This is a long overdue post, as I have carried out these tests time ago but never got around to publish the results. Dorin from DvB transformers sent me a pair of his transformers for testing. These are great devices for amp input stages, particularly for a nice Spud amp using medium mu output stages with 6P15P or 6e5P for example. Either PP or SE output, this will give you a great solution for a minimalistic design:
The configuration options are multiple, you can see what you can do with a similar transformer spec from DvB:
I did some tests without any Zobel compensation and here was the initial result:
The nasty peak at 40kHz can be easily corrected by adding a 8k1 resistor in series with a 1,600pF capacitor as Zobel arrangement across the secondary:
The transformer can do a nice flat response from DC to 40kHz (-3dB) in a 1:6 arrangement as shown above. This is really good.
The third harmonic is higher than the second which is due to the distortion introduced by the transformer. However, the overall THD is very low (0.0028%). It’s rather more interesting to see its performance when swinging larger volts. Here is the example at 0.008% for 5Vrms output level
The response at 10Vrms output level is shown below. The distortion harmonic profile changed with a higher H2 and decaying H3 and H4 which is nice to see. Overall THD is 0.006% @10Vrms which is very nice to see:
Overall, a great and flexible transformer to use in my opinion. A nice cathode follower to drive it to ensure a good HF response due to leakage capacitances in play and the reflection of the Miller capacitance of the output stage into the primary which is the challenge of using a step up transformer in a Spud amp.
Contact Dorin directly if you want one of this. He can be reached on his email account which is dorin.bodea at gmail.com.