| QRK Factory Trouble-Shooting Documents |
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Partial Update 07/31/2009 1117 hrs. Z
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QRK EQUIPMENT TROUBLE-SHOOTING GUIDE
TABLE OF CONTENTS
PRODUCT PAGES
12” & 16” Turntables 1-3
12” & 16" Tonearms 4-5
Electronic Variable speed units 6-7
Console Parts Cross Reference 8
Motor Identification Chart 9
Tone arm Parts Identification 10
Turntable Parts Identification 11
Equipment Production History 12
Prepared by
Robert Martin
9/16/80
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QRK
Equipment Trouble-shooting Guide
TURNTABLES 12" & 16" Types
PROBLEM Rumble ……..“Unit makes low frequency noise”, or; whirring sound comes through record.
*1. Cause Motor Capstan out of round; any heavy jarring of the turntable can knock the motor capstan out-of-true, causing misalignment on drive-wheel surfaces. Constant removal of.platter can be a cause: as platter comes down into the well it can push id1er wheel across to hit the motor shaft. A force as little as a flick of the finger can knock this off.
Solution: Determine if rumble is caused from capstan or motor itself. If it’s the capstan; it requires sending motor into plant to have new part pressed on. Item cannot be fixed in the field…… factory repair.
2. Cause: Shock Mounts; old and sagging from weight of motor assembly; causing the motor to shift positions resulting in misalignment of drive train and undue wear of drive surfaces.
Solution: Replace them, field repair.
*3. Cause: Idler Wheel out of round; misalignment of idler and motor capstan can cause wearing of drive surfaces. Leaving the turntable engaged in-gear, in as little time as over- night will create flat-spots on the face of the wheel causing noise when it is running
Solution: Replace it, field Repair
4. Cause: Acoustic feed-back; Turntable is not properly isolated from it’s mounting and noise is being fed-back (feed-back) or regenerated within the unit. Cabinet resonance comes from speakers causing cabinet to vibrate and inturn, vibrate turntable.
Solution: No real solution exist, as the situation is different in every case. General procedure is to isolate turn- table from direct contact with cabinet or mountings. Rework cabinet design.
.
*See note on page 2
DO NOT CONFUSE THIS WITH THE RUMBLE FROM MOTOR CAPSTAN OR IDLER.
-1-
*NOTE - How to determine motor capstan rumble from the rumble caused by flat
spots on idlers:
- Motor capstan rumble can be characterized by a whirring - constant almost buzzing sound rather highly pitches (125-250 Hz).
A quick test can be used to determine if the capstan is out-of-true:
Remove turntable platter and apply A.C. power to motor. Lightly
touch the upper most portion of the motor capstan with finger-nail edge Intermittent scraping will indicate capstan being out-of-true.
This is a factory repair - unit must be returned to plant.
The capstan is a pressed fitting and individually machined down to proper sizes while motor is running to insure concentricity of shaft.
Idler wheel noise much lower in frequency. The time/speed/rotation domain indicates that noise generated is almost sub-audible; and is characterized by a near sub-sonic rumble (30-100 Hz).
Usually idler is old and brittle and rubber is hardened. This is a field repair.
PROBLEM: Starting ”Unit starts slow "
Cause: This is usually an adjustment problem, an interaction of the idler assembly and motor. Sometimes dirty drive surfaces get oily and slipping occurs.
Solution: Thorough cleaning of all drive surfaces with rubbing alcohol and readjustments. Check shock suspension mounts for fatigue or sagging. If these are within accepted condition, suspect the motor start capacitor.
PROBLEM: Runs Erratic “Table wows & flutters”
Cause: Again check front panel torque adjustments for proper settings. A motor that doesn't have proper face-to-face contact with idler wheel assembly will cause slipping and speed variations.
Possibly the motor is worn and might need replacing.
Solution: Check torque adjustments, and check motor. On units with Micro-switch assemblies for speed indicators; check adjustment. Sometimes assembly will work loose and inhibit speed shift mechanisms’ movements and keep idler from making proper contact. Clean all drive surfaces.
-2-
PROBLEM: "Motor is NOISEY chatters and rattles”.
Cause: Too much start torque on front panel adjustments. Possible bad motor bearing assemblies. Bad shock mounts.
Solution: Motor bearings are the cause of "chatter!'. Overheating, too much pressure on drive train, misalignment of driven components all contribute to excessive lateral motor-bearing play. Since all of the motors used on turntables use pressed surfaces, they are NOT repairable; motor must be replaced. This can be done in the field. DO NOT CONFUSE WITH RUMBLE, MOTOR WILL EXHIBIT FREE LATERAL PLAY.
-INFORMATION ON MOTOR SPEEDS-
“speeds”: speed of the turntables is a fixed constant. Speed is determined by the motor-speed, motor-capstan size and platter inside dimensions.
Many people confuse the 3 front panel set-screws as speed adjustments. These are not! These are motor/idler torque adjustments and vary the platter start-up speed only!
Turntables can be set up to instant start with no overshoot in a small as a 1/16 of a revolution (22.5⁰). They can be over-adjusted too - causing a cued-up record to jump the grooves because of the massive start up 'kick"; an interaction of motor and shock mounts.
Speeds can be changed by altering the motor capstan sizes only - this requires sending in the motor to the plant to press-fit on new capstan with custom sizes for speeds.
NOTE: Capstan fittings for motors are not available to send out. Process requires that motor be sent in. Part is pressed on and ground down to proper size while motor is running to insure concentricity of the shaft. (Shop Repair).
-3-
EQUIPMENT TROUBE SHOOTING GU.IDE
-TONEARMS - 12" & 16" Types-
PROBLEM: Tonearm is noisey, crackles and is intremitant One Channel “drops out”
Cause: Suspect Headshell spring-loaded contacts; either the spring mechanism is fatigued or maybe the contacts are dirty or even tarnished. Arm-tube lock-nut is not secure and shell isn't seating properly into fitting.
Solution: Clean contact faces with alcohol, or pencil eraser to remove corrosion. Check phono cartridge contact wires and clips. Check tonearm tube assembly for continuity in wires. If spring contacts on shell are bad, the whole rubber plug assembly can be replaced. This repair is a factory repair, as it is a pressed fitting.
Problem: “One channel out, doesn’t work”
Cause: Open wiring in arm-tube assembly.. Loose connections at
arm-tube base where wires connect to output cord. Bad phono Cartridge. Wires shorted.
Solution: Continuity check on arm-tube shell contacts to the output CI Any open or' shorted circuits traced to the ann-tube will require complete arm-tube replacement. All the connections are to pressed in fittings and cannot be repaired.. This operation can be done in the field or in shop. Customer must be aware of tracking and realignment procedures to bring tonearm back into specifications.
PROBLEM: "tonearm "chatters" or rocks laterally
Cause: Possible horizontal-bearing assembly problem. Either pivot screws and nuts need tightening; or horizontal-bearing ball-bearing races are destroyed. You might be careful to note if its' the horizontal bearing as opposed to the vertical bearing and pivot housing assembly. Either the arm-tube rocks or the whole pivot housing is moving too.
Solution: If the problem is determined to be the horizontal bearing , the complete arm-tube assembly must be replaced. The reason for this is that the bearing is pressed-fit into tube and
by removing it, the seat is destroyed and will not securely hold a new bearing. If problem is traced to the pivot housing assembly; vertical bearing and pivot housing must be replaced. Factory or field repair.
-4-
PROBLEM: “Tonearm doesn’t track properly”
Tonearm pulls to one side or drags
Cause: Omni balance device is out of adjustment. Internal wires are twisted inside arm-tube and housing assembly. Twisting can be caused from tonearm being rotated 360º. The stop-key in the vertical bearing has been sheared.
Solution: Readjust the omni balance device as per manual instructions.
To relieve the wire pressure, tonearm must be disassembled at base where arm-tube wires are connected to output cord. The arm can be rotated to relieve pressure and the wires re-connected. Readjust arm and reset tracking according to the manual. This can be done in the field or shop.
PROBLEM: "cartridge Headshell rotates; or ; cartridge isn1t vertical to the record"
Cause: Because of the tight key-way on the arm-tube for the headshell;
customers sometimes twist head shell backwards and forwards as they pull shell out. If too much twisting is being done; the entire key-way and plug assembly will rotate in the end of the arm-tube. Since the key-way is a pressed fitting; once rotation or rocking is noticed - failure of internal leads and wiring is soon to follow. As this is a pressed fitting, the entire arm-tube assembly must be replaced. This can be done in either factory or field.
-5-
EQUIPMENT TROUBLING GUIDE
QRK Galaxy, Medalist, RCA BQ-52, QRK 16 SD
PROBLEM units starts slow, makes noise and “thumps”
Cause: Solenoid assembly pulling the idler wheel into drive position; too far in or out on adjustment tracks.
Solution: Clean drive surfaces and check the solenoid adjustment, refer to manual for procedures. Also check motor torque adjustment pot on vertical motor drive board.
PROBLEM: "LED” indicators flickering; intermittent operation, changes speeds all by itself.
Cause: Ribbon cable and connections carry the “command" signals from switch panel to electronics circuit board. Sometimes these work loose, and all of the subminiature pins & wires don’t make proper contact, resulting in "false" commands. The LED - Switch-button board shifts sometime and the panel buttons will "stick” as they hit the metal frame.
Solution: Recheck all ribbon cable connectors at both ends; including continuity checks. On front panel problems, loosen all screws and re-center switch-board so switches don't contact metal frame.
PROBLEM: “LED” display flickers and motor speed a[[ears to fluxuate.
Cause: Possibly voltage variations in power supply.
Solution: Check power supply for voltages, also check motor board voltages.
Suspect motor servo circuit components.
PROBLEM: “TURNTABLE DOESN’T CHANGE SPEEDS
Cause: Ribbon cable connections are suspect. Sometimes there is a reed relay failure.
Solutions: Check connectors and pins. Spot-check relays and driver transistors for proper voltage.
PROBLEM: "Unit changes seeds intermittently”
Cause: Since the motor is isolated from the turntable chassis, many times motor will build up static charges. When these dissipate they will cause switch circuits to trigger.
Solution: Check ground straps/connections.
-6-
-NOTE ON THE SPEED READOUTS-
You will note that when the turntable platter is off the speed indications still reads relative motor RPMs. The speed readout on galaxy’s are picked up from the motor; and not the platter.
In all other quartz-servo types of turntables the speed readout information is picked up in the servo feed - control-loop and displayed. These readings are picked from the servo command point; Sometimes the motor circuit doesn’t "lock" to these commands. And you will note there is always an outboard stroboscope assembly present to verify the platter speed readings.
On the "galaxy" types of variable-speed units, the speed information comes
from the motor itself and not the command circuits. It is felt that the information picked up at this point is a bit more reliable: as we are interested in what the motor is ACTUALLY doing, NOT what we are commanding it to do.
The last digit on the front panel readout may sometimes flicker between digits. The information displayed is constantly being updated and resolved within the motor regulation circuits. As there are la-Turn variable pots to adjust speeds; these can-be turned slightly to adjust the speed and get it to "lock-on one constant speed. A flicker of +1 number (10th) up or down from the desired speed is acceptable, you cannot [ measure*] or strobe this little of a fluxation, nor can you hear" it.
[*] At that time.
-7-
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TURNTABLE MOTOR IDENTIFICATION CHART
MFG. TYPE/STYLE DESCRIPTION DATE USED
1. General Industries 4-pole Black Square 2 wires 1950-1960
Low Profile 12” & Rondines &
“B” series 16”
2. Asland Hysteresis Black, round, elongated 1955-1965
Synchronous end caps, stamped logos 12” CVS B12 16”
3. Bodine Electric Synchronous Black, round, rounded 1965-1970
End caps, White/Silver 12” 16” Series
Mfg. Label with specs Collins, Spartas
Oil caps both ends.
4. Redmond Synchronous Black, Red-Silver mfg 1970-1973
Engineering label, Copper oil tubes 12” 16” Series.
Silver end caps B12-71, B12-72
5. Howard Industries Hysteresis Blue-Gray with White 1973-1975
Synchronous mfg. Label, Silver end 12” B1271-B1272
Caps with oil tubes (plastic)
6. Teac Synchronous Silver, round, low profile 12” 1975-1976
3” high, Plastic fan Custom II
Blue logo mfg. Label
7. W.S.M. , Inc. Synchronous Silver, elongated, unfinished 12” 1975-1977
look. labels half gone, Blue on Custom II
White Silver end caps.
8. Ashland Synchronous Black, 5” high flat end caps. 12” 1977-1978
Red-Silver mfg. Label Custom II
9. Shinano Kenshi Hysteresis Black, low profile, round. 12” 1978-1980
Has “ring adapter plate” on present [*]
Mount, has present QRK part/
Part number, White label [*as of 12/80].
(Compiled from data / Bob Martin/QRK/Broadcast Electronics/ Sparta/Russco. Further “ up-dated” motor "id" information from 1980-1993+ will be available shortly)
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99 KOLA STEREO September 4, 1979
Mr. Bob Martin
QRK ELECTRONIC PRODUCTS
1568 North Sierra Vista
Fresno, CA 93703
Dear Bob:
As per our telephone conversation of Thursday, August 30, I am responding with the following information.
Attached is a sheet that describes our measurement procedures and test results of tone arm cable capacity. Please note that one arm is several years older than the other, and both are your Model S-260 (16-inch). Although a reasonably accurate capacitance bridge was used, we've considered verifying our data using a grid dip meter.
Tone Arm A, as you will note, measured about 120 pF for each channel. The older arm however, B, came in at about 600 pF. Although its leads are slightly longer, we're convinced that a much higher capacitance cable must have been used. (Assuming a linear increase in capacitance with length purely for estimating purposes, we would expect to see no more than about 154 pF.)
An abbreviated investigation of six phono cartridge manufacturers indicates that recommended capacitive load ranges from about 100 pF to 500 pF (100 pF appears common
For CD-4 disc reproduction, whi1e 200 to 500 pF seems typical for stereo). The value stated should be the total load seen by the cartridge (both tone arm wiring and preamp input circuit). Proper capacitive loading is very important to optimize frequency and transient response of the cartridge.
Since we are contemplating the use of a Shure M75EJ
cartridge, rated for a 400 to 500 pF capacitive load, a 300 pF capacitor in parallel with Tone Arm A's capacity of 120 pF, and allowing 20 pF for the preamp's input circuit, the total load would be about 440 pF which is within the range specified. We will, however, have to severely reduce the length of Arm B's cables to reduce its capacity to at least 400 pF or so (600 pF appears to be totally unacceptable with any cartridge).
We have not had an opportunity to measure our 5-320 arms, purchased less than a year ago, although we assume we will find results comparable to Arm A.
Since we are experimenting with a high compliance cartridge, operating at a lower tracking force, we are naturally interested in reducing vertical compliance mass. We" are therefore curious to learn if you have considered offering a low-mass cartridge shell. High mass, as you well know,- can produce very high accelerating forces when tracking
a warped record, thus significantly increasing the chances of permanent stylus and record damage. for comparison, we measured the standard shell supplied with the Pioneer
PL-550 Turntable. It measured a little over 8-grams, while yours (without cartridge or mounting hardware) came in at 23.5-grams--just about three-times heavier!
The trend in home-consumer equipment is definitely toward low-mass, as Ortofon has demonstrated with its Concorde 30. The universal headshell and cartridge weigh only 6.5-grams! Not only do we believe that such a product addition would make excellent advertising material, but would also promote sales to current Rek-O-Kut tone arm users who are interested in upgrading the performance of their arm especially with high compliance phono cartridges. And Shure Brothers is
just one source that confirms the movement in broadcasting to-improve disc reproduction methods-and equipment.
In another area, we feel that your instruction sheet is superior to that offered many years ago, although we still find it somewhat incomplete. A common problem with age is that the cartridge shell contacts become tarnished, resulting in intermittent contact as well as introducing noise. We have found that the contacts may be cleaned with a pencil eraser (an ink eraser should not be used since it is more abrasive--often containing sand--which may eventually remove the silver plating).
Another problem is intermittent hum or noise as the arm is either manually moved in the horizontal plane, or as it tracks a record. This is apparently caused by loss of arm grounding due to dirty lateral arm bearings. An effective and rather permanent remedy appears to be lightly spraying the bearings with a good contact cleaner. One that does not contain a lubricant and dries without a residue is preferred to prevent future contamination resulting in increased friction.
We have also very carefully analyzed the construction and operation of the Omni-Balance, and are of the firm conviction that it cannot produce anti-skating as implied. Anti-skating is a force induced to push the arm toward the center of the record, to counteract natural phenomenon, and is precisely what “. . .provides equal pressure on both walls of the stereo groove. . ." The Omni-Balance is incapable of generating this force, which, by the way, should be nonlinear for best performance. It will balance the arm for operation in a plane other than horizontal as the instructions indicate, but horizontal is preferential to prevent other problems from occurring. Only if the turntable and tone arm are operated on an angle can the Omni-Balance be misadjusted to provide anti-skating force. The Balance does nothing if the arm is perfectly horizontal and may therefore be eliminated. We also believe that the instruction sheet should not imply that it provides anti- skating when it does not do so in the horizontal plane and under normal circumstances.
We would be pleased to learn what capacitive load values your engineering department has on file, and whatever comments you may have about our comments.
Thanking you for your consideration, I remain,
Cordially Yours,
RADIO STATION KOLA/KGUD
Dennis J. Martin
Chief Engineer
DJM:ce
enc.
3616 MDio Street, Suites 200-205
Riverside. Cfi 92501 (11~) 684-9992. 825-9952
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KOLA STEREO 99
Rek-O-Kut S-280-16” TONE ARM
CAPACITANCE TESTS
Test Instrument: Eico Model 950B Resistance-Capacitance-Comparator Bridge
Test Method: Minus terminal of Eico connected to RCA phono plug tip, plus to cable shield; no phono cartridge or cartridge shell. .
ToneARM "A" (estimated age 7 years)
120 pF each lead (with and without both cable shields tied together)
Notes:
1. Cable leads approximately 45¼ inches to RCA phono plug tips.
2. No ground wires, right channel shield connected to arm body.
TONE ARM "B" (estimated age 9 years):
600 pF each lead (regardless of arm ground connections)
Notes:
1. Cable leads approximately 58-inches to RCA phono plug tips.
2. Two ground wires: one bare stranded from stereo shield cable (with RCA plugs), and one brown solid from arm base; both connected together to arm body (right channel shield not connected to arm body).
Tested: 083179djm
3616 Main Street. Suites 200-205
Riverside. Ca 92501 (71~) 684-9992. 825-9952
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October 20, 1980
Mr. Joseph M. Engle
BROADCAST ELECTRONICS INC.
4100 North 24th Street
Quincy, IL 62301
Dear Joe:
Enclosed is a copy of the letter I sent to QRK a little over a year ago.
I did have an opportunity to talk with Bob Martin after he had received the letter, and found him most interested in our comments and working on a low-mass headshell. He apparently left QRK shortly thereafter, and the gentleman
to whom I later spoke was totally disinterested in upgrading and modernizing the tone arm, stating that it worked the way it was, and broadcasters still bought it.
As an addition to the original data, we recently measured two other headshells and a different QRK shell using an analytical scale. The results were: Supex 5.725.grams, Technics (from a SL-1500MK2 turntable) 9.316 g., and QRK
a staggering 22.79 g. (all measured without a cartridge or cartridge-mounting hardware). Reducing the weight of the headshell, by the way, will probably necessitate reducing the weight of the counter balance.
I'd be pleased to receive your reaction to our comments, and would be happy to supply any additional information.
Cordially yours,
RADIO STATIONS KOLA/KGUD
Dennis J. Martin
Chief Engineer
ce
enc.
3616 Main Street, Suites 200-205
Riverside, CO 92501 (714) 684-9992, 825-9952
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BROADCAST ELECTRONICS INC.
INTER OFFICE MEMORANDUM DATE October 22, 1980
TO B. Weirather FROM J. Engle
cc: B. Martin
F. Cherny
T. Humphrey
C. Kring
L. Cervon
Please see the attached correspondence. I would like comments from Engineering regarding this suggestion of reducing the head shell of the S-series tone arms to a more reasonable level. I have heard other verbal comments regarding the same thing.
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"From" BROADCAST ELECTRONICS Nov. 1980/ Tonearms Comparison
INTER OFFICE MEMORANDUM FROM B. Martin
TO C. Kring M. Tournear
L. Cervon P. Schmelzle
T. Humphrey E. Hayes
F. Cherny C. Fosmark
J. Engle
The attached comparison charts are designed to serve as a guide to be used in the familiarization of major items in the QRK product line. This is not intended to be a technical manual; rather, it is set up and presented so one can identify and have a- basis for comparisons of comparable products. .
Some of the products covered are: Turntables, tonearms and phono pre-amps.
Pointed out are some features common to all of the items; so A-B comparisons: can be made. The information was gathered directly from the manufacturers printed specifications, so, please keep in mind these specifications are sub- ject to change.
BM/kdd
TONEARM Comparison CHART ADJUSTABLE REMOVABLE TONEARM PROVISIONS
TRACKING HEADSHELL RESONANCE FOR ANTI-
FORCE IN ASSEMBLY IN Hz. SKATING
Rek-O-Kut S320 Less than 1g. Yes 9-12Hz Yes
Microtrak 303 1/10 gram Yes Less than 10 Yes
Shure M-232 1/- ½ grams Yes -------------- No
________________________________________________________________________________
16? MODELS
Rek-O-Kut S-260 Less than 1g. Yes 9-12Hz Yes
Microtrak 306 1/10 gram Yes Less than 10 Yes
Shure M-236 1- ½ gram Yes ------------ No
TYPE OF MATERIAL USED INTERNAL COST
ANTI-SKATE IN CONST. GROUND 11/80
12? MODELS DEVICE PROVISIONS
Rek-O-Kut S320 Adjustable Chromed plate Yes $110.00
Weight Aluminum
Microtrak 303 Fluid Laminated Wood & No $107.00
Brushed Aluminum
Shure M232 No Plastic and Yes $ 57.00
Polished Aluminum
____________________________________________________________________________________
16? MODELS
Rek-O-Kut S-260 Adjustable Chrome plated Yes $122.50
Weight Aluminum
Microtrak 306 Fluid Laminated Wood & No $120.00
Brushed Aluminum
Shure M-236 No Plastic and Yes -----------
Polished Aluminum
NOTES:
A. ALL 12? tonearms will mount on QRK 12C turntables.
B. ALL 12? & 16? tonearms have ½? standard cartridge mounting dimensions on headshells.
C. ALL 12? & 16? tonearms supplied with phono-plugs on output chords.
D. ALL tonearms use low-friction ballbearing surfaces at rotation points.
E. ALL 12? & 16? tonearms are completely manual in operation.
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| Concerns Re-design, problems/QRK/ ROK Tonearm Issues. |
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TO C. Kring FROM B. Martin
Reference: Letter 12/3/80 H. Mann
Subject: Rek-Q-Kut Tonearm Redesign
Curt, in an effort to answer and/or comment on the aforementioned memo from Engineering, attached are my findings regarding the 5-320/5-260 tonearms. I must confess; I am at a loss to produce all necessary engineering documents to support my statements, as the design specifications of the tonearms aren’t readily available. . I did, however, have a brief conversation with Harold Mann and was able to pin-point some of the items he does make reference to. So, attached are my ideas concerning the possible re-design or updating of the tonearm, as you requested..
BM/kdd
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| DATE December 3, 1980
TO R. Weirather FROM H. Mann
Cc: L. Cervon
H.Humphrey
C. Kring.
Subject: Rek-O-Kut Tonearm Redesign
PROBLEMS
1. Tonearm is incorrectly wired and has audio cables that are too long. Customer 'cannot connect tone-arm for minimum hum without modifying it. (Very frustrating and time consuming.)
2. “Omni Balance” appears to me to be non-functional.
3. Cartridge shell is high mass. Low mass is desirable for minimal record and stylus damage. Also, standard wire color code would be nice.
4. Cartridge shell/tonearm connector should be the (Japanese) industry standard, with gold contacts.
RECOMMENDED SOLUTION
PHASE I: (A.S.A..P )
Write simple ECN to correct problem #1 above, including hook-up instruction addendum sheet. E1iminate "omni’ balance" if marketing so desires.
PHASE II: (Next Summer)
Design "Rek-O-Kut II", which in addition, Would solve problems #3 and #4 above.
HEM:nkq
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Memo
Item
No. Comments/Suggestions
1. Investigation reveals there are a couple of things that are potential problems concerning the wiring of the tonearms. Of primary concern are the methods of the grounding and shielding of the unit. Presently there are 5 wires located in the arm tube and base-assembly: 4 are associated with the phono-cartridge (left channel output and ground, right channel output and ground) and one is physically attached to the arm-tube as a "chassis-ground". Current production calls for the chassis ground-wire to be terminated with the left channels ground; "isolating" the right channel ground..., thus setting the stage for a potential ground-loop problem. The ground-loop in this case being the preamp chassis and the tonearm tube-assembly at different, measurable electrical potentials, hence: A.C. hum.
The problem can be traced to a cost-related engineering change instituted a few years ago. It was decided to use a pre-cut, molded phono-cord (Switchcraft) rather than have production physically hand-cut the wire and solder the RCA type phono plugs. Since the Switchcraft catalog didn1t have a molded cord available to accommodate a.5 wire circuit, the decision was made to terminate the internal ground lead with one of the cartridge grounds, thus eliminating the external wire, and the time related to install.it.
Another wire related problem is the differences in gauges used. The arm-tube utilizes #38 AWG wire inside the assembly, while the headshell is provided with #24 AWG wire as contact leads. Quite possibly the reasoning being the headshell and the cartridge leads the user "hands-on" point when installing the phono cartridges, and the heavier gauge is to absorb the additional strain.
The length of the output cords is somewhat another problem. The Switchcraft output-cord presently used is a precut length with molded phono-plugs on one end, and timed-leads on the other; total length about 61. Until a few years ago, capacitance loading of phono cartridges wasn't of too much concern. The only thing people were watching was matched input impedences.
Technology today does take into concern the problems of mismatched capacitance figures and we can see almost all of the phono cartridges available (even broadcast types) print suggested operation characteristics under different capacitive load conditions. The loading is an interaction of the length and capacitance of the cable and the input capacitance of the preamplifier. Typically, a phono-cartridge will specify anywhere from 100 pf to 400 pf as a "normal" load. The cord we supply with the S-320/S-260 specs out as approximately 210 pf..., well within the "allowed” region.
RECOMMENDED SOLUTIONS: Concerning the shielding and ground-loop problem..., suggest engineering produce ECN requesting wiring changes eliminating the soldering of the arm tube assembly ground-wire to the cartridge grounds and bring it out as a separate external wire (22 A~JG) equal to the lengths of the output cords with a spade-lug attached for connection to preamplifier ground.
Concerning the wire colors and different gauges, suggest Engineering produce ECN calling for the standardization of gauges and adopting a "standard" color code, if none exists.
-1-
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Memo
item
No Comments/Suggestions
1.
Concerning the output cord, Engineering will have to investigate the feasibility of using a low-capacitance type of cabling. In all cases, it is better to be below a specified load-value and "build-up" to recommended operating conditions. The low-capacitance cable would allow this; but it is not commercially available in pre-cut lengths or with pre-molded connectors. A trade-off would be in cost, production assembly-time and additional expense of the installation of RCA type
of phono-plugs. As an alternative, we might look at -the possibility of continued use of the Switchcraft product. There is available a similar cable as we are presently using with molded phono-plugs at both ends, six feet in length. By going to this cable and cutting it in half, we can solve a couple of problems at once.
First, the shorter lengths will reduce the possibilities of the introduction of A.C. Hum. Secondly, it will cut the capacitance by at least 30 pf to 40 pf per foot and save the expense of purchasing and stocking the RCA type of phono- plugs. All this .at a mere cost of a few cents more than we're presently paying for the molded cable we now use.
2
The omni-balance weight was designed to provide additional balance for the tonearm; making it fully adjustable on the vertical plane as well as the horizontal plane. The fact that the arm-tube is bent, or off-set, is a pre- determined arc directly related to the grooves on the record disc. This
"bend" exhibits appreciable offset weight of the arm assembly as opposed to
the cartridge shell (with phono cartridge installed); the omni-balance weight properly adjusted, will "counter-balance" this offset and help maintain lateral compliance..., even to weights that are below 1 gram.
The transmission of stylus-vibratory energy to the tonearm can be minimized,
for all practical purposes, with a cartridge exhibiting degrees of high lateral and vertical compliances. Such conditions prevent development of the toneann resonance. It is a (measurable) fact the omni-balance weight helps dampen these vibrations (resonance) as much as 3 - 5 dbs. The fact the weight helps "load" the horizontal bearing assembly further assists solid mechanical coupling on contact points, reducing the number of possible resonance points.
RECOMMENDED SOLUTION: The omni-balance weight device does exhibit measurable effect on the balance and tracking of the tonearm; more noticeably at lighter forces (I gram and less). Concerning the original design applications; there
are existing mathematical and engineering formulas to support the use of this device. Based on this information, I feel it is important to maintain the mechanical integrity of the tonearm by leaving the omni-balance weight intact.
3
Reproducing sound from a phonograph disc is based on solid mechanical coupling between the cartridge stylus-tip and the record groove -not mere touch, but solid coupling. Most popular is the belief that the lighter the needle force, the lower the record wear. In general this is so, down to a certain point. Reducing the forces below that critical point will in fact actually wear the record faster. At, or near this point, a couple of other forces come into play. Stylus-tip mass and velocities (vibratory momentum) are our main concern; and this is a function of the phono cartridge and its- ability to "track" the horizontal and vertical walls of the record groove. Either the cartridge exhibits a high degree of compliance to move with these variations or it doesn't.
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Memo
Item
No. Comments/Suggestions
3.
In electronic sound reproduction, the tonearm has only one function - to maintain the cartridge and stylus in a predetermined relation to the record grooves. The tonearm structure and assembly should be such as to introduce no restraint to the free travel of the stylus across the disc - regardless of the mass required to attain this. With the counterweights and the omni-balance weight, the tonearm is adjusted ("balanced") in all vertical and horizontal planes. The headshell assembly is merely acting as an extension of the arm; providing a mounting platform for the phono cartridge.
~RECOMMENDED SOLUTION~: There seems to be some confusion regarding the inter- action of the tonearm and phono cartridges. Tracking of the record is a function of the cartridge-stylus. Providing the platform is the function of the tonearm. The tonearm is designed to provide the highest degree of compliance as a system. The headshell is an integral part of this assembly. Changing the mass of the shell would necessitate similar changes in the weights and counter-balances.
Less mass would change the resonance frequencies and quite possibly lead to a complete redesign. The Research and Development related costs incurred could be extensive; as we have no engineering expertise in tonearms, as such.
4.
The S-320/S-260 tonearms have been produced in one form or another for more than 20 years. In fact, we are still using some of the original tooling jugs and dyes. To take a broadcast standard that has been around and accepted for this amount of time and to re-standardize it to a Japanese Hi-Fi product code (not yet universal) just doesn't conform to any standard practices.
Presently, QRK/Rek-O-Kut related replacement parts account for more than 30%
of all BE replacement parts sold each month. You can well imagine the additional headaches caused in changing plugs and connectors at this stage: stock would have to have 2 types on hand for replacements, repeating type of brand-loyal customers (which most broadcasters are) couldn't interchange existing headshells with the "new" one, customer service would have to spend additional time trying to sort all of the related problems, etc.
QRK did, at one time, have gold-plated contacts on the shells. The use of this
was discontinued several years ago because of the problems encountered. Gold has been found unusable as contact points because of its susceptibility to
tarnish and oxydize. Resistance that resulted in the signal path was much higher than the values found on the plating presently used when oxidizing.
And, with the Gold Market fluctuating as much as it does today, we couldn't be
'guaranteed' a plating price that would remain fixed..., hence: a different finished-goods "cost" every production run.
RECOMMENDED SOLUTION: None. The past experience of the higher failure rates encountered in using Gold Contacts doesn't offset the gains in contact signal- performance. The suggestion that a change in plug standards for a unit where there are literally thousands in operation in the field, doesn't fall within any accepted, viable marketing concepts.
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