SOLVED Cobalt troubleshoot

[Redspacecadet74]

Hi, I’m hoping for some help with the Cobalt pedal I just built.

I plugged the pedal in and whilst there was some sound with the pedal switched on it was kind of muted and a bit fizzy. I checked the circuit and realised I had used a TL072 IC in place of the TL071 specified in the build instructions.

I assume this explains the sound issues, but I was hoping someone with more knowledge of circuit design could confirm this before I replace the IC with the correct one?

 

[Laundryroom David]

They’re different critters. Plop a TL071 in there and see what it does. You may be pleasantly surprised!

 

[Chuck D. Bones]

TL071 is a single version of the TL072 dual. Not interchangeable.

 

[Locrian99]

As was stated above they are not interchangeable this is because they have a different pin out. Typically you can swap op amps for the same type. A dual op amp like the tl072 can be swapped for say a 4558 because they are both duals the ground is pin 4 the +v in is pin 8 the outputs are pins 1 and 7. Your inputs are 2/3/5/6 2 and 6 being inverting. Where as the tl071 7 is your +v instead of 8 so it was trying to send +v to the one of the tl072s outputs. Pin 6 is the output so it was expecting to see output from an inverting input. This is why it won’t work.

 

[Redspacecadet74]

TL071 is a single version of the TL072 dual. Not interchangeable.

Thanks. I’ve ordered the correct TL071, hopefully that sorts it.

 

[Redspacecadet74]

As was stated above they are not interchangeable this is because they have a different pin out. Typically you can swap op amps for the same type. A dual op amp like the tl072 can be swapped for say a 4558 because they are both duals the ground is pin 4 the +v in is pin 8 the outputs are pins 1 and 7. Your inputs are 2/3/5/6 2 and 6 being inverting. Where as the tl071 7 is your +v instead of 8 so it was trying to send +v to the one of the tl072s outputs. Pin 6 is the output so it was expecting to see output from an inverting input. This is why it won’t work.

Thanks. I could have sworn I ordered the right one. Never mind, the correct part is on its way!

 

[Chuck D. Bones]

Do you have any other single opamps? LF356? NE5534? OP27? 741 (barf)? You could at least see if everything else is working.

Nice neat build. Very clean.

 

[Laundryroom David]

Thanks. I could have sworn I ordered the right one. Never mind, the correct part is on its way!

A TL071

 

[Redspacecadet74]

Do you have any other single opamps? LF356? NE5534? OP27? 741 (barf)? You could at least see if everything else is working.

Nice neat build. Very clean.

Good idea. The other opamps I have spares of are CA3130, JRC4580 and RC4558. Are any of those single opamps?

A TL071

ha ha, well spotted!

 

[Chuck D. Bones]

CA3130 is a single. If you use that, you will need to tack a 33pF (or 47pF) cap from pin 1 to pin 8 on the CA3130.

While you're waiting for your TL071, you could entertain yourself reading my 4-part article on the BD-2 over in Chucks Boneyard.

 

[steviejr92]

Good idea. The other opamps I have spares of are CA3130, JRC4580 and RC4558. Are any of those single opamps?

ha ha, well spotted!

RC 4558 i know for a fact is a dual opamp.
Do a quick google search itll tell you which is dual op amp and single op amp

 

[Laundryroom David]

Legit 3130s are getting a bit dear. Take care of those!

 

[Laundryroom David]

Do you have any other single opamps? LF356? NE5534? OP27? 741 (barf)? You could at least see if everything else is working.

Nice neat build. Very clean.

Super neat build. Really dig it!

 

[Chuck D. Bones]

Legit 3130s are getting a bit dear. Take care of those!

They're still in production. Tayda has 'em in stock. Mouser is currently out-of-stock on the thru-hole parts. When did they get so expen$ive? This inflation thing sucks.

 

[Laundryroom David]

They're still in production. Tayda has 'em in stock. Mouser is currently out-of-stock on the thru-hole parts. When did they get so expen$ive? This inflation thing sucks.

No idea. There's a couple of sellers on eBay asking about $10 a piece

 

[Coda]

CA3130 is a single. If you use that, you will need to tack a 33pF (or 47pF) cap from pin 1 to pin 8 on the CA3130.

While you're waiting for your TL071, you could entertain yourself reading my 4-part article on the BD-2 over in Chucks Boneyard.

Personally, I’m waiting for the HBO mini-series…

 

[Redspacecadet74]

Thanks everyone for your help. Does anyone know if I’m likely to have caused any damage to the TL072 by powering on the pedal?

 

[szukalski]

No idea. There's a couple of sellers on eBay asking about $10 a piece

It's a crap-shoot. Sometimes you can find a retailer who has stock and hasn't adjusted their prices yet. I was lucky to find TL072s for €0.35 each recently. Didn't last long.

 

[Chuck D. Bones]

Those chips are amazingly forgiving. You're probably fine.

 

[Redspacecadet74]

So, I swapped the chip for the correct TL071 and guess what, it works fine. Not that impressed with how it sounds through my Yamaha TR10 practice amp, but I’ll reserve judgement until I’ve tried it through my valve amp.

Cheers for all the help.