#660

[Fonotec]

660(front).jpg (1.89 MiB) Viewed 22095 times

{The coarse-groove cut shown on the microscope camera monitor is from a one-sided, 16" transcription disk pressing in red vinyl, having six, different, spoken-word advertisements for Cavalier Cigarettes.}

660(wood).jpg (1.5 MiB) Viewed 22095 times

'THE LATHE' (aka LS-76) #660, was originally used by Eva-Tone in their Clearwater, Florida plant, for mastering their flexible disks called, Sound Sheets, that were stapled into magazines...

Eva-Tone_Clearwater_79.jpg (39.47 KiB) Viewed 22861 times

This lathe was barely functional and not fully complete when I acquired it from then-owner flozki who had it parked in his neighbor's barn in the countryside of Switzerland. It has now been restored to finely-tuned operation and had all of its missing features replaced.

Refurbishments include:

• new (crystal-locked) turntable servo drive board viewtopic.php?f=3&t=94
• rebuilt tt motor (by MDI Precision Motor Works) Eva_Tone/74C00_tach.JPG
• new chrome-plated, steel thrust ball for turntable axle viewtopic.php?f=3&t=76
• logic supply crow-bar protection-circuit viewtopic.php?f=3&t=178
• modification of feed clock timer network viewtopic.php?f=3&t=219
• modification of LF-presence corner frequency on Variable Pitch board to improve lathe-automation during passages with strong bass content:
viewtopic.php?f=3&t=177&p=259#p263
• recap. of power supply (including large stud-mount types) with new regulators, and fuses added to the bipolar op-amp supplies
viewtopic.php?f=3&t=199
• all 70+ DIL chips replaced with ones that test 'good' on ABI Chip Master and Linear Master ZIF devices
• (NOS) JVC 4MD-20X (4-channel / stereo) cart with 4DT-20X (Shibata diamond stylus) on the 12” Stax tonearm
• custom chip tube nozzle made by George Alexandrovich, Sr. (of Fairchild)
• new rubber tubing for vacuum lines of chip tube and turntable
• NOS Spectrol potentiometer for 'Lines / Inch' adjustment
• new, seamless, ultrasonically-welded Mylar turntable-rim belt* and Mylar feedscrew-pulley belt (made by OEM, Butler Precision Belts).
• NOS Brooks-Mite gas flow reduction valve/meter (w/brushed glass ball floating indicator, of SCFH) for Helium-cooling cutting heads
• Nikon microscope with swiveling boom arm, as well as correct-vintage Ikegami video camera and monochrome CRT monitor, added, along with original wood-grain panels and black Formica shrouds for bottom of steel weldment, from #654 (the LS-76 from Rhythm Shack, in Miami)
• clone of the original LS-76 black wooden pedestal used for placing the camera monitor on the lathe table, behind the bedways, custom made by an ebay carpenter

* L. J. Scully designed THE LATHE to use a belt-driven turntable so that motor rumble (sound and vibrations) won't telegraph to the platter, which keeps it out of the groove. By using a seamless Mylar belt, there's no once-around disturbance, and the coefficient of friction precludes slipping. Kapton won't work in this application because its friction isn't quite sufficient, resulting in occasionally-audible flutter. Not so with the Mylar belts. Btw, the ply of the belt as well as the exact outer diameters of the capstan sleeve and the recessed platter rim (that the belt goes around) are crucial factors in the effective speed since the circuit that controls the turntable motor is only getting feedback from the tachometer (as 20 µs duty-cycle pulses), rather than from the turntable, itself. The diameters of the capstan sleeve on the motor shaft, and the rim of the platter that the belt goes around, are slightly augmented by the ply of the belt, so I made sure to order the correct, 3.0 mil belts, which make the strobe pattern lock without any drift, and I have inventory of these new belts for the future, though they last for decades in normal use.
________________________________________________________________________________________________________________________

Fully functional original L. J. Scully 1976-era disk computer circuits, based on Capps II pitch and depth computer with absolute polarity-discernment of control audio to permit nestled groove-turns...

Base pitch settings available between 100 and 600 LPI.

Turntable runout shows +/- ½ mil using depth-feeler gauge at the 15" diameter of the revolving platter.

This lathe's tone arm was converted from a 10" to a 12" by the addition of a custom fabricated 'stand off block' and a vintage Stax arm and headshell
Eva_Tone/Stax-12_660.jpeg


...the DIL chips across the seven cage cards are socketed for easy testing and replacement, and the through-hole components are easy to work with and, though in many instances may now be described as 'obsolete", or are only available in surface-mount form, they are, yet, obtainable on ebay, in good - to - NOS condition. Other circuits in this TTL gate / hybrid-op amp disk-mastering computer that are rare or hard to decipher have been solved via reverse-engineering and cloning the potted-module DATEL 'Econoverter' 6-bit A/D converter and ADC-89A8B 8-bit A/D converter (which are only used for lathe-automation and LPI-display signals, leaving program audio, of course, always-analog and unaffected by the lathe's converters) and by data-copying to NOS blank Signetics PROMs from known-good master device PROMs for the Display Processor's three, 7-segment l.e.d. numerical arrays for LPI display, which, by the way, is switchable, on-the-fly, between the selected Base-Pitch setting and 'live' expansions (whether logically (i.e., resulting from automation audio signals), or manually, invoked. The Expand switch on the console allows manual override to, both, fixed, and variable, pitch to operator-specified LPI. Manual overrides to variable pitch and variable depth allow de-expansion from Basic settings during quiet passages for optimum mastering.}

THE_LATHE...jpg (47.54 KiB) Viewed 22370 times

________________________________________________________________________________________________________________________


Ortofon drive package associated with #660

(2)GO741.jpg (190.81 KiB) Viewed 23398 times

+ (2) brand new Ortofon GO741 550-Watt cutting amplifiers, with new-old-stock, empty PCB cards that were freshly populated with components and calibrated to each other in 2015 (and, still, unused, other than for periodic testing), by the same Ortofon engineer who originally made them, Torben Rønne, and (1) GE741 refurbished dual power supply, with new stud mount caps by Kemet and new bleeder resistors. Also used with these amps is an Ortofon STL-732 treble limiter that takes its side-chain signals from each cutting amp, allowing the initial transient of loud treble through, and then quickly clamping any persistent, high velocity-making signals with a 2nd-order Bessel filter with a variably 'sliding' roll-off frequency, which is an effective remedy against pickup-cartridge tracing distortion, without muffling musically-significant treble bursts.

Both cutting amps chassis and that of the dual psu, as well as the STL-732, are 19" rack-mountable. The original Pabst AC fan for each amp and PSU chassis has been replaced with a 16-dB Thermaltake DC fan for quiet operation near lathe.

The GO741 cutting amplifier has the best frequency and phase response of all gramophone recording systems in the world. These amps can be used for CD4 quadraphonic cutting at half speed, when using the DSS731 cutting head, which has useful signal response up to 26 kHz. A half-speed-cut's 26-kHz bandwidth allows a full-speed-playback bandwidth sufficient for the ultra-sonic frequencies used in encoding and decoding the two extra, difference signals of a CD-4 recording's modulated carrier signal. The reason for using such an extended flat frequency and phase response in stereo records, which require no ultra-sonic decoding, is audiophile-quality 'transparency', similar to recording digital audio at higher sampling rates, where higher in-band frequencies don't get perturbed by close proximity to a steep roll-off filter.

Here's what the A channel chassis looks like inside (the original input transformers are still mounted, but have been bypassed for clearest sound. Can be put back if desired, and they're not bypassed in the main system down the hall, in Control C, since they sound really good. But for purity, the elimination of the iron stage is preferable when the sonic signature of the program being mastered to disk is of the highest quality.)

Ny_GO741(A).jpg (1.98 MiB) Viewed 22361 times

________________________________________________________________________________________________________________________

+ DSS821 (green) stereo cutting head (in original wooden box) - the Holy Grail of stereo cutting heads because of the wide bandwidth (to 24 kHz), ruler-flat frequency response (+/- 1 dB), and extra power-handling capability over the previous DSS models.

DSS821_#714.jpg (414.99 KiB) Viewed 23397 times

drive coils' DC resistances: 9.0 Ω ; 9.1 Ω
feedback coils' DC resistances: 189.1 Ω; 178.6 Ω

Here's the frequency and cross-talk response of a DSS731 cutting head powered by the GO741 amps (from the Ortofon
cutting head instruction manual):

OrtofonF_Xt.jpg (220.67 KiB) Viewed 22235 times

This vintage advertisement (below) shows Alan Blumlein's rocking-bridge design as implemented by Ortofon in a
cut-away schematic view of the insides of a Phonotec 'Phonohead' cutter. The green cutter for sale with THE LATHE,
however, is genuine Ortofon-made.

DSS_close_up_schem.JPG (3.26 MiB) Viewed 22340 times

________________________________________________________________________________________________________________________

If you have questions about THE LATHE or Ortofon cutting systems, please write to: gosub2k@andrewhamiltonmastering.com

Thanks for looking - &rew

[Fonotec]

Testing Drop, Lift, and Latch by pushbutton-activation

Here's a brief video Eva_Tone/Coil_Test.m4v of when I was testing the pivot block command functions on #660. The Drop test requires feed to be active, and I was running this lathe (#660) while using one of the restored cage cards (Fixed Pitch) from #662 (which likely was the ultimate lathe to leave the Scully factory) that was previously installed in a mastering studio in Nigeria. I only bought the (loaded) card cage, strobe circuit, and the LPI Display board from the control panel of that LS-76 because the platter appeared to be missing, as well as the microscope + camera and the swiveling boom arm for them, and the feedscrew was heavily corroded.
Nigeria/662_feedscrew.jpg
The proper responses of the Eva-Tone lathe, as shown in the clip, confirm that the repairs to the Nigerian studio's Fixed Pitch board (which is integral to the feed functions, and, therefore, Drop and Lift...) was successful. I've already tested the General Logic and Feed Servo boards from that lathe with positive results, as well. I've been replacing their original, dual-wipe IC sockets with screw machine sockets having gold-plated contacts. #660 has been a handy test-jig for the boards on #656, as well.


The carriage was positioned so that the stylus would be lowered, off, to the right of the platter, since I was just testing the drop and lift actions with the pushbuttons and also still had the red vinyl pressing on the turntable, rather than a cutting blank (or, 'lacquer'). The base pitch of 315 LPI is shown on the numerical display on the right side of the control panel. When I flip the 'Expand' switch, the pitch displayed changes to 170 LPI . * Then I press ''Drop', which unlatches the pivot block from the saddle yoke, thereby causing the cutting head to be lowered by the magnetic down-force of the basic depth voltage that's applied to the solenoid. Incidentally, the heat of the stylus (adjusted by a variable current rheostat from the control panel) and the (selected fixed-)speed of the turntable affect the depth of the cut, as well. For example, the ideal heat (for just-quiet surface-noise (hiss)) and depth (for, say, 2.5 mils groove-width-during-silence) settings on the control panel for cutting at 33+1/3 RPM, will result in a deeper cut (around 3 mils width) if used without adjustment at 16+2/3 RPM.

Coil_Test_poster.jpg (156.82 KiB) Viewed 22917 times

Because the 16" transcription disk isn't very flat, the groove goes in and out of focus on the microscope camera tv monitor when the turntable is revolving. But the mic;' can focus tightly on specific sectors of the pressing, as shown in the image at the top of this thread, which also has a brighter lamp setting, which enhances the contrast. I actually don't even play this old, one-sided pressing. It's merely being used as a dust cover for the oil well hole on the top of the platter until a lacquer is put in its place for cutting.


Lacquers are much flatter than pressings and allow a sharper and relatively steady image of the revolving groove while it passes under the mic', which helps in setting the depth of cut - evidenced by the width across the top (e.g., 2.5 mils, for silence).



* The Expand switch for manual overrides to Fixed and Variable Pitch invokes a coarse pitch which is adjustable via a potentiometer on the back of the control panel. That's the factory design, however, the potentiometer for adjusting the Expanded pitch on #656 has been moved to the front, as an 'in the field' mod. {Picture of Expand potentiometer (mounted in normal position on rear of control panel, with legend upside-down for reading with back of panel tilted forward, surrounded by cluster of pushbuttons) from #653 (formerly used at Sunshine Studios, in Florida), kindly provided by THD Vinyl Mastering, Oslo'}

Expand_potentiometer_Sunshine.jpg (100.88 KiB) Viewed 22875 times

[Fonotec]

Silent groove being cut (shown on microscope camera TV)

The_Living_Groove-poster.jpg (114.57 KiB) Viewed 22901 times

The 10" lacquer being cut (here: Eva_Tone/The_Living_Groove-desktop.m4v) is an Apollo 'dub' that had room at the end of its 'preferred' side for more test cutting, since no finish spiral was in the way. The selected base pitch is 315 LPI. The groove width (across the top) is approximately 2.5 mils (i.e., 2+1/2 thousandths of an inch). This implies that the depth of the groove's center line is 1.25 mils below the surface of the lacquer coating (of the aluminum disk), since, due to the right-triangle shape of the cutting stylus's tip, which points downward, like the triangle shape at the bottom of a necktie, the width of the cut (at any depth) is twice the depth.

100% available land (on disk) - (2.5 mils / 315 LPI) = 21% unused land between groove turns.

'The Living Groove...'

____________________________________________________________________________________________________

Hi-fi LP Master and reference cuts, with all-Ortofon cutting system on LS-76 (#656), available at `low-fi' prices
http://www.andrewhamiltonmastering.com/Rate_Card.html

12_in_LockOut.jpg (223.94 KiB) Viewed 22454 times