I have found IME the double Y as suggested by Steve H (our host) does enhance the mono listening experience as advertised. This is by comparison to the same mono record played in stereo. The Y connection lowers the noise floor, and reduces harmonic distortion produced by any differential mistracking, or difference artifacts introduced during stereo play. The reason you did not hear any difference, your comparison was single channel mono to dual mono. Single channel mono (the left or right channel at the cartridge Y'd to both channels on your amplifier) vs dual channel mono (both channels strapped across by selection of mono mode on your preamp) ... both versions produce clean mono reproduction with lack of sibilance and distortion, plus a lowered noise floor. My above comments apply to an unworn record. Records with wear will require varied mono hookups to achieve the cleanest play with the least fidelity loss, ie: left channel only, right channel only, or both channels strapped. The most practical mono setup is the double Y in my opinion, since this covers the majority of situations, new record or worn record and achieve greatly improved results. This is the most practical setup, sometimes as simple as flipping the mono switch on your preamp. Improved results does not mean best results. The best results are achieved through spot plays, in the trial of different mono playback methods. In my opinion, there is no convenient setup for this, which requires a time and patience, probably best left to preservation of a vinyl record to a lossless digital storage medium. Since all stereo cartridges produce a sum and difference signal, and that the stylus is free to move in all planes, the stereo cartridge is not the best solution in the reproduction of a mono record. There are painfully few true mono cartridges available, and many of them limited in frequency range. A true mono cartridge reproduces only the laterally cut portion of the groove, no sum signal, no difference signal, only ONE mono signal. The sibilance and distortion produced by a stereo cartridge are almost non-existent in a mono, given the same compliance and stylus shape. Since sibilance and harmonic distortion artifacts in stereo are almost entirely difference, and out of phase distortion, and created by vertical mistracking (venturing into the twilight zone of pinch effect) This same vertical mistracking of a mono cartridge will not be converted into an electrical signal, by virtue of the single pickup coil in a lateral alignment. A stereo cartridge strapped to mono is subject to any channel imbalance at the coils, any imbalance in the signal path before the Y strap. Again, 45/45 aligned coils are sensitive to vertical movement of the stylus, which in a mono record is pure noise. Just an afterthought, the sibilant issues in stereo playback occur mostly by vertical mistracking of the mono component. In other words, the stylus mistracks vertically in a laterally cut groove. An experiment to prove this point, play a sibilant record, switch to mono. The sibilance and/or distortion should go away almost entirely (in most instances) For everything, there is a season (meant to say reason) turn, turn, turn ... As a stereo cartridge is strapped to mono, all or most of the difference signal combines or sums, halving its output. Noise and distortion are also reduced by a factor of two or more.