Dirtbaby R6 substitute

[taeagan]

Hi everyone. I'm building a Dirtbaby and sadly I don't have a 150 ohm resistor for R6. I have a 200 or I can put a 100 and a 33 in series to make a 133. Looking at the schematic I'm guessing that this is not a critical value - it's in series between the output and the middle lug of the blend pot. But my electrical circuit theory is not the strongest, so I thought I'd reach out for some advice. Thanks in advance!

[madbean]

200 ohm is just fine.

[taeagan]

Cool, thanks for such a quick reply!

One other thing - the led, D2. Is that meant to be visible in the enclosure kind of like how the led in the naughty fish shows you the envelope response? Or can I just solder this led in flush to the board without worrying about getting the height right for the enclosure? And is 5mm green diffused prescriptive or just a recommendation?

[jimilee]

Its internal and 5 is recommended, I think Brian said it decreases the audio going in to the 2399 to prevent distortion you normally get as the repeats fade. Don't quote me on that though.


Sent from my iPhone using Tapatalk

[somnif]

You can read the story of where the trick came from here: http://www.diystompboxes.com/smfforum/index.php?topic=101149.0

Very clever, and very effective.

[somnif]

I realized I have a question pertinent here and will piggyback this thread.

The LED on the 2399 is listed as a 5mm diffused Green... but I'm not sure why. I checked the vf on the LEDs I have on hand and my 3mm greens and 5mm greens measure about the same (2.2-2.3V). Granted I am using a dirt cheap DMM and my electrical engineering prowess is nigh on non-existant.

But if all we care about is the voltage, does it matter the size? We just care that if the volts spike over 2.3V it leaks to ground rather than causing distortion.... right? If so, is there some appreciable reason to use a 5mm over a 3mm? (I only ask because its a tight spot on the board and the big old 5mm not fitting annoys me a little. Pedantic, no?)

[madbean]

I've used 3 and 5mm in various delay builds. Either should be fine for exactly the reason you stated.

[taeagan]

Thanks to everyone for the help.  I realized that I have a couple of other substitution issues that I need some advice on.  I'll list them in order of my suspected importance (least to most):

• R16 - It's listed as 20k.  Can I get away with a 22k or should I series two 10k's?
  C2 - Listed as 27pf, which I do not have.  I have 18pf or 39pf.  I can't tell exactly what it's doing in the circuit.
  There are seven 2n7 caps in the circuit.  Can I get away with 2n2's?  C6, C7, C8, C21, C22, C25, and C26. 

[taeagan]

Looking at the schematic and notes some more I'm guessing that R16 and C2 are not critical values, but that I shouldn't mess with the 2n7's. Is that a fair assessment?

[jimilee]

Shouldn't be an issue between those values.


Sent from my iPhone using Tapatalk