Facelift for a Dual 505-2

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Hi,

Well good luck with it, your going off on tangents I never explored.

In terms of separate arms and turntables compared to integrated,
I didn't consider the 505/2 arm the major weak point, but an LVX
arm will be better, and tuning of the decoupled mounting an area
I know nothing about, not the path I chose for simple mods, as
you can't "isolate" an arm from its mounting completely.

A few points though :

1) If still using the spring suspension a plinth rebuild is not effort
effective. Damping the plinth with bitumen spray is effort effective.

2) If still using the spring suspension substitution of a heavier arm
assembly / mounting will cause levelling problems requiring you
to add (a lot of) mass around the turntable to rebalance it.
(Or add a "helper" spring, which I did in one of my mods.)

3) The spring suspension is compromised laterally, allowing
the demonstrations of the dynamically balanced arm having
no problems with the turntable being tilted at extreme angles.

4) You might have issues with the minimum LVX arm height.

rgds, sreten.

I like Dual 505's, but not my choice to try and make fly.
 
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I am picking the Linn Lvx arm up later this evening and have been exploring various ideas about armboard mounting.

What are the recognized principles of securing a VTA arm to a board and then the board to the suspension?

Does the armboard effect the arm's mass?

Should there be damping between the arm and board?

Should the board be sound isolated underneath?
 
SIMDRAW.jpg
 
I came accross this thread by accident when I was preparing to post another topic. However, I was interested because I am also using a CS505 for a rebuild. The reason is that I want a semi auto unit but I cannot find anything else that would do the job apart from a CS5000 which has the added electronics complexity. I have also decided to add a second arm which is an Audio Technica AT1005 fitted with an AT120E cartridge. The dual headshell has been stripped of some mass by removing some extraneous bits and will now balance its VMS30E cartridge without any additional counterweights. The only other thing I have done is to remove all of the damping from within the suspension springs so it now bounces quite happily.
The Dual will be transplanted to a solid wood plinth sitting on Microsorber adjustable feet.
The AT arm will be mounted on the plinth to the left hand side of the Dual at the rear, facing accross the back of the dual unit. Obviously the AT arm cannot be used when the Dual unit is floating, so in this instance, the Dual will be clamped down to the plinth with three screws mounted where the current transit screws are. The AT arm height will be set up to this clamped down height.
There will be no dust cover as the unit will be quite wide and will be housed in a cabinet anyway.
Why am I doing all this? I want the semi auto function of the Dual but want to be able to use my beloved AT arm. I also want the removable headshell of the AT, the Dual headshell is now superglued together so is now fixed. The AT arm will feed into a separate pre amp and the Dual into the amps phono input
I'll post some pictures when complete.
 
Yes, I was sorely tempted toward the 5000, especially when one came up for sale locally at a good price. However, I would have probably kept it standard and that wouldn't have been very DIY would it, and I like a challenge. I have always promised to find a TT that does the AT arm full justice, and one day I will find one. However, for now, this seems like a good way of using it without breaking the bank.
 
Change of plan - the Dual 505 suspension and plinth will be discarded.

A Linn Sondek type suspension will be built along with a new plinth.

An externally hosted image should be here but it was not working when we last tested it.


I have three Linn springs but instead of the metal circus bearing I will use the existing Dual 505 bearing fitted into a wooden replica of the suspension plate.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.



The metal toplate from the Dual will still be used and cut, the pitch control and strobe platter will also be used but the arm board and arm will be Linn. Hopefully it will look like a Sondek with a smaller platter. The plinth is being built tomorrow.
 
If you are considering such drastic mods to the Dual, you may be interested in something I tried on a previous project. I mated a Thorens TD150 outer platter to a Rega subplatter using a machined adapter ring. This ring sat on the Rega subplatter, effectively increasing its diameter. The ring was machined with a step at its periphery to locate the Thorens platter. The Dual subplatter is not so different to a Rega so perhaps similar could be done to the Dual. I am not going to try this on my Dual as the original suspension would not cope well with the heavy Thorens platter. I’m not even sure whether it would foul anything on the Dual. Still, just a thought.
 
Oddly enough I had contemplated it but it would mean losing the "Dual 505" essence to the project. Also, the strobe markings and pitch control are an essential; different records have different weights and the speed fluctuates. This way means that there is control over the adjustment to get the speed correct for each record.
 
Try to restart an old thread :eek:

I have an old stock CS522 that works well, still. The automatic parts have little wear and the lubrication works. I have compared the TT to some modern TT, and it does sound very good and comparable to a few 'hot' models despite its age. The TT that can beats it, is the one that cost USD1000 in the Singapore market.

I have some experiences servicing and upgrading the Thorens TD124, the Pioneer PL12D and CEC BD2000. The CS522 is like a fine delicate old clock to me; refined engineering. The automatic start/stop features are particularly needed, because my wife would like to use the turntable.

The options I consider for the upgrades are:

1. Replacing the 16 pole AC motor running at 375 rpm by a DC motor with electronic control. (The AC motor is excellent, but, it still has a fair amount of vibration. This is inevitable with a Synchronous motor).

I have investigated several Nidec BLDC with PWM control. They are very quiet and smooth at rated speed of 1500rpm, But at low speeds below 500rpm, the reduced duty cycle of the 3 phase excitation and PWM frequency can make the motor jitter at times. I intend to run the motor at near 800-900rpm. This motor speed is suitable if I enlarge the sub platter diameter from 91.5mm to 110mm and the pinion at 4.5mm diameter. (814rpm from the motor) I am still investigating this option. I am getting a more precise PWM generator to check if the motor can run quiet and without jitter. The platter diameter can be achieved by machining a plastic adapter. I can have new brass 4.5mm pinion machined as well.

With the DC motor control, I can remove the mechanical speed adjust. Also I can run 33.33/45/78 from the same pinion.

Ebay sells a turntable DC motor that runs at 1000rpm, 1500rpm and 2000rpm with adjust. (I have successfully replaced the AC motor in the CEC BD2000 with this DC motor, running at 1550 rpm fixed. ) the adjustment of speed is not easy, with the help of a digital laser tachometer.

2. Improve the CS522 platter thrust bearing support. (the original consist of a rubber ring, a 20mm dia 1mm thick steel washer, a plastic holder with 5 polished ball bearings, and another 20mm steel washer)

Thrust bearings are not ideal for the most quiet rotational setup. The steel bearings have tolerances and they will contact the plates at different instances. There will be a repeatable run out, and non repeatable run out causing noise. The bearings have caused a clear wear ring on the washers. I am taking away the top 1mm washer, and replace it with 2 X 0.5mm Teflon washers. The ball bearing will be replaced with new ceramic balls which has much higher tolerances than steel balls. With the ceramic balls riding between the Teflon washers, the contact noise will be much lower. Such modern parts were not available 30 years ago.

The main shaft steel surface will be polished by a skilled technician to ensure smooth surfaces. The finishing of the shaft can be improved.

3. Replace the ULM arm with a CS-505-4 type tone arm assembly.
The old arm was designed to use the Ortofon OM5 type very light weight cartridge. I am getting help from Dualfred in Germany to replace the whole assembly to a new arm with proper 1/2 inch cartridge. The internal wiring will be modern copper wires. I am contemplating a new cart from LP Gear.

4. I am tempted to remove the automatic start feature. But on close examination of the mechanism, it is indeed very clever. What I can do is perform a proper cleaning and re lube with modern lubricants recommended in Dual service manual ( Silicone oil 300000, Adhesive oil, engine oil, grease etc).

5. Build a new plinth. This is not too difficult.

The beauty of DUAL is there are still a lot of parts available for tweaking.
 
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Its now about a month later. I have progressed to:

1. Built a new plinth using real wood. I found the original plinth was just a plastic casing with some chip board attached. The new plinth will add more strength to the structure and allows more damping of external disturbances.

2. I have ordered a new arm from Dualfred of German for the CS505-4, new 1/4in adaptor to mount modern cartridges (may still stick with Ortofon OM10 super), and counter weight. The 505-4 is a new incarnation of the ULM arm. I am in favour of low mass straight arm.

3. The arm 4 point pivots are similar design as many classic German turn table arms. The four points will all have new 5 ball bearings on the a. bottom pivot point, top pivot point, both sides on the arm carrier. The design is very simple, two pints on the vertical allows a rotational axis for horizontal movement, and two points on the horizontal to allow an axis for arm to swing up and down. Using a tool from Dualfred the adjustments for slight gap of bearing point for arm to move freely is not that difficult. My concern is the light arm that activates the mechanism to return the arm. It is a very clever design, but I have no intention to use auto stop. So I won't put the light arm back to the segment plate. The whole assembly is very light and can be tuned via the top bearing and side bearing, which are easily accessible.

Tonearm wire will be wired to a small board directly behind the segment, and run new shielded Beldon wires towards the headamp directly. 5 wires arrangement of (L+ L- , black arm ground, R+ R-) ; chassis ground is separately run. The original muting box and cheap long RCA cables will be removed.

4. Dismantled, cleaned and check the parts. The vertical armlift needs lubrication of 100000 cps oil. The arm lift control is via a long thin plate arm, and the level is plastic.

5. I have resprayed the top plate using automotive paint - from dull black to glossy black. Control knobs sprayed and renewed.

6. The sub platter inner surface and the bearing support checked and slightly polished. I obtained the adhesive oil from Dualfred for re lubrication. The assembly sits on 5 precision ball bearings. I have replaced them with 5 modern 3.12mm ceramic bearings for bicycle hubs.

7. Motor unit SM100 dismantled, oiled and checked. The rotor was placed back into the motor with paper shim placed on the surface to ensure an air gap, and prevent in contact with the stator poles. Shim removed when screwed are tightened and rotor rotation is ok. The 16 pole motor is of high quality. I want to keep the mechanical pitch control so I have to stay with this unit. The power board capacitors all appear cracked. Instead of driving the unit with mains power, I am in the process of building a a. 50hz sinewave generated by crystal oscillator and division down to 50hz square wave. Wave is 8th order filtered down to 50hz sine wave. Sine wave is pass thru opamp filters to give 0 degree phase and 90 degree phase. The two signals drive a twin TDA2030 amplifier board to power two 6v/110v 5VA transformers. The motor phases will be driven at 100v a.c. with some adjustments of the 90 degrees out of phase sources. When all calibration done, I will mount the SM100 box onto the plinth and mechanically decoupled from the top plate.

I have two CS522 right now so when all these are done, I can compare the sound quality before and after the changes. The original CS522 uses the Dual ULM45 cartridge, which I have new 145 needles from LP Gear. They may not sound as refined as the Ortofon OM10 super. The use of CS505-4 arm allows me to swap between Ortofon, AT95, Vessel cartridges.
 
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The 16 pole motor is of high quality. I want to keep the mechanical pitch control so I have to stay with this unit...When all calibration done, I will mount the SM100 box onto the plinth and mechanically decoupled from the top plate.



Hmm, might get somewhat tricky, as the pitch adjustment mechanism, including the knob, also needs to be fixed to the plinth then.


Best regards!
 
Hmm, might get somewhat tricky, as the pitch adjustment mechanism, including the knob, also needs to be fixed to the plinth then.
Best regards!

I am not at all pleased with the amount of vibration it exhibits now, despite all the adjustments and lubrication done... :( Many TT using AC motors has this defekt , so to speak.

I am trying out a Nidec PMDC using a more stable PWM. I am still investigating the settings. The PMDC has much less vibration, but makes a lot of whining audible noise :(.
 
I have completed the upgrade.

Here is the thread on 'Mango' a Lingo clone of pure sine wave power supply.
The optimal delay was not 90 degrees, but 120 degrees for Dual Synchronous motor. Motor has virtually no noise or vibration:

Synchronous Motor Driver for Dual CS522 or CS505 using SM100-1 motor

This is the completed CS522 aka using CS505-4 tonearm
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Despite the lightweight tonearm prefers a high compliance cart like Ortofon OM10 or OM20, in actual listening, it works extremely well with a AT95E during setup and trial.
I will be putting in a AT95EX needle on the cart.

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Simplified the mechanism of the CS522. I could have it as a semi auto start.
The Stop function is not desirable because the long alu arm is interfering with the tonearm segment free movement.

The 5 X 1.3mm ball bearings have been upgraded by 5 X high precision ceramic balls.
Together with the high viscosity adhesive oil from Japan (chain saw), the platter rotates very well indeed.

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