DvB (IN1166) input transformer test

IN1166 DUT
IN1166 DUT

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:

First test without Zobel compensation
First test without Zobel compensation

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:

With Zobel compensation
With Zobel compensation

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 distortion response is really good as well. Let’s have a look at the response of the IN1166 transformer with different input signals. Starting with a 1Vrms output:IN1166 THD 1Vrms range 2V

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

IN1166 THD 5Vrms



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:

IN1166 THD 10VrmsOverall, 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.



5 Replies to “DvB (IN1166) input transformer test”

  1. Hi Ale,

    Thank you! I hope it was a time well spent ♫☺ This is a quite old make (more than 6 months ago) I’m already working on next levels of complication, let’s say “make III”… ☺ I’ll keep you informed when the prototypes are ready.


  2. Always interesting to see measurements from audio transformers. I think every professional transformer manufacturer should publish those information to inform there costumers. Glad you did you measurements.

    Martin Mug, Netherlands

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