Help with tube screamer build

[poolhalljunkie13]

So I wanted to build my first pedal. A tube screamer clone. I built the one from here diyeffects.com/PDF/TSOD.pdf

Everything came out great. Solder work looked great. I ran into no problems what so ever. Put everything in the 125b box and turn it on and it's nothing but a loud humming noise with faint guitar in the background. Obviously I've checked everything and then some. I don't know what it could be.

The OP amp gets REALLY hot. So hot the first one stopped working. I switched it out only to have the same problem. So im thinking that my problem lies somwhere along with this OP amp as well because obviously the first one stopped working. Im posting several pics I took during the build. Can someone help me?



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[asmith]

I won't promise anything from my Google-Fu here, but:

Have you wired the power-supply backwards? Or put the op-amp in backwards? Apparently it will make an opamp overheat very quickly.

Also, I'm not sure how strong or tenuous the connection is, but when we wire our guitars backwards the shield ground connections head to hot and we get a ton of buzz. Perhaps this is a contributing factor to your own hum.

Hope that helps.

[poolhalljunkie13]

Well I got out my multimeter late last night and started probing around. first thing I notice is that Im getting 14.6 volts. Wow. Out of my 9v power supply. Right then I knew what the problem was. I wired up the battery cable to the pedal and put in a battery and everything worked fine. Hahaha. Never knew my power supply was putting out that much juice. I wander why it's doing that?

[ashcatlt]

Unless it's regulated, a wallwart generally will put out more voltage than specified when unloaded. It really only puts out 9V when it's supplying the current for which it's rated. But what kind of opamp is it? Most should be able to handle 14V without damage.

You're sure that it is a DC power supply of proper polarity, and that you wired the power jack properly?

[poolhalljunkie13]

Everything works perfect now. Everything was wired correct. The problem was the adapter I was using. It worked fine for other pedals but not for this DIY one. So I went and bought an actual 9v effects power supply and plugged it up and it works perfect now. Strange but that's how it goes.

[ashcatlt]

That's just frikken weird! Can you post us a pic of the labeling on the "bad" wallwart?

You didn't answer the question about the opamp either, but the link you posted calls for a 4558. These can handle 36V! So that wasn't the problem.

I do notice, though, that there's no reverse polarity protection in this circuit. You might want to look into adding it, just in case.

[poolhalljunkie13]

Sorry. Yeah it was the standard 4558. It could have been something else that knocked the chip out i really dont know. It got hot though. Too hot to keep your finger on it for more than 2 seconds. I had 2 adapters i was using. The one putting out 14.6 volts was labled with 9v output. It was just a standard adapter. The other was one of the adjustable ones from wal mart. It had the correct tip in and it was set on 9v and it was putting out 9v but it still made an awful noise when plugged in BUT worked fine on all my other pedals. I don't know. Weird. Regardless I've got a legit adapter now made for pedals and everything works perfect so Im just happy to have only wasted 2 days instead of many more. Im just glad I figured out it as soon as i did before I really messed the PCB up.

[poolhalljunkie13]

Is the reverse polarity on the d6? I heard or read something about that. Could you explain a little more? Please?

[ashcatlt]

I guarantee that it's not just labelled "9V". It says something about whereto it's AC or DC and, if DC, whether it's positive or negative barrel. These things are life or death! It won't kill you, but it will kill your pedals.

I don't see any reference to D6 on the board or in your link, but I could just be missing them.

There are two ways to do polarity protection aside from learning how to tell which adapted is right for the box and triple checking every time you plug it in:

The Wrong Way involves strapping a diodes across the power rails. You connect it before anything else between the +9V and GND. You orient it so that it only conducts if the GND is more positive than the "+9V". When the proper PSU is connected this diodes is reverse biased, and might as well not be there. Plug in the wrong wart, though, and this diodes starts conducting. It acts as a dead short right at the power supply, before the reversed voltage can get to the other sensitive components. Problem here is that the diodes acts like a dead short across the power supply, and pulls all the current the PSU can give, and maybe even some that it can't! This WILL exceed the rated current of the diodes and it will explode. It then becomes an open circuit, and - unless it managed to destroy the PCB tracks around it - the reversed voltage now has free reign to go blow up your opamps and electrolytics.

The Right Way is to put a diode in series with the +9V oriented such that it conducts when proper polarity is applied and just doesn't if the supply is reversed.

Guess which way most commercial pedals use?

[poolhalljunkie13]

After thinking about it, I remember when I first checked the pedal voltage the first time the voltage was negative. You know what that means? I didn't think my other pedals would be working though so I guess I didn't pay any attention to it. Plus I was pd off that at the fact that this crap wasn't working. But I should have connected the battery leads to start with so I could rule out the AC adapter sooner.

[ashcatlt]

Umph!

OK I'm done.

[poolhalljunkie13]

Jan 17, 2012 11:59:50 GMT -5 ashcatlt said:

Umph!

OK I'm done.

Thank you