I am aiming for 4 NCC200 amp boards with separate front and back end power supplies to drive my 2 way B&W P4 speakers. They are 88dB sensitivity and 8 ohms impedance which drops to 4 ohms at certain frequencies (dont know which frequencies). They are transmission line design with the port firing forwards and crossover at around 3.5Khz. The bass/mid filter is 1st order and the high frequency filter is third order with an air cored inductor in parallel with the tweeter. I love them.
As i will have two of the boards powering just tweeters i was wondering if i can decrease the transformer VA and capacitors considerably and concentrate on quality rather than quantity for the treble? I assume that tweeters do not need anywhere near as much current as the bass/mid. How low a VA could i get away with per channel ?
The backend of the mid/bass NCC are going to get 200 to 300VA each with 35V secondaries. The front ends i am planning 30 to 40 VA at 40V secondaries and will be using either the PFM gyrators or very simple gyrators with Tip31C/32C, 2k2 and 100uf Nhg.
I wish i knew how to work out how to measure what current the tweeters are drawing on their own when playing music at normal levels. I never listen very loud.
My current monoblocs have Nap140 transformer (it says 200Va on them although they do look a little small and single secondary of 27.5-0-27.5), minicap6 and ncc200 and they never run out of steam at my listening levels. I measured voltages on the output of the minicap6 and they dipped less than 1 volt when music was playing (at loud levels for me) compared to idle.
Stu
Designing psu for four monoblocs
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