LABORATORY TEST REPORT
Newport Test Labs measured the frequency response of the Lundahl Moving-Coil Step-Up transformer using the 24dB gain setting and found it extended from 9Hz to 110kHz –1dB, exceeding Lundahl’s own specification. Part of this extended response is shown in Graph 1, where you can see the response is just 2.5dB down at 5Hz and 0.2dB down at 20kHz. From 50Hz up to 20kHz it’s absolutely ruler-flat along the 0dB reference grid before it starts to roll-off slowly at 35kHz to be 0.1dB down at 40kHz, which is the extent of the graphing limit. Separation between the two channels was measured as being 84dB, which was maintained across the audio spectrum.
THD+N is shown in Graph 2, for a 1kHz test signal. You can see there’s a second harmonic distortion component at –90dB (0.0031% THD) and that’s about it.
It appears there is a 6th-order component, but it’s down at –95dB (0.0017% THD), which means it’s essentially buried in the noise floor at –100dB. There is some low-frequency noise, as you can see from the left end of the graph, which is mostly induced hum, since the transformer was being tested in a laboratory environment, which is electrically very noisy, but even in this noisy environment, overall signal-to-noise was measured as 72dB A-weighted, almost all of which was low-frequency. Above 200Hz, noise was more than 80dB down and above 1kHz, essentially 100dB down.
Intermodulation distortion (CCIF IMD) was almost non-existent, as you can see from Graph 3, as measured by Newport Test Labs. The two test signals at 19kHz and 20kHz dominate the graph, of course, but there’s only a single high-frequency sideband, at 18kHz, that’s 91dB down (0.0028%).
There is a regenerated signal at 1kHz, but it’s around 90dB down (0.0031%). Newport Test Labs measured the gain of the LL1931 transformers as 17.76dB in the 18dB gain setting, and at 23.36dB in the 24dB gain setting, with both channels being identical, which is significant sign of transformer quality. Winding transformers to this level of gain accuracy is a stunning achievement. The difference in level between Lundahl’s stated gain and Newport Test Labs’ measurements, on the other hand, are not at all significant because they would be due to the lab using a different input and output loads to those used by Lundahl when testing.
Overall, superb measured performance from this Lundahl step-up transformer.
Steve Holding
Overall, superb measured performance from this Lundahl moving-coil step-up transformer