The Korf Blog

The inside story: our research, development and opinions

23 February 2018
Closer to State of the Art
We have examined quite a few tonearms last year. Most were our own prototypes, but we took a break to measure a Rega RB300, and also have data for SAEC WE-308L. However, we haven't presented the measurements of a super-arm — until now.
Mørch DP-6 is one of those rare arms with correct geometry
The basic design of Mørch arms goes back to 1970s. UP-4 was a very light unipivot, designed to match then-fashionable ultra high compliance cartridges. Replaceable wands allowed exact mass matching without compromising rigidity.

As the high compliance/low tracking force fashion faded, Mørch responded with "double-pivot" DP-6 and so-called "precision" armtubes that feature an integral headshell. You can read about its ingenious bearing system, combining best features of the unipivot and knife edge, at their website.

Right from UP-4, Mr Mørch has correctly identified geometry as an overlooked obstacle to reproduction quality. High compliance cartridges were especially prone to "scrubbing" (anyone remembers the "Grado wobble?"), and putting the stylus and the pivot on the same plane eliminated its vertical component.
Stylus drag force is on the same plane with pivot
Almost 30 years later, Mørch DP-6 remains one of those rare arms with correct geometry. Not only is the stylus co-planar with pivots. Antiskating is applied on the same plane too. The counterweight stub is placed a bit lower to put the arm's center of mass exactly at the pivot, and the counterweights themselves are eccentric to allow for a (crude) adjustment of a lateral balance.

And this brings us to the downsides. It's not the most user-friendly tonearm on the market. While most boutique manufacturers have given up and use the Jelco arm-lift, Mørch uses their own that doesn't really work. Spring antiskating isn't marked at all, is infuriating to set up and isn't repeatable. Azimuth adjustment moves the stylus in 2 planes at once. Counterweight stub is marked with some red dots, but the resulting precision is about half a gram. Realistically, a test LP and a precision scale are needed to set it up — and not everyone has both and is willing to spend the time.

However, the UI problems do not reflect on the sonics. DP-6 is up there with the best tonearms available now for more or less reasonable money.

Let's see where Mørch stands with regard to measurements. First chart puts it against a Rega RB 300 and SAEC WE-308L.
The main resonant mode is at unusual 88 Hz and 0.8g. Please note I have changed the scale of the chart to make it visible. Fourth harmonic dominates at about 370 Hz and 0.13g. And then — smooth sailing.

There's a tiny counterweight stub spike, and the bearings ring exactly the same as SAEC's (which is quite good). But the most surprising thing is virtual absence of headshell resonance. Even past the accelerometer's own resonant frequency there's nothing. The arm wand vibrates as if it was one continuous piece.

This explains the low main resonance — having no mechanical "border" between the tube and headshell increases the effective length of the wand. It's a remarkable achievement. This might be responsible for unusual smoothness Mørch exhibits even with fairly harsh-sounding moving coil cartridges. The contrast with Rega's shouty headshell is obvious.
As we've seen many times, counterweight design matters a lot. But what about the number of counterweights? Mørch DP-6 manual states clearly: "It is an advantage to use as large or as many counterweights as possible." Is the difference between one and many measurable?
"Moerch 1" is with 3 counterweights, "Moerch 2" with one. The differences are within the error range.
What can we learn from these measurements?
1
Mørch's "vibration barrier free" arm wand design is ingenious and is probably responsible for much of its sonic signature. I wonder why no-one copied it.
2
Silicone-dampened "dual point" bearings work as well as preloaded knife-edge. It looks like almost any configuration is better than ball bearings.
3
The number and position of counterweights doesn't matter much.

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