A/B Box with Buffered Outputs using TL072

[GarryGirthOak]

ahhh right sweet. By the way. I've soldered the circuit together. I will probably go for a third attempt. But im basically getting this noise.

https://soundcloud.com/asher-gregory/what-is-this-noise

The noise appears when the volume on my guitar is turned all the way down. The noise reduces when the volume is on full. The noise is also amplified when the guitar is unplugged. The noise goes away when i short the singal to ground.

Does anyone know what kind of noise this is ?

I've made sure all the tracks were cut correctly. Made sure the soldering was fine and also made an effort to make sure there were no shorts. Is there something wrong with my veroboard layout? I'll obtain more parts tomorrow, breadboard it and test it again, see if it's definitely just the veroboard version that has the noise

[R.G.]

2. If not, what needs to be changed. I won't accept a answer that involves changing the OP-AMP.

Good for you! If what you've decided to use won't work the way you want it to, refuse to accept that answer. What does Mother Nature know about it, anyway?

[Derringer]

RG, I have faith that brother Garry knows that a TL072 is a workhorse of an opamp that is perfectly suited to this task. No? 

yeah, breadboard it first Garry and see what you've got.

The only thing I can think of is that maybe the second unused half of your opamp is somehow interfering, but I'm not sure why. 
Can't see from the vero but I'm assuming the trace cuts continue beneath the opamp?

[GarryGirthOak]

Well i did breadboard it first before soldering it to veroboard and it didn't have that noise. I'll breadboard it again, see what happens

[R.G.]

RG, I have faith that brother Garry knows that a TL072 is a workhorse of an opamp that is perfectly suited to this task. No? 

I have the same faith - but there aren't any perfect opamps, and an initial statement that no other solutions will be accepted is a dramatic narrowing of the options. No? 

[GarryGirthOak]

I purposely mentioned this so the discussion wouldn't go off track. Like i've seen allot of other threads do when asking a similar question. Out of the two or three threads i've made. two on this forum and the other on DiyAudio. This thread, thanks to Derringer, has been the only one that's been able to find a effective use for the other op-amp 

[GarryGirthOak]

Also R.G, any tips for soldering onto veroboard or creating vero board layouts? I would only imagine you have eons of experience 

[GarryGirthOak]

The only thing I can think of is that maybe the second unused half of your opamp is somehow interfering, but I'm not sure why. 
Can't see from the vero but I'm assuming the trace cuts continue beneath the opamp?

Yes there is trace cuts underneath the op-amp I got a slight idea of what im doing. Im thinking perhaps the +18v is too close to the input circuitry and that the parts are soldered to close together, perhaps spacing the layout by a few strips might help. Except for where the op-amp is...

[R.G.]

Also R.G, any tips for soldering onto veroboard or creating vero board layouts? I would only imagine you have eons of experience 

Yes, I do have some experience. 

Soldering on veroboard is like soldering onto PCB. It *is* PCB, just with wider traces and predefined holes. It's a bit more difficult to solder because the "pads" are as wide as the traces and the traces wick heat away from the area you're trying to solder faster than they do with a typical PCB where the trace is thinner than the pad. You'll need a slightly hotter iron and good cleaning on the copper, as well as good soldering technique.

I have done vero board layouts. I don't like them much, as they're larger and more complicated to assemble than PCBs. But the same techniques apply for laying out vero boards as for PCBs; you're just limited in that vero board limits where you can put parts and their orientation. It's good that most vero board layouts are small. The size and complexity to make them gets out of hand for complicated circuits. But for simple one-of-a-kind circuits, they're OK.

Your noise issue is probably the opamp oscillating when the input is opened. It happens. A shorting jack on the input should fix that. Or possibly it needs some  power supply bypassing.

Part of what's missing here is that you've neglected the invisible parts of the circuit - what is driving the input and what is loading the output. You're thinking about a guitar in; what if that's another effect cabled into the input? Also, what does this drive? Two parallel effects chains? Two amps? What is the input impedance of the things it will drive?

If the loads are amp inputs, or (well designed...) pedals, you can simply use one half of the opamp as a buffer and place two 10K pots on the output. Each pot output can be switched, and it will drive a modest length of cable or a ~1M load just fine.

See the AB/Y splitters and switching at geofex.com.