[Fwd: LF: Low Pass Filters]
Sun, 01 Mar 1998 10:21:53 -0500
> Decided to spend my spare time in the week getting my 4 x 2SK413 amplifier
> boxed and working. The amplifiers OK but I needed a drive source and a
> filter. All the original testing was done with a signal generator before the
> band was released.
> The drive uses a SGS Thopmson audio amp chip. The TDA2030. 11 sheets of data
> are available @ www.st.com under consumer products data. The performance is
> ideal with the output going smoothly from 0 to 11 Watts with a 24 Volt supply
> or 6W with 15V. The data suggests that the chip should have a 3dB point at
> 140k but when tested there was no sign of any reduction in power.
> The low pass filter was a combination of the info given by TONI HB9ASB
> together with data from the ARRL handbook. Based on a 0.01dB ripple
> chebyshev, if you're looking for a filter to try, the following may be useful
> to record
> LPF. 5 element pi design ( capacitive input)
> Ideal values. 22n 68.5uH 39n 68.5uH 22n. based on 160k
> Actual values used. All caps 1kV from RS.
> (4 x 4n7.) (76t on T-200-2.) (2 x 10n + 4 x 4n7.) (76t on T-200-2) (4
> x 4n7)
> With 76t of 1mm dia wire the toroids are almost full. I've used the remaining
> gap of 10mm to glue the toroid upright onto the PCB. (Thanks for info Toni)
> With the values used, the cut off is a little higher, with low insertion loss
> to 170k. A rough measurement with a scope, which is far from ideal, gave:
> 200k -14dB
> 2nd harmonic 272 -26dB
> 3rd harmonic 408 -42dB.