What's up with C7 on the 2012 Snarkdoodle?

[mgwhit]

C7 is 100n on both the Red Llama and Tube Sound Fuzz versions of the Snarkdoodle.  On previous versions, the board was spaced for a box film cap, but the pads and silkscreen on the 2012 edition seem set up for a ceramic disc.  Any idea what's up with that?

Also, does anyone understand the function of C7 in this circuit?  It appears to connect the 9VDC to pin 8 of the IC, but wouldn't a capacitor here block the DC?  It doesn't appear to be present in other schematics I've seen.

[jkokura]

The silkscreen image could be for a panasonic ECQ series cap as well, it's just the image that Eagle puts out. The pad spacing is still the same, so you should have no issues with any caps you use.

Jacob

[mgwhit]

Thanks, Jacob.  I just measured and the pads are spaced the same.  I was being fooled by the silkscreen.  I was working off the PDF -- board's still in the mail.

Any idea what the function of that cap is?

[DutchMF]

Hey MG,

The older version had the opposite with C4, BOM called for a ceramic and the silkscreen indicated a box/film cap. I built it according to the BOM and it functions perfectly. It is a freakin' LOUD pedal, but has some good sounds in it. If you have some suggestions to tame the beast (I already have one with a trimpot at the output, but haven't tried it yet), they're more than welcome, because as it is, it's of little practical use on my pedalboard.

Paul

[jkokura]

C7 is in parallel with D1 and C6, providing power filtering going into the CMOS IC.

Jaocb

[mgwhit]

The older version had the opposite with C4, BOM called for a ceramic and the silkscreen indicated a box/film cap. I built it according to the BOM and it functions perfectly. It is a freakin' LOUD pedal, but has some good sounds in it. If you have some suggestions to tame the beast (I already have one with a trimpot at the output, but haven't tried it yet), they're more than welcome, because as it is, it's of little practical use on my pedalboard.

Thanks, Paul.  Yeah, I read your thread about the volume issue.  I'm gonna breadboard this tonight and see what I think of it.  One thing I've noticed from demos is that I don't really like the far side of the drive knob.  I think I'd like to test 500kB and 1MA pots in that position.  I'll let you know how mine turns out.

[mgwhit]

C7 is in parallel with D1 and C6, providing power filtering going into the CMOS IC.

I know that's technically true, but I highly doubt that the circuit designer intentionally paralleled 100u and 100n caps to provide 100.1uF of DC filtering.     Besides, why does it connect to pin 8, which is missing from every other schematic I've found for the RL/TSF?  At this point I'm just curious.  If I do get around to breadboarding it tonight, I'll try it with and without C7 and report back.

[DutchMF]

I really need to get myself a breadboard, so I can try stuff like this out a bit easier. I'll keep an eye out for your posts, as I'm really curious about the results, good luck!

Paul

[madbean]

C7 is in parallel with D1 and C6, providing power filtering going into the CMOS IC.

I know that's technically true, but I highly doubt that the circuit designer intentionally paralleled 100u and 100n caps to provide 100.1uF of DC filtering.     Besides, why does it connect to pin 8, which is missing from every other schematic I've found for the RL/TSF?  At this point I'm just curious.  If I do get around to breadboarding it tonight, I'll try it with and without C7 and report back.

It is very common to place a small ceramic or film cap in parallel with a large electrolytic for filtering DC ripple. Electrolytic caps are not terribly good at filtering high frequency noise which can come from poorly regulated DC wall warts. If you are using a well regulated supply or batteries, the 100n is not needed.

It's connected to pin8 of the 4049 because that is the ground pin of the IC. Look at the schematic again and you will see that pins 8, 7, 9, 11, and 14 are all grounded.

[mgwhit]

It is very common to place a small ceramic or film cap in parallel with a large electrolytic for filtering DC ripple. Electrolytic caps are not terribly good at filtering high frequency noise which can come from poorly regulated DC wall warts. If you are using a well regulated supply or batteries, the 100n is not needed.

It's connected to pin8 of the 4049 because that is the ground pin of the IC. Look at the schematic again and you will see that pins 8, 7, 9, 11, and 14 are all grounded.

Thanks, Bean, and apologies to Jacob.  Eating crow as I type.  I was aware that pin 8 was a ground point, I just didn't understand why the schematic drew it like that.  I suppose it doesn't matter, though -- ground is ground.

[jkokura]

No worries.

A good key on these things is to check the datasheet. If you look at the 4049 datasheet you'll be able to see the details on the chip including ground and power inputs and such.

Jacob

[mgwhit]

I really need to get myself a breadboard, so I can try stuff like this out a bit easier. I'll keep an eye out for your posts, as I'm really curious about the results, good luck!

Paul, I breadboarded the Red Llama values last night, but didn't get to crank it until this morning.  I subbed an A1M for Gain (because I want more overdrive and less fuzz) and an A100K for Volume (because pedalpartsplus didn't have an A10K with PCB-mount lugs).

I'm not thrilled with it, but I found some sounds I could live with in the middle of the Gain knob.  It's pretty scooped, and the bottom end is way too wooly, but I could dial in the output volume pretty well even if it was on the low side of the Volume knob.  The last quarter of the Gain knob gets totally compressed and wooly, and I doubt I'll spend much time over there.

I'll monkey with the output capacitor and volume knob values later today and see if I can tighten up the bottom end a bit.  (Keep in mind that my set-up is a Telecaster through a tweed Princeton, so there's already some weak low-end going on.)

I would definitely try the audio taper pot on the Gain, though.

[oldhousescott]

C1 and C3 will affect the low end. Reducing those values will tighten the low end. I'd probably leave C5 as is.

You might try going to a 250kA or even 100kA pot for the gain if you find you don't use the upper quarter turn of the 1MA pot.

If reducing C1 and/or C3 makes it too bright, try increasing C2 and/or C4.

[mgwhit]

C1 and C3 will affect the low end. Reducing those values will tighten the low end. I'd probably leave C5 as is.

You might try going to a 250kA or even 100kA pot for the gain if you find you don't use the upper quarter turn of the 1MA pot.

If reducing C1 and/or C3 makes it too bright, try increasing C2 and/or C4.

Well, I went ahead and changed R5 anyway.   I just wanted to compensate for the higher value Volume pot, and 1u @ 100K produced the same corner frequency (1.6 Hz) as the stock 10u @ 10K.  Definitely sounded less flabby.  Also allowed me to get a film cap in place of the electrolytic.  I think I could go a smidge lower and still be happy.

But everything you've said about C1 and C3 makes sense, too.  I'll tweak those values tonight.

[DutchMF]

This is turning in quite an experiment! Makes me wonder why the Red Llama was/is so popular, when it's actually so loud it's almost unusable. The only thing I can think of is using it as a main distortion-source, but I can't see many people doing that...... The bass isn't much of an issue for me, with a Marshall and my Framus Diablo my bass is thight enough! 
Right now I'm thinking about leaving the gain pot as it is, and changing the volume for a 100k, as I like the ridiculous amount of gain. Shame I'll have to de-solder the pot, so proud of how I got the whole deal in there...

Paul