Nostalgiatone Bass Overthruster

[johnk_10]

i just built a Nostalgiatone Bass Overthruster and everything works until i start running the gain control at the higher settings. then the led clippers start pulsing and alternating lighting up and the distorting cuts in and out. I've never had a pedal do this before. Any ideas as to what would cause that?

 

[johnk_10]

btw here's the build schematic:

 

[johnk_10]

build doc:

https://guitarpcb.com/wp-content/uploads/2026/09/2023-NostalgiTone-Bass-Overthruster.pdf

 

[swelchy]

sounds like the opamp is hitting a ceiling... pics of your build and where did you get your IC's

 

[johnk_10]

i get my IC's from mouser.

 

[jwin615]

22x gain on a 9v bass circuit seems like a LOT. 072 is probably latching.
If you roll the volume down on the bass, does it stop latching?
May need to lower R5

 

[johnk_10]

22x gain on a 9v bass circuit seems like a LOT. 072 is probably latching.

If you roll the volume down on the bass, does it stop latching?
May need to lower R5

no, it makes no difference, changing R6 from 2k2 to a 8K2 solved it, but i wish it had more dirt.

 

[johnk_10]

i got that info form the designer.

 

[johnk_10]

Ok,after boxing up it started cutting in and out at extreme with the 10K resistor for R6 again so I replaced the TL072 with an OPA2134 and an 8K2 for R6 and it works perfectly now.
here's some pics of the build:

 

[Chuck D. Bones]

My 1st guess is the problem is poor contact in those cheap stamped metal sockets. If changing the opamp corrected the problem, that would support the unreliable contact root cause. TL072 should work fine there. Changing R6 should not cure the problem. My next guess is there is a cold solder joint that we can't see in the photos.

The TL072 is no more susceptible to latchup than the OPA2134. Latchup occurs in these two devices if either input is driven too close to the power supply rails. In this circuit, the 1st stage opamp output is expected to saturate at high GAIN settings. That's normal behavior.