Battery Eater

[MetalUpYerEye]

My Dr. Boogey eats batteries like a monkey in a banana forest. They hardly last more than an hour, is this normal?

[petemoore]

a monkey in a banana forest. I think that'd be a 'jungle'...
    Dr. Boogey eats batteries...doesn't sound normal..
     They hardly last more than an hour...doesn't sound right at all.

[John Lyons]

If you only get an hour out of a battery you must have a short to ground somewhere.
Everything else seems ok? Does the battery get hot?

[MetalUpYerEye]

It didn't seem right to me that Dr. Boogey would eat batteries like that. Here's exactly what happened...

When I finished the circuit I tested it with a new battery and installed the new battery when I boxed it up. I also biased the jfets with the fresh battery (by ear, not by multimeter). After about an hour or so of use (give or take 30 minutes) everything started sounding crappy, the way my MD-2 sounds when the battery dies. I figured maybe there was some movement inside the box and it accidently shifted a trimmer causing my fets to become improperly biased. So I ripped the poor bastard open and tried to bias again with the same batt and it wouldn't bias, it just sounded crappy. So I got another new battery and it biased right up like nobodys business and sounded B/A again. I used it for a short practice session and it worked fine, then the next day I plugged it in and the sum'bitch is giving me the same crappy sound as before.

I dont think theres a short to ground unless I really missed something, it was a fantastically clean build. The battery doesn't even get warm during use, if it did I would have noticed it when I changed the battery the first time around.

Oh and...

My monkey lives in a forest.

[George Giblet]

I suspect the 100uF cap is around the wrong way.

Measure the JFET voltages.  That should show any other problems.

[MetalUpYerEye]

Ok. I checked the 100uf electrolytic and its oriented the correct way; + is toward the trimmers and - is toward ground. I'll have to buy a multimeter to check the voltages as i've been able to get thus far in DIY without one. Is it possible the electrolytic is shit? I stole it off a PCB from an old stereo i've had around for 5 or 6 years that I was going to trash. I really flogged the stereo with about 3-4 hours of daily use for about 4 years or more. I read somewhere that electrolytics have a somewhat limited lifespan of 8-10 years or so, could that be the problem?

[calpolyengineer]

That could be. I too salvage parts from old electronics (as do most everybody here) and as a rule of thumb I never reuse the electrolytic caps.

-Joe

[George Giblet]

I have a feeling the 100u might not be the problem, but you never know.  What you could do is pull it and put a different cap in.  Anything in the 10uF to 1000uF region should be ok to prove the point, then replace it.

[zachary vex]

what value are you using for the LED resistor?

what current draw on the battery (using the current setting on the meter... remember, this goes in series with the battery and circuit, and start on the 10A setting for fuse safety.)

[Rick]

Zach's gotta' good point to check first ...if that current limiting resistor to the LED is too low in value, it wil suck your battery very quickly. And since your circuit is working fine with a new battery, I think this might be the case - ...else you do have a short somewhere. It could be just a tiny leaky bit of copper between traces. Get out your Dremel tool or just scrape with whatever you've got between any suspect traces. Good luck   ...Rick

[MetalUpYerEye]

Ok, a few things...

George; once i've replaced the cap with another 100uf do I just use another battery and play for awhile to see if that was the problem? Is there another way I can test it without chewing through battery after battery?

Zach; The first time around I had the same thought, I had hooked the LED up with a 47k resistor. I didn't realize it until after I had boxed but the LED didn't work. After the battery died I just ripped the LED out altogether so now it is a physical impossibility that the LED is causing this because the LED is in my parts bin.

Rick; As a personal rule of thumb, I scrape between any seemingly problematic areas before testing and boxing it up. I'll get a multimeter tomorrow so i'll be able to give you guys some voltages but any other ideas are certainly welcome.

[brett]

Hi
JFETs use a mA or two, so if it works properly, it has to be a power supply short or the 100uF cap.
Disconnect the 100uF cap for a while - it's not completely necessary.
cheers