The Korf Blog

The inside story: our research, development and opinions

7 February 2019
Jelco SA-750DB Measurements
Continuing our tradition of measuring other people's tonearms, today we will have a closer look at a 9" version of a Jelco SA-750D. Although it's been discontinued, a very similar tonearm is still being sold as Jelco TS-550S.

The SA-750 line has been around under different names for a long time, at least since the mid-1980s (for example, Sumiko Premier MMT is the same tonearm). After the world grew tired of Rega RB300, these Jelcos became the "default" OEM tonearm on a lot of turntables, from mundane to exotic.

Technically, Jelco took JVC's "put all bearings in one plane" idea as implemented in UA-7045 and added a small viscous bath for damping in both axis at once. Antiskating is with a dial and a spring. Counterweight is loosely screwed onto the stub and has a dial for rough downforce setting. Newer TS-550S has a slightly different, and probably better, counterweight arrangement.
Unlike most tonearm manufacturers, Jelco specifies the bearing quality in the form of "sensitivity"
Unlike most tonearm manufacturers, Jelco specifies the bearing quality in the form of "sensitivity" — the force needed to deflect the arm in horizontal and vertical plane. 40 milligrams sound impressive, but this is measured at the stylus. Adjusted for the effective distance, this translates to 0.00008 N/meter (80 microNewton/meter). It's fairly typical starting torque for standard small ball bearings. To give an idea of what precision bearings are capable of, Technics EPA-100 was specified at 5mg (10 microNewton/meter starting torque).

Please note that "sensitivity"/bearing starting torque is not the same thing as flexure bearing's stiffness. Flexure bearing's starting torque is exactly zero.
Our black SA-750D came with a beautiful HS-25 magnesium headshell, to which we have attached the usual Endevco Picomin 22 accelerometer. To make the measurements consistent, we used the same Audio Technica AT7V medium compliance moving magnet cartridge.

Let's see how our little Jelco compares. First, let's match it with a similar-looking 1970s tonearm — the SAEC WE-308L.
Easy to see that both are more or less in the same league. SAEC's main resonance is a lot higher due to its longer and thinner armtube, but I think the shorter 308 would've measured almost the same as 9" Jelco. The ancillaries give similar peaks. And Jelco's ball bearings are quite good — almost as quiet as SAEC's preloaded knife edge. Despite unimpressive starting torque, those are precision bearings after all!
Then, let's compare Jelco SA-750D to the tonearm it displaced as default OEM choice, the Rega RB300:
And here, except for the bearings, Jelco feels quite a bit worse. But as one looks closer, the high frequency divergence between the lines point us to very different quality of Rega and Jelco's headshells. Latter is a lot better. You can see how Rega's more advanced design is let down by inferior bearings and that thin flat headshell.

Out of the two, I would probably still choose an RB300 for high-energy cartridges, but I understand why so many people switched to Jelco.
Finally, let's do the comparison with an arm that costs quite a bit more — Mørch DP-6:
Here, Jelco is outclassed everywhere except the amplitude of main resonance. Mørch's counterweight arrangement is better. Mørch's bearings are better. Even Mørch's headshell is better. It's easy to understand why DP-6 sounds more transparent and natural compared to Jelco, even with low energy cartridges. With stiffer moving coil cartridges, these small differences will be amplified many times over.
We also tried to measure the impact of fluid damping on the overall vibration picture. No discernible differences were found. The effects of viscous damping are probably limited to very low frequencies resonances only.

Jelco SA-750D's popularity speaks for itself, and appears to be well-deserved
Jelco SA-750D's popularity speaks for itself, and appears to be well-deserved. Its relative lack of overall rigidity is compensated by quality bearings and a good headshell. It's also well-built and a pleasure to hold, install and use.

I am not a magazine reviewer, and thus I usually refrain from judging other companies's current products. But I must admit that I never warmed up to Jelco's sound, like I did to SAEC WE-308L's or JVC UA-7045's. The colourations it impaired and the dynamics it took away, made my daily listening session rather boring. I understand why Jelco have completely redesigned their new series.
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