Not happy with Jelco 750L / SPU combination

[f1eng]

It is more or less a technical problem only, sound wise it sounds good. But I do get more cracks in my records since I use the SPU that's why I checked everything again last afternoon.

But now i have your attention, how do you cope with the load of the SPU? My Synergy needs a load resistance between 20 - 50 ohm. My tube phono pre (MM) does have an input impedance of 47k and I use a SUT of 1:20, I have soldered a 22k resistor in parallel with the 47k input resistor, now i have a load of 37.5 ohm. If I omit the 22k the high frequencies ar making me nervous.

Ronald.

More cracks on the record could simply be the elliptical stylus on the synergy reads the groove (including the damage) better than the conical...
OTOH a 20:1 SUT is a mismatch to a SPU so it will not be performing to specification. I am not sure what the effect of the load resistor may be, but I would bet the differences you hear between 103 and SPU are due to one matching the SUT and the other not, there will be a big difference in HF, as it seems you have found.

My advice is to do it all by ear. I would say any differences you dislike between SPU and 103 are 50x more likely to be due to loading mismatch with the SUT than the arm.

[kor952]

More cracks on the record could simply be the elliptical stylus on the synergy reads the groove (including the damage) better than the conical...
OTOH a 20:1 SUT is a mismatch to a SPU so it will not be performing to specification. I am not sure what the effect of the load resistor may be, but I would bet the differences you hear between 103 and SPU are due to one matching the SUT and the other not, there will be a big difference in HF, as it seems you have found.

My advice is to do it all by ear. I would say any differences you dislike between SPU and 103 are 50x more likely to be due to loading mismatch with the SUT than the arm.

Frank, thank you for your explanation why I should not use a grooveless record for AS adjustments.
I mentioned the cracks (and also some real nasty plops and ticks and on one record even a jump to the next groove) because I am sure they are new and I fear that the first 'faulty' SPU Synergy I had is the cause of them.
About the SUT, I think a 1:30 SUT is advised for SPUs in general but the Synergy has a rather high output of 0.5 mV compared to the others. A 1:10 would do but than the load resistance will be 470 ohm wich is to high, that is why I strapped my SUT to 1:20 (can't go higher) but than the load resistance is still to high (117 ohm). To get the right load resistance I soldered the 22k in parallel with the 47k and I like the sound this way (the right load resistance removes a edgy sound) . As long as the load resistance on the secondairy side of my SUT is above 10k the SUT is doing fine (according to the Lundahl technical data).
The sound of the Synergy is fine and I prefer it a bit above the sound of the 103R but I still have my doubts about the tracking capabilities of SPUs.

Ronald.