Lundahl LL1931 moving coil stepup transformer
Description:
Surfing the web I discovered that Ortofon had designed a new Moving Coil stepup transformer Verto and that the stepup transformers was delivered by Lundahl, which we have had very good experience with from our 6C33 amplifier. It was getting exciting and it got even better when I looked at Lundahls web and discovered that they had made a new Moving Coil stepup transformer: the LL1931. This is from the data sheet description:
"LL1931 is a high performance moving coil step-up transformer. The transformer combines our unique uncut amorphous cobalt core and our dual coil structure with Cardas high purity copper wire in an over sized design. The objective is to provide the best possible MC transformer, cost-no-object. The dual-coil structure greatly improves immunity to external magnetic fields from power supplies, motors etc.. The transformer is housed in a mu-metal can."
So I ordered two LL1931, and build a Moving Coil stepup transformer, and I must say I am very pleased with the finished result. The sound is better compared to my Nelson Pass (x)ono Moving Coil preamplifier, the LL1931 has less hum and I have got rid of very low frequency subsonic sounds.
Update: I would recommend that you perform the balanced to unbalanced modification on the input of the stepup transformer as this for me has removed all hum in 18 dB mode, see below in gallary for what to modify!
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With the new enclosure it was possible to add a switch between the two amplification factors: 18dB and 24dB. I will have to modify my Lenco L75 to support 18dB mode, as the Lenco case ground is connected to left signal ground according to the 5 DIN standard and this is incompatible with the LL1931 input grounding scheme. I think this is okay, and maybe I will get rid of the very small amount of hum I experience when I crank the volume to 100%? I choose not to add a unbalanced/balanced switch as my RIAA amplifier doesn't support this. I have changed the chassis ground connection so it is connected direct to the chassis and not the transformer input, this has removed most of the hum in 18dB configuration.