Tonepad Filter Sample + Hold idea

[chicago_mike]

Simple idea I think

I want to add a LPF option since its at "stock" a BPF.

SO, looking at the schematic, I think I tap a line off of pin 12 of IC 1B.  Before or after the .03uf to ground.

Split the bandpass output and then I can add a spdt , tie the middle to output, before the 3k3. and the other lugs tie to BPF and LPF respectively.

Am I correct? It looks correct to me. But I can't seperate the schematic from the pdf to illustrate my idea here.

I could also tap off of pin 3 or 4? of IC1A for the HPF, but thats too thin for bass.

Should work no?

[moosapotamus]

Good idea, worth trying. I might hack into mine to give it a try if I have time. I really like the FSH1 but overall I think it's a bit too thin for bass in general. Really needs a clean blend at the very least.

I think you could tap off anywhere along the node connecting IC1b pin 12 and IC1a pin 3.

So then you would cut the trace going to the 3k3, or lift the end of the 3k3 that ties to the 100k/100k/Q2? Then the middle lug of the SPDT would go to the lifted end of the 3k3, one outside lug would go to the 100k/100k/Q2 junction, and the other outside lug would go to node connecting IC1b pin 12 and IC1a pin 3?

Am I understanding your idea, restating it correctly?

~ Charlie

[chicago_mike]

Yeah, 

That should be the LPF out right? I have a schematic of a variable state filter using the CA3280 ota and its damn near the same.

I also have the Agent 00Funk schematic and its the same, more or less too. He just adds an opamp before goint to the output.

[chicago_mike]

Uh oh.....

A notch filter...

is that LPF + BPF?  I have some center-on's lying around.

I dont have to do anything to the .03 going to ground off the 13700 right?

[moosapotamus]

Looking at the LM13600 datasheet, figure 14 shows a state variable filter that looks a bit like the one in the FSH1. I'd say you're right about where to tap the LPF output.

I think a notch filter is LPF + HPF. But I don't see where you would get a HPF output from the filter in the FSH1.

~ Charlie

[TELEFUNKON]

subtract the LPF from the dry signal?

[chicago_mike]

Looking at it again, I think your right..

I could just use a 10k pot and blend between the band pass and low pass. I like useless controls.

[chicago_mike]

Great I had the datasheet already and finally took a look at it...

Shows a real simple multiplexer and a ramp and hold.....

[chicago_mike]

The Bandpass works. the Lowpass is very low in freq and when I switch I get a loud pop so I wonder if I need pulldown resistros on the 2 outer legs of the switch.

[chicago_mike]

I wonder if I need a 100k off the LPF tap.

[chicago_mike]

Okay so I am trying it..

And it is almost working. I have a few days before I embark on a month long tour so hopefully I get it working by then.

Oh, im kinda having an issue with the sample+hold function but I think its down to the trimmers.  I get the ticking ONLY when I play and ONLY if the knobs are set to a high freq sound. SO I thinks thats pretty good for starters.

Should have this licked this weekend.

[oskar]

I wonder if I need a 100k off the LPF tap.

Rather a buffer I think, as your're tapping into the output of an OTA. If you're using the tonepad board you have a free darlington stage in IC1/pin 7 and 8.

[chicago_mike]

Hmmm....

Ill have to try that.

[chicago_mike]

OKay so I take the signal into pin 7, and out of pin 8, tie a 5k to 10K to ground and then back to the SPDT.

Looks about right.

Might need a cap tied to ground off of pin 7.

Should be an easy enough mod.

[chicago_mike]

Something like this??

[oskar]

Yeah. Make the resistor the same size as Q2 ~10k for same level.
And of course you need a dc filtering cap if your going to have a direct output like on your drawing.
I think the job is probably worth it...   

[chicago_mike]

Something like this then.

[chicago_mike]

Ill try this asap. The only current issue I have with my FHS-1 ( tonepad) is low output volume. Not sure what to change for that.

[chicago_mike]

Its been a while and I totally forgot about this pedal. Its been collecting dust.

So I am working on the LPF output mods tonight and just redrawing the filter in eaglecad now.

Something I noticed:

The Agent 00Funk out from the filter goes to one amp of a 074 to a 4.7 polar to out.

The FSH-1 does not have an output opamp. Im wondering if its worth the effort to breadboard a 741 or similar for output from the filter.

Anyways..I should have the pedal working this week.

[Gila_Crisis]

i've done something similar on my DOD FX25 clone so that i can switch between LP an BP filter modes.

there the pin 9 is the out of the LP, 4 the one for the HP and pin 8 is the out of the BP.

for the FX25 references: http://topopiccione.atspace.com/PJ11DODfx25.html

and just take a look here too: http://www.diystompboxes.com/smfforum/index.php?topic=73021.0