PT2399 --> high gain overdrive? (with sound clip)

[Zounds!]

I built a Madbean Cave Dweller using this layout -- http://tagboardeffects.blogspot.ca/2014/04/madbean-cave-dweller.html

By mistake I discovered that by connecting the top row between the first two cuts to the second row between the first two cuts of that row via a capacitor, the dry signal turns into a pretty high gain distortion or overdrive (which cleaned up with the volume knob on my guitar), and the delay still worked as it should. It isn't the most refined sound, but it was a cool discovery, and one which I am sure I'm not the first to stumble upon or utilize....Googling or searching this site for "pt2399 distortion" however gets me the expected unrelated results (sorry if this is a rehash!), so I wanted to see if anyone could explain what is going on here and if there is any way to lower the volume, as the distortion comes with a  pretty big volume jump. I'm thinking I'll put it on a toggle switch, as it's so simple and sounds fairly decent to me. The Cave Dweller really muddies up my dry signal, which is especially noticeable with a distortion or fuzz pedal going into it, not a huge deal with a clean signal. With this little mod the sound is much clearer and doesn't lose all its bite -- it might have too much bite actually, which hopefully I can figure out a way to tame a bit. Thanks for any insight!

[mth5044]

Have a look at the schematic

http://www.madbeanpedals.com/projects/CaveDweller/CaveDweller.pdf

From your description, it sounds like you are simply bypassing that first 750k resistor, so I'm guessing you are overdriving the pt2399 input. You could turn that 750k into a variable resistor using a pot, possiblly 1Meg as 500k wouldn't get you enough resistance to get the normal sound, unless you add a series resistor.

To control the volume and keep the high gain, you could out a volume pot at the end of the circuit.

[Zounds!]

I replaced the 750k resistor with a C1M pot (maybe not the best taper but I had it on hand) and put a 220pf cap between the lugs, which I think is effectively a treble bleed(?). The dry signal brightens up a ton when the pot is turned to the "clean" side and is now almost 99% uncolored sounding when the repeats are turned off. At this point it might even be slightly brighter sounding than the bypass tone, which helps the dry signal stand out from the repeats. I tried an A100k pot as a volume control which works, but when the newly added gain pot is turned up to the highest gain (full clockwise), the volume pot needs to be almost completely counterclockwise to be near unity volume, and a slight nudge puts it way over the top loud....it has WAY more output than could ever be useful. Will have to experiment with values and tapers I guess. Thanks for the tips mth5044!

EDIT: dry signal when the pedal is engaged sounds almost identical to bypass with this mod, but it sucks a noticeable amount of high end off if you put a fuzz or distortion in front of it. Not as bad as the original circuit, but far from perfect.

[davent]

You might be interested in the Noise Ensemble.
http://www.diystompboxes.com/smfforum/index.php?topic=87493.0

[aron]

Ace Frehley would love your Noise Ensemble!!!!!!

[Zounds!]

Hey that Noise Ensemble is cool! Much glichy-er than what I've got here, but probably something I'll have to try out.

Here is a sample of what my pedal sounds like with no other effects or EQing: https://www.dropbox.com/s/94g2vpsnm05cqm7/cave%20dweller%20with%20overdrive.wav?dl=0

(pardon the single coil hum on the overdrive sections! last section is with a humbucker so is quieter)

0:00 - Bypass
0:14 - pedal engaged, no overdrive, no repeats
0:27 - clean delay sound
0:54 - max overdrive + delay
1:09 - same, but with volume on guitar rolled off
1:34 - a moment of heavy riffing with max overdrive (and some delay I think)
2:06 - more overdrive riffing without any delay because I was having fun

It does get sort of splatty with the milder overdrive sounds (in between clean and maximum on the gain pot), so I've been sticking to the high end of the gain pot and using my volume to tame it a bit. Gets pretty fuzzy, which I'm into! 

[midwayfair]

Those last few pins of the PT2399 are inverting op amp stages, running on 5V. If you like the sound and don't need the delay part of it, there are cheaper chips and simpler circuits you can use to get it. I'm not mentioning this to stymie experimentation but because you might not be aware of what's in the chip.

[Zounds!]

Ah that makes sense, as the sound is pretty familiar. Thanks for the insight! And thanks for sharing your findings with tweaking this pedal online (I saw your Nature Dweller video on YouTube video and some posts of yours)!

I definitely wouldn't build this just for the overdrive, but it is a simple and usable (I think) added tonal option in an already simple and good sounding build that I'm psyched to have stumbled upon.  Also cool t know that I could do this to other PT2399 circuits. I'm giving this to a friend who is just starting on guitar so she might dig the multi-fx quality since she doesn't have a pedal collection (yet!).

[Zounds!]

So now that I have an output volume pot on this build it is really easy to crank it up and let it oscillate wildly and just turn the volume down as it gets more and more out of control. I just did this and eventually the sound completely cut out. I switched to bypass and had signal, switched back and it was still silent. After 1 or 2 seconds it kicked back in and it functions as it should. It's almost as if it crashed and then needed to reboot. Will letting that happen damage the PT2399?

I also realized that a buffer before the circuit is necessary for the gain knob to deliver anything close to good sounding, so I built one in.

[anchovie]

You might be interested in the Noise Ensemble.
http://www.diystompboxes.com/smfforum/index.php?topic=87493.0

Thanks for mentioning! I'm still rather proud of it.

The Noise Ensemble gets its dirt by setting up the first stage of the 2399 as a comparator, so it's a case of maximum gain or nothing. I've tried expanding on it a few times to make the gain variable, but anything less than maximum didn't sound as appealing! 

[Zounds!]

Bump! Anybody want to weigh in on the likelihood that oscillation to the point of "crashing" will damage the chip? When it's phrased like that it doesn't sound like such a good idea, but what do I know? Also wondering if this has something to do with the gain pot being added to the circuit. I've never experienced such a thing with other self-oscillating PT2399-based delays....