the home of the turntable

Dual 701 repair

twice the fun

Re: Dual 701 repair

Postby alfonsol » 09 Jun 2013 21:48

Hello gerarduvar,

there are 2 rubber pieces in the counterbalance.

one is a ring that i think is supposed to dampen the leaf spring for the big counterweight.

the other is hidden behind the little counterweight on the base of the counterbalance.

note: when i said counterbalance i mean the whole assembly.
alfonsol
member
member
 
Posts: 38
Joined: 22 Jun 2010 05:29
Location: Chile

Re: Dual 701 repair

Postby alfonsol » 10 Dec 2013 02:20

it's been a long time, but i managed to get a new counterbalance( not exactly the same, but it works) also i got a new cue lever( mine was broken) and the cover for the strobe.
the turntable works very well.
alfonsol
member
member
 
Posts: 38
Joined: 22 Jun 2010 05:29
Location: Chile

Re: Dual 701 repair

Postby dualcan » 24 Dec 2013 22:27

A remarkable job!
I did not think that you would get a turntable in that condition to work again-Bravo!
Luckily, the eds 1000 motor and its electronics are ok. When these units were new, and we had a problem with them, we were obliged to sent them back to the factory for refurb. This (mechanical) motor is not a Dual product, but comes from a neighbor, by the name of "ebm-papst St. Georgen GmbH & Co. KG". Address sound familiar?? The same motor was also used in the revox B790 turntable and many a hair was lost by my friend Juergen at their authorized revox agency who had the unfortunate task of servicing that unit... Look up revox service manual in the library section above, to see what complexity can be...
Something particular to eds 1000 (701/721) was that they could static discharge and a tiny zap was audible in the system. This was caused by the EDS mechanicals because the rotor ax was not grounded enough to chassis. This could happen especially in northern climes where heating system and drier air plus carpeting is a great source for static) discharge. The solution was to replace the original lubricant in the lower rotor support (big brass center screw, seen page 19 is access point) with abrol-x GF60 (Kd part 236889).
As you may know, lubricants do not necessarily only reduce friction, they are also used to create friction, as in the lift system. In this case the lubricant is also an electric conductor.
Lastly on the motor, many people see the electronics as old fashion and out of date for that time. Indeed, so did we, since it uses ac 181 etc. germanium transistor as we did ten years before, and silicon units were already de rigeur. Well, the reason for the backtrack is speed. Only germanium units could deliver the pulses fast enough for the stators and although the transistor look like your average germaniums, they were actually individually paired at the factory to the closest possible pairings, and sold only as sets (228 899). Remember too, there where no IC's....
The problem with the counterweight is unfortunately fatal. When new, these units were supplied with a transport screw positioned in center rear and reaching inside to hold the actual weight. This was to avoid damage to the sensitive mountings of the weight during transit. Problem was that people don't read instructions and therefore balanced the tonearm by the usual turning of the outer cage- without removing said screw. Exit one counterweight. The Factory paid a heavy price for replacement counterweights, and that is why this design was dropped like a hot potato, and never used on another unit. Once the weight is sheared off the spring, it can not be repaired. Even if you get the exact or original internal parts, it is virtually impossible to get the resonance realigned since the alignment apparatus was laboratory grade and each one individually tuned to fall in the 2 to 15 hertz window, the desired resonance window for tonearms. Why 8 to 15 hertz? Below eight is usually foot traffic and music does not go that low, as can be seen here:
http://djfrobot.blogspot.ca/2010/04/eq- ... ments.html
The idea is therefore to keep resonance of the tonearm/cart within those points and "antiresonate"or decouple below and above. Hence the complicated set up within the weight. The factory did not take back any counterweights for re-manufacture because it was cheaper to produce new and very few parts could be salvaged anyways. The 721 has a re-engineered version, and is not prone to damage. You did the right thing with getting another weight. All 1219/29 version fit or even just straight remounting the weight to the shaft would work as a back up.
I saw also the tonearm wire you replaced and some suggestions as to the replacement thereof. Lets look at the sound cabling in general. Originally all units had 2 single coaxial, (not only shielded but true coaxial) wires.
These were replaced by cheaper 5 wire flimsy looking wires. Now Dual would not go cheap on the most important item for sound if not necessary. (It did a bit with the second version of the 701 in cosmetics, but I digress.. BTW,yours is the first version..)The reason to go from Coax to unshielded cable is impedance. The Coax is hi capacitance and the unshielded is low cap. The low cap is needed for (here is a blast from the past)quadraphonics. The only way to get four channels out of two flanks of a record , is to encode over the L and R signals. That requires frequencies in the 30 plus khz range, which special carts could reproduce IF the cable was low cap. Since then, all tonearm cables were changed to low cap type. For your tonearm I would suggest that you use inner conductor of the cheap airline earphone buds. These are about the smallest diameter I can think of and present the least amount of tension toward the tonearm. You need to Carefully remove the outer coating of each channel of cable , remove the neg return and only use the positiv/centre cable- times 5.
We also were agents for Ortofon at that time, and it was and still is a major player in sound, not only in reproduction but also in cutting. Their top of the line moving coil cart, the MC 30 was very close to the price of the turntable if memory serves, without the possibility of consumer stylus replacement. This cart was a natural for the 701, but if the client went extreme with the rest of the equipment then a very slight hum was perceptible. After trying to get help from the brass, and getting nowhere, I took it personal and spent time analyzing every part from stylus to cynch/RCA connector. The problem with an extreme low output cart is that of ground-loop. Think of a chain where every link is a closed circle. This type of wiring existed on the normal wiring set-up and is inconsequential in moving magnet carts, with higher output.
The trick here is to keep the cart wires all separate right to the cynch connectors, including the tonearm ground cable (black wire/chassis/separate chassis wire to amp).
Here is how tonearm is wired to remove ground loops. The first thing to do is to break the short on the pc board, between your black and blue wires, as seen on your photo
download/file.php?id=52.
Put a jumper cable between your black cable (center track of pc board) and the tonearm head solder lug (also visible in photo as solder blob inside head.) Now run 5 wires (the ones made from ear buds or similar from each pc track trough tonearm and follow routing to muting switch as seen in fig 15 page 14 of manual. In the muting switch (which was forgotten in the parts list somehow....) cut all wire bridges between chassis ground/ green and blue cables and reconnect individual cables to each section of the muting switch as before except the black cable, which goes to chassis. That chassis point gets a separate ground wire to go to the sound system ground. The other cables are wired, Red / right channel hot with its ground green (as in your colours) and white / left channel and its ground blue. Now you have eliminated the ground loops. If you think that cured the hum for the mc 30 ortofon, nope, my problem only was slightly improved... I'll come to that at another point in time.
Unfortunately I see you are missing the diffuser (item 24) which covers the strobe. This ocular shim has the advantage of adjusting the viewing angle of the strobe to a more comfortable angle.
As to changing the capacitor in the ac box, here is a list of Duals that have a "Knallfrosch" (here is a new German word- after steuerpimpel)- or exploding frog. Why exploding -because they can and will. Many Duals use this type of suppressor or multiple suppressors in their ac circuits. These may look like capacitors but are RC networks such as .47uf/100ohms combos. All these units must be changed when you see a crack in the case. In my parts, I have new pc power board, never used, but the caps are cracked (age related),and potential firecracker.
This issue is well covered in the German forum Dual-Board.de
Here is a link to the affected Duals with these very potential crackerjacks.
http://www.dual-board.de/index.php?page ... 3%B6schen*
Take care when replacing them and use rc combos such as the Rifa or equvalent:
http://www.conrad.de/ce/de/product/4561 ... VAC630-VDC
In the 701 it is C51 and C52. Much information can be had over this issue on the Dual-Board forum.
Lastly I would suggest that when you remounted the Gimbal bearings, the play should be set so that pins 39 and 51 just touch bearing bottom, then back-off 1/4 turn, then tighten counter nuts, recheck play as I have outlined in another case:
Disconnect from mains power supply. Put anti-skate dial and tracking force dial to zero. Be careful not to damage stylus-you can perform this test with stylus removed and tonearm balanced without stylus. Next balance your tonearm perfectly (it should float horizontally when seen from the side. Now take the smallest size stamp and put it on top of the tonearm head (over Cartridge). The tonearm must lower towards record. This checks the vertical movement. Remove stamp and move tonearm over towards the record/platter center. Apply anti-skate force 1 on the anti-skate dial. The tonearm must return to tone arm support completely. This verifies the horizontal friction
Hope some of this information is of assistance to you,
and enjoy a marvelous product.
k
Klaus Adlhoch, fmr. Assistant Service Manager,
Noresco -N.Q.I.-Dual of Canada,
Area of expertise: Tech Training and Consumer Service P.R.
Associated with Dual till Thompson era.
Favorite Duals: TG 12a, 1009, 721.
dualcan
senior member
senior member
contributor
 
Posts: 857
Images: 78
Joined: 15 Nov 2013 23:53
Location: Sorel-Tracy Quebec

Canada

Re: Dual 701 repair

Postby alfonsol » 28 Dec 2013 17:10

Thank you dual can for your info.
I already changed the "Knallfrosch" with the RIFA.
Also I found a diffuser on ebay and I installed it.
I will check the bearings on the tonearm.
Actually the wires in the photo are my first attempt to rewire the tonearm. Then i used the ones from a cheap USB mouse that are more flexible.

I will try to post some pictures of the turntable today.
alfonsol
member
member
 
Posts: 38
Joined: 22 Jun 2010 05:29
Location: Chile

Previous

Return to Dual