Part 6 – More Testing

It has been a while since my last blog entry. I got fixated on DL103R, and for a reason – it is an excellent yet hard to control cartridge. I became obsessed with modifying the tonearm to eliminate or at least reduce resonance at approximately 12kHz.

Let me spoil it for you – I had to give up. Perhaps this cartridge is simply impossible to control? Perhaps its obsolete design explains the reasonable price? Surely, elastomers available on the market 60 years ago were different from those used in modern cartridges.

I made some modifications and ran several tests. The graphs below show some improvement in sound quality despite looking quite alike.

I used the 800Hz – 20kHz Ortofon signal for my testing. The green line and the blue line respectively represent vibration and sound frequency (up to 20kHz).

Modification 1

I added one clear Teflon washer to the arm base. The modified arm performed marginally better than the original.

Modification 2

This was a barely visible yet significant structural modification. I introduced oil damping which meant rebuilding the arm base and the cueing lever. It had little damping effect but (IMO) improved sound quality.

Modification 3

I applied a thick damping mat near the cartridge, down the middle, and then by the base of Benny’s carbon fibre arm. None of these modifications had any effect, hence no graphs.

This made me wonder what vibration occurs in the middle and at the end of the tonearm, near the base. Perhaps there is nothing to be damped?

Both graphs above show resonance at the same frequency points. This is good news as it means that vibration stays in the headshell.

How does the arm perform with a sensor fitted to the base?

Stillness. Nil vibration.

Is something wrong with the arm base? I replaced INOX with PA6 aluminium and rebuilt the whole thing. What now?

Disaster! This looks a bit like DL103R on unmodified arm but without resonance at 8kHz. The vibration amplitude is much higher, similar to that generated by Pro-Ject turntable with 2M Red cartridge.

Let’s check AT33PTG2 cartridge on this arm:

It appears that even a well damped cartridge such as AT33PTG2 can get a bit unsettled on some tonearm types. That’s good to know.

So, what about AT33PTG2 on arm with INOX base and damping oil?

This looks quite good.

Clearly, higher range cartridge models should not underperform with the BA12 tonearm – which bodes well for sound quality.

What did we learn from this series of testing?

  • PTFE damping of tonearm base is effective to a limited degree.
  • Damping effect of oil is also minimal.
  • Tonearm base should be made of austenitic steel (widely used AISI304 is fine).
  • Vibration is transmitted between the cartridge and the arm tube. It means that mechanical waves move from the cartridge onto the headshell and along the arm, which is good.

It is also worth mentioning that the intuitively built Immersion tonearm is not that different from its modified version. Turns out it is actually quite good.

My current plans for further research include oil damping tests on more advanced cartridges and trying out an Aluminium 7075 headshell mount.

Keep your eyes peeled for the next blog entry.