Filter

[Dr.EM]

Hi. I built one of these very nice 24db lowpass minimoog filters;

**broken link removed**

But I wondered if it was possible to make a highpass version of it, and if so, how? Any ideas?

 

[Russlk]

That looks more like an adjustable distortion circuit, I never saw a lowpass like that before. Perhaps if you used an inductor in place of the .068 cap between the emitters, it would be more high frequency. I think you would need a DC blocking cap in series.

 

[Nigel Goodwin]

That looks more like an adjustable distortion circuit, I never saw a lowpass like that before. Perhaps if you used an inductor in place of the .068 cap between the emitters, it would be more high frequency. I think you would need a DC blocking cap in series.

It looks strange because it's voltage controlled, and gives a log response, hence the strange connection of a number of transistor pairs. Don't forget, this was pre-opamp (at least IC ones!).

 

[Dr.EM]

Hmm, inductors. They'd have to be pretty big for audio frequency use, right? You think it may not be possible at all, with that design, and to get the same sort of response?

Another question on it, if I removed say 2 of those capacitors and transistor pairs, would that make it a 12db instead (very uneducated guess, sry)

 

[Nigel Goodwin]

Why not try a more modern design?, rather than something which is practically prehistoric!.

 

[Dr.EM]

It is an old design, but its one of the best for actual sound.

 

[Nigel Goodwin]

It is an old design, but its one of the best for actual sound.

When I next email him, I'll ask the guy who had the original idea for the MiniMoog about it? (he was also a major designer on the original Moog as well).

 

[Dr.EM]

Wow, you actually know the guy who designed them, nice! That would be great if you could btw, cheers!

 

[Nigel Goodwin]

Wow, you actually know the guy who designed them, nice! That would be great if you could btw, cheers!

I've emailed him, I'll let you know what he says!.

You might like to look at
for an interesting history!.

 

[Dr.EM]

Cool, an interesting read

I actually can't find a single schematic for a 24db voltage controlled high-pass filter, or even a 12db. I know it exists...