Hi, There has to be a wiring problem as they work fine. I attached a jpg file that shows how to get various load values. Note that they are different depending on what step up ratio you choose. Now back to the question ...the transformer impedances on the input vs output side are governed by the square of the number of turns. If you ignore the losses (minimal often) in the case for these SUTs a 1 to 8 ratio will give an impedance ratio of 64. Thus if the input desired is 300 ohms the output will be about 19.2K. So you will need to add resistors to the input stage to get that. Since it is already 47K you will need to put a 32K resistor in parallel with it. This can be right at the SUT. No resistor additional there will give an input impedance of about 700 ohms. When you use the 16 to one ratio you can not get an input value over about 180 ohms (47000 divided by 256).
Now to help all folks that use LOMC with phono preamps. The SUTs are
really really sensitive to picking up hum. I normally put them in their own steel box (about 10cm on a side) and attach them with RCA cables and jacks. Inside a chassis it can drive you nuts trying to get the hum low. Grounding is key as is the physical location and orientation of the power transformer as well as anything else that can transfer hum or noise. A large chassis, maximum spacing and serious attention to grounding (both paths and sizes) matters hugely. You all have been warned.
BTW. While the LL1678 and 9226 are quite nice and do the job quite well (especially for the price) my personal choices are the PLT-1 from Softone Audio and the SAC 220A from Silk Audio. Both are slightly more costly, but in the world of SUTs not greatly so. Chocolate vs vanilla again
Good listening
Bruce
Attachment:
LL1678a.jpg
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