Moerch DP8 mini review

[Thomas_A]

This is a mini review of the Mørch DP-8 tone arm with some measurements. There are not many reviews of such around, but given the unusual design of this tone arm, I am going to make a try. I went from a Linn Akito tone arm to a Mørch UP-4 unipivot tone arm a few years ago, mostly because the bearings of the Linn were going bad. I bought a used one quite cheap and since the installation is quite easy (only differs 1 mm from the Linn tone arm mount), I went for it. I have been interested in the DP-8 as well, but given its price I thought this would never be in my possession. However, a used one came up (barely used at all) I did a purchase.

The design is unusual in that it carries high mass and inertia in the horizontal plane and the bearing is also very damped. It also feels when moving it, very different from the UP-4 arm. The side weights also contribute to the tracking weight since they weights are asymmetrical. I used the 4 g tone arm wand for these tests.



First up is the test of resonance and I used the Denon low frequency sweep for this (4-100 Hz) which is left and right including crosstalk with the Shure brush in up position. As can be seen there is a fundamental resonance around 9 Hz, but also a tonearm resonance at 60 Hz.

Comparing the same sweep using the UP-4 arm the tone arm resonance is not there. So somehow the more heavy DP-8 makes the tone arm resonance show up.

Using the Shure damping brush, the vertical resonance should be damped while the horizontal should be affected only a little, which I also see below. There is a slow decrease of the response from 30 Hz (note: my phono preamp contribute to about -1 dB fall off at 10 Hz), and the fundamental resonance seems to be around 14 Hz. Still there is a tonearm resonance at around 60 Hz.

The resonance is not really showing in the frequency plot script, and probably it is averaged out. There is however another resonance between 300-400 Hz, barely noticeable in the main signal (se also cross-talk signal).

So what does this high inertia do to the response? It should stabilise the response in hoisontal direction where most of the bass is (below 100 Hz). The beats in the song "Billie Jean" in Michael Jacksons album "Thriller" shows one of the benefits.

First with the UP-4 arm:

And the DP-8:

There is significantly less of resonance excited by the beats.

Another potential benefit of the more stable arm is better speed stability. During resonance the cartridge can "scrub" and cause flutter around the fundamental resonance. This is clearly shown in the UP-4 arm, having small peaks around 8-15 Hz.

These peaks vary in level during measurements and can be higher than what is shown in the figure. With the DP-8, I can see only small peaks around the resonance and they are very stable. (Note that the speed is a bit off, the trim pots of the Axis player needs to be readjusted. That is irrelevant for the test.)

Lastly a short note of the subjective sonics. I could upload comparable songs as well, but choose not to in this review. Overall it sound a bit more "quiet" between tracks and also more dynamic, especially the bass region. Stability of certain notes is also evident, together with more detail. On the negative side, there are tonearm resonances there which however, are probably less audible.

Overall, I would recommend this arm if you are into vinyl playing. Yes it is expensive, but so can other "good gear" also be in the HiFi world. I am a bit surprised though that the arm could contribute to the quality as much as it really did. There should be more tone arms designed this way. It really does something.

 

[Balle Clorin]

Very good work, @Thomas_A
For you to compare..arms And what W&F track did you use?

 

[Thomas_A]

Thanks Balle,

not shure why you see a difference between the SME V/Gyro graphs. Same for L and R? I would be interested to see the response with Q-damping with and without brush as well. And if you can see a difference in scrubbing FM modulation (both damping and inertia would affect that).

Been thinking of the 60 Hz resonance of the DP-8 a bit more. I think it is something to do with the dual pivot + ball bearings + counterweights that introduce the resonance. If it would be arm tube resonance, I would see it with the UP-4. The uni-pivot bearing has an advantage that it has less parts that could introduce a resonance. That said, I can't really hear anything from the resonance of the DP-8, yet. (I don't think it is 60 Hz mains hum from the record, in that case it should show up also in the UP-4 arm, and you do not see it in your measurements as well.) I will dig into it a bit more and see if the balancing of the side weights and/or counterweights might affect this.

 

[Hiten]

Congratulation ! Nice tonearm.

60hz resonance.
A minor tightening of screws on side weights perhaps ?
Also i see they have different weight of wands for different models. A little heavier wand would perhaps help ?
Or
Some proper weight, tube/half cut sleeve (or something like that) on wand just for experiment to see if resonance shifts ?

 

[Thomas_A]

Thanks,

what I need to redo is to set the centre of gravity, which means I need to turn the side weights a bit, something I did not make correct. The tonearm moved too quickly to 0 when balanced out; ideally it should move very slowly to 0 point when balanced out. I am hesitant if this plays any part of the resonance seen, but I will nevertheless remeasure and update the review if needed.

 

[Balle Clorin]

Could the UP-8 60hz be a antiskate effect?, it only shows up in the crosstalk channel…
I had a clear resonance in my Denon 51F before ( bump in the main channel and peak in the crosstalk channel) . It went away after servicing the arm ( repair man said he adjusted some bearing screw )


Effect of Q damping, no brush

Brush or not on some records

FINALE!! Brush effect vs damping

Sorry no data with damping +brush

 

[Thomas_A]

Could the UP-8 60hz be a antiskate effect?, it only shows up in the crosstalk channel…

No, I don't think so. Same frequency in both channels but a bit different level. I will see if balancing the centre of gravity affects something.

 

[Thomas_A]

Did an adjustment of the centre of gravity. This affects mostly tracking, and not so much resonances. And I got the same result with a 60 Hz resonance.

Have spent quite much time listening to music and I am quite impressed of what I hear. We usually measure static signals. Dynamic handling is probably another area to measure. This arm gives something in speed stability, detail and dynamics that I've not heard before. The reason I think is due to less scrubbing of the stylus. It follows the groove and remains stable during bass beats, resulting in less stylus movement due to record imperfections and more headroom for music signal. One example is the "Billie Jean" track, but I think this is a general issue for conventional tone arms.

 

[his047]

I am confused about the graphs: the graphs for the DP8 reference 'left' and 'right' channels while the graphs for the UP4 reference lateral right and lateral left.

Of course you are right about the bass which is always cut laterally. The point of the DP8 design is that the arm has different effective mass in the horizontal and the vertical plane. If you measure left and right channels you are measuring lateral +45° and lateral -45°. Such a measure does not show the (audio) strength of the arm: that the bass (which is always and only cut laterally) does not have a resonance peak in the audible part of the signal and is therefore phase coherent.

I am not sure I understand what you mean by 'scrubbing'. Could you explain?

The 60 Hz resonance is a mystery to me. It does not show on my own DP8/Blue dot/SPU Royal when measured with the Dr Feickert Adjust+.

But overall I agree with you that the DP8 is something special.

 

[Thomas_A]

I am confused about the graphs: the graphs for the DP8 reference 'left' and 'right' channels while the graphs for the UP4 reference lateral right and lateral left.

Of course you are right about the bass which is always cut laterally. The point of the DP8 design is that the arm has different effective mass in the horizontal and the vertical plane. If you measure left and right channels you are measuring lateral +45° and lateral -45°. Such a measure does not show the (audio) strength of the arm: that the bass (which is always and only cut laterally) does not have a resonance peak in the audible part of the signal and is therefore phase coherent.

I am not sure I understand what you mean by 'scrubbing'. Could you explain?

The 60 Hz resonance is a mystery to me. It does not show on my own DP8/Blue dot/SPU Royal when measured with the Dr Feickert Adjust+.

But overall I agree with you that the DP8 is something special.

Yes, this lateral is confusing, sorry for that. I made the UP-4 recording at another time point and named the files differently. It is the same track from the Denon record, which is left and right low frequency sweep. I don't know the Adjust+ tracks, are they left and right separately or mono? Since I use the same arm wand as with the UP-4, the difference of the 60 Hz signal must be the tonearm body.

The third graph when the Shure damping brush is activated (damps vertically mainly) clearly shows that the DP-8 arm is damped with high inertia in the horizontal plane. Which is why this arm is a bit special.

Scrubbing occurs when the stylus moves due to record imperfections and cause FM/speed instability. This shows up as peaks around the resonance frequency when testing for speed stability. The DP-8 has clearly lower and less variable peaks of scrubbing than the UP-4 arm, shown on the speed stability test. Scrubbing can also occur for dynamic bass signals, as shown in the Billie Jean track, where the resonance is excited by the bass beat. The stylus just bends and cause flutter. Since the speed stability is using a static 3150 Hz signal, the impact of dynamic signals i probably much greater (again Billie Jean), causing quite nasty speed instability where the ear is quite sensitive.

The stylus bending around resonance also steal dynamic headroom/increase distortion.

Don't listen to records on FM!

I don’t mean FM radio, I mean FM as in Frequency Modulation Distortion (FMD, or pitch instability). FM occurs as a result of the stylus tip scrubbing along the groove during tonearm mass/compliance resonance or transient events. The amount of scrubbing depends on the amplitude of the resonance...

www.diyaudio.com

 

[his047]

Yes, this lateral is confusing, sorry for that. I made the UP-4 recording at another time point and named the files differently. It is the same track from the Denon record, which is left and right low frequency sweep. I don't know the Adjust+ tracks, are they left and right separately or mono? Since I use the same arm wand as with the UP-4, the difference of the 60 Hz signal must be the tonearm body.

The third graph when the Shure damping brush is activated (damps vertically mainly) clearly shows that the DP-8 arm is damped with high inertia in the horizontal plane. Which is why this arm is a bit special.

Scrubbing occurs when the stylus moves due to record imperfections and cause FM/speed instability. This shows up as peaks around the resonance frequency when testing for speed stability. The DP-8 has clearly lower and less variable peaks of scrubbing than the UP-4 arm, shown on the speed stability test. Scrubbing can also occur for dynamic bass signals, as shown in the Billie Jean track, where the resonance is excited by the bass beat. The stylus just bends and cause flutter. Since the speed stability is using a static 3150 Hz signal, the impact of dynamic signals i probably much greater (again Billie Jean), causing quite nasty speed instability where the ear is quite sensitive.

The stylus bending around resonance also steal dynamic headroom/increase distortion.

Don't listen to records on FM!

I don’t mean FM radio, I mean FM as in Frequency Modulation Distortion (FMD, or pitch instability). FM occurs as a result of the stylus tip scrubbing along the groove during tonearm mass/compliance resonance or transient events. The amount of scrubbing depends on the amplitude of the resonance...

www.diyaudio.com

So if I understand you correctly, the Denon Record contains Lateral +45° and Lateral -45° f-res sweeps. The Feickert Adjust+ has Lateral and Vertical (+/- 0°) f-res sweeps.

For my combination (DP8-blue dot-Ortofon SPU Royal N) they look like this (Vertical to the left, Lateral to the right. The Vertical frequencies <5 Hz are [accidental] needle-drop):

This is a sweep for tonearm resonances in the audio band which does not show your 60 Hz resonance:

 

[Thomas_A]

The Denon contains pure left and right signals (i.e. +/-45°), so these will excite both horizontal and vertical resonances at the same time (that also will show up in the crosstalk channel). I've updated the plot legends not to cause confusion. If one looks at the fundamental resonance at 9 Hz, the crosstalk signal is out of phase with the main signal at resonance. This means that the main resonance is in the vertical direction (which is what is expected when using the arm undamped in this direction, in my case Shure V15V/JICO with brush up):

Doing the same for the 60 Hz signal gives neither in or out of phase, meaning that the resonance occurs both vertical and horizontal.

That the signal is not seen in mono or in the main signal (or it is actually seen as a small glitch in the frequency response) is because it is 15/20 dB lower in signal than the main signal. While I don't like to see these resonances, they are probably low enough not to be audible during music play. If you want to see these resonances you need higher resolution. Alternatively, looking at a blank groove between music grooves so see if resonances show up in quiet passage.

The simple unipivot design of the UP-4 seems however better with respect to resonances, since it contains fewer parts that can resonate. The DP-8 on the other hand is more complex and may contain parts that resonate. The main point is to keep these at low enough level not to be an audible problem. Of course these resonances also can vary individually between arms of the same make and type, since parts can vary in tolerances. Also, the arm wand and cartridge you use is different from mine, which can cause shifts in resonance frequency and level. I can't say - would then need another measurement with the Denon test record.

 

[Thomas_A]

Very good work, @Thomas_A
For you to compare..arms And what W&F track did you use?
View attachment 382924

Sorry. Used my copy of Tacet. But any good one can be used. Hungaraton? A copy of this is on the way to me as well.

 

[Thomas_A]

One possible cause could be resonance in the top plate. I did not tighten the Axis suspension screws as much this time and will see if this might change things. It is far fetched cause but anyway should be checked.

 

[Thomas_A]

Change of antiskate: no change
Tightening collar to arm screw: no change
Tightening turntable suspension screws: no change

The only thing "adjustable" left is to remount and/or tighten the collar against the top plate, but then I need to remount the whole arm. But again, it is very tightly fastened already.

 

[his047]

Speaking about the UP4, Mørch told me that the first prototype had a resonance (he did not specify at which frequency). This was cured by loosening the counterweights. Is it possible that you have over-tightened the lateral weights?

According to Mørch, everything should be 'finger-tight' rather than tightened to maximum torque.

 

[Thomas_A]

Speaking about the UP4, Mørch told me that the first prototype had a resonance (he did not specify at which frequency). This was cured by loosening the counterweights. Is it possible that you have over-tightened the lateral weights?

According to Mørch, everything should be 'finger-tight' rather than tightened to maximum torque.

Regarding the lateral weights, I have just tighten them enough to be snug on the side bars. Regarding the counterweight, I have only the lightest asymmetrical one and not the tracking force weight loaded. It is enough to set the tracking force to 1.4 g. With the UP-4 I had the heaviest weight (underslung, as this is needed for the UP4 unipivot) close to the pivot + the tracking force weight to get correct balance. So that is another difference. That said, the UP-4 is quite sensitive when setting the arm in the arm rest; it makes a sound in the speakers. Not so much with the DP-8 actually. So the arms differ. I still do not know if the arm collar to the top plate needs better tightness. That is the only thing I have not tried + se if balancing the lateral weights differently and use a heavier counterweight.

The UP-4 is completely "clean" up to 100 Hz.

vs DP-8, where you can see there is a visible inconsistency in the frequency response and a peak in the crosstalk signal.

I did a measurement of the 7.5 g armtube as well, and if my memory is correct the resonance was closer to 70 Hz than 60 Hz. I don't think I have the measurement left though. From Korf the DP-6 seems to have the first resonance at 88 Hz.

Closer to State of the Art

korfaudio.com

 

[Thomas_A]

I wonder if damping oil of the pivots would make any difference to the resonance? Moerch does not recommend it, and I do understand that it will flatten the main resonance out (lower Q) which has a certain disadvantage. But it could also help damping the 60 Hz resonance. (UP-4 has and needs damping at the pivot I do not have the instructions for doing that with the DP-8 however. @his047 do you have such an instruction?)

Edit: I see now how one can add damping fluid for the vertical direction.

 

[his047]

@Thomas_A: the horizontal bearing is a clipped ball bearing pre-soaked in silicone oil, so there is nothing to change there. I do not think that damping the vertical axis is going to make any difference, though.

Having owned an LP12 from 1978-1982, I have a particular bee in my bonnet about the poor quality of Linn's products. So I think that may be related to the 60 Hz resonance. Is it possible that the resonance might be related to the routing of the tonearm cable?

 

[Thomas_A]

@Thomas_A: the horizontal bearing is a clipped ball bearing pre-soaked in silicone oil, so there is nothing to change there. I do not think that damping the vertical axis is going to make any difference, though.

Having owned an LP12 from 1978-1982, I have a particular bee in my bonnet about the poor quality of Linn's products. So I think that may be related to the 60 Hz resonance. Is it possible that the resonance might be related to the routing of the tonearm cable?

Linn Axis is a bit different from the LP12 at the time they co-existed, and it shows excellent data. It has been in my service since 1990, and it was just until recently I changed the pulley and added the heavier LP12 platter.

https://www.audiosciencereview.com/...vinyl-measurements.20278/page-39#post-1721704

Tonearm cable routed ok, so I really can't blame the Axis or setup issues for the resonance; UP-4 with 500 000 cst oil worked perfect for stability and no resonances (but undamped it was a disaster). I do however think damping will give a difference, but whether the 60 Hz component is affected is unclear. I will test this tomorrow.