You'll never get accurate amplitude of a particular frequency (36 Hz or something else) with FFT. Except the case when frequency is multiply to SampleRate/FFTWindowLength.

For example, if you have a signal with a single sin tone and you're using 1024 point FFT with 44100 sample rate, the accurate frequencies will be 0, 43, 86, 129, .. 22007, 22050. All other frequencies will be detected with an error. You may decrease error value by using a bigger FFT window.