Lpb-1 - volume issue

[Blownapart]

Hi there,

I have just started an interest in pedals and their circuitry - I have just completed my first kit build for a delay pedal.  (yay!)

The interest mainly started when I bought my Lpb-1 boost pedal, and found it was essentially unusable due to the lack of range in dialing in the boost level.  The thing is either off, or between 95% and 100% in terms of volume.  Ie knob at 7 o’clock is off, at 7.15 it is at 95%, and then all the way round at 5 it reaches 100%.  

Is this normal for the pedal?  Or could this be a faulty pot?  
I am about to purchase a 2nd Lpb-1 (for peanuts!) just to compare..  

It would be great to get to the bottom of this and even better if I could learn more about circuits in the process.  Who knows, perhaps even play around with a mod!

Any wise words and recommendations welcome!

thanks,

BA
 

 

[Mr.Grumpy]

 

On 3/23/2021 at 5:00 AM, Blownapart said:

Is this normal for the pedal?  Or could this be a faulty pot?  

It shouldn't be. The pedal will go to zero volume with the control turned all the way down, but the volume should increase gradually and smoothly all the way to maximum.

The LPB-1 is probably one of the simplest production pedals on the market. It uses a single transistor, a high gain (?) 2N5088 in a voltage-divider bias scheme for stability and symetrical amplification, i.e., it's made not to distort. The volume/output control is a 100 K Ohm pot, on schematics where it's marked, it specs an "A" (audio taper) potentiometer.  the other components are 4 fixed resistors, and two film caps, one for input and one for output. 

True bypass footswitches are common problem in pedals that have them, and sometimes cause low output when the pedal's engaged, ect. 

[daddymack]

I will guess you have a bad pot if the taper is not performing correctly. This pedal design, as noted above, is venerable and pretty basic. They sell for, what, $40?