My freshly finished 4P1L preamp.
An externally hosted image should be here but it was not working when we last tested it.
unfortunately I have only one transformer for heater, with two independent secondaries
OPT is made by Tatic Audio, check here:
Untitled Document
OPT is made by Tatic Audio, check here:
Untitled Document
Here are some measurements 
THD 0,012%
THD 0,012%
An externally hosted image should be here but it was not working when we last tested it.
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that is the best I can do with my little knowledge
No audible hum on 96dB speakers
Your potmeter is close to the power supply and can be picking up radiation. What's behind the potmeter?
That was a 64 step relay attenuator, but I replaced it with cheap epay smd attenuator
To much noise from relay attenuator.
Yesterday I tried to reverse wires on primary of OPT and got something strange.
Originally Freq response was falling on both ends with positive impulse response.
10Khz square wave looks very sharp, almost like triangle wave.
With reversed wires I got negative impulse response but with much better (wider)Freq response and very good shape of 10kHZ square wave on my scope.
How to determine what is a proper way to connect wires of primary of unknown transformer?
Originally Freq response was falling on both ends with positive impulse response.
10Khz square wave looks very sharp, almost like triangle wave.
With reversed wires I got negative impulse response but with much better (wider)Freq response and very good shape of 10kHZ square wave on my scope.
How to determine what is a proper way to connect wires of primary of unknown transformer?
Maybe I misunderstood, post a picture of the new situation.
Generally speaking an output transformer must have high bandwith so the HF pole is far away from 20KHz. This demand is counteracted by the need for inductance which is derived from lots of windings. What your OPT might be suffering from is stray capacitance, interfering with the integrity of the signal. Triangle shaped square waves at the output is no good sign. What's the level?
The right way to connect is with the highest bandwith.
Generally speaking an output transformer must have high bandwith so the HF pole is far away from 20KHz. This demand is counteracted by the need for inductance which is derived from lots of windings. What your OPT might be suffering from is stray capacitance, interfering with the integrity of the signal. Triangle shaped square waves at the output is no good sign. What's the level?
The right way to connect is with the highest bandwith.
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