Part 3 – Stiff Benny

Good stiffness (or rigidity) is considered a prime feature in turntable and tonearm design. 

From the very outset, I decided to follow the above principle with Benny which has led to quite a few challenges.

Due to the increased possibility of resonant vibration within plinth layers, platter bearing or tonearm, extra care should be taken when rigidly connecting turntable parts together.

Apart from stiffness, you should also ensure the best possible transfer of mechanical waves (see Part 2 – Soundquake). This can be achieved through perfect alignment of all joining surfaces. Mess it up and only a part of the wave gets transferred while the remaining part generates vibration.

The use of speaker and amplifier spikes, cones or pads is a well-known method of isolating vibration. All these products are intended to reduce the surface area of the points of contact and enable damping of mechanical waves. The BennyAudio design principle is quite the opposite – transfer maximum energy out of the tonearm.

Tonearm parts:

  • Headshell
  • Locking nut
  • Arm tube
  • Tube and body fixings
  • Counterweight
  • Suspension
  • Base and pivot fixings

Headshell

The cartridge mounting point may vary depending on the stylus position in the headshell. Correct stylus position is more important than the cartridge position. On a turntable with premounted tonearm, the overhang is typically preset at the factory. The mechanism should align itself as long as you correctly set the distance between the pivot axis and the stylus.

Headshell pins, solder and wires coupled with poor rigidity of a traditional locking nut have a detrimental effect on sound quality. The overhang distance in a traditional headshell can be finely adjusted by moving the cartridge a few millimetres back or forward but this will also affect the cartridge azimuth which can be problematic. Turning the cartridge even slightly will change its alignment with the headshell slots, generating unwanted stress force.

This is when the concept BennyAudio headshell comes in.

The above piece is made of 4mm thick carbon fibre sheet. I decided to outsource its production to a manufacturer working with a precise CNC machine. 

The use of a single cartridge mounting point allows for azimuth adjustment and helps to avoid unnecessary stress force. Distance between the pivot axis and the stylus is regulated by the locking nut while maintaining desired rigidity. The cartridge has (IMO) the best possible headshell mounting point. Thick carbon fibre makes for a light and rigid headshell. At the moment, I see no need for improvement there. 

Headshell-tube connector

A very important turntable part that firmly holds headshell and tonearm tube together. 

The connector in Benny does provide sufficient rigidity but there is room for improvement there:

  • Modify the surface area of headshell to connector and connector to tonearm contact points.

I currently use a manufacturer with the best CNC machines on the market who will also be helping me examine the effect of resonance on this turntable part.

Arm Tube

I remain loyal to carbon fibre tubes. The current one is 1mm thick.

I will check:

  • Performance of a thicker wall tube (2mm) and its impact on effective tonearm mass and improved energy transfer along the tube.
  • Spot damping inside the tube (through the full length of the tube).

At some point, I would like to build a tube with variable thickness wall (a bit like SAT). I already know how to do that but will stick with the 2mm tube plan for now.

Body

Turntable body is very important as it connects arm tube with counterweight, ensures solid tonearm suspension, and enables smooth adjustment of the anti-skating mechanism.

A lot can happen there. I will:

  • Change the arm tube fixing screw to a clamp.
  • Test simultaneous damping of suspension and counterweight.
  • Test damping oils of various density.
  • Decide whether to use steel or aluminium.

Tonearm Base

The current Benny tonearm base has RCA sockets and is rigidly attached to the plinth via POM cylinder.

I will look into changing:

  • Method of fixing the pivot needle within the base.
  • Method of fixing the base to the plinth.
  • Design of the entire base.
  • RCA sockets location.

I will also develop VTA system for the tonearm.

Slowly but surely, the blog is approaching the performance testing phase – see the next entry for more details.

Kontakt