My new design, the slackfilter

[Mick Bailey]

I've just built an Uglyface with LFO and incorporates switched diodes to give ramp up and ramp down as well as regular triangle modulation. This has proved to be very useful and I wonder if you could incorporate this feature into the design.

[slacker]

awww
i was really looking forward to this one, i dont imagine im the only one either

Sorry, if it's any consolation I'm working on something similar and hopefully better at the minute. It's based on the Oscar synth filters that Paul Perry posted recently. It's probably going to be a month or two before it's ready but I'll definitely post a layout this time.

I've just built an Uglyface with LFO and incorporates switched diodes to give ramp up and ramp down as well as regular triangle modulation. This has proved to be very useful and I wonder if you could incorporate this feature into the design.

I'm not sure if the existing LFO could be modded to incorporate that, but you can splice basically any LFO you want into the design.

[cathexis]

Sorry, if it's any consolation I'm working on something similar and hopefully better at the minute. It's based on the Oscar synth filters that Paul Perry posted recently. It's probably going to be a month or two before it's ready but I'll definitely post a layout this time.

I'm really looking forward to this, your Echo Base was a great design, one of my favourite pedals!
/LARS

[Boogdish]

I'm ordering the parts for this today.  I'm excited.  I'm planning on building it with a send/return so that clean guitar can control the envelope generator and fuzzed out guitar gets sent through the filter.  I'll be making my own layouts for this and if I can get it to work, I'll post em for the rest of you.

I had one question, though.  After each of the switches to select what type of filtering is a 47k resistor.  The other sides of all of these switches meet at a common point.  Would it be a bad idea to put a single 47K on the common side of these switches instead? 

[Tuemmueh]

I'm ordering the parts for this today.  I'm excited.  I'm planning on building it with a send/return so that clean guitar can control the envelope generator and fuzzed out guitar gets sent through the filter.  I'll be making my own layouts for this and if I can get it to work, I'll post em for the rest of you.

I had one question, though.  After each of the switches to select what type of filtering is a 47k resistor.  The other sides of all of these switches meet at a common point.  Would it be a bad idea to put a single 47K on the common side of these switches instead? 

I am TOTALLY looking forward to your results!

[slacker]

I'm ordering the parts for this today.  I'm excited.  I'm planning on building it with a send/return so that clean guitar can control the envelope generator and fuzzed out guitar gets sent through the filter. 

That's a really good idea, nice to see someone still playing about with this

I had one question, though.  After each of the switches to select what type of filtering is a 47k resistor.  The other sides of all of these switches meet at a common point.  Would it be a bad idea to put a single 47K on the common side of these switches instead? 

I think you need the 3 resistors, because they split the signal to the 3 inputs and stop them interacting with each other. I think if you just used one it would work fine if you just selected one input, but selecting more than one wouldn't work properly.

[Fancy Lime]

Hi Ian,

sorry to resurrect such an ancient thread. However, I recently tried something very similar but was not as happy with the results as you seem to have been a decade ago. Unfortunately all the links seem to be broken. Do you mind uploading the schematics again? I'd really like to compare them with my fruitless experiments and see if it is worth giving the Steiner another shot.

Thanks,
Andy

[Fancy Lime]

Hi,

please excuse the nagging. Does anyone have the schematics? I'd be really interested in an improved Steiner Filter design. Show of hands: who else?

Thanks,
Andy

[bluebunny]

The Wayback Machine has it here.

[Fancy Lime]

Thanks Marc! Damn, I always forget to check the Wayback Machine. Sorry bout that, I'll make a note.

I'm looking forward to applying this principle to a simplified envelope filter. I've been meaning to cultivate the synth ripple sound a bit but then got sucked into vactol circuits, which do not ripple all that well. With diodes as control elements this should work much better.

Does anyone know why the design would use 2 diodes replacing one resistor (if you fold back the symmetrical expansion) but 4 replacing the other? That reduces the Q of the filter, which is later made up for by the gain of the BC109-BC179 pair. Seems more complicated than necessary. May it have to do with balancing the characteristics of the three filter types?

Once we are at it: Does anyone know which diodes are best suited for this sort of thing? We want them to have a consistent and (ideally) linear R-vs-I behavior over a fairly wide range. Not exactly a spec that many diodes are made for, is it? I'd be guessing regular old 1N4148's would be a good start? I would expect that rectifier diodes have a steeper (in this case worse) R-vs-I curve, right? LED's might have a too high breakdown voltage for a 9V circuit in this configuration. Ge-diodes are sometimes nice and flat in R-vs-I but probably too inconsistent. Can someone enlighten me concerning Schottkys? I would expect them to be steep but I don't really know.

Andy

[PRR]

Plain old Ge/SI diodes have a moderately predictable V/I over many decades of current, and pretty much all the same.

Actually transistors obey The Law very darn good; diodes are doped for more conductance and tend to have a bend in the plot (though often beyond the currents you will likely use).

Yes '914/4148 or 1N400x. This is a chance to use-up the '4001s you bought by mistake (before you realized that '4007 are the same price as '4001 in DIY lots).

[Fancy Lime]

Transistors instead of diodes, eh? I had briefly thought about the possibility of doing just that. The working principle of the diodes in a Steiner Filter isn't all that different from the ones in a Diode Ladder Filter after all, and that works a lot better when implemented with transistors, as Bob intended. I put that on the back burner when I realized that the complexity and parts count would be almost identical to a 2-Pole Transistor Ladder Filter, which somehow appeals more to me, mojo-wise.

But how about using the intrinsic diodes of BJT's instead of "diode diodes"? Any benefit there like better linearity, better matching or anything of the kind? Does your assessment that transistors obey The Law apply also when they are used as diodes or only when used "properly"?

Thanks,
Andy