Pye Audio: PX2 Transformer Interface

After decades of manufacturing measurement tools and consumer electronics in England, Pye Audio merged with Phillips in 1960, forming Pye TVT Limited. Their studio technologies impacted an era of seminal records from the late ‘60s through the mid-‘70s. Then, the brand was curiously dissolved in 1986. The first coordinated effort to restore and expand on that legacy with innovations came in 2020, when Avedis Audio secured rights to the Pye brand in the United States and founded Pye Audio. While studying a vintage Pye transformer, Avedis Audio principal Avedis Kifedjian [Tape Op #132] was inspired to create the PX2: The world’s first taste of American Pye.

The PX2 is a passive, fully analog, 2-channel transformer interface and ground isolation system that is deceptively simple to operate. It integrates three distinct features capable of improving signal-to-noise performance. The circuit is optimized for line level audio signals from balanced or unbalanced cables via XLR combo input jacks and provides two transformer-coupled XLR outputs. A ratio switch for each output determines how the corresponding transformer is tapped. In 1:1 mode, the output level (less negligible insertion loss) is the same as at the input, and the input impedance is reflective of the load on the output. In 1:2 mode, the output level is doubled (+6 dBu), and the input impedance is then one-fourth that of the load on the output. This mode is ideal for boosting low-output sources without raising the noise floor.

The PX2’s ground-lift system is brilliant and has been patented by Avedis. Most equipment designers include a ground lift switch at the outputs, but Avedis makes a solid case for lifting the ground at the input stage instead. When engaged, it breaks ground loops as expected while filtering out any potential RFI induced from the floating ground. The custom transformers at the heart of PX2 significantly increase the common-mode rejection ratio (CMRR), resulting in the attenuation of background noise from source electronics and audio cables. Some of my outboard gear benefited from the enhanced CMRR more than others. The most notable improvement was realized with PX2 strapped across the outputs of a standalone analog filter.

I was given two review units, so I loaned one of them to a local dream pop artist who has a few noisy vintage synths, including a Roland JUNO-106. I advised her to try out the PX2 between her synths and audio interface. She was blown away by the dramatic mitigation of background hiss and improved clarity of her patches. She purchased her own PX2 and returned the review unit to me only after hers arrived. It’s now an integral part of her recording chain. I hear a lot of productions that I describe as having an overall “gray” sound because they suffer from so much low-level noise. The PX2 can create a blacker background for tonal colors while increasing the perceived depth of the stereo field when using it to process DAW mixes in analog. However, the noise-reduction capabilities of PX2 are reduced in hybrid mixing when noise is already printed on individual tracks.

I also observed that, even when sending audio through PX2 at line level, transformer saturation is introduced, and transients are softened. I evaluated a stereo mix printed through an analog loop, with and without the PX2 inserted. A null test of the two files revealed the sonic signature of uniform harmonics across the audio spectrum, with a low-mid bump. Sometimes, that character is magic across full mixes, and other times only on subgroups. In any case, that saturation sounds more believable than most plug-in emulations.

The PX2 also performs well in live music scenarios. The benefits of its advanced ground-lift system in unpredictable stage environments are impressive, but the PX2 truly distinguishes itself from direct boxes in the way it balances audio signals. Direct boxes intended for high impedance instruments are commonly used to balance low impedance sources such as synths and buffered pedals. In such cases, input signals are padded by the direct box and then boosted back up with a mic preamp, often resulting in a higher noise floor. The PX2 can efficiently balance low impedance signals for a cleaner, bigger sound in front of house and monitor mixes. Each PX2 is built at the Avedis Audio workshop in California and, though backed by a three-year warranty, will likely serve engineers and synth-geeks reliably for decades.