SOLVED Chela builds have fizz in note decay

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mekrob69

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Good morning,

I recently built 2 chela clones, one with nicer components and one with cheaper stuff. The one with nicer components does sound better, but both seem to suffer from a grainy breakup behind the signal, especially at lower gain settings (which I don’t see in the demo videos by EQD). Once the gain is cranked that blends with the saturation of the pedal, which is fuzzier than I was ready for.


Here is a video showing the problem. At lower gain settings it’s very obvious, after about half gain it’s not super noticeable because the whole signal gets so saturated.

After a lot of research last night my two best guesses are the TL072 being bad or the LEDs, I was curious if a clear/white LED would help, because a gut shot reveled the Talons uses clear LEDs rather than red.
 
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I would wager that the TL072s are the culprit. I recently built 5 Klon circuits and ALL of them had fizzy tails. I replaced the TL072s with ones from Mouser and the problem went away. The batch I first used in the Klon circuits were from Tayda. Good luck!
 
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Cybercow said:
I would wager that the TL072s are the culprit. I recently built 5 Klon circuits and ALL of them had fizzy tails. I replaced the TL072s with ones from Mouser and the problem went away. The batch I first used in the Klon circuits were from Tayda. Good luck!
Click to expand...
I just ordered some more, some from Mouser and some from Guitarpedalparts, fingers crossed!

Do you have any recommended method for removing the non-socketed IC? Will I need to remove the pot over the back side of the IC?

Thank you :)
 
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Forward voltage on a white LED is about double compared to a red LED from memory. That would mean much less distortion for the same gain settings. Of course, if the rest of the circuit has been altered to be optimised for red instead then changing to white would give less distortion, but also wouldn't match the sound of the original.
 
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mekrob69 said:
Good morning,

I recently built 2 chela clones, one with nicer components and one with cheaper stuff. The one with nicer components does sound better, but both seem to suffer from a grainy breakup behind the signal, especially at lower gain settings (which I don’t see in the demo videos by EQD). Once the gain is cranked that blends with the saturation of the pedal, which is fuzzier than I was ready for.


Here is a video showing the problem. At lower gain settings it’s very obvious, after about half gain it’s not super noticeable because the whole signal gets so saturated.

After a lot of research last night my two best guesses are the TL072 being bad or the LEDs, I was curious if a clear/white LED would help, because a gut shot reveled the Talons uses clear LEDs rather than red.
Click to expand...
Just to be sure, Can you show a good picture of the PCB showing all the resistors?
 
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PJS said:
Forward voltage on a white LED is about double compared to a red LED from memory. That would mean much less distortion for the same gain settings. Of course, if the rest of the circuit has been altered to be optimised for red instead then changing to white would give less distortion, but also wouldn't match the sound of the original.
Click to expand...
Okay, since this pcb is designed around red LEDs I will leave those alone, thanks for the interesting info
 
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jesuscrisp said:
Just to be sure, check IC voltages.
Do your clipping LEDs both light up when playing?

Otherwise a lot of that sort of fizzy decay can usually be attributed to clipping LEDs.
Click to expand...
How do I check IC voltage?

I will check if the LEDs light up tonight. I was under the impression that frequently clipping LEDs don’t light up since they are being used as a diode not a light. Do you mean that fizzy the decay is a part of using clipping LEDs, or that something is up with the LEDs ?
 
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music6000 said:
Resistors are all Good!!!
Do you have a OPA2134 you can try in place for the TL072?
If you don't, you can also try JRC4558.
Click to expand...
Great to hear! What were you looking for?

I have neither, this is my first build, so I don’t have many extra parts. I did order 4 more TL072s from two different sources so hopefully those work. But I will keep those other ICs in mind, especially with future builds/sourcing
 
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mekrob69 said:
I just ordered some more, some from Mouser and some from Guitarpedalparts, fingers crossed!

Do you have any recommended method for removing the non-socketed IC? Will I need to remove the pot over the back side of the IC?

Thank you :)
Click to expand...
Mind you, the Chela circuit has clipping diodes that are ALWAYS in circuit, which means the signal will ALWAYS be getting a 'haircut' by those clipping diodes. Also, it is NOT an exact replica of the EQD Talons after which it is designed. And in either case, it is considered a hi-gain overdrive circuit. Most hi-gain OD builds will add distortion to the signal.

So with that in mind, and you still want to replace the unsocketed opamp - There are at least two ways to remove an un-socketed IC. One is destructive - using fine-tipped clippers, cut each leg of the IC very close to the IC body. That way, each leg can be heated and pulled from the hole once the solder flows. Some clean-up afterwards is often required. Putting it back without a socket is then easy. If you want to put in a socket, it would be best to remove the pot covering the solder-side of that IC location.

The other method is to first remove the pot that covers the solder-side of the IC location, then proceed to desolder each leg of the of th IC until it comes free. More often than not, unless one is very confident with their soldering skills, it is till a good idea to cut the legs from the body of the IC be removing (desoldering) those legs. And with the pot removed, adding a socket will be much easier.

Even for those of us with a high level of soldering/desoldering confidence, removing ICs (or sockets) is always a PITA. Have a good solder-sucker, flux and often-times adding a touch more solder to a joint for removal of a lead/leg can help. A good pre-fluxed solder-wick can also help with the clean up. And remember the 10-second rule. Never have a hot soldering iron on any given solder point for more than 10 seconds at a time - with adequate cooling time between trying to cleanup the same solder joint.

Also, its good to keep in mind that electronics is a fickle mistress and if replacing the opamp does not correct the problem, do not be afraid to use (or make and use) a signal tracer to pinpoint from where the the distortion comes. If you're not familiar with a signal tracer, it's an easy look up and build one with a quick Google search. Mine is just an alligator clip attached to a short bit of insulated wire attached to a 0.1µF 250v orange-drop capacitor which in turn is connected to a six inch piece of insulated wire with about a quarter inch stripped and tinned for touching the various points in the signal path. The cap is simply to prevent any DC from being passed thru the signal tracer should the tip come in contact with a DC source.

In summary, considering the circuit is a hi-gain OD, and these are your first builds, you may want to ponder the idea that it just might not be the circuit for you - and it may actually be performing precisely as intended by the vendor. There are many factors in YouTube video demos that come into play that few consider when making a decision based on such YouTube demos. The amp(s) used, the pickups on the guitar, any off-board/off-screen pre-processing that may have been employed.

When I started building I was disappointed by many builds that I though would be one thing, but turned out differently than I'd hoped. It happens more often than not in the beginnings of the sojourn down the pedal building path.

Good luck!
 
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Cybercow said:
Mind you, the Chela circuit has clipping diodes that are ALWAYS in circuit, which means the signal will ALWAYS be getting a 'haircut' by those clipping diodes. Also, it is NOT an exact replica of the EQD Talons after which it is designed. And in either case, it is considered a hi-gain overdrive circuit. Most hi-gain OD builds will add distortion to the signal.

So with that in mind, and you still want to replace the unsocketed opamp - There are at least two ways to remove an un-socketed IC. One is destructive - using fine-tipped clippers, cut each leg of the IC very close to the IC body. That way, each leg can be heated and pulled from the hole once the solder flows. Some clean-up afterwards is often required. Putting it back without a socket is then easy. If you want to put in a socket, it would be best to remove the pot covering the solder-side of that IC location.

The other method is to first remove the pot that covers the solder-side of the IC location, then proceed to desolder each leg of the of th IC until it comes free. More often than not, unless one is very confident with their soldering skills, it is till a good idea to cut the legs from the body of the IC be removing (desoldering) those legs. And with the pot removed, adding a socket will be much easier.

Even for those of us with a high level of soldering/desoldering confidence, removing ICs (or sockets) is always a PITA. Have a good solder-sucker, flux and often-times adding a touch more solder to a joint for removal of a lead/leg can help. A good pre-fluxed solder-wick can also help with the clean up. And remember the 10-second rule. Never have a hot soldering iron on any given solder point for more than 10 seconds at a time - with adequate cooling time between trying to cleanup the same solder joint.

Also, its good to keep in mind that electronics is a fickle mistress and if replacing the opamp does not correct the problem, do not be afraid to use (or make and use) a signal tracer to pinpoint from where the the distortion comes. If you're not familiar with a signal tracer, it's an easy look up and build one with a quick Google search. Mine is just an alligator clip attached to a short bit of insulated wire attached to a 0.1µF 250v orange-drop capacitor which in turn is connected to a six inch piece of insulated wire with about a quarter inch stripped and tinned for touching the various points in the signal path. The cap is simply to prevent any DC from being passed thru the signal tracer should the tip come in contact with a DC source.

In summary, considering the circuit is a hi-gain OD, and these are your first builds, you may want to ponder the idea that it just might not be the circuit for you - and it may actually be performing precisely as intended by the vendor. There are many factors in YouTube video demos that come into play that few consider when making a decision based on such YouTube demos. The amp(s) used, the pickups on the guitar, any off-board/off-screen pre-processing that may have been employed.

When I started building I was disappointed by many builds that I though would be one thing, but turned out differently than I'd hoped. It happens more often than not in the beginnings of the sojourn down the pedal building path.

Good luck!
Click to expand...
In which case, you must feed the beast by building more pedals. If you haven’t boxed it, I wouldn’t. I have quite the pile of builds I decided not to box, some are some I had fabricated myself.
 
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Cybercow said:
Mind you, the Chela circuit has clipping diodes that are ALWAYS in circuit, which means the signal will ALWAYS be getting a 'haircut' by those clipping diodes. Also, it is NOT an exact replica of the EQD Talons after which it is designed. And in either case, it is considered a hi-gain overdrive circuit. Most hi-gain OD builds will add distortion to the signal.

So with that in mind, and you still want to replace the unsocketed opamp - There are at least two ways to remove an un-socketed IC. One is destructive - using fine-tipped clippers, cut each leg of the IC very close to the IC body. That way, each leg can be heated and pulled from the hole once the solder flows. Some clean-up afterwards is often required. Putting it back without a socket is then easy. If you want to put in a socket, it would be best to remove the pot covering the solder-side of that IC location.

The other method is to first remove the pot that covers the solder-side of the IC location, then proceed to desolder each leg of the of th IC until it comes free. More often than not, unless one is very confident with their soldering skills, it is till a good idea to cut the legs from the body of the IC be removing (desoldering) those legs. And with the pot removed, adding a socket will be much easier.

Even for those of us with a high level of soldering/desoldering confidence, removing ICs (or sockets) is always a PITA. Have a good solder-sucker, flux and often-times adding a touch more solder to a joint for removal of a lead/leg can help. A good pre-fluxed solder-wick can also help with the clean up. And remember the 10-second rule. Never have a hot soldering iron on any given solder point for more than 10 seconds at a time - with adequate cooling time between trying to cleanup the same solder joint.

Also, its good to keep in mind that electronics is a fickle mistress and if replacing the opamp does not correct the problem, do not be afraid to use (or make and use) a signal tracer to pinpoint from where the the distortion comes. If you're not familiar with a signal tracer, it's an easy look up and build one with a quick Google search. Mine is just an alligator clip attached to a short bit of insulated wire attached to a 0.1µF 250v orange-drop capacitor which in turn is connected to a six inch piece of insulated wire with about a quarter inch stripped and tinned for touching the various points in the signal path. The cap is simply to prevent any DC from being passed thru the signal tracer should the tip come in contact with a DC source.

In summary, considering the circuit is a hi-gain OD, and these are your first builds, you may want to ponder the idea that it just might not be the circuit for you - and it may actually be performing precisely as intended by the vendor. There are many factors in YouTube video demos that come into play that few consider when making a decision based on such YouTube demos. The amp(s) used, the pickups on the guitar, any off-board/off-screen pre-processing that may have been employed.

When I started building I was disappointed by many builds that I though would be one thing, but turned out differently than I'd hoped. It happens more often than not in the beginnings of the sojourn down the pedal building path.

Good luck!
Click to expand...
Resistors are all Good!!!
Do you have a OPA2134 you can try in place for the TL072?
If you don't, you can also try JRC4558.
Update: I didn't realize your Build doesn't have the Socket that was in your initial Test Bench Picture.
the OPA2134 is the smoothest OpAmp I know for pedals!
I use DIP8 Machined Sockets.
I think it maybe the LED Clipping that you may not like,
You may want to try 1N4148 Diodes in that position pictured Below:

Machined Socket with TL072 -1N4148.jpg
 
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Also, I think your TL072's are Fake, Texas Instruments TL072 do not have the Indent in them at the top centre
If you look at my Picture directly above you will see what a Genuine Texas Instruments TL072 with Machined Socket should look like!!!
I have added the 1N4148 Diodes to the Pic also:

F0304239-01
FAKE
s-l400.jpg
 
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Update: After reading @Cybercow’s post above, this looks like the same post. If yes, nice write-up!

By the way, a respected pedal builder on a Facebook group posted this week about a batch of pedals he’d just built which exhibited the same issue with the Tayda TL072s. Here’s his post:
 

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