DS-1 Clone Weird Clipping Help

[Fuzzy_BYU_ME]

Hey all,

I'm working on a modded DS-1 Clone based on the Aion Comet project, and I'm getting some weird results. When I roll the volume down on my strat and play lightly, everything is great. It sounds like a nice warm overdrive. But, if I pick hard at all or roll the volume pot up, I get this awful initial clipping. It sounds a lot like my Fuzz Factory when I turn up the comp and gate knobs. It's super gated, synthie, lo-fi, almost with upper octaves in there, in the worst way possible. As the note decays, this nasty clipping goes away, and it goes back to the warm overdrive type sound I am getting if I play softer.

I figured it was from either 1) clipping diodes, 2) weird op-amp clipping, or 3) first gain stage clipping. I have an on-off-on switch for the clipping diodes, so I can pull them out of the circuit easily and get the same result, so it's not the diodes. To check the op amp, I measured the voltages on it and those all look normal. I swapped out the TL072 I'm using with an RC4558 with the same effect. And this weird synth clipping is present with the gain knob all the way up or down, which I think tells me this is coming BEFORE the signal hits the op amp.

This leads me to believe there is something weird going on in the boost transistor, Q2. I am using a 2N5088 transistor for Q2. I tried replacing with a different 2N5088 (I checked the hFE and got around 450, which I believe is in spec) and got no change. I figured maybe there is just too much gain, so I swapped the bias resistors from 22 to 1k, and from 100k to 150k ohms. This seemed to help reduce the synthy clipping a hair, but it is still very present.

Any ideas what could be causing this problem? I'm really at a loss of what would be causing such a weird sound. Thanks y'all.

[Fuzzy_BYU_ME]

Sorry, just wanted to clarify the bias resistor changes. As labeled in the ElectroSmash schematic, I changed R5 from 100k-150k, R9 from 22 to 1k, and R8 from 10k to 82k.

[GibsonGM]

Have you tried using an audio probe to limit the guessing on where the problem first occurs?

[duck_arse]

Sorry, just wanted to clarify the bias resistor changes. As labeled in the ElectroSmash schematic, I changed R5 from 100k-150k, R9 from 22 to 1k, and R8 from 10k to 82k.

link to your circuit diagram? list of your mods? photos of your build? all would be helpful.

if you increase the collector resistor [smash R8] you will increase the gain of that section. why not go back to the 10k, and change the emitter resistor [smash R9] to 33R or 47R or 56R or 68R ..... to reduce the gain some?

I notice on the ElectroSmash circuit that they have included C2 AND C3, with their own private bias[-ho], having (only partially) cut out the fet bypass. the same seems to apply for C13, R19 and R20.

[Fuzzy_BYU_ME]

link to your circuit diagram? list of your mods? photos of your build? all would be helpful.

The PCB and schematic I'm working from can be found here: https://aionelectronics.com/project/comet-boss-ds1-distortion/

I incorporated pretty much all of the part substitutions seen on page 3. I plan to add the Big Muff clipping mod on a toggle switch, but haven't done so until this gets resolved.

Have you tried using an audio probe to limit the guessing on where the problem first occurs?

The audio probe was a fantastic idea, thank you! Turns out that the clipping is actually coming from the first op amp stage, coming out from pin 7 of the op amp. I tried putting R23 (as seen on the Aion schematic, the resistor going in series into the op amp) back to 47k, where as I had it at 20k based on suggested mods. This gave me yet more headroom before the sharp clipping happened, but didn't eliminate it. I think I'll try lowering the 82k resistor in the transistor back to 10k to lower the boost a bit and see if that helps. If that doesn't, I may increase R23 some more, maybe 100k or something.

Beyond those fixes, I don't know what else to try.

[alexradium]

i experienced the same problem in an original Boss DS1,it had a fried opamp,it was a M5223,i tried to substitute it with an rc4558 and tl072 and got the same results you are describing.
The key is in the opamp,in its capability of having a huge boosted signal coming from the transistor,that has the tendency to throw the bias voltage around and creating that fuzzy clipping.
Next week i will have here a TL2262 which is used in the MXR 78,basically the same circuit,i am confident that could solve the problem.

[ElectricDruid]

Fried op-amp is possible. You want something that can cope with being overdriven, certainly. 4558 is a good bet. If you have something else handy (even in another pedal) just swap it over and check. If the new one is the same, it isn't that.

I wonder if diode D6 could be in backwards? That'd give you a splatty distortion as soon as the input level went over the forward voltage (only 0.65V or so).

HTH,
Tom

[Fuzzy_BYU_ME]

Thanks for the advice, everyone! I got it to a satisfactory solution. I can't say the gross clipping will never happen again, but it only happens at this point when I reeeeally crank on it with loud pickups, and it's just for a split second, and it's mostly just noticeable when playing a single note. I think considering the nature of the problem, it doesn't seem possible to make the problem never happen, so I'm pleased with this compromise. The pedal now sounds awesome. Low gain sounds warm and dynamic, higher gain sounds responsive and aggressive, without getting too muddy. Super pleased, considering how low the DS-1's reputation is (although I did modify it quite a bit).

For future posterity, I tried swapping the TL072 with a JRC4558, and that made it way worse actually. So the TL072 was definitely the way to go. I tried putting R6 (from Aion schem) back down to 10k, but that made things horrible, so I put that back to 82k again. Then I increased R7 (Aion schem) until I got to 3.3k and was ultimately satisfied there. So... there ya go. You can definitely tell that decreasing the gain on this transistor reduces clipping, so turning the gain knob all the way down almost makes it a clean boost. But I kind of like that.

Now, time to add the Big Muff Pi clipping diodes at the front. I also plan to add the JHS Synth Mod to it as well, so we'll see how that goes.

[pinkjimiphoton]

sounds to me like it may be an "arcing" someplace in the signal path with a capacitor having a bad solder joint.  that can make that wretched static noise at the initial attack happen. try reflowing any suspect areas with some fresh solder. suck out most of the old and go fresh, a lot of times that will cure the problem.
its weird, cuz temperature and humidity can make it go away... or come back.
hopefully ya solve your issue. peace!