Ocelot OC2 distorting after several months of use?

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Wizardofwoz66

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I built an ocelot for a buddy several months ago, and all of a sudden about a week ago he complained that it was doing weird things. I met up with him today, and it's definitely distorting when hit hard (he's playing a bass with pretty hot active pups). I tested it on a few guitars and my passive pup bass at home, it's definitely clipping something in the circuit, because the lower output guitars didn't do it - gotta be something not getting enough voltage I would think? The clipping happens regardless of pot positions unless all are at 0 since they're all essentially just passive volumes for individual octaves. I opened it up and there's nothing obviously wrong with it (all ICs are seated properly in sockets, no broken solder joints etc). Any thoughts on where to begin here? It's strange that it started out of nowhere.
 
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Synchrony Pedalworks said:
There is a string in the forum about this circuit and distortion. If my memory is correct, it was due to an IC (TL072). An easy, risk free option is to sub out the IC’s and see if the problem improves.
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I did try searching first and was unable to find anything already posted about this. I'll try swapping out some 072s, though I just built another set of four and they're all doing it. I did some googling and apparently this is an issue even in the original circuit, it doesn't like super hot pickups https://www.talkbass.com/threads/oc-2-distorting-any-suggestions.560060/

A few folks in there suggested a compressor before it to essentially act as a limiter, I'm wondering if there's an easy way to put a diode limiter in to help. Unfortunately not sure where exactly in the circuit it's distorting
 
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Wizardofwoz66 said:
I did try searching first and was unable to find anything already posted about this. I'll try swapping out some 072s, though I just built another set of four and they're all doing it. I did some googling and apparently this is an issue even in the original circuit, it doesn't like super hot pickups https://www.talkbass.com/threads/oc-2-distorting-any-suggestions.560060/

A few folks in there suggested a compressor before it to essentially act as a limiter, I'm wondering if there's an easy way to put a diode limiter in to help. Unfortunately not sure where exactly in the circuit it's distorting
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Good information. I can see how high output pickups contribute to the problem. I do not know how to add the diode limiter.
 
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Synchrony Pedalworks said:
Good information. I can see how high output pickups contribute to the problem. I do not know how to add the diode limiter.
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Yeah, just unfortunate that I tested with a lower output guitar lol. The guy who I sold this one to (I sold him two at the same time) said it just started, but I think that's untrue based one what I'm seeing now. He's got a five string active Ibanez bass that I assume is just rocking one of the op amps. I know how to put a limiter in, just not sure where it needs to go lol this is not a particularly simple circuit unfortunately.
 
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Do you hear the distortion in the original nonpitched signal, or just the octaves? If it's both...
Could try changin Rf(R5) on the input buffer for less gain.
Gain is currently at 4.5 there.
A 7k would get you 3.6
5k - 2.8
Can quickly test by clipping a 20k in parallel with the 10k R5 for 6.67k.(or solder an 1/8w to the other side)

If that fixes it, could squeeze a 5k resistor in series with a 5k trimpot maybe?
 
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jwin615 said:
Do you hear the distortion in the original nonpitched signal, or just the octaves? If it's both...
Could try changin Rf(R5) on the input buffer for less gain.
Gain is currently at 4.5 there.
A 7k would get you 3.6
5k - 2.8
Can quickly test by clipping a 20k in parallel with the 10k R5 for 6.67k.(or solder an 1/8w to the other side)

If that fixes it, could squeeze a 5k resistor in series with a 5k trimpot maybe?
Click to expand...
It is in the non pitched signal too, this is a good point! I'll give this a shot tonight, thanks!
 
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Good to know this is an issue. I haven’t built an oc-2 yet, but I’ve been planning on designing a board for one that integrates some interesting mods, and I think in this case I’ll add a dipswitchable limiter on the front end too.
 
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Bricksnbeatles said:
Good to know this is an issue. I haven’t built an oc-2 yet, but I’ve been planning on designing a board for one that integrates some interesting mods, and I think in this case I’ll add a dipswitchable limiter on the front end too.
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Nice! I attempted to squeeze this circuit onto a board that would fit a 1590B (by request), it was my first attempt at laying out a PCB...doesn't work lol. I do have signal at the end, but none of the knobs do anything and I have no octaves :ROFLMAO:. I will report back after trying a different resistor in the buffer either tonight or tomorrow. I guess putting a limiter directly after the buffer should have roughly the same effect as reducing the gain
 
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Active basses outputting 4Vpk-pk is not unheard of which obviously bumps up against the headroom of a 9V pedal. I’ve never had issues with my active guitars with the oc2 but basses running off 18v as opposed to 9v isn’t uncommon. I’ve had other distortion issues with the oc2 but it’s not what you’re describing here.

Part of me wants to say just tell the player to turn down their volume (lol), but short of that here’s a few things I’d try with the unexpectedly hot signal:

- as @jwin615 suggested lowering the gain of the first op amp stage, but if the signal is already hitting the rails before this stage this won’t solve much
- raising power supply to +12v, +15v, or +18v - the main limiting factor in the oc2 (in terms of ic failure) are the cmos ics that have an absolute maximum supply voltage of 20v, with 18v being the max suggested from their datasheets.
- adding input clipping diodes will introduce different distortion but could help reduce the op amp saturation distortion from further amplifying a signal hitting the rails. would be as simple as adding two diodes in opposite directions to ground in series with a resistor at the input
- an input attenuation pot either external or trim
 
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finebyfine said:
Active basses outputting 4Vpk-pk is not unheard of which obviously bumps up against the headroom of a 9V pedal. I’ve never had issues with my active guitars with the oc2 but basses running off 18v as opposed to 9v isn’t uncommon. I’ve had other distortion issues with the oc2 but it’s not what you’re describing here.

Part of me wants to say just tell the player to turn down their volume (lol), but short of that here’s a few things I’d try with the unexpectedly hot signal:

- as @jwin615 suggested lowering the gain of the first op amp stage, but if the signal is already hitting the rails before this stage this won’t solve much
- raising power supply to +12v, +15v, or +18v - the main limiting factor in the oc2 (in terms of ic failure) are the cmos ics that have an absolute maximum supply voltage of 20v, with 18v being the max suggested from their datasheets.
- adding input clipping diodes will introduce different distortion but could help reduce the op amp saturation distortion from further amplifying a signal hitting the rails. would be as simple as adding two diodes in opposite directions to ground in series with a resistor at the input
- an input attenuation pot either external or trim
Click to expand...
My 7 string with Fishmans clips this, as does my Les Paul which is just high output passives, but I assume there's no way that's hitting the rails, so I'm thinking the buffer may be the fix. It's easy enough to try, I just don't know if it'll ultimately cause unwanted level drop. I'll try clipping diodes in at the input, this is similar to a limiter at that point too, it's just not clean lol.

The dude who bought this and is buying the others is someone who will definitely not bend on doing anything on his end unfortunately lol. No way he'll deal with tuning an internal trimpot to his bass or turn down and I don't trust him to use 18V because he'll fry something else, pretty sure he daisy chains everything. I built him a TC preamp which, if he plugs in 18V, will wreck the charge pump and/or electrolytics lol.
 
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Wizardofwoz66 said:
My 7 string with Fishmans clips this, as does my Les Paul which is just high output passives, but I assume there's no way that's hitting the rails, so I'm thinking the buffer may be the fix. It's easy enough to try, I just don't know if it'll ultimately cause unwanted level drop. I'll try clipping diodes in at the input, this is similar to a limiter at that point too, it's just not clean lol.

The dude who bought this and is buying the others is someone who will definitely not bend on doing anything on his end unfortunately lol. No way he'll deal with tuning an internal trimpot to his bass or turn down and I don't trust him to use 18V because he'll fry something else, pretty sure he daisy chains everything. I built him a TC preamp which, if he plugs in 18V, will wreck the charge pump and/or electrolytics lol.
Click to expand...

Yuuuup everything you said is what was going through my head as I was thinking about solutions. Sounds clear it’s not before the first op amp though. Sort of caught in between a rock and a hard place if lowering the buffer gain helps the clipping but affects the octave generation. Probably not that hard to fix that too but would require a deeper dive
 
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finebyfine said:
Yuuuup everything you said is what was going through my head as I was thinking about solutions. Sounds clear it’s not before the first op amp though. Sort of caught in between a rock and a hard place if lowering the buffer gain helps the clipping but affects the octave generation. Probably not that hard to fix that too but would require a deeper dive
Click to expand...
The worst part is my bass is low enough output that it doesn't clip lol, so even if I get it to stop clipping the guitars, I won't know until he plugs in. He plays in a pop/rock cover band, dude needs to get a Jazz Bass and call it a day lol. Only time I use the OC2 I've built myself is for CKY stuff and it's all distorted already so I don't have to care haha
 
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Wizardofwoz66 said:
The worst part is my bass is low enough output that it doesn't clip lol, so even if I get it to stop clipping the guitars, I won't know until he plugs in. He plays in a pop/rock cover band, dude needs to get a Jazz Bass and call it a day lol. Only time I use the OC2 I've built myself is for CKY stuff and it's all distorted already so I don't have to care haha
Click to expand...

Do you have a spare boost you could use while testing with your bass?
 
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finebyfine said:
Active basses outputting 4Vpk-pk is not unheard of which obviously bumps up against the headroom of a 9V pedal. I’ve never had issues with my active guitars with the oc2 but basses running off 18v as opposed to 9v isn’t uncommon. I’ve had other distortion issues with the oc2 but it’s not what you’re describing here.

Part of me wants to say just tell the player to turn down their volume (lol), but short of that here’s a few things I’d try with the unexpectedly hot signal:

- as @jwin615 suggested lowering the gain of the first op amp stage, but if the signal is already hitting the rails before this stage this won’t solve much
- raising power supply to +12v, +15v, or +18v - the main limiting factor in the oc2 (in terms of ic failure) are the cmos ics that have an absolute maximum supply voltage of 20v, with 18v being the max suggested from their datasheets.
- adding input clipping diodes will introduce different distortion but could help reduce the op amp saturation distortion from further amplifying a signal hitting the rails. would be as simple as adding two diodes in opposite directions to ground in series with a resistor at the input
- an input attenuation pot either external or trim
Click to expand...
Yeah, if his bass is that hot, there's not a ton to be done without voltage conversion. It'll possibly be a struggle getting unity out at 9v. Maybe that output stage can be raised some? Or swapped?
If you get it nailed down and not clipping for you anywhere, but it still clips on his bass, that's not really on the builder or the pedal. CMOS can only take so much signal.
If I plug my 110v toaster into a 220v outlet and it bursts into flames, Cuisinart doesn't owe me another toaster...
I'd be curious about his rig as well. Is he running something before this pedal that's overdriving it? Has he changed something recently(maybe put a new battery in the bass?)?
 
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Feral Feline said:
Compressor in front will reduce the hot bass to manageable levels and give the Ocelot-tracking something to better latch on to...
Click to expand...
I mentioned this to him yesterday, I dunno if he wants to run a comp. Dude is kinda a pain but he's a friend and I love him so here we are lol. I basically sold this to him at build cost so I've been attempting to find solutions that don't take up a ton of my time
 
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