus!) is perpendicular to the record surface. Twist the arm wand about the pivot point to bend the paper clip until the cartridge is precisely plumb. Repeat until stylus tip rests on 13mm line, the post centered in slot so post makes no contact with plinth. Snug wing nut to fix post. Return arm to rest. Tighten wing nut. Double-check 13mm. 2. Check that there is no rolling – not even a wobble. Adjust by bending inner loop of the paper clip snug around all-thread, yet so it doesn’t impede arm’s horizontal or vertical motion. □ *Arm might be sensitive to skating across record due to torque from wiring. Gently allow arm to descend and float free away from plinth. Check that wiring is not biasing arm inward (very slightly outward is OK). Rearrange wires to lay in a loose coil. Try inverting loose coil, or twist\untwist until arm stays still. To secure cable, wire-tie only beyond coil opposite arm. 3. Check that the arm and cartridge are parallel with the platter. Adjust wing-nut after unlocking pivot post nuts under plinth. Relock the nuts underneath, and note overhang has changed. □ 4. Check tracking pressure with reading surface of gauge at record height. Set VTF for the stylus in use (see cartridge specifications – commonly 1¼g for high compliance styli; 3g for low). If counterweight cannot reach lightest desired VTF, ≤1g, add a ⅜-16 nut etc. at back of ⅜-16 all-thread.9 Preamps vary in their connections. Consumer audio uses unbalanced phono plugs (“RCA”), while professional installation preserves the pickup’s balanced wiring with a 4-terminal strip. □ Connect five (5) wires to preamp inputs and ground lug. If using RCA plugs, each counts as two (2) connections. If using a PCB preamp, clamp twisted wires under input screw terminals. 5. Check overhang of 13mm. Viewing from above straight down, check that the stylus cantilever (not the body of the cartridge behind it) remains tangent across a 12in LP. (This verifies both the 13mm overhang and 18º offset angle of the arm head.) Adjust by loosening wing-nut and moving pivot post in slot in plinth, relocking to have no contact with it. □ If preamp provides selectable capacitive load, select Cload according to cartridge manufacture’s spec., minus cable capacitance. Results in flattest frequency & phase response.7 □ Place a sacrificial record and note how the arm tracks the groove. Is the stylus pulled to one side of its grip? Does needle jump when mildly thumping the plinth? If so, double-check that wiring is not biasing arm inward (very slightly outward is OK). 6. Check that wiring is not biasing arm inward (very slightly outward is OK). Rearrange lay of cable in a loose coil. Try inverting the coil, or twist\untwist so arm stays still. Wiretie gently only on the side of the coil away from the pivot. □ If the preamp has individual channel gain controls, play a monophonic record and adjust for equal channel output levels. Results in best soundstage for well-made stereophonic records, and lowest vertical distortion artifacts for all monophonic discs. 8 7. A remaining critical adjustment is the resonance of the combination tonearm & stylus. If not optimized, resonance can produce an unnatural bump in low bass, accentuate rumble, and cause the stylus to lose contact with, or jump out of the groove. Adjust resonance for 8~12Hz by varying mass (moment of inertia) with cartridge weights or BluTack. □ Again play sacrificial record. Does needle jump when mildly thumping plinth? If so, increase VTF (not above mfgr’s spec.) and retry. Also see resonance test & adjustment below. This completes constructing the experimental 12in tonearm. True, for $600~2500 and up you can buy a better arm than you just made. Or can you? Assembling dozens of kits as a teenager (and designing & building many more custom electronic devices since), I have found much greater value than if I had had no hand in making them. Hadn’t had more long term satisfaction than the instant of pleasure unwrapping store-bought stuff. Even if this is your first experience, if you have (or can borrow?) the tools, you might likely find this project only moderately challenging. (Or recruit the person with the tools?!) And soon just to Enjoy! 7. Fine tuning– adjust arm resonance; preamp interfacing If you were successful following the instructions above, your experimental 12in transcription tonearm will likely work, and sound amazingly good, as mine did even the first time out. But tonearms are critical energy transducers, with many dependent variables. Before playing other than a sacrificial record – and remembering to return the arm to rest whenever not playing a record – fine-tune these variables, as instructed next in italics… To measure arm-stylus-platter resonance: With the turntable still, gently plant the stylus in a silent groove (lead-in or run-out). Tap pivot post lightly with a wood\rubber screwdriver handle. A free recording app’s spectrum analyzer (or expensive singletriggered digital oscilloscope, DSO?!) likely will show a broad resonance bump, if not too attenuated by high-pass filtering of the preamp. If >12Hz, add to the tonearm’s mass – add Blue-tac, or small cartridge weight, and then re-adjust VTF, or use a higher compliance stylus (18~25CU, to 30 max). If <8Hz, decrease tonearm’s mass, or use lower compliance stylus (10~14CU).10 Using the Spectrum view of Audacity (freeware audio recording\editing app), look for a resonance peak along the horizontal axis in the region <30Hz. In the DSO screenshot below, the prototype’s resonance was adjusted to a nearly ideal 11Hz, down from an initial resonance of 14Hz that exceeded the high limit. (The arm project is intentionally higher than the ideal 10Hz because it is easier to add mass than to subtract it.) Add or subtract cartridge weight or BluTack as required to either lower or raise, respectively, the resonance frequency to approach 10Hz. And ideally dampen the response to reduce its relative amplitude, as in the screenshot, despite the high level impulse 9 7 Details are in the “Tuning…” paper at www.filmaker.com/papers.htm . 8 Ibid. The “Tuning…” paper also describes a DIY $30 preamp. p6 For the low mass 12in arm as built, use styli specified 18~30CU tracking 1~1¼g. Add mass for styli 10~16CU and VTF ranging 2~5g. 10 The equivalent circuit is L (mass) in parallel with a C (compliance). Experimental 12in transcription phonograph tonearm– Robin Miller ©2016 (tap on pivot post). This image shows, after adding washers of decreasing sizes under the cartridge mounting nuts atop the wand, plus readjusting VTF, mild resonant “ringing” at a very acceptable 11Hz, diminishing in time (within several cycles). As work of this paper concluded, I built a second prototype, following the instructions above. It took 5hr, taking my time, as you, should, dear reader. A medium compliance stylus tracked at 1.0g with no issues! (See §9.) This is good performance for a 12in arm. The lower VTF means skating is negligible. The unipivot design has proven worthy, simplicity itself, and apparently requires no exotic materials or expense. Walter O. Stanton himself is the inventor, having applied for a Patent in 1957. 8. Conclusion – further considerations, and what to expect? The final touch making the 12in tonearm is correcting its arm-stylus-platter resonance. Use a free recording app’s “spectrum analyzer,” or as above, a Digital Oscilloscope, that shows resonance lowered to a nearly ideal 11Hz (from an initial 14Hz) by adding a few #6 washers at the cartridge. As styli vary in compliance, changing styli alters resonance. Whenever swapping styli differing in compliance, it is prudent to re-measure resonance. (I don’t trust “marketing” specs, so I measure the resonance anyway.) Underscoring that resonance can change with different styli, even claimed to be direct substitutes, the screenshot above is with a new-old-stock (NOS) D5100EL made in the 1980s by Stanton. But in contrast, a new N500-6 by the modern incarnation of Stanton resonated at 22Hz, potentially troublesome, and requiring much correction. 11 Now it’s safe mechanically to play a good record. However, the sonic qualities of the cartridge (frequency & phase response) will depend on integrating it properly with the preamplifier (“phono stage”). Using MI or MM pickups, a load mismatch can cause sound to be too dull, or too bright. Or bass relatively too weak, or boomy. Imbalanced L\R levels ruins the soundstage in stereo, and passes distortion in mono. Solutions are found in “The tuning of phonograph reproduction by proper cartridge loading & channel balancing” at www.filmaker.com\papers.htm . Channel-balanced cartridge with preamp within ±½dB, also after proper C-loading – see “The tuning of phonograph reproduction by proper cartridge loading & channel balancing” at www.filmaker.com\papers.htm . [Turntable is salvaged 1940s Rek-O-Kut G2 16in 78\33⅓rpm (no 45 yet).] Properly aligned, the experimental pivoted 12in tonearm has offset angle 18º and overhang 13mm, within <±¼º and <±¼mm (as fine as you can set them). Very early straight arms (later used by scratch DJs) of 0º offset angle and 0mm overhang create(d) 5~10% distortion, deemed acceptable until the high-fidelity era >1948, when expectations improved an order of magnitude to <1%.12 But for any audio component, 0% distortion implies no coloration, which also evolved in subjective preference by some. Audiofan magazines have been complicit in forming popular opinion, touting in vague unscientific terms which colorations (actually distortion or altered frequency response) “sounds best” to the golden-eared. Advertisers’ hype and inverted price-forvalue claims should be taken with a grain of salt. Studies show that most listeners become habituated perceptually, remaining fixed in taste until re-acclimated. My dad often advised me: “Better to question the answer than to answer the question.” So I trust opinions of those reviewers who use unbiased double-blind methods, and who try to confirm subjective opinions with the admittedly imperfect objective measurements we engineers use. Total harmonic distortion (THD) due to tracking error for various disc sizes & speeds is in red in the simulation overleaf. It’s a low 0.47% maximum, actually 0% at two null-points across a 12in stereo LP. For 16in ETs, with their higher linear velocity at the outside groove, it is 1.25% max.13 Calculated for higher speeds, THD for 78s and 7in 45s is just 1% max. Note that a fine 9in tonearm can be aligned at best to 0.70% THD max. Worse sounding intermodulation distortion (IMD) is likely comparable. There are other forms of distortion and artifacts; all forms are most audible playing recordings of acoustic instruments, and the human voice, in genre including classical, jazz, folk, choral, speech, etc. We unconsciously remember our experience hearing these acoustic sources live, and so have a reference in memory that is distortion-free. On the other hand, reproduction of electric instruments – rock, heavy metal etc. – offers little or no memory reference, as each guitar amp or produced effect sounds different. For this or any tonearm, pivoted or not, tracking distortion may be masked by tracing distortion caused by poor performing styli, due to pinch-effect (2nd harmonic, out-of-phase in stereo), poid tracing (3rd harmonic), or prior wear of groove, or tip, or both. Artifacts are aggravated with a spherical stylus playing inner grooves, where linear groove speed is half that outside. Properly mixing L & R preamp signals for monophonic records cancels pinch-effect, therefore monophonic reproduction from a groove (mono or stereo) is inherently cleaner than stereo replay! 12 Tangential-tracking turntable-tonearm units have zero tracking angle error, so no distortion due to it. 13 11 Broadcasters and professional gear manufacturers considered comparable IM distortion of 10% to be “inaudible” until the hi-fi era! Experimental 12in transcription phonograph tonearm– Robin Miller ©2016 Due to too low compliance (unspecified) of more recent cantilevers. p7 Simulation shows harmonic distortion (red curve) due to mistracking a 12in LP is 0.47%. Calculated for 78s & 45s, THD is 1% max. For 16in ETs, while outer groove shows highest angular error, high linear speed reduces its max THD to 1.25%. While these distortion products are not recorded in the groove, and might be avoidable by better replay, there are of course distortions baked in during recording, mixing, and disc mastering processes. Now we might be back to reproduction distortion of 10+% overall, before loudspeakers add still more!14 Acknowledgements: Peer reviewers R A Bruner and G H Aykroyd and their spouses. My lover, partner, critic, & best friend Nancy D. And audiofans on several forums who made $30 preamps per my “Tuning…” paper, asked questions, questioned my answers, and shared their results. Brand names mentioned are registered ® or trade-mark ™ their owners. Frequency & phase response will be dictated principally by the combined cartridge & preamplifier (“phono stage”). Since 1953, most records are mastered using the standard “inverse RIAA” characteristic, which must be reversed in the preamp. 15 Previously, labels used hundreds of combinations of Turnover, Rolloff, & Rumble filters, and often kept them trade secrets.16 NB - The experimental 12in (305mm) tonearm was tested at VTF 1~5g with standard play (SP, coarse-groove) ETs & 78s 0.5x3.0mil elliptical; and for fine-(micro-)groove LPs & 45s, 0.7mil spherical, 0.4 x 0.7mil elliptical, and 0.3 x 2.8 mil Stereohedron styli. Compared with conventional spherical (erroneously called “conical”) tips with circular cross-sections, elliptical and advanced line-contact profiles decrease tip\record wear & distortion while increasing high frequency response, especially in loudish inner grooves. Recommended for any phonograph replay are elliptical diamond tips of (side radius x width): 0.5x2.0mil for ETs, 0.5x3.0 for 78s, and for microgroove 33⅓ & 45rpm, 0.3x0.7mil elliptical or 0.2x3.0mil (up groove walls) “line-contact\Shibata” e.g. Stereohedron\II (Pickering\Stanton), Paratrace (Expert), etc. Users and reviewers too often overlook the need for properly loading a moving magnet (MM) or moving iron (MI) pickup. Resistance (R) load is mostly standardized at 47kΩ. In parallel with the 47kΩ, capacitance (C) is typically 275pF (pico-Farad), and is the sum of distributed C of the wiring and lumped C inside the preamp. It is possible for the combination of cartridge & preamp to attain performance of ±¼dB from 30~15,000Hz.17 I hope you enjoy making and using the DIY 12in tonearm – there is great experience and satisfaction to be had. Please share, as I have, your experience on internet audio forums, etc. And enjoy many years playing phonograph records a little better. _____________ 14 Also listening room acoustics, speaker crosstalk comb-filtering, etc. Replicating live hearing full-sphere 3D reproduction, e.g. the author’s HSD-3D using 10 speakers – see www.filmaker.com/papers.htm . Demonstrations by appt. in Bethlehem PA or the Univ. of Parma, Italy. 15 EIA standard adds, for replay only, an infrasonic filter <20Hz. 16 For RIAA, turntable “Rumble” filtering is below 50Hz, “Turnover” is 500Hz, and “Roll-off” is above ~2kHz, down 13.7dB at 10kHz. 17 Robin Miller is a pianist & bandleader, Peabody-winning filmmaker, and audio engineer with more than 50 years in music recording & mixing films, television specials, and historic restorations. With Filmaker Technology he is a Patent-holder (full-sphere 3D audio reproduction) who designs, integrates, and publishes re Ambiophonics and other audio innovations. Cf. “Tuning…” paper at www.filmaker.com\papers.htm with $30 DIY preamp. I don’t plan (yet?) to turn an old bicycle into a turntable! p8 Experimental 12in transcription phonograph tonearm– Robin Miller ©2016 9. Addenda – pictorial tips, reports in use, 2nd prototype. Shortly after making the 1st DIY “SteamPunk” 12in tonearm and drafting this white-paper, a 2nd prototype confirmed both the instructions and performance. The 1st tonearm was disassembled (except for machining & wiring) and reassembled by the author’s grandsons, age 10 & 8, who then delighted in their handiwork’s ability to play “old records.” Their father, the author’s Gen-X son, became hooked, and now frequents used record stores. Here are a few pictorial tips, and tracking a high compliance cart at 1g. Turntable mounted on deeper plinth for the 12in arm. DIY stylus pressure and overhang gauges are at back. The turntable’s 9in arm is still usable. An equally steampunk plinth adds 5in to the depth to accommodate the 12in arm pivot and armrest. Fastened to the turntable’s original screw mountings for its feet, the rubber feet were relocated to the plinth. At back are the slot for the pivot post to adjust overhang, and the armrest mount. 12in transcription tonearm is the 2nd arm for a used 2-speed direct-drive turntable ($37 at auction). Out-of-pocket costs total less than $100 for the 2-arm phonograph (plus pickups & styli), including a $30 RIAA preamp in the author’s “Tuning…” white paper at www.filmaker.com\papers.htm. With outcome much higher performing than expected, the author has permanently assigned the “model RM-305 SteamPunk Transcription Tonearm” as primary arm on a 3-speed archiving turntable (Technics SP-15) for professional conservator work. -0A DIY stylus pressure gauge for measuring vertical tracking force (VTF). After cutting “parts” out of thin corrugated cardboard, straight pins hold all together. Flap still provides rigidity for the beam. Beam is “exercised” to elongate pin holes for freedom of movement. One penny weighs 2.5g. A Stanton 681 calibrated cartridge with compatible new-old-stock (NOS) Pickering D72E elliptical (0.4x0.7mil) stylus tracked with no issues at 1g. p9 Experimental 12in transcription phonograph tonearm– Robin Miller ©2016