Jump to content

Recommended Posts

I have had a few questions about my modified Technics EPA100 so I thought I'd start another thread detailing the modifications and how/why these improve the sound.  I'll split this into multiple posts with the results and then pics of the mods.

 

Firstly IMO the EPA100 is a very good arm straight out of the box as long as the bearings are in good condition. The modifications shown here can be applied to any tonearm as they follow the basic fundamentals of Physics.

 

The tonearm has by far the hardest job in the analog chain. It has to hold the cartridge rigidly preventing any chaotic movement while allowing the stylus to track the groove. To complicate things no LP is perfectly centered and flat meaning the tonearm also has to allow the cartridge to move back and forth as well as up and down still with no chaotic movement. I'm amazed that it works at all.

 

The OEM CW has dynamic damping, this is a weight in silicone oil controlled by a spring inside the CW. Adjusting the damping loosens and tightens the weight against the spring. The problem is this type of damping only works at a specific frequency, get this wrong and you have a wobbly bit on the end of a spring waggling around on the end of a cantilevered beam. The solution was to make a new stainless steel CW and brass stub. The stub is held into the back of the arm with a set screw, the stub is threaded so the CW screws onto the stub and locks with a brass ring holding the CW rigidly on the back of the arm so no more wobbly bits.

 

Viscous damping was also added at the same time similar to the damping on an SME. The purpose of this is to prevent the cartridge exciting arm/cart resonance.

 

As can be seen from the plots just replacing the CW with one rigidly mounted to the back of the arm significantly reduce these AM sidebands and boy is this audible in added clarity. Adding the viscous damping was less of a WTF moment but still audible.

 

plots in sequence

Stock EPA100

New CW and stub

New CW, Stub and damping

 

300Hz_OEM.thumb.jpg.3100336eab5b52a68216716cd56d6892.jpg

 

300Hz_CW_nodamp1.thumb.jpg.c0638224db1fab2e7bf85a4ea4d62d47.jpg

 

300Hz_CW_damp11.thumb.jpg.5c70bf80b88cb7d454a346fa2fa80947.jpg

Link to post
Share on other sites

Here are pics of the CW and stub mods. The latest version the locking ring is brass in place of the aluminium in the photo.

IMG_20210105_170359238.jpg

IMG_20210105_105647337.jpg

  • Like 3
Link to post
Share on other sites

Next on the modification list was to replace the VTAF base seen in the first pic of my last post with a far more rigid mounting arrangement. The EPA100 base is very well made it would not be out of place on the zoom of an expensive microscope. BUT because it need to move and has no locking feature it MUST vibrate.

 

The solution was to machine a new base with a far more rigid locking mechanism.

 

I don't have before and after measurements here all I have are after spectral analysis of a 1kHz signal, but this looks very clean.

R_CH_THD.jpg

Link to post
Share on other sites

Pics of the base. The collar also stiffens the arms post.

 

VTA is adjustable on the fly.

 

 

IMG_20210514_143835333.thumb.jpg.75fa91f09495540591f78157905ce3e3.jpgIMG_20210514_143759701.thumb.jpg.86580395e64d97a46987e4fb61b1114a.jpg

  • Like 3
Link to post
Share on other sites

Turntable modifications are some of my favourite tweaks, and tone arms - as I have just witnessed in my own system - play a huge role. Good topic 👍

  • Like 1
Link to post
Share on other sites

Yes the mods are so simple but the results are staggering.

 

In the last photo you'll notice the O rings placed on the arm wand. These were placed using a stethoscope to listen to the arm at the mount.

 

I am a firm believer in a rigid tonearm mounted to a well damped plinth. I have found resin/bentonite to be the best plinth I have come across.

  • Like 1
Link to post
Share on other sites
1 hour ago, Warren Jones said:

 

In the last photo you'll notice the O rings placed on the arm wand. These were placed using a stethoscope to listen to the arm at the mount.

 

 

That is indeed fascinating, Warren.  :thumb:

 

But I have a few Qs:

  1. where exactly did you put your stethoscope?  Against the arm-mount bolted to the plinth?
  2. and what were you listening for?
  3. can the results be codified?  EG. say, an O-ring should be placed at 1/3rd and 2/3rds along the wand?

Andy

 

Link to post
Share on other sites
Posted (edited)

Hi Andy,

 

1. very good question and something I forgot to add to my post as it's quite fundamental  to the test.

 

I put the stethoscope on the antiskate dial as this was the best place I found to listen to the arm. Putting it on the plinth resulted in a very damped sound. I found no difference in sound from placing the stethoscope on the bearing housing or antiskate dial so I used the dial as it was easier.

 

When I placed the O rings on the arm wand I was listening for ringing in the arm. I floated the arm then tapped the tube with a pencil, this way I could hear any resonance in the arm. I then positioned the O rings to provide the best damping.

 

I also played music with the volume right down and listened to the arm in the same way. It's a very interesting exercise as with no damping the music is clearly audible at the bearing housing as the damping increases the music becomes more muffled and lower in volume. Indicating attenuation in the energy traveling down the arm. Physics tells us that when energy waves hit a boundary depending on the type of joint and the materials some energy will be reflected back, so damping this energy as it travels down the arm means less energy reflected which will also be further damped as it travels back to the cartridge.

 

The other thing that was interesting was to float the arm and tap it in various places, there was no difference in sound between tapping the headshell or arm tube but tapping the CW the sound was a different frequency but still well damped. What this highlights is even with a removable headshell once the collet is tightened the headshell and arm wand become a unified system and resonate together at the same frequency. So all those plots you see on the net that show arm resonance different for the wand and fixed headshell have a question mark over their validity.

Edited by Warren Jones
Link to post
Share on other sites

Interesting, I had not juiced the o rings. Now I have little knowledge in this area, but what happens to natural vibrations created by the cartridge in the groove, when it travels up to the o ring? Does it get absorbed or dissipated or does it reflect back into the cart?

 

I have seen heat shrink placed on FR arms before...

Link to post
Share on other sites

BTW I also added a small bit of foam ear plug just behind the headshell collet this did damp but as I haven't disassembled the arm I didn't add more earplug further down the arm wand. I'll do this at some stage as I think it would a better job. The O rings are easy.

 

Now to your question and this answer will be a little long winded.

 

Firstly the difference between vibration and resonance.

 

Vibration is just that a structure vibrating at 1 or many frequencies.

 

Resonance is cumulative and builds over time. A structure like a tonearm has ONE resonant frequency for each side of the pivot, this becomes a little more complex due to the compliance of the cartridge and the system will have 2 or 3 resonant frequencies due to this compliance.  The damping with O rings will do very little for these resonances, these are better damped by oil.

 

Newtons 3rd law states that every action has an equal and opposite reaction. To put this in terms of the cartridge/stylus, as the groove imparts force on the stylus to move it the stylus also pushes back on the groove with equal force. these forces must be dealt with or they will smear the sound. I'll start another thread that covers TT motor and platter reaction so I'll just touch on it here, it's important as the amount of energy going back into the tonearm will be the vector sum of the vibration directly from the cartridge and reflections from the LP.

 

Vibrations  travel in a structure very similar to waves in a pond when the vibrations encounter an object in this case a joint the amount of energy reflected will be proportional to the acoustic impedance of the material that make up the joint. So if the arm wand is aluminium and the headshell is aluminium the reflection of energy will be far less that if the HS is carbon fiber and arm is aluminium, there will still be some reflection due to the less than perfect mating between the aluminium parts but far less reflected energy than CF to ally.

 

So adding an O ring to the outside of a tube will not result in reflection in the tube. The O rings provide some constraining of the tube and as physics has it my O rings ended up 1/3 and 2/3's from the pivot as measured from pivot to the end of the headshell NOT the end end of the tube.

 

I hope this clarifies it a bit better.

  • Thanks 1
Link to post
Share on other sites

When I sent my Linn Ittok LVII to Audio Origami for rewiring and a service he highly recommended filling the arm tube with foam to damp vibrations. I can't say how much difference the foam made but the whole package was certainly worthwhile.

  • Like 1
Link to post
Share on other sites

This exercise has taught a number of key things.

 

1. Reducing vibrations reflected back to the cartridge has a significant impact on sound quality. Damping plays a role here. Damping vibrations in the arm tube is bidirectional so vibrational energy is reduced in each direction.

 

2. Stiffness can not be under played. The last mod I did was to machine the 32mm arm post sleeve. This was done only to make changing arm height easier for platter testing. I didn't expect to hear a difference, but I was wrong. Spacial information improved as did micro detail. The only conclusion that can be drawn is the additional rigidity provided by the 32mm post reduces micro movement in the arm holding the cartridge more stable.

 

I guess the lessons here is that almost any tonearm can be improved by additional stiffness and some well placed damping. There is no reason these mods can't be adapted to any tonearm.

  • Like 1
Link to post
Share on other sites

On 17/05/2021 at 8:33 AM, Warren Jones said:

I guess the lessons here is that almost any tonearm can be improved by additional stiffness and some well placed damping.

I remember when people laughed at Linn when they suggested doing up the cartridge screws tight enough to damage the arm gimbals ("dismount the arm before tightening") and then put 3 screws on the Troika.

Link to post
Share on other sites
  • Recently Browsing   0 members

    No registered users viewing this page.



×
×
  • Create New...