Bass Overthruster problem

[John Kallas]

i just finished building the Bass Overthruster but there’s a problem with the drive control. whenever i try to turn it past 1/2 way the clipping leds pulse back and forth and the signal cuts in & out with the pulsing. i thought that they should light up in unison and just get brighter when the gain increases (more distortion). what’s going on here? I triple checked my build and there aren’t any cold or missing solder connections or wrong parts placements.

HELP!!!! i want to get this circuit working properly!

 

[John Kallas]

everything else is working properly.

[Barry]

So one step at a time.

Before I ask for photos and voltages, the first thing based on what you are saying that I want to know is are you using an Active Bass?

[Barry]

While I wait for your response, and since I will be going out soon, I will address a couple of things.

The behavior of the two clipping LEDs is normal. D3 and D4 are wired in opposite polarity, so they respond to opposite halves of the signal waveform. They are not intended to light in unison.

The part I want to investigate is the signal cutting in and out when you increase the Gain control. You mentioned that everything else is working properly, so before we start looking for bad components or solder joints, I have an additional question:

When the signal cuts out, does it come back immediately when you turn the Gain back down, or does it stay out until you play another note?

If you can, let me know what the input source is, active or passive, and exactly what happens as you slowly turn the Gain control from minimum to maximum.

[John Kallas]

thanks for the reply. i’m using passive basses. and yes, the signal comes back when i turn the gain down.

[John Kallas]

BTW, i’ve built about 800-1000 pedals so i’m not new at this.

[Barry]

Okay, that’s helpful. Since you’re using a passive bass and the signal comes back when you turn the Gain back down, let’s start with the obvious things before getting into troubleshooting.

First, please post a clear, well-lit photo of the top side of the PCB. Try to get the entire board in focus and close enough that I can clearly read the resistor color bands and see the component placement. I want to double-check the resistor values and make sure everything appears to be in the correct location.

I was just playing mine earlier today using an Active Ibanez.

Also, when you slowly turn the Gain up from minimum while playing, approximately where does the signal start cutting out in the rotation?

Are you using a C Taper 500K pot?

Does it happen at the same point every time?

[Barry]

I have built thousands and I still make mistakes. I am pretty sure we all do.

I plan on going out but BRD will join in as well.

[John Kallas]

i have to get ready for a gig so i won’t be able to reply until later tonight. i’ll post pics when i get back home. thanks!

[brd]

I’ll watch for a reply. go melt some faces.

[brd]

I’m on EST, I’ll check back in the morning.

I’m curious what color LED’s you used, and if  they were anything special like super-brite or ultra-brite.

If you used a socket for the op-amps, I would suggest trying another TL072 if you have one handy, just because it’s easy.

[Author]

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