[AH] HPF from LPF (was Re: [AH] system 100 versus 100m)

From mikekent
Sent Wed, Nov 9th 2005, 19:46

> I have a pretty big 100m (8x191j, 40 modules) with 15 vcf=B4s and it gets
> pretty booooring
> sometimes with only lpf=B4s I can tell you, however that is going to change
> soon..... ;)

You can probably get a HP or BP filter type of effect with your large
system, although you may need to make one special patch cable for it.

If you send a signal into a low pass filter and then mix it back with the
original signal with reverse polarity, you can emulate a High Pass Filter.

______                     ________
|    |--Polarity Switch--->|      |
|VCO |     _______         | MIX  |---------->
|____|---->| LPF |-------->|______|
           |_____|

Or:

______    ______                     ________
|VCO |--->|    |--Polarity Switch--->|      |
|____|    |MIX |     _______         | MIX  |---------->
|VCO |--->|____|---->| LPF |-------->|______|
|____|               |_____|


One cable needs to have its wires crossed to switch the polarity.

Add another LPF on the end of that chain to get a Band Pass Filter.

It works in theory but I've never actually tried it. I just patch into my
Steiner Parker multimode filter to get HPF or BP. But this might be a low
cost solution if you've got all those modules already available.

Let us know the result if you try this.

Regards,
Mike.

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