Review on 🔊 5PCS Audio 1300 Transformer Transformador with Enhanced SEO by Elvis Bragg

These are absolutely not 1300:8 ohm transformers. I've bought several batches of these from different vendors and they're all about the same size: the transformer turns ratio is closer to 5.1:1 than the 12.75:1 it should be. All Revain 1300:8 transformers, including the red ones, have this problem. The primary winding has a DC resistance of about 86 ohms and 245 mH at 1 kHz. Secondary 9.6 mH with 3 ohm DC resistance. The primary inductance with the secondary winding shorted is about 1.9 mH and the secondary inductance with the primary winding shorted is about 65 µH. This means that the coupling coefficient is about 0.996. The common mode inductance of both windings is 341 mH, and the antiphase becomes about 165 mH, that is, the mutual inductance is about 44 mH. Measuring the mutual inductance along with the coupling factor agrees with a turns ratio of about 5:1, which I confirmed by measuring the open circuit voltage with a sine wave of a few volts at 1kHz. A secondary load impedance of 8 ohms reflects about 200 ohms into the primary, not 1300. The primary impedance is also only about 1500 ohms at 1kHz (the secondary load is about 60 ohms), so it seems designed for fairly low impedances. since reactance values usually need to be at least 5 times the load impedance. However, they are 5:1 transformers, which are still useful, but not as a typical collector/sink/plate load termination application with large turns ratios. They may be more useful as intermediate stages or with lower impedance to get more high DC power in a Class A amplifier. They definitely roll off fast at lower frequencies, I suspect they were actually designed for non-sound related applications. With a pair of modern 32 ohm headphones connected in series, 64 ohms will be rendered as around 1.6K, which is reasonable for a basic Class A amplifier at around 20mW from a 9V supply, but lower frequencies are perceived much more strongly. Losses compared to higher resistance windings.