Thorens TD160 modifications.

 

There are numerous modifications to the Thorens TD 160 turntables posted on the Web. The good starting point would be here:

http://www.theanalogdept.com/thorens_tweaks.htm

My goal was to do essential modification that could actually (potentially)  improve the sound, and not to copy some questionable ones.

 

My modifications included:

1. Damping sheet metal to reduce rumble and resonances in the audible range of frequencies. The original metal chasses:

 

 

 

 

- to lower the rumble I used all common recommendations.

The first and the simplest step is to dump chasses in the motor surrounded area with the absorbing material like dynamat. That is a standard procedure already discussed in the numerous posts.

The second step is to adjust the belt tension.  You need the correct belt tension otherwise the turntable goes too slow or too fast. You need the correct belt tension otherwise the platter wouldn’t be centered, and the tonearm base would knock on the sides of the well.

The only way to adjust that tension conventional way is to try a few belts of the various length. (Proper dimensions would be: width 3.5 - 4mm, Thickness 0.8 - 0.9mm, length 510 – 520 mm. Because of the rubber nature, there are always some variations).

 

- to lower platter resonances that could penetrate in the amplifier via the pick up cartridge I used standard damping of the sub-platter with cork adhesive sheets, plus damping of the bearing shaft with rubber ring.

 

2. Idea of the suspended sub-chassis is to balance the mass of sub-chassis, platter and tonearm, so the system will become independent from the influence of the outer
vibrations. Lets say that with belt pulling in the horizontal direction, and suspension springs acted in the vertical direction, it is impossible in theory to have the sub-chassis  be forbidden to do any lateral movement (it is impossible in theory to achieve three-dimensional dynamic equilibrium). All three conical springs are symmetrical, and do not provide any means of the compensation in the horizontal direction in the ideal symmetrical position. The only force that resists to the belt tension is the friction in the rubber grommets and resistance of the bended springs.  

 

What I use here was a special compensator that not only provided a way to center sub-platter in the horizontal direction, but also adjust the tension to the optimum value. (I couldn’t find on the web anybody else who is doing that additional spring based compensation to the belt tension mod).

After applying the horizontal adjustment it is much easier to achieve the vertical balance traditional way, so the system tonearm – sub-chassis would swing perfectly vertical. (See the bounce test)

 

Construction of the compensator is not finalized yet, but simplified version looks like that:




 

3. Platter bearing was damped with additional damping collar underneath of the traditional damping ring.

 

 

4. The AC motor and main bearing were lubricated with motor oil.

 

5. The new belt was installed. To provide the proper tension I bought a few belts of the different sizes and after testing all of them I choose one with dimensions:  0.8 x 3.5 mm cross section and 510 mm length.

 

6. Original cheap rubber feet were replaced with better quality conical rubber feet to improve turntable isolation from the stand.

 

7. Cosmetic and convenience upgrade. Tiny flimsy pins – hinges were replaced with bronze screws of the certain shape and size.

 

Upgrades that I passed on.

 

1. New plinth. Lower turntable – rack/stand coupling.

That is the most questionable modification. The common advise is to build a thick heavy plinth, after that the person who did it would find out it did not sound well (better?), so next step would be to cut a big hole in that plinth (and canceling by that the purpose of the heavy plinth) in order to “open” the box.

I don’t think this is an improvement. The heavy plinth decoupled from the sub-chasses by springs as it done in Thorens design is acting as the part of the turntable stand rather than the part of turntable itself. Means, no effect whatsoever. Heavy plinth with soft sprung feet would create double suspended mechanical system with multiple resonances. That would hurt already weak resistance to the “step” shocks of suspended turntables badly.  (I did an extensive test of the different feet during Fons TT modification).

Instead, for the particular modification, I kept the original bottom, but replaced the original small stiff rubber feet with soft conical rubber feet that provide better isolation from the stand without adding new resonances.

 

2. Tonearm replacement. Original TP16 tonearm is pretty good, well balanced and has unique features like magnetic anti-skate compensation (no additional friction). Effective mass 16 gram makes it the perfect fit for the moderate to low compliance cartridges like popular moving coil Denon DL-160 and many others. Upgrade in the sub 1K range to the better quality tonearm, not just the replacement with another one, would be limited to the SME 3009 variations with effective mass below 10 gram. Which is ok, but would narrow down the cartridge choice to the Shure V15 only.

 

That is what I think. I would like to discuss some physics behind suggested modifications, you could contact me nbsaudio@comcast.net

 

Michael Kazarinov