LPB 1 Karma's a b$tch

[DuoJet]

I got caulky (can't spell it correctly here). I'll admit it- I thought my first project was too simple to screw up. I finished my last solder joint, plugged in the battery, hooked it up and was ready for a brief but satisfying victory dance. I was greeted by the loudest damn BLAAAAAAAAAARNNNNNN I have ever hear come out of my amp that wasn't the result of me %^&*ing up a chord on stage.

I am building an LPB 1 for pete's sake. I see this posted EVERYWHERE as a basic beginner circuit. Boy am I humbled.

First of all, I've rewired it twice and checked and rechecked the pinout on Q1 and the problem is the same: when the battery is disconnected and the pedal switched ON the volume pot works but the thing buzzes slightly. When the battery is connected and the switch turned on the volume pot seems to peak in the middle of its travel and decrease at what should be its apex. Oh, and touching any metal surface on the guitar stops the incessant buzz but still no signal from the pickups. What have I done to the ground?

Oh, and one more thing: I was told by my local electronics shop that using film capacitors would be the same as using Electrolytic. Could this be part of my problem?

[ode2no1]

there aren't any electrolytics in the schematic anyway so that wouldn't be it. what about the switch wiring?

[DuoJet]

Shouldn't be the switch but stranger things have happened. Perhaps I'll bypass the switch and see if it works... Would this affect the battery connection issue and the pot taper like it has?

[CynicalMan]

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

What are your voltages? Do you have any pictures?

It sounds like a disconnected ground somewhere. Test out all of your grounds to make sure they're connected.

[DuoJet]

It does seem that grounding is the issue here. Would I lose signal completely if my grounds were broken or would I still hear some signal from my guitar bleeding through, because I'm hearing NOTHING now!

Here are some pics of this project- be easy on me, it's my first time!

   

   

I haven't mounted it to a project box yet as the ultimate goal is to get this working as an onboard boost in my guitar. 

Thanks for all the help so far- I'll have some resistance readings up tomorrow.

[mnordbye]

Can you link us the schematic and layout that you used? It will be easier for us to check the board then.

By the way, where did you get those yellow perfboards? They look cool.

[Solidhex]

What is the resistor connected to the emitter? Although there's a shadow over it, I'm seeing a 370K? (Orange,violet,yellow,red 2% tolerance) that should be around 390 ohm. Big difference between those.

[DuoJet]

Yep, the problem was right under my nose, I was soldering like a drunk gorilla. Since I learned how to pay attention to detail and SLOW DOWN I managed to rebuild the circuit and it works! The only problem is that when I strum hard on the guitar there is a loud clipping sound in the attack, almost like I have a diode in there. I'm using a 2n4401 as the transistor in the schematic (5088) is proving impossible to find. Would this substitution cause this distortion? I'm going to build another tonight to see if the problem persists. I'm so close to completing my first working project! Does anyone have any ideas?

[blueduck577]

t when I strum hard on the guitar there is a loud clipping sound in the attack, almost like I have a diode in there.

You built it correctly, that's just the nature of the LPB-1.  A quick estimate puts the collector around 2V.  This thing doesn't have that much headroom.

The transistor substitution shouldn't make any difference in this circuit.

[Solidhex]

 Does it do that when the volume on the pedal is turned down? Could just be your preamp clipping. Its meant to be a loud circuit.

[DuoJet]

t when I strum hard on the guitar there is a loud clipping sound in the attack, almost like I have a diode in there.

You built it correctly, that's just the nature of the LPB-1.  A quick estimate puts the collector around 2V.  This thing doesn't have that much headroom.

The transistor substitution shouldn't make any difference in this circuit.

Thanks for the insight. I am hitting the poor thing with fairly heavy pickups so that would explain the clipping. I was looking for a cleaner boost so I'm going to have a go at the AMZ Mini Boost tonight. Does anyone have experience with both of these circuits that could tell me if the MB will overdrive in the same way?

[DuoJet]

Also, would swapping out a resistor help limit the amount of signal heading into the lpb1?