LED for LFO speed - Small Stone

kismet78 · June 09, 2008, 05:28:09 PM

I'm about finished rehousing my ri small stone w/ the gamut of usual mods plus some others: vibrato, univibe, phasefilter, depth knob, split the color switch into 2 separate switches, and a bypassable mosfet boost on the end w/ a level knob.

Before I close it up I'm wondering if there's a way/good place to splice in a LED on the LFO that will blink with the rate?

kismet78 · June 10, 2008, 01:37:13 PM

No love for flashy lights?

frequencycentral · June 10, 2008, 02:01:31 PM

You could try a LED going to earth preceded by a resistor, 4k7 maybe, from pin 6 of the LFO OTA, just before the 100ohm resistor.

http://files.muziq.be/schematics/eh_smallstone.jpg

kismet78 · June 10, 2008, 02:16:36 PM

Thanks. I'll give that a shot later tonight.

frequencycentral · June 10, 2008, 02:24:37 PM

http://blackouteffectors.com/

Nice looking pedals BTW!

kismet78 · June 10, 2008, 02:36:26 PM

Thanks! They're doing pretty well.

And just for disclosure's sake, my LFO/LED info request is for a personal rehousing/modding project, not a thinly-veiled attempt at free R&D or anything like that. I've watched a few people crash and burn pulling shit like that recently.

puretube · June 10, 2008, 05:19:16 PM

Quote from: kismet78 on June 10, 2008, 02:36:26 PM
And just for disclosure's sake, my LFO/LED info request is for a personal rehousing/modding project, not a thinly-veiled attempt at free R&D or anything like that. I've watched a few people crash and burn pulling sh*t like that recently.

Wrong Forum?

kismet78 · June 10, 2008, 05:22:34 PM

Quote from: puretube on June 10, 2008, 05:19:16 PM
Quote from: kismet78 on June 10, 2008, 02:36:26 PM
And just for disclosure's sake, my LFO/LED info request is for a personal rehousing/modding project, not a thinly-veiled attempt at free R&D or anything like that. I've watched a few people crash and burn pulling sh*t like that recently.

Wrong Forum?

You tell me.

Anyway, it was just a side comment, but my intent is to stay OT here, so:

can you confirm frequencycentral's recommendation on putting the LED off pin 6 of the LFO OTA?

puretube · June 10, 2008, 05:35:34 PM

Might depend on what`s:

Quote"my ri small stone"

is it the same schemo as linked to in reply#2?

kismet78 · June 10, 2008, 05:43:19 PM

There are a few value differences that I've noticed as well as a completely different pcb layout. Unfortunately, it doesn't seem as if anyone has ever bothered to trace a RI, as the Issue J seems to be the only schem floating around. So it's hard to say if it's JUST a few minor value differences, but from what I can tell it's the schematic should be the same structurally, same OTAs, etc.

puretube · June 10, 2008, 05:46:11 PM

How many OTAs ?

[EDIT]: well...anyway: just try it...

kismet78 · June 10, 2008, 05:47:32 PM

Quote from: puretube on June 10, 2008, 05:46:11 PM
How many OTAs ?

5

puretube · June 10, 2008, 05:49:53 PM

Quote from: puretube on June 10, 2008, 05:46:11 PM
How many OTAs ?

[EDIT]: well...anyway: just try it...

bump for edit...

kismet78 · June 10, 2008, 05:57:22 PM

Ah, didn't see you edit.

I'm going to give it a go when I get home. I just wanted to get a bit more confirmation before I resume hacking at it. It's by far the most delicate board/traces I've ever had the pleasure of working with. Pads are lifting left and right, so at this point I only went to go in with a very deliberate mission.

frequencycentral · June 10, 2008, 06:37:59 PM

If you don't want to hack about to try it - use a couple of crocodile clips, one to the 100ohm resistor leg, the other to ground. That way you could 'probe' to see where's best. I would guess the LFO out is sine or triangle, which would make the LED fade on and off (might look cool!). Elsewhere in the LFO circuit you might find a square wave (?), which might be better if you want straight blinking. Failing that, if you're still desperate for blinking you could use a single opamp comparator to turn the sine/tri into a square. My guess is that you won't want to go that route though!

One other way that might work to get blinking not fading from a sine/tri would be:

pin 6 > 0.1u cap > 4K7 > LED > ground

Put a 100K resistor to gound from between the cap and the 4K7. Play about with the cap value until the LED stays on for the desired length of time. You may need to put a diode before the cap???

kismet78 · June 10, 2008, 06:39:23 PM

That's exactly what I will do. Thanks.

frequencycentral · June 10, 2008, 06:57:02 PM

Bump: EDIT

kismet78 · June 11, 2008, 03:36:11 AM

OK, progress.

Tapping the 100ohm from pin 6 didn't give me anything. So I started poking around...

I got a really smooth, synced fade in/fade out by tapping one side of the 4k7, opposite V+. Then I found a slightly choppier (but still not quite on/off) blink on one side of the 30K (between pin 2 and the 30K), which I believe is 27K (R19) on the Issue J version. The ground side of R19 didn't give me anything. I upped the limiting resistor to 33K. That's where I found it gave the best on/off definition with these particular LEDs. Lower values were too "on".

Thanks for everyone's help!!!

kismet78 · June 11, 2008, 12:29:15 PM

How am I affecting the LFO by doing this? I was trying hard to hear a difference and I didn't, but it was late at night and I couldn't turn up.

frequencycentral · June 11, 2008, 12:53:37 PM

Glad you worked it out

I doubt you will be loading the LFO by any detectable amount - similar LFOs in modular synths may successfully run heaps of other stuff, let alone one extra LED.

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LED for LFO speed - Small Stone