The Korf Blog

The inside story: our research,
development and opinions

10 July 2019
Putting a Cap on a Denon DL-103
The subject of headshells turned out to be so engrossing that I didn't want to interrupt the series by other things, however interesting they might be. Now that the measurements are over, we can breathe a sigh of relief and busy ourselves with something unrelated.

A few months ago I got an email from Steve Bedard. Steve came up with an interesting and well-reviewed way of improving Denon DL-103's performance. It's an aluminium cap that slides over the cartridge. The cartridge doesn't need to be modified in any way, and the installation is completely reversible. Steve's website offers a lot more detail:

Steve asked me whether I would be interested to do a vibrometry comparison between the regular and "capped" DL-103. Of course, I immediately agreed, and Steve sent me "the Cap".

The Aluminium Body Cap comes in a nice little box, complete with 2 long non-magnetic #3-48 screws and an instruction leaflet. Just like Steve's website, the leaflet is beautifully designed and illustrates the mounting process well.

The only thing that caused confusion was a recommended VTF adjustment of -3.5 grams. After scratching my head a bit I set it to DL-103's recommended 2.5 grams. Then it dawned on me: the "Cap" weighs 3.5 gram, so Steve probably had in mind the fact that I need to decrease the downforce by 3.5 grams! I can imagine someone setting 3.5 g VTF by mistake.
I thought that the measured differences, if any, would be fairly insignificant, and I would need something flexible enough to highlight them. For that reason I have decided to use a Jelco SA-750DB tonearm and the HS-25 headshell that came with it.

Mounting the cap+cartridge combination was as easy (or as difficult) as mounting the DL-103 itself. The fit is tight but not too tight, and the supplied screws should be fine for all but the thickest headshells.

Once mounted, the VTA adjustment is needed as the cap makes the cartridge 1.3mm taller. The stylus guard that comes with the Denon doesn't fit over the cap, calling for a bit of extra care.

To see if there's any measurable difference between the standard Denon DL-103 and the one equipped with a "Cap", I've used the same methodology as for the typical tonearm resonance measurements. The accelerometer was attached to the top front of the headshell, and the vertically modulated 0 to 20 kHz sweep recording was played. The output from the accelerometer was conditioned, amplified and converted to g.
I needn't have worried about the differences being too small to measure. They turned out to be absolutely huge.

The DL-103 is known for generating a lot of excess mechanical energy that goes straight into the headshell. There's this big 7 kHz peak, dominating over the main armtube resonance at about 300 Hz, its harmonics, counterweight resonances etc. This is also approximately where the DL-103 has its 2-3 dB frequency response notch when measured with pink noise rather than a sine sweep.

Putting an aluminium cap over the plastic DL-103 body resulted in the resonant peak shifting down to about 3800 Hz, becoming slightly smaller but increasing in Q. Other effects included a smoother overall resonant picture, and lower counterweight resonances (although I suspect the reason for the latter is the change in counterweight position).
I've put the resonances at and above the accelerometer's own resonant frequency of 11 kHz on a separate chart with a linear, rather than logarithmic, X axis. By its nature, such measurements are very approximate as said resonance masks just about everything.

Still, we can see that the magnitude of accelerometer's own resonance is a lot lower with a "Cap". It seems that the increase in rigidity has more than halved the high frequency energy transmitted into the headshell.
Subjective Evaluation
Sometimes, you can guess the subjective effect just by comparing the vibrometry charts. The rule of thumb seems to be the higher the main resonance frequency is, the better. This clearly isn't such a straightforward case: while the main resonance shifted lower, the change in whole picture suggests that a lot more is going on.
Just like with the measurements, the audible improvements weren't subtle
For critical listening sessions, I switched back and forth a few times between the factory DL-103 and the one encased in the "Cap" (I have 2 DL-103s with close serial numbers that sound very similar).

Just like with the measurements, the improvements weren't subtle. I was especially impressed by the change in the stereo scene. It became slightly wider and gained substantial depth. Subjectively, linearity improved. Sibilance, which is a known problem with a DL-103/Jelco combo, became a lot more manageable — the 4 kHz peak seems to excite the bearing resonances a lot less than the 6 kHz peak. I noticed no negative effects of "capping" a Denon.

To sum everything up, Steve Bedard's Aluminium Body Cap significantly changes the measured vibration profile of a DL-103. In my opinion, its use noticeably improves the subjective performance of the cartridge.
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