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Optical, J, and K photometric observations of the KV UMa black hole X-raynova in its quiescent state obtained in 2017-2018 are presented. A significantflickering within light curves was not detected, although the averagebrightness of the system faded by $\approx 0.1^m$ during 350 days. Changes inthe average brightness were not accompanied with the increase or the decreaseof the flickering. From the modelling of five light curves the inclination ofthe KV UMa orbit and the black hole mass were obtained: $i=74^{\circ}\pm4^{\circ}$, $M_{BH}=(7.06\div 7.24)M_{\odot}$ dependently on the used massratio. The non-stellar component of the spectrum in the range $\lambda=6400\div22000$\r{A} can be fitted by a power law $F_{\lambda}\sim \lambda^{\alpha}$,$\alpha\approx -1.8$. The accretion disk orientation angle changed from oneepoch to another. The model with spots on the star was inadequate. Evolutionarycalculations using the "Scenario Machine" code were performed for low massX-ray binaries, a recently discovered anomalously rapid decrease of the orbitalperiod was taken into account. We showed that the observed decrease can beconsistent with the magnetic stellar wind of the optical companion whichmagnetic field was increased during the common envelope stage. Severalconstraints on evolutionary scenario parameters were done.

Optical, J, and K light curves of XTE J1118+480 = KV UMa: the mass of the black hole and the spectrum of the non-stellar component