Why invent what others have already invented before us... If you need a decent mixer simply and quickly, use the wiring that has been made available to the general public, see below. Everything is obvious and therefore no comment is necessary.
Perhaps we will limit ourselves to just a few practical notes, such as: careful design of the transformer and appropriate choice of material, encapsulation of the entire board so that the entire shielded structure is mechanically strong, stable and compact. It is ideal to use a cast aluminum alloy, which is available at an incredibly low price (by today's prices) from Conrad Electronic (unfortunately only in Germany) and is produced by the Canadian company Hammond. The use of high-quality and temperature-stable components, capacitors should be selected only from mica or high-quality ceramics, or ceramic material with the NPO mark. It is sold by GM Electronic and can be recognized by the black dot on the cap of the capacitor. Beware of confusion, the sellers here are completely ignorant and if you don't check what they give you, you will discover ordinary, low-quality "pillows" at home... We can replace the TUF-1 double-balanced mixer, for example. SBL-1, UZ-07, UZ-10 or others with the same input/output parameters.