Some useful directions for transformer picking.
1:1 ratio Line Level Transformers
Line level transformers can be used for ground isolation between different apparatus or for converting unbalanced to balanced lines and vice versa. For the physics of balanced lines please refer to the link. The practical reason for balanced lines is that you can have the preamplifier, DAC, computer, next to you and the amplifier across your listening area next or between the loudspeakers.
In the picture below there are some line transformers, far left is a pair of high Z Ampex transformers taken from an old four track 1/2 inch tape recorder, in the middle is a pair of UTC LS141 transformers that can serve also as a splitter, next is a pair of Peerless E204 600Ω/600Ω transformers.
All these are old and out of production transformers , my favourites and recommended of new production are Sowter 3575 or 1470 and Lundahl 1684 and 1690 .
1:1 ratio Line Level Transformer
With Volume Control
Below is a pair UTC A-21, 600Ω/600Ω line level transformer with a volume level control and a leaf switch that serves as an input selector, the knob is an antique RCA.
Moving Coil Cartridge step-up transformers
In case your phono preamplifier does not support MC cartridges it is certain that you might need a moving coil step-up transformer.
On the left in the picture below there is a pair of Harman Kardon XT-3 Microphone transformers. On the right there is a couple of UTC-016 and LL1681 (on the top) transformers. In the middle on the top there is a pair of Sennheiser microphone transformers and on the bottom is a pair of Lundahl 1922 transformers .
Be sure that there are a lot of X-lent step-up transformers of new production out there. Some that I have tried with good results with the Denon DL 103R cartridge is the LL1681 @ 1/13, the LL1922 connected in 1/8 configuration and also the LL1678 @ 1/16 configuration.
A future experiment will be the Sowter 9990 @ 1/20 ratio.
I have to inform you that I don’t recommended step-up ratios higher than 1/16 as extreme high ratios make problematic transformers. Also keep in mind that a cartridge that produces an output of less than 1/2 mV can not excite properly most step-up transformers.
Also note that you must break free from the madness of seeking vintage shitty and rare transformers just because someone claims that they are the Holy Grail for MC cartridges.
Single ended and Push-Pull Output Transformers
Undoubtedly my favourite output transformers for SE or PP configuration are the Japanese, made by Tamura, Hashimoto or ISO/Tango. They don’t just look nice but they are of the best quality. Unfortunately they cost a king’s ransom but they worth every yen. So if you can afford them, please use them.
I have to add in my favourites list the X-lent, Swedish Lundahl transformers that are a mind puzzling riddle to connect and as beautiful as a SAAB car.
The honourable mention goes to the One Electron UBT-3 transformer which is a killer bargain for its sound quality.